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Insect Species

INRA is working to build a database of molecular and morphological data to identify crop pests - insects, disease - at international level. Interview with Jean-Claude Streito, agronomist and entomologist at the Centre for Biology and Management of Populations, INRA Montpellier.

Marmorated stink bug (Halyomorpha halys), polyphagous crop pest detected in Switzerland in 2007 and France in 2012. Smartphone application developed within the framework of  AGIIR, a citizen oversight programme. © INRA
By Pascale Mollier, translated by Inge Laino
Updated on 11/24/2014
Published on 10/15/2014

Tell us about your project for a new database.

Jean-Claude Streito: We want to create a reliable molecular database to identify crop pests, be they insects, nematodes or diseases. Right now there is no such database. The biggest DNA database, GenBank, consists mostly of human and mouse sequences but decidedly few for pests. When it comes to insects, many errors are made in identifying specimens for which we have sequences. When we compare to our own sequences for specimens that we ourselves have identified according to species, the error rate is over 80% for fig wasps, for example! There is a European database, but only for quarantine organisms, i.e. around 300 pest species.

Ideally, we would have a molecular marker for each pest. That is, a sequence that would allow us to identify the species beyond the shadow of a doubt, and to differentiate between neighbouring species. That accounts for a minimum of 3,000 insect species in terms of crop pests in France and similar species.

For starters, we’re focussing on tomato and grapevine (1), and aim to identify marker sequences for a maximum number of species associated with these crops, be they viruses, bacteria, fungi, insects, nematodes, etc., from different geographical regions.

Why is identifying species important?

J-C S.: When it comes to pests, we have to be swift with a diagnosis so that we can curb damage to crops. Of course, the first diagnosis comes from direct observation in the field. That is where the smartphone app developed at INRA Bordeaux comes in very handy. By comparing pictures, we can recognize pests based on morphological criteria (2). In fact, after the moth and Asian hornet, a module was opened very recently to track a new crop pest, the marmorated stink bug. But that is not always enough, because several insect species look a lot alike, and only DNA analysis allows us to distinguish one from the other…provided we know the marker sequence of the species. Ideally, PCR testing might be possible in the field, as is already the case for viruses.

Diagnoses are also very important in detecting invasion by a non-indigenous pest introduced through transport or trade. We have to be able to run targeted controls at customs to stop dangerous species without being accused of hindering free exchange or casting the net too wide…

Are you also interested in auxiliary insects?

J-C S.: Auxiliary insects are used as a biological method to combat pests. In order to be able to promote biological methods, we have to be able to accurately identify species. It’s important for the companies that market auxiliary insects. It’s also a necessary condition to run risk analyses when new auxiliaries are needed. For example, right now we have a company asking us to accurately identify the six auxiliaries they market. We’ve been able to determine the species morphologically for the ladybugs, stink bugs and mites. We have not been able to do so, however, for the lacewing of the genus Chrysoperla, because it involves several species grouped together which resemble each other morphologically and are marketed under the same name… because it’s hard to identify these insects morphologically, we are developing a molecular identification key, but some species are still missing for us to be able to validate it.

Auxiliary insects are often a real taxonomic puzzle. For example, the stink bug that preys on the genus Macrolophus, sold to combat whiteflies and thrips that attack tomato, were marketed under the name caliginosus (a species that are a bad match for tomatoes!), while in fact they belong to the species M. pygmaeus. It was by comparing morphological and molecular characteristics that the error was corrected. Another example is the whitefly Bemisia tabaci, which is actually a grouping of about 30 species that we are unable to distinguish morphologically, but which have different features of life history with a significant impact on agriculture.

How do you feed your database?

J-C S.: To implement our database, we are tapping into our network of entomologists, and when that is not enough, we go out and recruit in several countries. We are currently preparing missions in South Africa, Chile and California, where grapevines grow, to collect in particular new species of cochineal and leafhoppers that we don’t have yet. We also use sequences already registered in existing databases, when they are reliable. We have an internal database made up between 10-15,000 insect DNA sequences (3). We regularly discover new sequences never before recorded! (4).
 
(1) Lycovitis project funded by the metaprogramme SMACH

(2) AGIIR app, used as a participatory scientific tool to track three invasive species: the Asian hornet, pine processionary moth, and, more recently, stink bug.

(3) Database implemented by different projects funded by the SPE division, the metaprogramme SMaCH, Casdar or other European projects.

(4) Three insects are named after Jean-Claude Streito, who discovered them: Chaetabraeus streitoi Gomy, 1996 (Coleoptera, Histeridae), Corduba streitoi Moulet, 2005 (Hemiptera, Coreidae), and Tinicephalus streitoi Matocq 2007 (Hemiptera, Miridae).

Contact(s)
Scientific contact(s):

Associated Division(s):
Plant Health and Environment, Forest, Grassland and Freshwater Ecology
Associated Centre(s):
Occitanie-Montpellier

To each species its barcode

A barcode is a fragment of DNA that allows one species to be distinguished from another. In other words, sequences vary only slightly between individuals of the same species, but widely between individuals of different species. The image of the barcode, which is particularly evocative, was born in Canada in the early 2000s. One of the most frequently used barcodes is a fragment of approximately 650 base pairs, contained in the mitochondrial gene of cytochrome oxydase (COI), a protein involved in the respiratory chain. It works for some insect groups, like fruit flies, but not for others, like certain beetles or auxiliary insects. For them, another barcode is used, namely a region of non-coding nuclear ribosomal DNA that is highly polymorphic (ITS2). There are other barcodes for bacteria, fungi, etc.