Arxiu de la categoria: ARTHROPODS

Insects are becoming smaller: miniaturization

According to different studies, multicellular organisms tend to become smaller and smaller through time. This phenomenon is called miniaturization and is considered one of the most significative evolutionary trends among insects. Miniaturization is a driving force for diversity and evolutionary novelties, even though it must deal with some limitations.

Learn more about this phenomenon and met some of the most extreme cases of miniaturization among insects through this post.

Why are animals becoming smaller?

For some years now, multiple studies suggest there is a widely extended trend to miniaturization among multicellular animals (i. e. organisms composed by more than one cell).

Miniaturization is a remarkable natural phenomenon headed to the evolution of extremely small bodies. This process has been observed in different non-related groups of animals:

  • Shrews (Soricomorpha: Soricidae), mammals.
  • Hummingbirds (Apodiformes: Trochilidae), birds.
  • Diverse groups of insects and arachnids.

To know more about giant insects, you can read Size matters (for insects)!

Diversification and speciation processes have given place to lots of new species through time, all of them constantly competing for limited space and food sources. This scenario turns even more drastic in tropical regions, where diversification rates are extremely high.

Learn about the ecological niche concept by reading “The living space of organisms“.

Facing the increasing demands of space and resources, evolution has given place to numerous curious phenomena such as miniaturization to solve these problems: by becoming smaller, organisms (either free-living or parasites) gain access to new ecological niches, get new food sources and avoid predation.

Despite many animals tend to miniaturization, this phenomenon is more frequently observed among arthropods, being one of their most remarkable evolutionary trends. Moreover, arthropods hold the record of the smallest multicellular organisms known to date, some of which are even smaller than an amoeba!

Guinness World Record of the smallest insects

The smallest arthropods are crustaceans belonging to the subclass Tantulocarida, which are ectoparasites of other groups of crustaceans, such as copepods or amphipodes. The species Tantulacus dieteri is still considered the smallest species of arthropods worldwide, which barely measures 85 micrometers (0,085 millimeters), thus being smaller than many unicellular life beings.

However, insects do not lag far behind.

Mymaridae

Mymaridae (or fairyflies) are a family of wasps inside the superfamily Chalcidoidea from temperate and tropical regions. Adults, ranging from 0.5 to 1 millimeter, develop as parasites of other insects’ eggs (e. g. bugs, Heteroptera). For this reason, fairyflies are very valuable as biological control agents of some harmful pests. Also, they are amongst the smallest insects worldwide.

Currently, the one holding the record as the smallest known adult insect is the apterous (wingless) male of the species Dicopomorpha echmepterygis from Costa Rica, with a registered minimum size of 0.139 millimeters. They neither have eyes nor mouthparts, and their legs endings are deeply modified to get attached to the females (somewhat bigger and winged) time enough to fertilize them. They are even smaller than a paramecium, a unicellular organism!

You can read “Basic microbiology (I): invisible world” to know more about unicellular organisms.

Male of D. echmepterygis. Link.

Fairyflies also include the smallest winged insects worldwide: the species Kikiki huna from Hawaii, with and approximate size of 0.15 millimeters.

Trichogrammatidae

Like fairyflies, trichogrammatids are tiny wasps of the superfamily Chalcidoidea that parasite eggs of other insects, especially lepidopterans (butterflies and moths). Adults of almost all the species measure less than 1 millimeter and are distributed worldwide. Adult males of some species are wingless and mate with their own sisters within the host egg, dying shortly after without even leaving it.

The genus Megaphragma contains two of the smallest insects worldwide after fairyflies: Megaphragma caribea (0.17 millimeters) and Megaphragma mymaripenne (0.2 millimeters), from Hawaii.

A) M. mymaripenne; B) Paramecium caudatum. Link.

Trichogrammatids also have one of the smallest known nervous systems, and that of the species M. mymaripenne is one of the most reduced and specials worldwide, as it is composed by only 7400 neurons without nucleus. During the pupae stage, this insect develops neurons with functional nuclei which are able to synthetize enough proteins for the entire adulthood. Once adulthood is reached, neurons lose their nuclei and become smaller, thus saving space.

Ptiliidae

Ptiliidae is a cosmopolitan family of tiny beetles known for including the smallest non-parasitic insects worldwide: the genera Nanosella and Scydosella.

Ptiliidae eggs are very large in comparison with the adult female size, so they can develop a single egg at a time. Other species undergo parthenogenesis.

Learn some more about parthenogensis by reading “Immaculate Conception…in reptiles and insects“.

Currently, the smallest Ptiliidae species known and so the smallest non-parasitic (free living) insect worldwide is Scydosella musawasensis (0.3 millimeters), from Nicaragua and Colombia.

Scydosella musawasensis. Link (original picture: Polilov, A (2015) How small is the smallest? New record and remeasuring of Scydosella musawasensis Hall, 1999 (Coleoptera, Ptiliidae), the smallest known free-living insect).

Consequences of miniaturization

Miniaturization gives rise to many anatomical and physiological changes, generally aimed at the simplification of structures. According to Gorodkov (1984), the limit size of miniaturization is 1 millimeter; under this critical value, the body would suffer from deep simplifications that would hinder multicellular life.

While this simplification process takes places within some groups of invertebrates, insects have demonstrated that they can overcome this limit without too many signs of simplification (conserving a large number of cells and having a greater anatomical complexity than other organisms with a similar size) and also giving rise to evolutionary novelties (e. g. neurons without nucleus as M. mymaripenne).

However, getting so small usually entails some consequences:

  • Simplification or loss of certain physiological functions: loss of wings (and, consequently, flight capacity), legs (or extreme modifications), mouthparts, sensory organs.
  • Considerable changes in the effects associated with certain physical forces or environmental parameters: capillary forces, air viscosity or diffusion rate, all of them associated with the extreme reduction of circulatory and tracheal (or respiratory) systems. That is, being smaller alters the internal movements of gases and liquids.

So, does miniaturization have a limit?

The answer is yes, although insects seem to resist to it.

There are several hypotheses about the organ that limits miniaturization. Both the nervous and the reproductive systems, as well as the sensory organs, are very intolerant to miniaturization: they must be large enough to be functional, since their functions would be endangered by a limited size; and so, the multicellular life.

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Multicellular life reduction seems to have no limits. Will we find an even smaller insect? Time will tell.

Main picture: link.

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Known the Asian hornet or ‘assassin hornet’ in 5 steps

In recent years, reports of invasive species entering the Iberian Peninsula have grown at an alarming rate. One of the most recent cases is that of the Asian hornet, also known as the yellow-legged hornet and dramatically called ‘assassin hornet’, which is well-stablished in northern regions of the Iberian Peninsula and which has recently been confirmed to nest in the very center of Barcelona.

What do we know about this species? Why is it known as the ‘assassin hornet’?

1. Where does it come from and how did it get here?

The Asian hornet (Vespa velutina) is a social wasp native to the Southeast Asia. It was for the first time recorded in Europe in 2004, at southeast France, where it is currently well-spread. According to most of sources, it is believed that some founding queens accidentally arrived France inside boxes of pottery from China.

Some associations of beekeepers from the Basque Country confirmed the presence of the Asian hornet in the Iberian Peninsula in 2010. From that moment on, the Asian hornet started spreading toward other regions: it was recorded in Galicia in 2011, in Northern Catalonia and in some areas of Aragon in 2012, in some areas of La Rioja and Cantabria in 2014 and in Mallorca, in 2015.

Dynamic map by José Luis Ordóñez – CREAF

Meanwhile, this species spread toward Italy, Portugal, Germany, Belgium, Sweden and, occasionally, the United Kingdom. It presence in Japan and Korea, where it is an invasive species too, was confirmed some years before.

It was recorded for the first time in Catalonia in its northern comarques (‘counties’), specifically in Alt Empordà, and in 2015 almost 100 nests of this species had already been recorded. Nowadays, the Asian hornet is well-spread in Girona and Barcelona provinces.

On July 13th of this year (2018), the Generalitat de Catalunya (Government of Catalonia) confirmed the first record of an Asian hornet nest located in the very center of Barcelona city, close to one of the main buildings of the University of Barcelona; a few days before, it had also been detected in Vallès Oriental and Baix Llobregat.

2. How can we identify it?

The Asian hornet size varies between 2 and 3.5 cm, approximately. Queens and workers have a similar morphology except for their size, being workers smaller than queens.

This species can be recognized by the following morphological traits:

  • Thorax entirely black.
  • Abdomen mainly black except for its 4th segment, which is yellow.
  • Anterior half of legs, black; posterior half, yellow.
  • Upper part of head, black; face reddish yellow.
Dorsal and ventral view of Vespa velutina. Picture by Didier Descouens, Muséum de Toulouse, CC 3.0.

If you think you have found an Asian hornet and meant to notify authorities, first of all make sure it is the correct species. This is of special importance as some native species like the European hornet (Vespa crabro) are usually confused with its invasive relative, thus leading to misidentifications and removings of native nests.

Vespa crabro. Picture by Ernie, CC 3.0.

3. Why is it also called ‘assassin hornet’?

The Asian hornet is neither more dangerous, venomous nor aggressive than other European wasps. So, why is it dramatically called ‘assassin hornet’?

Larvae of this species feed on honeybees caught by adult hornets. Honeybees usually represent more than 80% of their diet, while the remaining percentage is compound of other arthropods. Adult hornets fly over hives and hunt the most exposed honeybees, even at flight. A single hornet can hunt between 25 and 50 honeybees per day. Hornets usually quarter them and get only the thorax, which is the most nutritious part.

In Asia, some honeybees have developed surprising defensive mechanisms to fight against their predators, like forming swarms around hornets to cause them a heat shock.

Take a look to this video to known some more about this strategy (caso of Japanese honeybees and hornets):

On the contrary, European honeybees have different defensive strategies that seem to be less effective against invasive hornets than they are against the European ones, which are also less ravenous their Asiatic relatives and their nests, smaller. In addition, the absence of natural predators that help to control their populations makes their spreading even more easier.

Several associations of both beekeepers and scientists from Europe have been denouncing this situation for years, since this invasive species is causing severe damages to both the economy (honey and crop production) and the environment (loss of wildlife -insects and plants- biodiversity) due to the decrease in wild and domestic honeybees.

4. How do their nests look like and what I have to do if I find one?

Asian hornets usually make their nests far from the ground, on the top of trees (unlike the European hornets, which never construct their nest on trees at great highs); rarely, nests can be found on buildings near non-perturbated areas or in the ground. Nests are spherical-shaped, have a continuous growth, a single opening in their superior third from which internal cells cannot be appreciated (in European hornet’s nests, the opening is in its inferior part and internal cells can be observed through it) and can reach up to 1 m height and 80 cm diameter. Nests are made by chewed and mixed wood fibers, leaves and saliva.

Nest of Asian hornet. Picture by Fredciel, CC 3.0.

If you find an Asian hornet nest, be careful and don’t hurry: don’t get to close to it (it is recommended to stay at least 5m far from the nest), observe and study the nest and observe if there are adults overflying it. If you find a dead specimen, you can try to identify it (REMEMBER: always staying far from the nest!). Anyway, the most recommendable thing is to be careful and call the authorities (in Spain, to the emergency phone number: 112).

5. There are preventive and management measures?

Currently, preventive and management measures proposed are the following:

  • Protocols for a more efficient detection of nests.
  • Early detection of the hornet by installing traps.
  • Constitution of an efficient communication net to provide information of the presence of this species between regions.
  • Removal of nests.
  • Capture of queens.
  • Improving the habitat quality to minimize the settlement of the Asian hornet and enhacing the settlement of native bees.
  • Study the possible introduction of natural enemies.

In the following link, you can download the PDF (in Spanish) made by the Spanish Government (2014) where these and more strategies are widely explained.

Citizen participation is a key point when fighting against the spreading of an invasive species; the same happens with the Asian hornet. Some associations of beekeepers, like the Galician Beekeeping Association (Asociación Gallega de Apicultura, AGA) and its campaign Stop Vespa Velutina, give educational conferences about this species and place traps to control their populations. Also, some students of the University of the Balear Islands have developed a mobile app to inform about the expansion of the Asian hornet.

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Although knowledge of this species has been improved, there is still much work to be done. We will see how its populations evolve in the coming years.

Main picture by Danel Solabarrieta on Flickr, CC 2.0.

 

Insects feel through their antennae

Insects perceive their surroundings through different organs, among which antennae are some of the most important. Antennae appear in a lot of incredibly diverse shapes and sizes, and every group of insects develops one or more models. We encourage you to know more about their origin, functions and diversity through this post.

The origin of antennae

Antennae are paired sensorial appendages located in the anterior parts of insects’ body. Except for chelicerates (spiders, scorpions…) and proturans (non-insect hexapods), all arthropods, either crustaceans, hexapods (diplurans, springtails -Collembola- and insects), myriapods (centipedes and millipedes) and the extinct trilobites, have antennae when being adults.

In crustaceans, antennae appear in the two first head segments: a first pair known as primary antennae or antennules, and a longer second pair known as secondary antennae or just antennae. Usually, secondary antennae are biramous (that is, they have two main branches), even though some crustaceans have undergone ulterior modifications so antennae appear as uniramous appendages (with a single branch) or even get reduced.

Types of antennae in crustaceans. Picture obtained from Wikipedia (link).

However, the rest of arthropods only have a single pair of uniramous antennae. Hexapods (like insects), which seem to be closely related to crustaceans according to the pancrustacean model, seem to have just preserved the secondary pair of antennae typical of crustaceans.

According to some authors, antennae appear to be true appendages; that is, they would start to develop during the embryological development from a head segment the same way legs do. However, this segment would have evolved into a reduced and inconspicuous piece, now being unappreciable. Moreover, antennae can also regenerate like legs.

How do insects feel through antennae?

So, what does this title exactly mean?

Antennae are microscopically covered with tiny hairs known as sensilla, which are not related with hairs found in vertebrates since they are made of chitin (as the rest of insect’s cuticle) instead of keratin.

Picture above: antennae under electronic microscope. Picture below: detail of the sensilla. Both images taken from cronodon.com.

Despite being almost identical at the first sight, there are different types of sensilla: chemoreceptorial sensilla have an inner channel through which suspended molecules enter (e.g. pheromones), while mechanoreceptorial sensilla are retractable and move at the slightest pressure or when the insect changes its position with respect to the ground (in this case, these are called proprioceptor sensilla).

So, insects taste, smell, touch and communicate in part through antennae, thus allowing them to gather information about food sources, potential mates (pheromones), enemies, dangerous substances (e. g. a poisonous plant), nesting places and migratory routes (as in the case of the monarch butterfly). Other organs, such as legs, palpi and even the ovipositor (organ for laying eggs) sometimes have sensorial cells.

Inside and in the base of sensilla there are sensorial neurons connected to the insect’s brain; specifically, a brain region known as deutocerebrum. In chemoreceptorial sensilla, molecules bind with specific receptors that send nervous signals to the antennal lobe through the sensorial neurons. This lobe is somewhat like the olfactory bulb found in vertebrates.

Types of antennae in hexapods

Except for the proturans, which are wingless hexapods, diplurans, springtails (collembola) and insects develop different types of antennae. These are divided in two main groups:

  • Segmented antennae: springtails and diplurans. Each segment has an own set of muscles that moves it independently from the rest of the antenna.
  • Flagellate antennae: insects. Just the first segment located at the base of antennae in contact with the insect’s head (the scapus) has an own set of muscles, so the antennal movement depends entirely on this segment.

Parts of insects’ antennae

The three basic segments of insects’ antennae are the following:

Antenna of an inquiline wasp belonging to the genus Synergus (Hymenoptera). Picture by Irene Lobato.

1) Scape: basal segment that articulates with the insect’s head and the only one that has an own set of muscles. The scape is mounted in a socket called torulus.

2) Pedicel: the second antennal segment or the one that comes just after the scape. This segment has a relevant role since it contains the Johnston’s organ, which is a collection of sensory cells. This organ is absent in non-insect hexapods (springtails, diplurans).

3) Flagellum: the rest of antennal segments that form the antennae, which are individually known as flagellomeres. These flagellomeres are connected by thin membranes that allow them to move as a whole despite not having muscles.

Thousands of antennae!

From this basic pattern (scape + pedicel + flagellum), each group has developed numerous antennal models based on their lifestyle:

  • Aristate

These are very reduced antennae with a pouch-like shape and a small bristle that emerges from its third modified segment.

Example: a very extended model among flies (Diptera).

Left: picture by M. A. Broussard, CC 4.0; right: picture of a fly of the family Sarcophagidae by JJ Harrison, CC 1.0.
  • Capitate

Capitate antennae have a club or knob at their ends.

Example: usually found in butterflies (Lepidoptera) and in some beetles (Coleoptera).

Left: picture by M. A. Broussard, CC 4.0; middle: picture of a beetle of the species Platysoma moluccanum by Udo Schmidt, CC 2.0; left: a butterfly, public domain.
  • Clavate

Unlike the capitate ones, clavate antennae get progressively thicker in their ends.

Example: moths (Lepidoptera), carrion beetles (Silphidae, Coleoptera).

Left: picture by M. A. Broussard, CC 4.0; right: beetle of the species Thanatophilus sinuatus (Silphidae) by Wim Rubers, CC 3.0.
  • Filiform

This is the simplest model of antennae: long, thin and made of equally sized and shaped segments.

Example: cockroaches (Blattodea), crickets and grasshoppers (Orthoptera), longhorn beetles (Cerambycidae, Coleoptera), bugs (Heteroptera).

Left: picture by M. A. Broussard, CC 4.0; right: cockroach of the species Periplaneta americana by Gary Alpert, CC 3.0.
  • Flabellate

These are quite similar to pectinate and lamellate antennae (see below), but with thinner and flattener segments that make them to look like a folding paper fan; also, these thin projections occupy all the antenna, and not only the terminal segments as in lamellate antennae. This model is found in males of some insects, thus having a large surface for detecting pheromones.

Example: beetles (Coleoptera), wasps (Hymenoptera) and moths (Lepidoptera).

Beetle male of the genus Rhipicera. Picture by Jean and Fred, CC 2.0.
  • Geniculate

These are bent, almost like a knee joint. The first antennal segment (scape) is usually located before the joint. The rest of segments together are known as funicle.

Example: some bees and wasps, especially in chalcid wasps (Hymenoptera), weevils (Curculionidae, Coleoptera).

Left: picture by M. A. Broussard, CC 4.0; right: picture of a parasitoid wasps of the species Trissolcus mitsukurii, public domain.
  • Lamellate

The terminal segments enlarge to one side in form of flat and nested projections, thus looking like a folding fan.

Example: beetles of the family Scarabaeidae (Coleoptera).

Left: picture by M. A. Broussard, CC 4.0; right: picture of a beetle of the family Scarabeidae, public domain.
  • Moniliform

Unlike filiform antennae, the segments of moniliform antennae are more or less spherical and equally sized, thus giving these antennae a string of bead appearance.

Example: termites (Isoptera), some beetles (Coleoptera).

Left: picture by M. A. Broussard, CC 4.0; right: picture of a termite by Sanjay Acharya, CC 4.0.
  • Pectinate

Segments have a lateral projection, so they look like combs.

Example: sawflies (Symphyta, Hymenoptera), parasitoid wasps (Hymenoptera), some beetles (Coleoptera).

Left: picture by M. A. Broussard, CC 4.0; right: picture of a beetle of the family Lycidae by John Flannery, CC 2.0.
  • Plumose

Plumose antennae look like feathers as their segments have numerous thin branches. Having a bigger antennal surface allows them to detect more suspended molecules, like pheromones.

Example: mosquito (Diptera) and moth (Lepidoptera) males.

Left: picture by M. A. Broussard, CC 4.0; right: moth male of the genus Polyphemus by Megan McCarty, CC 3.0.
  • Serrate

Each segment is angled or notched on one side, thus making these antennae to look like saws.

Example: some beetles (Coleoptera).

Left: picture by M. A. Broussard, CC 4.0; right: picture of a beetle of the family Chrysomelidae by John Flannery, CC 2.0.
  • Setaceous

These antennae are bristle-shaped, being thinner and longer in their ends. They are quite similar to filiform antennae, but thinner.

Example: mayflies (Ephemeroptera), dragonflies and damselflies (Odonata).

Left: picture by M. A. Broussard, CC 4.0; right: picture of a dragonfly, public domain.
  • Stylate

Similar to filiform antennae, but the terminal segments are pointed and slender, looking like a style. The style can either have bristles or not.

Example: brachycerous flies (Diptera).

Left: picture by M. A. Broussard, CC 4.0; right: picture of a brachycerous fly of the family Asilidae by Opoterser, CC 3.0.

You can read more about the different antennal models here and here, or take a look to the antennal gallery by John Flannery.

Main picture by Jean and Fred, CC 2.0.

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If you know more antennal models or curious facts about insects’ antennae, feel free to share it with us by leaving a comment below!

How would it be a world without bees?

In recent years, the idea of a world without bees has transcended numerous social and political spheres. The scientific community has been warning about the disappearance of bees during years without any consequence. But now, it has become an issue of major concern, acquiring a media relevance like never before. At the end of 2017, the EU decided to take matters into its own hands to prevent this tragic ending for bees.

Why would it be a problem that bees disappear from Earth? And which measures has the UE take in order to address this problem?

The DDT and Rachel Carson

The use of pesticides has been a common agricultural practice from the very beginning of agriculture. At the beginning, the use of organic chemicals derived from naturals sources, as well as inorganic substances such as sulphur, mercury and arsenical compounds, was very common. However, they eventually stopped being used due to their toxicity (especially, phytotoxicity). The growth in synthetic pesticides accelerated in the mid-twentieth century, especially with the discovery of the effects of DDT, which became one of the most widely used pesticides of all time. DDT became famous due to its generalist insecticidal effects and low toxicity to mammals and plants, being used to eradicate household pests, fumigate gardens and control agricultural pests.

Picture above: cover of a March 1947 brochure on DDT from the U.S. Department of Agriculture (source). Picture below: kids being showered with DDT during a campaing against poliomyelitis, which was believed to be transmitted by a mosquito (source).

DDT resulted to be very effective against insect vectors of deadly diseases such as malaria, yellow fever and typhus, thus becoming even more popular.

However, the overuse of this and other pesticides eventually began to cause severe human and environmental health problems, because some of these products started to contaminate soils, plants and their seeds, and to bioaccumulate within the trophic nets, finally affecting mammals, birds and fishes, among others. The indiscriminate use of pesticides and their effects were denounced by Rachel Carson through her most famous publication, “Silent Spring”, which was distributed in 1962.

Silent Spring, by Rachel Carson (source).

From Carson to the neonicotinoids

Since Carson denounced the abusive use of pesticides, the world has witnessed the birth of many new substances to fight crop pests. Since then, researches have focused on finding less toxic and more selective products in order to minimize their impact on both human and environmental health. Could we say it has been a success?

Yes… and no. Although their use stopped being so indiscriminate and famers started betting on the use of more selective products, there were still some open fronts. Fronts that would remain open until today.

Between 1980 and 1990, Shell and Bayer companies started working on the synthesis of a new assortment of pesticides to face the resistances that some insects have acquired to some of the most widely used substances those days: the neonicotinoids. Neonicotinoids are a class of neuro-active insecticides chemically similar to nicotine; they effect the insect nervous system with a high specificity, while having a very low toxicity to mammals and birds compared to their most famous predecessors (organochlorides, such as the DDT, and carbamates). The most widely used neonicotinoid nowadays (and also one of the most widely used pesticides worldwide) is the imidacloprid.

However, far from getting famous for their effectiveness, the use of neonicotinoids began to get controversial for their supposed relationship with the disappearance of bees.

How do these pesticides affect bees?

For some years now (2006 onwards) the neonicotinoids are in scientists’ spotlight as one of the main suspects of the disappearance of bees. However, it has not been until now that something that scientists had been denouncing for years has finally been assumed: that neonicotinoids cause a greater impact than it was thought.

Dead bees in front of a hive. Public domain.

Unlike other pesticides that remain on plant surfaces, some studies state that neonicotinoids are taken up throughout their tissues, thus being accumulated in their roots, leaves, flowers, pollen and nectar. Also, that nearby fields are polluted with the dust created when treated seeds are planted and that plants derived from these seeds will accumulate a major amount of pesticide than sprayed plants (as it is explained in this publication of Nature). This causes bees (as well as other pollinating insects) to be exposed to high levels of pesticides, both in the crops themselves and in the surrounding foraging areas. These same studies have revealed with less support that these products may persist and accumulate in soils, which may affect future generations of crops.

Some of the negative effects on bees that have been related to neonicotinoids are:

In addition to the effects of neonicotinoids, other important causes must be taken into account: climate change, less food sources and changes in soil uses.

What would happen if bees disappear?

Colonial bees (like honeybees) are the most famous among bees. However, they only represent a mere portion within the great diversity of known bees, most of which have solitary life habits and build their nests inside small cavities. The ecological importance of solitary bees is equal to or greater than that of honey bees, but effects that neonicotinoids have on them are still poorly studied. Together, bees are among the most efficient pollinating organisms.

Solitary bee entering in its nest. Public domain.

According to this study carried out in German territory and published in POLS One at the end of 2017, a large part of flying insect diversity (including numerous pollinators) and up to 75% of their biomass have decreased in the last three decades due to the interaction of several factors. And if that was not enough, the authors say that these numbers can probably be extrapolated to other parts of the world.

What would happen if both colonial and solitary bees disappear?

  • Disappearance of crops. The production of many crops, such as fruit trees, nuts, spices and some oils, depends entirely on pollinators, especially on bees.
  • Decrease in the diversity and biomass of wild plants. Up to 80% of wild plants depend on insect pollination to reproduce, as it happens with many aromatic plants. A decrease in the vegetal surface would lead to serious problems of erosion and desertification.
  • Less recycling of soil nutrients. With the disappearance of the plants, the washing and deposition of soil nutrients would go down.
  • Less biological pest control. Some solitary bees are parasitoids of other solitary bees and other groups of insects (natural enemies); their absence could trigger the recurrence of certain pests.
  • Negative effects on higher trophic levels. The disappearance of bees could cause a decrease in the diversity and biomass of some birds that feed on pollinators.
  • Disappearance of bee-derived products, such as honey or wax.

The UE bans the use of neonicotinoids

Facing this reality, several governments have tried to limit the use of pesticides as a part of the measures to stop the decline of bee populations and the resulting economic losses. To give some examples, since 2006 the biomass of honey bees has decreased by 40% in the US, 25% in Europe since 1985 and 45% in the United Kingdom since 2010, according to data published by Greenpeace.

To date, the more restrictive measures limited the use of neonicotinoids in certain situations or seasons. But at the beginning of 2018, the EU, after preparing a detailed report based on more than 1,500 scientific studies carried out by the EFSA (European Food Safety Authority), decided to definitively ban the use of the three most used neonicotinoids in a maximum period of 6 months in all its member states after demonstrating that they are harmful for bees: imidacloprid, clothianidin and thiamethoxam.

Will the objectives of this report be accomplished? We will have to wait …

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Although slowly, the fight against the abusive use of pesticides is paying off. However, we will have to see if the gap left by some products is filled with other substances or if governments commit to adopt more environment friendly agricultural models.

Main picture obtained from [link].

Some insects and other arthropods you should not confuse

Untrustworthy and sensational news about insects and arthropods are constantly shared through social networks, spreading tergiversated data and confusing amateur users. As a result, this usually leads to misidentifications and unnecessary alarmism toward harmless organisms.

Here we bring you a brief list of some insects and other arthropods that are usually confused and how to tell them apart. Don’t get tricked!

Spiders VS ‘Anything resembling them’

Spiders (Order Araneae) probably are some of the most feared arthropods among users for two main reasons: they are venomous and there are a lot of other arachnids that resemble them. So, it is quite understandable some people have serious doubts when finding an organism with eight long legs and a grim face.

However, most of these spider-like organisms are harmless and  unable to weave webs:

Harvestmen: unlike other arachnids, harvestmen or daddy longlegs (Order Opiliones) don’t have their body divided into two parts (prosoma and opisthosoma) by a thin waist, so they remind off a ‘ball with legs’. Also, they only have a pair of central eyes very close to each other. They neither have venom glands nor silk glands, so they can’t bite nor weave webs. They live in moist places, caves and near to streams and harvests. They are usually confused with spiders of the Pholcidae family because of their long legs.

Pholcus phalangioides (Pholcidae) (Picture by Olaf Leillinger, CC 2.5)
Harvestman (Picture by Dalavich, CC 3.0)

Solifugae: also known as camel spiders, Solifugae is an order of tropical arachnids characterized for having a segmented body and a pair of conspicuously large chelicerae forwardly projected. However, and despite their menacing appearance, they aren’t venomous (even though they bite can be very painful) nor weave webs. They inhabit desert and arid places, some of them are nocturnal and the diurnal ones move quickly looking for shadows to escape from sunlight.

Camel spider (Picture by Swen Langel, CC 2.0).

Amblypygi: also known as whip spiders or tailless whip scorpions, Amblypygi is an order of tropical arachnids that are neither spiders nor scorpions. Despite their menacing appearance, as it happens with camel spiders, whip scorpions don’t have venom glands. They have a pair of big thorny pedipalps ended in a pincer for grabbing preys, while the first pair of legs, which are filiform and segmented, act as sensory organs (not for walk). They don’t weave webs and have nocturnal habits.

Amblypygi (Picture by José Eugenio Gómez Rodríguez on Flickr, CC 2.0)

Pill bugs VS Pill millipedes

When playing in a park or in some natural place as a kid, you some time probably found a small animal, full of legs that rolled up when being touched.

These organisms are commonly known as woodlice. Woodlice belong to the suborder Oniscidea, a group of terrestrial crustaceans within the order Isopoda. They have a tough, calcarean and segmented exoskeleton, and inhabit moist places.

Armadillidium vulgare, Oniscidea (Picture by Franco Folini, CC 2.5)

Woodlice of the family Armadillidae, also known as pill bugs, are usually confused with pill millipedes (Subphylum Myriapoda, Class Diplopoda, Superorder Oniscomorpha), both groups with a similar external appearance and able to roll up into an almost perfect sphere as a defensive mechanism (convergent evolution).

Glomeris marginata, Oniscomorpha (Picture by Stemonitis, CC 2.5).

To tell them apart, you have to count the total number of legs per segment: if it has only a pair of legs per segment (one at each side of the segment), it is a pill bug; if it has two pairs, it is a pill millipede.

Bees and wasps VS Hoverflies

We talked widely about the main differences between bees and wasps (Order Hymenoptera) in this postThis time, we introduce you the hoverflies or syrphid flies (Order Diptera, Suborder Brachycera, Family Syrphidae), which resemble a lot to bees and wasps.

Resemblance of hoverflies to bees, wasps and bumblebees is a clear example of Batesian mimicry, which we explained widely in this post about animal mimicry. Moreover, hoverflies mimicry goes even further, since some of them also imitate the flight and the hum of these hymenopterans.

Hoverfly (Public domain picture, CC0).
Honey bee (Picture by Andy Murray on Flickr, CC 2.0)

To tell them apart, you have to pay attention to their eyes, antennae and wings: since they are flies, hoverflies have a pair of big compound eyes that occupy almost all their head, very short antennae with eight or less segments and a single pair of wings (the second pair has evolved into small equilibrium organs, the halteres), while wasps, bees and bumblebees have smaller compound eyes that occupy only the sides of the head, longer antennae with ten or more segments and two pairs of functional wings. Moreover, female hoverflies don’t have the abdomen ended in a stinger, so they are completely harmless.

Ladybugs VS Pyrrhocoris apterus

If you look for ladybugs pictures on Internet, you’d probably find a picture of this insect:

Public domain picture (CC0)

This is Pyrrhocoris apterus, a very common insect in the Palearctic area (from Europe to China) and recorded to the USA, Central America and India. You can find it on common mallows (Malva sylvestris), from which they eat seeds and sap, and they usually congregate in big groups because of their gregarious behavior.

Ladybugs are coleopterans (Order Coleoptera) with a more or less globular shape; they are carnivorous (with a diet based mainly on the intake of aphids) and can fly. Their first pair of wings are hard (elytra) and form a kind of shield that encloses the second pair of membranous wings.

Ladybug Coccinella septempunctata (Public domain picture, CC0)

On the other hand, Pyrrhocoris apterus is a bug (Order Heteroptera) with a depressed body, phytophagous habits and, unlike ladybugs and other bugs, it is unable to fly. Moreover, it doesn’t have a hardened shield.

Mantises VS Mantidflies

Mantises (Order Dyctioptera), which were widely addressed in this post, are very alike to this insect:

Mantispa styriaca (Picture by Gilles San Martin on Flickr, CC 2.0)

This insect belongs to the family Mantispidae (Order Neuroptera), also known as mantidflies or mantispids. This group is very well represented in tropical and subtropical countries, and just a few species are known from Europe. They have a pair of raptorial legs like those of Mantodea which they use for grabbing their preys.

Neuropterans, like mantidflies, green lacewings and antlions, have two pairs of similar sized wings with a very complex and branched venation. In Mantodea, the first pair of wings are smaller and harder than the second one, which are membranous and functional for flying; also, this second pair doesn’t have such a complex venation like that of neuropterans.

Mantodea (Picture by Shiva shankar, CC 2.0)

Mantidflies of the genera Climaciella and Entanoneura have a body coloration like that of some wasps, but they are totally harmless.

Climaciella brunnea (Picture by Judy Gallagher on Flickr, CC 2.0)

Mosquitoes VS Crane flies

Have you ever seen a giant mosquito and dreaded its bite? Well, you can stop being afraid of it.

These giant ‘mosquitoes’ (Order Diptera), which are commonly known as crane flies or daddy longlegs (Family Tipulidae), are totally inoffensive (and somewhat clumsy). They are distributed all over the world and inhabit moist places, like meadows and streams. Adults feed on nectar or don’t feed; in any case, they don’t suck blood!

Females have the abdomen ended in a kind of stinger; however, it is only their sharp ovipositor (not a stinger like those of bees or wasps).

Female crane fly (Picture by Irene Lobato Vila)

Dragonflies VS Damselflies

Both groups belong to the Order Odonata and have very similar appearance and behavior, being very common near sitting waters and lakes.

Two thirds of the Odonata are dragonflies (suborder Anisoptera), while the other third are damselflies (suborder Zygoptera). An easy way to tell them apart is by paying attention to their wings at rest: in dragonflies, wings are held flat and away from the body, while in damselflies they are held folded, along or above the abdomen.

On the other hand, eyes of dragonflies are large and touch in the vertex of the head, of which they occupy most of its surface, while those of dragonflies are smaller and are usually located on the sides of the head.

Dragonfly (Public domain image, CC0)
Damselfly (Picture by Xosema, CC 4.0)

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If you know about any other insect or arthropod that can be confused, let us know it by leaving a comment!

References

Venomous and poisonous arthropods: what makes them different?

After talking about venomous mammals, fishes and lizards, ‘All you need is Biology’ brings you this post about venomous and poisonous arthropods. We will try to explain you what makes them different and which arthropods produce some kind of toxic substance (and how they do it). It will probably surprise you!

Venomous vs poisonous animals

Although some people normally use these words interchangeably, they really mean the same? The answer is NO.

A venomous animal develops specialized organs or elements (such as fangs, teeth or stings) to actively inoculate venom inside the body of their victim as an offensive or defensive mechanism. On the other hand, a poisonous animal does not develop these type of organs, but specialized tissues or glands that produce toxins that are released passively as a defensive system; others acquire these substances from their diet. Sometimes, the toxin is not produced in any specific organ, but integrated within body tissues as a defense against predation.

Despite these differences, once in the body venoms and toxins can cause similar damage, which depends on their mode of action, the assimilated amount and the victim’s features. In humans, effects caused by these substances range from irritation, inflammation or redness to severe systemic damage in cases of powerful poisons.

Venomous and poisonous arthropods

Arachnids

Arachnids (subphylum Cheliceromorpha) include two of the better known venomous arthropods: spiders and scorpions. Both groups develop specialized organs to inoculate venomous substances which use either to hunt and defend themselves against predators or potential enemies.

  • Spiders

The specialized organs for venom inoculation in spiders are the chelicerae, a pair of preoral appendices typical of Cheliceromorpha which they use to grab the food. Spiders’ chelicerae, which are fang-shaped, are related to basal venom glands. These fangs have an internal duct that finish in a terminal opening through which venom is released and injected inside victims’ bodies like a hypodermic needle.

Spiders have the most evolved form of chelicerae: jackknife chelicerae. The two parts of the chelicerae come together like a folding knife, and when threatening to attack, the spiders rise the chelicerae and open the angle of the fangs.

Spider’s chelicerae. Public domain image (CC0) obtained from pixabay.

Some of the most dangerous spiders for humans are the Australian funnel-web spiders (genera Atrax, Hadronyche and Illawarra). Their venom is toxic to sodium channels, which results in the massive release of neurotransmitters.

“Funnel web spider” of the species Hadronyche cerberea. Have you noticed the drop of venom in its chelicer?. Picture by Alan Couch on Flickr (CC 2.0).
  • Scorpions

The most distal part of the scorpion tail, the telson (an additional segment found in several arthropods), has become a venomous organ that ends in a stinger. Like chelicerae in spiders, telson in scorpions is related to venom glands that contain toxic substances.

Scorpion of the species Centruroides vittatus, common in the middle of EUA and in the north of Mexico. In red, telson ended in a sting. Public domain image (CC0).

Scorpion venom is usually rich in neurotoxins that alter both the central and the peripheral nervous system of the victim by dissociating the parasympathetic and sympathetic nervous systems. In humans, the effects of their sting vary from intense local pain (with minor inflammation) to cardiac arrhythmias and acute pulmonary edema, like in the Indian species Hottentotta tamulus, which is considered one of the most venomous scorpions in the world.

BE CAREFUL! Neither all arachnids nor related groups are venomous; e. g. harvestmen, camel spiders and whip spiders (Amblypygi) ARE NOT venomous.

From left to right: harvestman (Daniel Jolivet on Flickr, CC 2 .0), camel spider (CC 3.0) and whip spider (Geoff Gallice on Flickr).

Myriapoda

The subphylum Myriapoda is divided in two classes: Diplopoda (millipedes) and Chilopoda (centipedes), and both produce toxic substances.

  • Millipedes

Millipedes, which have an elongated body composed of a lot of segments with two pairs of legs (rarely just one pair), are detritivores and inoffensive. However, they release toxins (alkaloids, benzoquinones, phenols) as a defensive mechanism to prevent predation. Some of these released substances are caustic and can burn the exoskeleton of other arthropods or cause skin and mucous inflammation in bigger animals.

Millipede toxins are produced inside repugnatorial or odoriferous glands and then excreted through small micropores located at both sides of the body when being crushed or feeling threatened.

At the first sight, micropores are difficult to see. Picture by Thomas Shahan on Flickr (CC 2.0).

TRIVIA: black lemurs from Madagascar (Eulemur macaco) grab and bite millipedes to stimulate their secretions, and then rub them all over their body. It is thought that lemurs cover themselves on millipede’s toxins since these work as insect repellent.

If you want to learn some more about this behaviour, don’t miss the following video. We recommend you to stay until the end…the final result will probably surprise you!

  • Centipedes

Centipedes also have a segmented body like millipedes; however, each segment has just a pair of legs. While millipedes are detritivores, centipedes are carnivorous arthropods that hunt their preys actively. To do so, they have developed two large forcipules originated from the first pair of legs which can inject venom contained in glands in the trunk of the animal. They also bite when feeling threatened.

Forcipules of Scolopendra cingulata, by Eran Finkle (CC 3.0).

The Scolopendra genus causes the most severe injuries. However, despite causing an intense pain when stinging, almost all envenomations caused by centipedes spontaneously resolve without complications.

Insects

Despite their diversity, there exist just a few cases of venomous/poisonous insects (class Insecta).

  • Beetles

Some beetle families (Coleoptera order), such as Meloidae, Oedemeridae and Staphylinidae (Paederus and Paederidus genera) contain toxins within their hemolymph which are released by compression as a defensive strategy against predators. These substances cause skin burns, redness and inflammation in humans.

Sptaphylinidae of the species Paederus littoralis, from Spain, France and Italy. Picture by Alvesgaspar (CC 4.0).

Meloidae and Oedemeridae hemolymph contain cantharidine, while the one of Paederus and Paederidus contains pederine, a substance that is exclusive of females of these beetles and of certain marine sponges, and which is thought to be produced by symbiont bacteria.

  • Bugs

Although some bugs (suborder Heteroptera) are better known for being disease vectors, they also cause different types of skin injuries in humans due to the release of caustic and inflammatory substances as a defense when being compressed (e. g. Pentatomidae family) or by the injection of salivary enzymes that are normally used to kill and dissolve preys (e. g. Belostomatidae family).

Belostomatidae. Public domain image (CC0).
  • Hymenopterans

Most of wasps, bees and ants (Hymenoptera order) produce toxins as a defensive mechanism. In most of those cases, females develop a stinger at the end of the abdomen resulting from the evolution of the ovipositor (Aculeata infraorder); however, there are also some groups that defend themselves by biting.

Ants (Formicidae family) usually attack by biting, but some species, such as those in the group of the fire ants (Solenopsis spp.) and the bullet ants (Paraponera spp., Dinoponera spp.), also have stingers like bees and wasps. Formic acid probably is the best-known toxin produced by ants, but is unique to the Formicinae subfamily; fire ants, for example, inject piperidine alkaloids. The sting of the bullet ants, which are distributed throughout center and south America, is considered the most painful sting for humans caused by an insect according to the Schmidt Index (which considers it to be as painful as a gunshot!).

Red ant of the species Solenopsis invicta (left, public domain image (CC0)) and bullet ant of the species Paraponera clavata (right, April Nobile / © AntWeb.org / CC BY-SA 3.0).

Females of most of bees and wasps within the Aculeata group develop an abdominal stinger. Their venom is usually rich in phospholipases, producing effects ranging from local inflammation to severe anaphylactic reactions (when suffering of hypersensibility or after being attacked by thousands of insects, as it has happened several times with the killer bee in America). The sting of the tarantula hawk (Pepsis formosa) from Mexico and southern USA, is considered the second most painful after the one of the bullet ant.

Pepsis formosa, a tarantula hawk. Public domain image (CC0).
  • Butterflies and moths

A lot of butterflies and moths (Lepidoptera order) produce toxins either during their larval stages, adulthood or both as a defensive mechanism against predation.

Sometimes, caterpillars are covered by urticant bristles or hairs that cause skin lesions (erucism), as in the case of the pine processionary (Thaumetopoea pityocampa), a harmful plague for pines which is very spread in southern Europe and America.

Pine processionary caterpillar nest, by John H. Ghent (CC 3.0).

On the other hand, adults of some species, like those of the monarch butterfly (Danaus plexippus) and Zygaena spp., both showing flashy colors (aposematism, a type of animal mimicry), develop toxins within their corporal tissues to prevent predation. The monarch butterfly obtains these substances by feeding on toxic plants of the Asclepias genus.

Zygaena transalpina, by gailhampshire (CC 2.0).

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Have you found this information interesting? Do you know any other venomous or poisonous arthropod? Feel free to leave your comments below!

References

The main image is of public domain (CC0) and was downloaded from Pixabay.

Insects and microorganisms symbiosis: the endosymbionts

Symbiotic relationships are an important motor for organisms’ diversification and evolution. The relationships insects have established with some endosymbiotic microorganisms (that is, those inhabiting the inner of their bodies) have provided them of a lot of surprising physiological and ecological adaptations. 

The value of the relationship between insects and their endosymbionts

The major cause for insects’ evolutive and adaptive success is their potential to stablish beneficial relationships with other life beings and, especially, with those microorganisms inhabiting their insides: the endosymbionts.

Some years ago, it was considered that the greatest contribution of endosymbiotic microorganisms to the physiology of insects was their role in feeding habits, which would explain, at least in part, the diversity of diets among insects. However, it has been shown that endosymbionts affect many other physiological traits.

Types of endosymbiosis in insects

Endosymbiotic microorganisms can be found inside the gut, in the spaces between cells and inside cells.

Generally, the more internal the endosymbiotic microorganisms are within the host’s body, the closer their relationship with the insect is. The four most common types of endosymbiosis in insects are explained below, from the most external and least close relationship to the most internal and closest one.

Gut microbes

Gut microbiota of insects is composed both of prokaryotes (unicellular, without nucleus, like bacteria and archaea) and eukaryotes (unicellular or pluricellular, with nucleus, like protozoans) that live outside the gut cells. They usually inhabit the hind part of insect’s gut (hindgut), either moving freely in its lumen or remaining attached to its walls. In some phytophagous insects, likes termites and cockroaches, the hindgut is a chamber without oxygen (anaerobic) where fermentation of cellulose and other complex sugars takes place.

 

Worker termite gut; the green part corresponds to the hindgut without oxygen. Figure belonging to the following paper: Brune, A. (2014). Symbiotic digestion of lignocellulose in termite guts. Nature Reviews Microbiology, 12(3), 168-180.

In termites, this anaerobic chamber contains facultative anaerobic prokaryotes (they can develop either with or without oxygen) and obligate anaerobic prokaryotes (they can only develop without oxygen), such as spirochetes and methanogens, which aid in digestion. In addition, in some worker termites, this chamber also contains protozoans that play a major role in the digestion of wood cellulose (Have you ever seen a piece of furniture pierced by termites?).

Unlike other endosymbionts, gut microbes are horizontally transmitted between insects; that is, insects don’t inherit gut microbes from their parents, but they should acquire them throughout their lives. In termites, acquisition of gut microbes takes place through a process called trophallaxis: the workers, which are the only able to feed by themselves, digest the food and transmit the resulting product mixed with gut microorganisms to the rest of the colony members through their mouthparts.

Trophollaxis. Picture by Shutterstock.

Moreover, microorganisms are removed during molting processes, so termites (and other insects performing trophollaxis) can acquire them again through trophollaxis.

Endoparasites

Parasites that live and/or develop inside an organism are known as endoparasites. They are also horizontally transmitted between insects.

Insects stablish fairly more relationships with pluricellular endoparasites than with microorganisms, being the pluricellular endoparasites the most harmful for insects in general terms; these are the cases of insect parasitoids (of which we talked in this post) and nematodes (able to transmit deathful bacteria to insects).

The most relevant endoparasitic relationship between insects and microorganisms, and the only one we are going to explain here, are vectors: the insect (or vector) serve as a container to the parasite until it reaches the definitive host. Parasites transported by vector usually are pathogenic protozoans harmful to vertebrates, like Trypanosoma (Chagas disease), Leishmania (leishmaniosis) or Plasmodium (Malaria).

Mosquito of the genus Anopheles, the major vector of the protozoan causing malaria worldwide: Plasmodium. Public domain image.

Extracellular and intracellular symbiosis

Unlike gut microbes and endoparasites, extracellular and intracellular endosymbionts are vertically transmitted generation after generation; that is, the insect inherits them from its parents

  • Extracellular endosymbionts

Extracellular endosymbionts, which can be both prokaryotes and eukaryotes, can be found in different organs of the body (even in the intestine along with the gut microbes). In any case, they never penetrate inside the cells. However, some species can be found outside and inside cells.

Since many extracellular microorganisms can also be intracellular, the possibility that they are found, in an evolutionary sense, in a transition stage between gut microbes and intracellular endosymbionts has been discussed.

An interesting case of extracellular endosymbiosis takes place in some species of aphids of the tribe Cerataphidini. Generally, aphids stablish a close relationship with an intracellular endosymbiont bacteria (Buchnera), but in some species of the aforementioned tribe these bacteria are substituted by extracellular unicellular yeast-like fungi (YLS or ‘yeast-like symbiont’) which inhabit the cavities between organs and inside different adipose bodies. Like Buchnera in the rest of aphids, YLS would play a key role on aphid feeding habits, participating in the production of essential nutrients.

Ceratovacuna nekoashi (Cerataphidini). Link (CC 2.5)

It is suggested that YLS would have evolved from an entomopathogenic fungus (that is, harmful to insects) whose lineage would later have derived into beneficial endosymbiotic organisms.

  • Intracellular endosymbionts

It is considered that at least 70% of insects has endosymbiotic microorganisms inside its cells. There exist two types of intracellular endosymbionts:

Mycetocyte symbionts or Blochmann bodies

Bacteriocytes or mycetocytes are specialized adipose cells containing endosymbionts which can be found in some groups of insects. These cells are vertically transmitted to the offspring and gathered together forming organs known as mycetomes o bacteriomes.

Blochmann bodies, or simply the endosymbionts inside mycetomes, are related to three groups of insects: Blattaria (cockroaches), some groups of heteropterans within Homoptera (cicadas, rust flies, aphids, etc.) and Curculionidae (curculionid beetles).

Buchnera aphidicola inside a mycetome of the aphid Acyrthosiphon pisum. The central element is the mycetome’s nucleus. Buchnera cells, which are round, are located packed in the citoplasm of the mycetome. Picture by J. White y N. Moran, University of Arizona (CC 2.5).

The most well studied case is the relationship between Buchnera and aphids. This intracellular bacterium recycles the uric acid and some other nitrogenous wastes produced by the aphid in order to produce the amino acid glutamine, which is then used by this same endosymbiont to produce other essential amino acids necessary for the aphid to develop. It is also considered that Buchnera produces vitamin B2 (riboflavin). This can explain why aphids have such a high reproductive rate and a big evolutive success despite having a diet rich in carbohydrates (which they obtain from plant’s sap) and poor in nitrogenous compounds.

It has been confirmed that Buchnera cells decrease in number when nutrients are scarce. This suggests that aphids use Buchnera cells as an alternative food source in difficult situations. So, aphids take more advantages from this relationship than Buchnera.

Guest endosymbionts

In this case, the guest (endosymbiont) alters some physiological traits of the insect to obtain some advantage.

Guest endosymbionts usually affect the sex ratio of insects (proportion of males and females in a population) as well as other reproductive traits. Guest endosymbionts that alter the sex ratio are known as sex-ratio distorters. Some guest microbes inhabiting the cytoplasm of insect’s cells are vertically transmitted to the offspring through ovules, so they need a higher proportion of female insects to guarantee their own perpetuity. To alter this proportion, they use different methods: male killing, induction of parthenogenesis, feminization or cytoplasm incompatibility, for which they usually induce changes at the genetic level.

One of the most well-studied cases is Wolbachia, an intracellular bacterium capable to induce a sex-ratio bias through almost every of the aforementioned methods.

Phenotypes resulting from insects infected with Wolbachia. Figure belonging to the following paper: Werren, J. H., Baldo, L. & Clark, M. E. 2008. Wolbachia: master manipulators of invertebrate biology. Nature Reviews Microbiology, 6(10), 741-751.

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Do you know any other relationship between microbes and insects? Leave your comments below!

References

  • Bourtzis K. Miller T. A. (2003). Insect Symbiosis. CRC Press.
  • Douglas, A.E. (1998). Nutritional interactions in insect-microbial symbioses: Aphids and their symbiotic bacteria Buchnera. Annual Review of Entomology, 43: 17–38.
  • Vega F.E., Blackwell M. (2005). Insect-Fungal Associations: Ecology and Evolution. Oxford University Press, USA.

The cover image is a montage made by the author from two images: 1) bacterium vector (by Flaticon from www.flaticon.com) and 2) termite vector (obtained from www.allstatepest.com.au).