Category Archives: Entomology

Instead of toxic chemicals, use helping plants to get rid of crop pests

by Piter Kehoma Boll

Finding efficient ways to deal with agricultural pests in crops is a challenging work. Currently, as we all known, the main strategy to control such pests is the use of chemical pesticides. However, this approach only serves the interests of those seeking profit over well-being, as we all know that such pesticides increase the risk of several health issues in those consuming the crops. More than that, chemical pesticides not only kill the targeted pest but many other life forms, causing a devastating effect on ecosystems.

The cross-striped cabbageworm (Evergesis rimosalis) is a common pest in plants of the genus Brassica (kale, cabbage, mustard) in the eastern United States. Photo by iNaturalist user margaridamaria.*

Fortunately, there has been an increasing interest in finding alternative, healthier ways to deal with the problem. One way is the production of genetically modified organisms (GMOs) that are naturally resistant to pests. There are, however, two main problems with this approach. The first one is that the population in general has an irrational fear of GMOs, apparently believing that they can be more harmful than the poisonous chemical pesticides, which is completely absurd. The second problem with GMOs is that the technology to create them is dominated by the same companies that produce most pesticides and, as all big companies, only seek profit and do not give a damn about the people and the environment.

A third strategy is the use of natural enemies of the pests to control them in organic farms. Although many natural enemies are great doing their job, they may also cause negative impacts by interfering with the surrounding ecosystems. Many crop pests are not native from the area where they are pests, i.e., they are invasive species and, in order to control them efficiently, a predator from its native area must be introduced as well, and this predator may end up becoming a threat to other species that it elects as food.

Coleomegilla maculata is a common predatory lady beetle in the eastern United States. They are great to control agricultural pests locally but should not be deliberately introduced elsewhere. Photo by Riley Walsh.*

Fortunately, some nice strategies have been recently developed. One of them includes the use of additional plants in the fields that change the way that pests behave without posing a threat to surrounding areas. These additional plants consists of two types: trap crops and insectary plants.

The common buckwheat Fagopyrum esculentum has been used as an insectary plant. Photo by iNaturalist user jimkarlstrom.*

A trap crop, as the name suggests, is an additional crop that is not intended to be commercially exploited, but serves as a trap for the pests. Instead of attacking the main crop (called the ‘cash crop’), the pests are attracted to the trap crop, reducing their density in the cash crop. This system is more efficient if the trap crop is similar to the cash crop, such as another plant of the same genus, or another variety of the same species, because it must be as attractive to the pest as the cash crop, or perhaps even more attractive.

Insectary plants, on the other hand, are intended to attract other insects to the plantation, especially predatory insects that prey on the agricultural pest. Insectary plants should produce flowers in abundance, thus attracting many insect species, which will increase the interest of predators in the area. However, when used alone, insectary plants will only provide predators to control the pest in crop plants that are near the insectary plants and, as they are usually planted in an area surrounding the plantation, they would not protect the plants that are near the center of the plantation.

In a recent study, Shrestha et al. (see references) decided to combine trap crops and insectary plants together with the cash crops in a strategy that they called a ‘botanical triad’. The cash crap was organic cabbage (Brassica oleracea var. capitata) planted in the eastern United States; the trap crops were three other crops of the genus Brassica: mighty mustard (Brassica juncea), kale (Brassica oleracea var. acephala) and collard (Brassica oleracea var. italica); and the insectary plants were buckwheat (Fagopyrum esculentum) and sweet alyssum (Lobularia maritima).

Kale (Brassica oleracea var. acephala). Photo by David Adreas Tønnessen.*

As a result, the number of herbivores (i.e., crop pests) was larger in the trap crops than in the cash crop. The trap crops were, therefore, more attractive than the cash crops for the pests. The presence of insectary plants increased the number of predatory and parasitoid insects, such as lady beetles and parasitoid wasps, in the trap crops when compared to treatments without insectary plants. The number of parasitized pests also increased in the presence of insectary plants.

Field layout of the study by Shrestha et al. (2019).**

In general, the “team work” of trap crops and insectary plants greatly reduced the influence of agricultural pests on the cash crops. The trap crops attracted the pests to an area close to the insectary plants, allowing the predators to reach them.

Efficient ways to raise crops organically are possible. We just have to focus on a healthy ecosystem and not on money. If we work together, we can defeat the “Big 6” corporations that dominate the food production in the world. They are the real pests.

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Reference:

Shrestha B, Finke DL, Piñero JC (2019) The ‘Botanical Triad’: The Presence of Insectary Plants Enhances Natural Enemy Abundance on Trap Crop Plants in an Organic Cabbage Agro-Ecosystem. Insects 10(6): 181. doi: 10.3390/insects10060181

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*Creative Commons License This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

**Creative Commons License This work is licensed under a Creative Commons Attribution 4.0 International License.

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Friday Fellow: Luna Moth

by Piter Kehoma Boll

It’s been a very long time since the last time I presented a lepidopteran here, so today I decided to go back to this amazing group of insects. The species I chose for today is quite popular, maybe the most popular moth in the world. Its name is Actias luna, commonly known as the luna moth.

Adult luna moth in the Unites States. Photo by Andy Reago & Chrissy McClarren.*

The luna moth is native from Canada and the United States. It is a quite large moth, with a wingspan of about 8 to 12 cm, although some individuals can be as big as 18 cm. Its wings, covered with scales as usual in lepidopterans, have a light green color. The forewigs have a brown anterior border that connects to two eyespots (one on each wing) by a stalk. The hindwings also have one eyespot each, but they are not connected by a stalk to the border. The hindwings also have a long tail that is characteristic of the genus Actias and somewhat resembles the similar (but shorter) tails in some butterflies, such as those of the family Papilionidae. Males and females are very similar and can be often distinguished by the size of the abdomen, which is much thicker in females.

In colder climates, such as in Canada, the luna moth has one generation per year, but southern populations, in places where the climate is warmer, can have up to three. The females lay eggs on suitable plants to serve as food for the larvae. There are several identified tree species that are used as food, including birches, walnuts, hickories and persimmons. The larvae feeding on a tree never, or very rarely, reach a number that can cause significant damage to the plant.

Third instar larvae. Photo by Wikimedia user Kugamazog~commonswiki.**

The eggs are brown and laid in irregular clusters on the underside of the leaves. They usually hatch one to two weeks after being laid and originate small, green larvae. The larvae are green in all instars and pass through five of them during a period of about 7 weeks. The fifth and final instar then descends the tree in which it lives to reach the ground. There, it starts to spin a silk coccoon and, after finishing it, turns into a pupa. In warmer regions, the pupa takes about two weeks to become an adult, but in colder regions it enters into diapause over winter, taking about nine months to complete the cycle.

A fifth-instar larvae building its coccoon. Credits to Virginia State Parks staff.*

When females become adults, they search for a suitable tree of its preferred species (usually the same species in which it was born) and emits pheromones to attract males. Adults lack mouth parts and, therefore, do not eat, living only enough to mate and lay eggs. The nice long tails on the hindwings, more than just beautiful, seem to decrease the ability of bats to detect them using their echolocation.

Pupa beside an empty coccon. Photo by Wikimedia user Kugamazog~commonswiki.**

The luna moth is one of the most popular insects in North America. In fact, it was the first insect ever to be described from the continent, being named Phalaena plumata caudata by James Petiver in 1700. When Linnaeus started the binomial nomenclature for animals in 1758, he renamed it Phalaena luna as a reference to the Roman goddess of the moon.

Beautiful specimen in Canada. Photo by Alexis Tinker-Tsavalas.***

Although not considered a vulnerable species at the moment, the luna moth faces some threats caused by human interference, such as habitat loss and damage caused by invasive species. Fortunately, due to its popularity, it is likely to have considerable support from the public for its conservation when that time comes.

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References:

Lindroth RL (1989) Chemical ecology of the luna moth: Effects of host plant on detoxification enzyme activity. Journal of Chemical Ecology 15(7): 2019–2029.

Millar JG, Haynes KF, Dossey AT, McElfresh JS, Allison JD (2016) Sex Attractant Pheromone of the Luna Moth, Actias luna (Linnaeus). Journal of Chemical Ecology 42(9): 869–876.

Wikipedia. Luna moth. Available at < https://en.wikipedia.org/wiki/Luna_moth >. Access on 11 July 2019.

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Friday Fellow: Chinese Banyan Wasp

by Piter Kehoma Boll

During the past three weeks, I presented a fig tree, the Chinese Banyan, a thrips that parasitizes it, the Cuban Laurel Thrips, and a mite that parasitizes the thrips, the Cuban-Laurel-Thrips Mite. However, I haven’t wrote yet about one of the most interesting creatures that interacts with a fig tree: its pollinator.

In the case of the Chinese Banyan, its pollinator is the fig wasp Eupristina verticillata, which I named the Chinese Banyan Wasp. As all fig wasps, this species is very small and completely adapted to live with figs. They cannot survive without the exact fig species with which they interact and the fig species cannot reproduce without that exact wasp. How does this works?

Let’s start our story with an adult female Chinese banyan wasp. The females are black and very small, measuring around 1 to 1.2 mm in length only. This female is flying around looking for a young fig which will serve as her nest and her grave.

This is what a female Chinese Banyan wasp loooks like. Photo by Forest & Kim Starr.*

A fig, in case you don’t know, is not a real fruit in the botanical sense. It is actually a special kind of inflorescence called a syconium that is basically a flower-filled sack. The inner walls of a fig have many tiny male and female flowers and the only way to get to them is through a tiny hole at the fig’s appex. And this hole is only open during the initial stages of the fig’s development.

Chinese Banyan figs in their early stage. You can see the hole marked by a darker “areola” around them. That is the place through which a female fig wasp enters the fig. Credits to Wikimedia user Vinayaraj.**

When the female Chinese Banyan fig wasps is flying around, she is looking for a fig that is at this exactly stage of development. Once she finds one, she crawls inside the fig through that tiny hole. She usually loses her wings while doing that because the passage is too narrow. She evens needs to use her especially adapted mandible to help her go through. Once inside the fig, she looks for the female flowers, which are located at the base of the fig, away from the entrance. The male flowers, located right at the entrance, are not mature yet. However, the female wasps arrived with pollen that she gathered elsewhere (you will learn about that soon). When she reaches the female flowers, she introduces her ovopositor (the long structure at the end of her abdomen that is used to lay eggs) inside the female flower and lays one egg inside the flower’s ovary. Her ovopositor needs to have the exact size to reach the ovary to lay the egg. If it is too short, she is unable to complete her task. And while she is moving from flower to flower to lay eggs, she ends up pollinating them. After she has finished, she dies still inside the fig.

The ovaries that received an egg start to grow into a gall (a “plant tumor”) by influence of the insect and serve as food and shelter for the larvae that hatch from the eggs. A larva grows, pupates and turns into an adult inside a single gall. When the wasps have finally reached their adult stage, they leave the gall in which they were born. This happens when the fig reached its mature stage.

Males are the first ones to emerge. They are even smaller than the females and have a yellow to light-brown color. They gnaw their way through the gall and, once outside it (but still inside the fig) they start to look desperately for female wasps to inseminate. They do that by tearing other galls apart and, when a female is found trapped inside, they inseminate her. After that, the males dig a hole through the fig to the outside and die soon after, never experienced the external world.

A male Chinese Banyan wasp (right) compared to a female. Photo by Forest & Kim Starr.*

Female wasps then leave their galls and move towards the hole opened by the male. While doing that, they move over the now mature male flowers and become covered in polen. After leaving the fig, they search for another fig that is in its early stage of development, restarting the cycle.

When a female leaves a mature fruit, she needs to find an immature one soon after that because she will die in a couple of days. In other words, the only way for this to work is if there are figs in the right stage all year around, and that is what happens. Differently from most plant species, which produce flowers in a specific time of the year, fig trees are always flowering. Well, not exactly. One individual fig tree produces figs only in a specific period of the year. All the figs of that tree ripen at the same time, i.e., a fig tree has an intra-individual synchrony of flower maturation. However, other trees of the same species have different moments to produce flowers, i.e., there is an inter-individual asynchrony of flower maturation. This assures that a wasp will always find a fig at the suitable maturation stage when there are enough fig trees around and also assures that a fig tree will not be fertilized by its own pollen.

As I mentioned when I presented the Chinese Banyan, this tree can only produce viable figs when the wasp is present, so that populations introduced outside of their native range will only reproduce if the waps is introduced as well. However, the wasp will be unable to survive if there are not enough fig trees to provide it with figs all year round. It is a delicate relationship between a tiny, fragile and short-lived insect and a huge, resistant and long-lived tree. And they need each other to survive.

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References:

Cook J, Rasplus J-Y (2003) Mutualists with attitude: coevolving fig wasps and figs. TRENDS in Ecology and Evolution 18(5): 241–248.

Kjellberg F, Jousselin E, Hossaert-McKey M, Rasplus J-Y (2005) Biology, Ecology, and Evolution of Fig-pollinating Wasps (Chalcidoidea, Agaonidae). In Raman A, Schaefer CW, Withers TM (Eds.) Biology, ecology and evolution of gall-inducing arthropods. v.2. New Hampshire, Science, p.539-572.

McPherson JR (2005) A Recent Expansion of its Queensland Range by Eupristina verticillata, Waterston (Hymenoptera, Agaonidae, Agaoninae), the Pollinator of Ficus microcarpa l.f. (Moraceae). Proceedings of the Linnean Society of New South Wales: 126: 197–201.

Weiblen DG (2002) How to be a fig wasp. Annual Review of Entomology 47: 299–330.

Wiebes JT (1992) Agaonidae (Hymenoptera, Chalcidoidea) and Ficus (Moraceae): fig waps and their figs, VIII (Eupristina s.l.). Proceedings of the Koninklijke Nederlandse Akademie van Wetenschappen 95(1): 109–125.

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Tospovirus and thrips: an alliance that terrifies plants

by Piter Kehoma Boll

I recently presented a thrips in the Friday Fellow section, in that case a thrips that infects mostly fig trees. This group of insects, which make up the insect order Thysanoptera, is poorly known by the general public, but is certainly known by gardeners and farmers, as they can be a serious nuisance for many plant types.

We could imagine thrips as being kind of the mosquitoes of plants. They pierce the surface of plants and suck their juices just like mosquitoes do with vertebrates. And we all know that a mosquito bite may lead to much more than a small blood loss and local irritation of the skin. Many parasites use mosquitoes as vectors to travel from host to host, including protists such as Plasmodium falciparum, which causes malaria, and many types of virus, such as those of the genus Flavivirus, which cause the yellow, dengue and zika fevers.

A similar thing happens in the association of thrips with plants. A special genus of virus, called Tospovirus, infects many plant species and uses thrips as a vector. Inside the thrips bodies, the viruses reproduce after infecting the epithelial cells of the gut and, from there, travel via blood to the salivary glands and, when a thrips perforates a plant, the virus is injected in it. The cycle is basically the same used by Flavivirus in mosquitoes and ticks to infect vertebrates. Isn’t it amazing how a virus such as Tospovirus can infect both an animal and a plant? But what exactly is the disease caused by these viruses?

Basil leaf infected with the tomato spotted wilt virus. Photo by Scot Nelson.**

One of the most common Tospovirus is the so-called Tomato spotted wilt virus (TSWV), which is considered one of the most economically devastating plant viruses in the world. It can infect many crops, such as tomato, tobacco, bellpepper, peanut and basil. The symptoms vary from plant to plant, but usually include stunting, poorly developed fruits, commonly with ring spots on the surface, and necrosis of the leaves. It is transmitted to plants by thrips of the genus Frankliniella, mainly the western flower thrips Frankliniella occidentalis. Although the virus usually needs several hours to be able to reinfect a plant after infecting a thrips, in ideal conditions the time can e as short as five minutes.

The western flower thrips Frankliniella occidentalis. Photo by Dave Kirkeby.*

But why would a thrips feed on an obviously sick plant, all ugly and full of spots? They would certainly prefer a healthy plant, but that would prevent the virus to spread. As a result, the virus developed several strategies to attract the thrips. The TSWV is able to increase the amount of free aminoacids in infected plants, and these are essential nutrients for egg production in thrips. As a consequence, infected plants become more nutritious and attract more thrips. Feeding on infected plants, the thrips will certainly get infected and at the same time ingest more nutrients than non-infected thrips. Thus, a sick thrips actually has an increased fitness and usually lays more eggs. The plants would certainly get effing scared if they were able to have emotions.

The Soybean vein necrosis virus (SVNV) is another Tospovirus of economic concern. As it names suggests, it attacks mainly soy plants, and its main vector is the soybean thrips Neohydatothrips variabilis. Infected soybean thrips produce significantly more offspring than non-infected ones, although heavily infected individuals lay few viable eggs. How do thrips bypass this problem? It’s simple! Once they are infected, they stop feeding on infected plants and prefer non-infected ones, which increases their reproductive success by avoiding becoming heavily infected and at the same time they spread the virus further to non-infected plants. A nightmare for the plants once more.

Soybean thrips Hydatothrips variabilis. Photo by Even Dankowicz.***

A recent study investigated the relationship of another Tospovirus-thrips pair, this time of the iris yellow spot virus (IYSV), which commonly attacks garlic and onion plants, and its main vector, the onion thrips, Thrips tabaci. Infected thrips did not show an increased daily fecundity but had an increased lifespan, allowing them to lay more eggs simply because they lived longer.

Iris yellow spot virus lesion on an onion leaft. Extracted from https://vegetableguide.usu.edu/diseases/onion/iris-yellow-spot-virus

But the effect of Tospovirus on thrips can go further. For example, although plants infected by the TSWV release more aminoacids that attract and increase the fecundity of thrips, the infections still seems to have some deleterious effects on the insect. Infected males of Frankliniella occidentalis increase their consumption of food juices and increase the transmission of the virus. Females, on the other hand, seem to need nutrients that cannot be found in plants. As a result, they increase the consumption of eggs of the two-spotted spider mite Tetranychus urticae, with which they often coexist. Although primarily herbivorous as most thrips, the western flower thrips eventually feeds on mite eggs, and being infected by TSWV makes females become more eager to eat eggs. This is certainly not a strategy of the virus itself as the other ones, since a female that is feeding on mite eggs does not contribute for the virus’ reproductive success. Nevertheless, this is an interesting phenomenon that show us how the interactions in a trophic web can be dynamic, changing, for example, due to an uninentional side effect of a virus trying to survive.

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References:

Keough S, Han J, Shuman T, Wise K, Nachappa P (2016) Effects of Soybean Vein Necrosis Virus on Life History and Host Preference of Its Vector, Neohydatothrips variabilis , and Evaluation of Vector Status of Frankliniella tritici and Frankliniella fusca. Journal of Economic Entomology 109(5): 1979–1987. doi: 10.1093/jee/tow145

Leach A, Fuchs M, Harding R, Nault BA (2019) Iris Yellow Spot Virus Prolongs the Adult Lifespan of Its Primary Vector, Onion Thrips (Thrips tabaci) (Thysanoptera: Thripidae). Journal of Insect Science 19(3): 8. doi: 10.1093/jisesa/iez041

Shrestha A, Srinivasan R, Riley DG, Culbreath AK (2012) Direct and indirect effects of a thrips‐transmitted Tospovirus on the preference and fitness of its vector, Frankliniella fusca. Entomologia Experimentalis et Applicata 145(3): 260–271. doi: 10.1111/eea.12011

Stafford-Banks CA, Yang LH, McMunn MS, Ullman DE (2014) Virus infection alters the predatory behavior of an omnivorous vector. Oikos 123(11): 1384–1390. doi: 10.1111/oik.01148

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Friday Fellow: Cuban Laurel Thrips

by Piter Kehoma Boll

Last week I presented the magnificent Chinese banyan Ficus microcarpa. Today I’m bringing a little insect that loves it but is not loved in return, the Cuban laurel thrips, Gynaikothrips ficorum.

As its name suggests, the Cuban laurel thrips is a thrips, i.e., an insect of the order Thysanoptera. Adults of this species measure about 3 mm in length and have a black and elongate body and two pairs of thin wings that fold over the dorsum when at rest. Its mouth parts, as typical of thrips, are asymmetrical, with a reduced right mandible and a developed left mandible that it uses to cut the surface of plants in order to suck its juices. It is, therefore, a plant pest.

Adult Cuban laurel thrips in Hong Kong. Photo by iNaturalist user wklegend.*

The Cuban laurel thrips prefers to feed on juices of fig trees, such as the Chinese banyan from last week. It’s common name, though, is a reference to another fig species, Ficus retusa, commonly known as the Cuban laurel. Both fig trees, as well as the thrips itself, are native from Southeast Asia. Other, less common host plants include Citrus trees and orchids. They prefer to feed on young, tender leaves, and cause dark, usually purplish red dots, on the leaf’s surface. It is common for the leaf to curl and become hard, eventually dying prematurely. Although most infestations do not cause serious damage to the plant’s development, the curling of the leaves can reduce a plant’s ornamental value.

Ugly curled leaves caused by the thrips’ infestation in New Zealand. Photo by Stephen Thorpe.*

The reproduction of the Cuban laurel thrips is basically constant, so that several generations occur across one year. The adults take advantage of the curled leaves produced by their feeding behavior and use them as a protection to put their eggs. The immature stages, after hatching, remain inside the shelter provided by the curled leaf. They are transparent in the first two instars and then become light yellow. Only the last, adult stage, is black.

When you open the leaf, you can find a whole family. Here you can see the eggs (small white grains) and several immature specimens in different stages. Photo by James Bailey.*

Since the Cuban laurel thrips makes ornamental plants ugly, humans are always trying to find ways to kill them, especially by using pesticides or, sometimes, natural predators of the thrips. But the little insect can also fight back. When the thrips accidentally fall on people’s bodies, they tend to bite, most likely by accident, but this can end up causing a serious and annoying itch. That’s the price for messing with them.

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References:

Denmark HA, Fasulo TR, Funderburk JE (2005) Cuban laurel thrips, Gynaikothrips ficorum (Marchal) (Insecta: Thysanoptera: Phlaeothripidae). DPI Entomology Circular 59

Paine TD (1992) Cuban Laurel Thrips (Thysanoptera: Phlaeothripidae) Biology in Southern California: Seasonal Abundance, Temperature Dependent Development, Leaf Suitability, and Predation. Annals of the Entomological Society of America 85(2): 164–172. doi: 10.1093/aesa/85.2.164

Piu G, Ceccio S, Garau MG, Melis S, Palomba A, Pautasso M, Pittau F, Ballero M (1992) Itchy dermatitis from Gynaikothrips ficorum March in a family group. Allergy 47(4): 441–442. doi: 10.1111/j.1398-9995.1992.tb02087.x

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Friday Fellow: Common Grainlouse

by Piter Kehoma Boll

No matter where you live in the world, if you had flour or grains stored for too long, you may have found some sort of insect that appeared in this food, feeding on it. There are many insect species that exist as kitchen pests, including moths, beetles and also our fellow for today, the common grainlouse Liposcelis bostrychophila.

The common grainlouse, also known as the house psocid, is a member of the insect order Psocoptera, which include most species known as lice, such as booklice, barklice and common parasitic lice of mammals and birds. It is a very small insect, measuring only about 1 mm in length as an adult, and is wingless. Probably of tropical origin, it was first identified from specimens collected under tree bark in Mozambique but, during the 20th century, it started to spread quickly around the world.

Common grainlice on old whole wheat flour. Photo by iNaturalist user sea-kangaroo.*

In its natural habitat, which are likely tropical forests, the common grainlouse is not very common. However, once he ended up inside human residences, he found the perfect spot to thrive. Stored food, especially grains, are like a food paradise for them. With food being transported from one country to another, the common grainlouse conquered the whole planet in a few decades. And they are not only associated with stored food, but with almost any sort of plant matter, including straw used in mattresses and sometimes in partition walls. Despite feeding on these materials, the common grainlouse usually does not cause serious damage to them and the main problem is that its population tends to grow enormously, making it become kind of a nuisance by being there.

The reproduction of the common grainlouse occurs almost exclusively through parthenogenesis, in which females are able to generate offspring from unfertilized eggs. Males are very rare and have only been recorded recently for the first time. This is likely one of the reasons why this species is so successful invading new environments, since a single female is able to originate an entire population. There are reported cases of houses so heavily infected that the walls were completely covered by grainlice.

Several methods have been tried to contain the advance of this little creature, but most are unsuccessful. They appear to be quite resistant to chemical pesticides and even entomopathogenic fungi, i.e., fungi that infect insects. Their cuticle has a peculiar chemical composition, different from that found in other insects, that prevent fungal spores to germinate.

We can conclude that the common grainlouse is a species that is here to stay, no matter what we try to do to get rid of them.

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References:

Lord JC, Howard RW (2004) A Proposed Role for the Cuticular Fatty Amides of Liposcelis bostrychophila (Psocoptera: Liposcelidae) in Preventing Adhesion of Entomopathogenic Fungi with Dry-conidia. Mycopathologia 158(2): 211–2117. doi: 10.1023/B:MYCO.0000041837.29478.78

Turner BD (1994) Liposcelis bostrychophila (Psocoptera: Liposcelididae), a stored food pest in the UK. International Journal of Pest Management, 40(2), 179–190. doi: 10.1080/0967087940937187

Yang Q, Kučerová Z, Perlman SJ, Opit GP, Mockford EL, Behar A, Robinson WE, Steijskal V, Li Z, Shao R (2015) Morphological and molecular characterization of a sexually reproducing colony of the booklouse Liposcelis bostrychophila (Psocodea: Liposcelididae) found in Arizona. Scientific Reports 5: 110429. doi: 10.1038/srep10429

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Friday Fellow: Turnip Sawfly

by Piter Kehoma Boll

After beetles, which make up the order Coleoptera, the second most diverse group of insects is the order Lepidoptera, which includes butterflies and moths. However, the order Hymenoptera has the potential to eventually surpass Lepidoptera and get closer to the beetles because a lot of new species are being constantly described.

The most widely known hymenopterans are bees, ants and wasps, but a huge part of their diversity is made up by the so-called sawflies. One of these species is commonly known as the turnip sawfly and scientifically named Athalia rosae.

Turnip sawfly in the Netherlands. Photo by Herman Berteler.*

The turnip sawfly is found throughout the Paleartic Ecozone, from western Europe to Japan, and his common name comes from the fact that its larvae feed on plants of the family Brassicaceae, which includes the turnip, as well as the cabbage, among others. The larvae is considerably large and resembles a caterpillar, having a dark gray, almost black dorsal color, and is lighter close to the feet. When they are about to turn into a pupa, they dig into the ground, build a cocoon and remain there until they become adults.

A larva in Denmark. Photo by Donald Hobern.**

The adults measure about 6 to 8 mm in length, the females being larger than the males. The body and the legs have a yellow to orange color, darker on the dorsal surface of the thorax, which also has two large black spots. The head and the antennae are black.

An adult in Germany. Photo by Martin Grimm.*

Hymenopterans in general are characterized by a unique sexual determination in which females are diploid, i.e., have two sets of chromosomes, and males are haploid, having only one set. Matings conducted in the laboratory with the turnip sawfly, however, were able to produce anomalous combinations, including diploid males and triploid females and males. Apparently this is possible due to sex being determined by one allele in one chromosome, so that males are always homozygous and females always heterozygous, but this must be explained in another post. The fact is that the study of this peculiar system in this species is helping to understand how sex determination evolved in hymenopterans.

In adult in Russia. Photo by Roman Providuhin.*

One last interesting thing to mention about the turnip sawfly is that it is able to bypass the defense mechanisms of the plants on which its larva feeds. Plants in the family Brassicaceae produce a group of compounds called glucosinolates that give them their characteristic pungency and bitterness, such as in mustard and horseradish. These compounds are used by the plant as a defense against pests that feed on them. However, the turnip sawfly is resistant to this compounds and is able to sequestrate them and store them in their hemolymph, i.e., their “blood” in concentrations much higher than found in the plants. When attacked by a predators, such as ants, the larva releases drops of its hemolymph in a sort of defensive bleeding and can stop the attack.

The turnip sawfly may be a nuisance for humans and their crops, but it is certainly a fascinating animal.

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References:

Müller C, Agerbirk N, Olsen CE, Boevé JL, Schaffner U, Brakefield PM (2001) Sequestration of host plant glucosinolates in the defensive hemolymph of the sawfly Athala rosae. Journal of Chemical Ecology 27(12): 2505–2516. doi: 10.1023/A:1013631616141

Müller C, Boevé JL, Brakefield PM (2002) Host plant derived feeding deterrence towards ants in the turnip sawfly Athalia rosae. In: Nielsen J.K., Kjær C., Schoonhoven L.M. (eds) Proceedings of the 11th International Symposium on Insect-Plant Relationships. Series Entomologica, vol 57. Springer, Dordrecht. doi: 10.1007/978-94-017-2776-1_18

Naito T, Suzuki H (1991) Sex determination in the sawfly, Athalia rosae ruficornis (Hymenoptera): occurrence of triploid males. Journal of Heredity 82(2): 101–104. 10.1093/oxfordjournals.jhered.a111042

Oishi K, Sawa M, Hatakeyama M, Kageyama Y (1993) Genetics and biology of the sawfly, Athalia rosae (Hymenoptera). Genetica 88(2–3): 119–127. doi: 10.1007/BF02424468

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*Creative Commons License This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

**Creative Commons License This work is licensed under a Creative Commons Attribution 2.0 Generic License.

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