outils de détermination des espèces - Bois et forêts des tropiques

90BOIS ET FORÊTS DES TROPIQUES, 2005, N° 283 (1)FOCUS / TERMITESSynopsisIDENTIFYING TERMITES:TOOLS FOR SPECIESDETERMINATION(THE EXAMPLEOF RETICULITERMESIN EUROPE)Magdalena KUTNIK,Anne-Geneviève BAGNÈRESTwo termite genera occurin Europe: the Kalotermes (whichfeed on dry wood) and Reticulitermes(subterranean termites). The Reticulitermesare the most abundant in thenatural environment, but they areincreasingly found in urban environments,where their arrival essentiallycorrelates with human activity. Sixspecies (including one described in2003) and one sub-species are currentlyknown in Europe, mainly in thesouthern countries (Spain, Portugal,France, Greece and Italy). They arecontinuing to spread, and theirappetite for cellulose is causing agreat deal of damage wherever woodis used as a construction material.All termite species are very similar inmorphology, but they react quite differentlyto the various products usedin termite control treatments. It istherefore important to identify thetarget species clearly so that themost appropriate treatment can beused. Research on the differentspecies and their identification alsohelps to track both their evolutionaryhistory and their expansion.The three main techniques used fortermite identification are morphologicalobservation, analytical chemistryand molecular biology.Morphological observationof termitesTermite societies are organised intocastes (workers, soldiers and reproductives).The head of the worker termitefeatures a rigid skeletal part, thepost-clypeus, whose flattened shapein characteristic in the species R. santonensis.Reproductives of thisspecies have yellow tibias. All otherspecies have black tibias, except theCorsican sub-species. Finally, themouthparts in R. santonensis soldiershave a characteristic shape.This means that morphological criteriacan only distinguish R. santonensisfrom all other subterranean termitespecies.ChemotaxinomyMost termite castes are blind, andcommunicate only through chemicalsignals. These are essentially pheromonal(volatile sexual or trackingpheromones and contact pheromonesallowing recognition among individuals)or allomonal (defensive substancesin soldier termites)In all termites, the body is covered witha cuticle containing long-chain hydrocarbonswhose properties and quantitiesvary with each species. Thesehydrocarbons enable termites torecognise each other by touchingantennae. Reticulitermes soldiers havea defensive gland at the front of thehead, which contains terpenes that areemitted when they are under attack.The nature of these defensive substancesis also specific to each species.The specific nature of these chemicalsignatures may be used to distinguishbetween species. The hydrocarbonsand terpenes can be extracted byplunging the termites into an organicsolvent, then separating the substancesby gas chromatography.Analyses of these compounds providean effective basis for distinguishingbetween all European species of termites.The technique is widely usedbecause it is both quick and cheap,but it still requires special preparationof the samples to be identified.Molecular phylogenyand genetic fingerprintingDNA extracted from a single termitecan be amplified with the polymerasechain reaction technique. Thesequence obtained is then analysedby computer. DNA sequences arecharacteristic in each species andmay be used simply as genetic fingerprints.As well as their value as a taxonomictool, molecular studies on Europeantermites have contributed new informationthat has helped to clarify relationshipsbetween species. Thesestudies have successively focusedon proteins, mitochondrial DNAsequences and nuclear DNA (encodingor not). Today, mitochondrialsequences, which remain very consistentover the evolution of a species,are the tools most commonly used todetermine relationships between termitespecies. The most exhaustivelyresearched mitochondrial genes intermites are those coding forenzymes in the respiratory chain andfor ribosomal RNA. An overall phylogenesisfor the Reticulitermes familyin Europe was recently established byanalysing sequences of this type.An overall taxonomic review ofEuropean termites is currently underway. These termites are causing considerabledamage to residentialbuildings and are continuing tospread into urban areas. Studies inanalytical chemistry and molecularbiology are helping to distinguishbetween the species concerned andto better adapt control methods totheir highly specific ecology that is asyet little understood in Europe.