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Diaeretiella rapae and Asaphes vulgaris are two insects that lay their eggs within the aphid bodies. In particular, Diaeretiella rapae (a hymenopteran species belonging to Braconidae) is an aphid parasitoid  particularly studied for its attack to the aphid Brevicoryne brassicae, whereas Asaphes vulgaris (a wasp belonging to the family Pteromalidae) is a secondary insect parasitoids that develop at the expense of a primary parasitoid, thereby representing a highly evolved fourth trophic level.

As reported by Jim Conrad here:

The story begins when a tiny wasp inserts an egg into the aphid. In about two days a wasp grub hatches and feeds on the living aphid by osmosis for about six to eight days, killing the aphid. During this time the larva expands in size so that the aphid’s body swells, giving it a bloated appearance. The larva cuts a slit in the bottom of the aphid, and, working from inside the aphid, attaches the dead aphid to the leaf with silk and glue. Then the wasp grub still inside the mummy molts to the pupal stage as the dead aphid turns from green to brown, becoming a “mummy.” After four or five days a wasp emerges from the pupa inside the mummy and exists the aphid by cutting a circular hole in the mummy’s top.

As a consequence you can see round-shaped aphids with a round hole in their abdomen after the emergence of the wasps or, if you are very lucky or very patient, you can see the wasp emergence as occurred in the marvellous photo below (from John H Gagnon).

 

Up to date, mummies have been regarded just as witness of the wasp presence  or dissected (before wasp emergence) to evaluate the rates of parasitism, along with morphological identification of the parasitoid species.

Starting from recent studies  demonstrating the potential of environmental DNA such as insect exuviae or faeces for invertebrate specimen identification, Yann-David Varennes and colleagues hypothesized that aphid DNA can be amplified from both full and empty mummies along with parasitoid and hyperparasitoid DNA and that PCR followed by single-stranded conformation polymorphism (PCR-SSCP) analysis will enable species-level identification of aphid, parasitoid and hyperparasitoid from both pre- and postemergence mummies.

According to the published results, DNA is amplifiable in empty aphid mummies for as long as 3 weeks after parasitoid emergence. However, the simultaneous identification of several species in a single mummy sample was rare, which hinders the accurate inference of trophic links. Furthermore, the amplification and identification of both parasitoids and hyperparasitoid were successful also for empty mummies (i.e. after emergence). As Authors stated:

To our knowledge, the detection of hyperparasitoid DNA within empty aphid mummies has never been reported, and our results illustrate the possibility of using generalist primers to circumvent the difficulties of designing a specific primer. (…) However, the lack of simultaneous detection of species from one single mummy indicates the need for further research to technically improve the method before its application to field-collected samples. Further areas of research include mitigation of preferential amplification, species-specific bias in DNA preservation and amplification and the potential of the proposed PCR-SSCP approach to separate a large number of species.

 

ResearchBlogging.orgVarennes, Y., Boyer, S., & Wratten, S. (2014). Un-nesting DNA Russian dolls – the potential for constructing food webs using residual DNA in empty aphid mummies Molecular Ecology DOI: 10.1111/mec.12633

Neonicotinoids and fipronil are currently highly used insecticides applied in different cases, including seed coating,
bathing, foliar spray applications and trunk injection. These compounds are commonly used for insect pest management since they are very effective due to their disruption of the neural transmission in the central nervous system of organisms. Indeed, neonicotinoids bind to the nicotinic acetylcholine receptor (nAChR) , whereas fipronil inhibits the GABA receptor. Both pesticides produce lethal and a wide range of sublethal adverse impacts and even low-dose exposure over extended periods of time can culminate into substantial effects.

According to literature data, neonicotinoids and fipronil can have negative effects on physiology and survival for a wide range of non-target invertebrates in terrestrial, aquatic, wetland, marine and benthic habitats, but their effects on non-target species has been frequently debated.

A definitive reply could come from The Worldwide Integrated Assessment of the Impact of Systemic Pesticides on Biodiversity and Ecosystems (WIA), the most comprehensive study of neonics ever undertaken that examined over 800 scientific studies spanning the last five years.

The conclusionspublished in the international journal Environmental Science and Pollution Researchclearly indicate that:

Overall, the existing literature clearly shows that present-day levels of pollution with neonicotinoids and fipronil caused by authorized uses (i.e. following label rates and applying compounds as intended) frequently exceed the lowest observed adverse effect concentrations for a wide range of non-target species and are thus likely to have a wide range of negative biological and ecological impacts. The combination of prophylactic use, persistence, mobility, systemic properties and chronic toxicity is predicted to result in substantial impacts on biodiversity and ecosystem functioning. The body of evidence reviewed in this Worldwide Integrated Assessment indicates that the present scale
of use of neonicotinoids and fipronil is not a sustainable pest management approach and compromises the actions of numerous stakeholders in maintaining and supporting biodiversity and subsequently the ecological functions and services the diverse organisms perform.

At present pesticides represent the first defense line in the field, whereas these chemicals need to become the last resort in the chain of preferred options that need be applied first. In particular, preferred options should include organic farming, diversifying and altering crops and their rotations, inter-row planting, planting timing, tillage and irrigation, using less sensitive crop species in infested areas, using trap crops, applying biological
control agents, and selective use of alternative reduced-risk insecticides.

 

 

further-readingFurther reading:

Gibbons, D., Morrissey, C., & Mineau, P. (2014). A review of the direct and indirect effects of neonicotinoids and fipronil on vertebrate wildlife Environmental Science and Pollution Research DOI: 10.1007/s11356-014-3180-5

J. P. van der Sluijs, V. Amaral-Rogers, L. P. Belzunces, M. F. I. J. Bijleveld van Lexmond, & et al. (2014). Conclusions of the Worldwide Integrated Assessment on the risks of neonicotinoids and fipronil to biodiversity and ecosystemfunctioning Environmental Science and Pollution Research : 10.1007/s11356-014-3229-5

Originally posted on Parasite Ecology:

Last week, I talked about the new Godzilla movie and how I thought that the MUTOs should have been parasitoids.  This week, let’s talk about some awesome, real life parasitoids: parasitoid wasps (Aphidius ervi).

Quickly, the life cycle works like this: the female wasp finds an aphid nymph, she stabs the aphid with her ovipositor, and then she typically lays one egg inside the aphid.  After one day, the egg hatches into a larval parasitoid, and the larva hangs out inside the aphid while eating the aphid’s innards.  After about one week of this, the aphid dies.  Actually, the aphid’s corpse becomes a “mummy,” and the larva pupates inside the mummy before eventually emerging as an adult parasitoid.  Mating happens, and then the female wasps go off to infect more aphids.

But here’s an interesting complication: some aphids are protected by bacterial symbionts (Hamiltonella defensa). …

View original 346 more words

ResearchBlogging.org Genome sequencing projects have been for long time possible goals for few model organisms and required the concerted effort of large consortia. The fast progress in high-throughput sequencing  and the simultaneous development of several low-cost bioinformatic tools made possible for individual research groups to generate de novo draft genome sequences for any organism of choice.

Due to the high cost and the considerable effort involved in such a project, the important first step is to thoroughly plan step-by-step the workflow involved in genome sequencing, assembly and annotation with particular reference to large and complex genomes. In order to facilitate this planning, Robert Ekblom and Jochen B. W. Wolf published in Evolutionary application a sort of tutorial entitled “A field guide to whole-genome sequencing, assembly and annotation” and targeted at scientists interested in plan whole-genome sequencing projects. As they wrote:

Here, we introduce the workflow of a typical whole-genome sequencing project conducted by an individual research group. This field guide aims at introducing principles and concepts to beginners in the field and offers practical guidance for the many steps involved. It builds largely upon our own experience with vertebrate genome assembly. We limit the scope to genomic data, focusing on large and complex genomes (…). We discuss sequencing, assembly and annotation, highlighting typical routines and analytical procedures. Our intention is not to provide a comprehensive review of sequencing technology, assembly algorithms or downstream downstream analyses, as this has already been performed. For these topics, we instead list exemplary literature and provide relevant entry points.

eva12178-fig-0001I frequently use data from genome project, but I never planned a whole-genome sequencing of my aphids, but… what does it really mean to plan a genome sequencing? The figure at right represents the workflow of a typical de novo whole-genome sequencing project that Ekblom and Wolf suggested in their tutorial (as figure 1).

Among the first decisions when starting, a genome sequencing project is the choice of sequencing platform, the type and amount of sequence data to generate. The latter is often limited by project funding, and the former may depend on which sequencing technology is promptly available. Currently, most genome projects use a shotgun sequencing strategy for genome sequencing and there is a clear trend moving away from traditional Sanger sequencing (~1 kb sequence reads) and Roche 454 sequencing (up to 800 bp) towards short read technologies such as Illumina HiSeq (at present typically 150 bp) and SOLiD (typically 50 bp).

After sequencing you have to plan how to assembly, validate and annotate your genome of interest and to allow other users to improve your first draft assembly and annotation, all available raw data should be uploaded in public databases.

It is a huge work… but I would like to thank all the scientists that made this with thier experimental models making available for all of us a huge amount of data for future work. As Ekblom and Wolf wrote:

The possible development of rapid and compact sequencing solutions that may be applied directly in the field situation would be particularly useful for many conservation applications. Another important area of progress lies in the usage of low-quality samples, obtained from noninvasive sampling or museum material that would allow monitoring of genomic diversity through time. Developing ways of storing and sharing genomic data will also be crucial, to make the most efficient use of these resources for conservation. In spite of these promising developments, we need to be aware that science alone is not sufficient to meet future conservation challenges. The technical transition from conservation genetics to genome-scale data therefore needs to be tightly accompanied by a discussion of how applied conservation biology can best benefit from genomic data.

 

Ekblom, R., & Wolf, J. (2014). A field guide to whole-genome sequencing, assembly and annotation Evolutionary Applications DOI: 10.1111/eva.12178 (the paper has been published as open access manuscript)

During summer I’m free from work with class students (just few oral examinations) so that I have more time to look for updated genome annotations. At present there are at least three intriguing news related to insect genomes. The first is related to the pea aphid Acyrthosiphon pisum Annotation Release 101. Pea aphids are host-plant specialists, they can reproduce both sexually and asexually, and they have coevolved with an obligate bacterial symbiont. The A. pisum genome has extensive gene duplication in more than 2000 gene families as well as loss of evolutionarily conserved genes. Gene family expansions relative to other published genomes include genes involved in chromatin modification, miRNA synthesis, and sugar transport. Gene losses include genes central to the IMD immune pathway, selenoprotein utilization, purine salvage, and the entire urea cycle.

Annotationhttp://www.ncbi.nlm.nih.gov/genome/annotation_euk/Acyrthosiphon_pisum/101/

Genome: http://www.ncbi.nlm.nih.gov/genome/?term=txid7029[orgn] The second update is related to the red flour beetle Tribolium castaneum Annotation Release 102. Tribolium castaneum is a common pest that evolved the ability to interact with a diverse chemical environment, as shown by large expansions in odorant and gustatory receptors, as well as P450 and other detoxification enzymes.  Tribolium now represents the third best invertebrate model for genetic and molecular studies  after Drosophila and Caenorhabditis elegans.

Annotation: http://www.ncbi.nlm.nih.gov/genome/annotation_euk/Tribolium_castaneum/102/

Genome: http://www.ncbi.nlm.nih.gov/genome/?term=txid7070[orgn] The last one is related to the jewel wasp Nasonia vitripennis Annotation Release 101.  Nasonia is an emerging genetic model, particularly interesting for evolutionary and developmental genetics. Key findings include the identification of a functional DNA methylation tool kit, the presence of several hymenopteran-specific genes (including diverse venoms), the lateral gene transfers among Pox viruses and the rapid evolution of genes involved in nuclear-mitochondrial interactions that are implicated in speciation.

 

Annotation : http://www.ncbi.nlm.nih.gov/genome/annotation_euk/Nasonia_vitripennis/101/ Genome: http://www.ncbi.nlm.nih.gov/genome/?term=txid7425[orgn]

More than 40 years ago James Mallet published in Trends in Ecology and Evolution a paper entitled “The Evolution of insecticide resistance: have the insects won?”  where he stated at the end of the paper:

The insects have won for the moment in tropical malaria control, and they seem to be winning in cotton, among a number of other crops. Pest susceptibility is a valuable natural resource that has been overexploited. Better management of this susceptibility resource will require a better knowledge of the ecology and population genetics of insects, as well as the political will to make resistance management strategies work.

I’m not sure that insects won, but I’m sure that we are not winning this battle so that… what is the future of insect control? In the last decades we used different kinds of insecticides that were costly not only for farmers, but also four our health and for the environment where we live. The World Health Organization estimates that there are 3 million cases of pesticide poisoning each year and up to 220,000 deaths, primarily in developing countries. Children, for instance, are particularly vulnerable to the harmful effects of pesticides and even very low levels of exposure during development may have adverse health effects.

At the same time more than 500 crop pest insects already evolved resistance to conventional insecticides. Mosquitoes that are capable of transmitting malaria are now resistant to virtually all pesticides used against them. Many populations of the corn earworm, which attacks many agricultural crops worldwide including corn, cotton, tomatoes, tobacco, and peanuts, are resistant to multiple pesticides. Lastly, the green peach aphid Myzus persicae is resistant to more insecticides than any other insects and it should merit a gold medal for insecticide resistance since  M. persicae indeed has a documented resistance to 71 synthetic chemical insecticides.

So… what is the future for insect control in the field? Pesticides represented a significant progress in controlling pests, but there is another way. It involves listening to plants, which have fought this battle much longer than we have!

A nice summary of this “new way” has been recently published in an intriguing editorial by entitled “Listen to the plants” by Kat McGowan. As she wrote, plants are talking to bugs in a language we can try to understand:

When a caterpillar or a beetle starts chewing on a leaf, the plant responds by synthesizing its own defense chemicals in an attempt to drive away the insect. It also releases a chemical plume into the air, a message that can be intercepted by creatures nearby. Other plants respond to these alerts by producing their own chemical weapons, substances that repel leaf-eating insects. Predators that eat plant pests also detect the signals, using them like beacons to locate their prey.

The first evidences that plants might be able to communicate with one another came more than 40 years ago, now we have to crack the plant code so that we can understand when a plant could be damaged and make plants less attractive for pest crop. At the same time, as McGowan wrote:

Plants aren’t the only ones listening to these messages. Predatory bugs and caterpillar parasites sniff out the emissions of a plant being eaten, and like Batman responding to a bat signal in the night sky, swoop in for the rescue. 

ResearchBlogging.orgA proof of the results we could obtain understanding the plant language comes from the “push-pull” system developed by the  International Center of Insect Physiology and Ecology in Kenya in collaboration with Rothamsted Research, the most famous agricultural research station in the world (here a free report on this method). According to this strategy, farmers  use some plants whose emissions repel pest crop insects, keeping them away from the grains. Then they “pull” insects using plants that  attract them increasing the field yields in view of the reduced damages due to insects.

Genetically engineered sentinel plants could be stationed in fields like canaries in the coal mine—the first to get attacked and the first to raise the alarm, so valuable crops get a head start on making their own defenses. Crops that naturally produce pest-attracting volatiles could instead be genetically silenced, a way of cloaking them so that the bugs don’t even know they’re there.

Plants coexisted with pest crop insects since long time so that we have to understand how they detect their enemies and recruit their protectors. By understanding how the crops that feed us deploy their own defenses, we can turn plants into our allies by learning to speak their language.

 

Further reading:

Hassanali, A., Herren, H., Khan, Z., Pickett, J., & Woodcock, C. (2008). Integrated pest management: the push-pull approach for controlling insect pests and weeds of cereals, and its potential for other agricultural systems including animal husbandry Philosophical Transactions of the Royal Society B: Biological Sciences, 363 (1491), 611-621 DOI: 10.1098/rstb.2007.2173

Pickett JA, Woodcock CM, Midega CA, & Khan ZR (2014). Push-pull farming systems. Current opinion in biotechnology, 26, 125-32 PMID: 24445079

Sobhy, I., Erb, M., Lou, Y., & Turlings, T. (2014). The prospect of applying chemical elicitors and plant strengtheners to enhance the biological control of crop pests Philosophical Transactions of the Royal Society B: Biological Sciences, 369 (1639), 20120283-20120283 DOI: 10.1098/rstb.2012.0283

Peñaflor, M., & Bento, J. (2013). Herbivore-Induced Plant Volatiles to Enhance Biological Control in Agriculture Neotropical Entomology, 42 (4), 331-343 DOI: 10.1007/s13744-013-0147-z

Several hemipteran species are involved in mutualistic relationships with ants so that aphids produce honeydew, a sweet waste product enriched in sugar and aminoacids, that ants collect as a supply for their diet. In return, ants defend hemipterans from natural enemies, such as ladybirds and parassitoid wasps.

IMG_2277_2A well-studied example is the aphid-ant mutualism and about 60% of the aphid species is involved in a mutualistic relationship with ants, called myrmecophily. The strength of this mutualism is highly variable in aphids and, as reported in the aphid genus Chaitophorus, the mutualism may be obligate, facultative or non-existent at all suggesting that myrmecophily is an evolutionarily labile trait in aphids.

About ten years ago, Alexander W. Shingleton and colleagues published in the journal Molecular Phylogenetics and Evolution the first aphid phylogeny reconstructed specifically to elucidate the evolutionary pattern of ant tending amongst a group of homopterans. According to their data, myrmecophily has been apparently gained and lost at least five times in the genus Chaitophorus.

This high rate of evolutionary change in ant–aphid interactions suggests that this mutualism is not due to co-evolutionary adaptations so that aphids can be in touch with different ant species and in literature there are very few examples of aphids being wholly dependent on a single species of ant. In some cases, aphids seem to be in symbiosis with a single ant species, but this is more a consequence of the relatively low diversity of ants rather than a dependence of the aphids on that particular ant species. As Shingleton suggested in 2003:

This tolerance of aphids for a wide variety of ant mutualists may relate to their extremely specific diet. Most aphids are mono- or oligophagous, showing a high degree of host specificity. A mutualistic monophagous aphid that also associates with only one or two species of ants will doubly limit its ability to colonise new host plants, as it will not only be restricted to plants of a certain species, but also to plants located near the nest of the mutualist ant. This may be selectively disadvantageous and limit the strength of the relationship between any one species of ant and aphid,

ants_aphids_sugar by Charles ChienInterestingly, although almost all aphids produce honeydew, are susceptible to predation and co-occur in the same habitats as ants, some species only established a mutualism with ants so that it is intriguing to understand the origin of such a symbiotic relationship.

At this regard, Shingleton et al. suggested in 2005 that the pattern of ant mutualism among aphids may be explained by differences in feeding position on their host plants so that there was a strong association between feeding on woody parts of the host plant and ant tending. According to this hypothesis, ant tending may therefore be one method of escaping interspecific competition by allowing an aphid to feed at a site unavailable to untended species. This means that if you feed yourself in a risky place, you need some protection and ants can help you. As Shingleton suggested in 2005:

It follows that aphids feeding on deeper phloem elements have evolved additional traits to better attract ants, as an evolutionary response to tending. Several of these traits have been identified. For example, tended aphids appear to adjust the quality and quantity of their honeydew to successfully attract ants. In particular, tended aphids increase the honeydew concentration of melezitose, a trisacharide particularly attractive to ants. There is evidence that such adjustments incur costs to the aphids, which are likely to increase if there is competition between aphid species for ant partners. We suggest that only in species feeding on deeper phloem elements will the costs of these traits be outweighed by the benefits of protection from predators.

The natural history of the Chaitophorus–ant mutualism suggests therefore that it is ‘easy’ for an aphid lineage to gain or lose tending. Ants can be induced to tend even non-myrmecophilic species such as C. tremulae if there is no other available source of carbohydrates, although they prefer to tend myrmeophilic species such as C. populeti when given a choice. The pattern of myrmecophily amongst the Chaitophorus species may be better understood as a hierarchy of ant preference, with different species varying in attractiveness to ants. Ant preference may in turn be influenced by honeydew quality, quantity, and availability. Host plant species, feeding position on the host plant, and competition with other aphids for the attention of ants may all influence whether an aphid species is actually tended or not. The pattern of myrmecophily amongst the aphids may therefore depend on a number of subtle differences between species.

Proatta-butteli_section-break

Shingleton, A., & Stern, D. (2003). Molecular phylogenetic evidence for multiple gains or losses of ant mutualism within the aphid genus Chaitophorus Molecular Phylogenetics and Evolution, 26 (1), 26-35 DOI: 10.1016/S1055-7903(02)00328-7
Shingleton, A., Stern, D., & Foster, W. (2005). The origin of a mutualism: a morphological trait promoting the evolution of ant-aphid mutualisms. Evolution, 59 (4) DOI: 10.1554/04-584

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