Fopius arisanus, le droit à l'erreur : spécificité parasitaire et sélection de l'hôte chez un parasitoïde ovo-pupal de mouches des fruits Tephritidae
Résumé
Many Tephritid fruit flies are major pests of fruit crops. Their management needs techniques suiting the context of sustainable agri culture development, as is biological control. The use of Fopius arisanus (Sonan) in Hawaii belongs to the greatest success of this technique. This egg-pupal parasitoid was therefore introduced in late 2003 in La Reunion to control the populations of the eight local tephritid pests, especi ally Bactrocera zonata (Saunders). This study gathers the experimentations carried out on the innate behaviour of F. arisanus females: how do they recognize, accept and locate their host inside its habitat? Fopius arisanus parasitized all local tephritid pest species but rejected the eggs of the Muscidae Stomoxys calcitrans (L). It therefore preferred the eggs of speci es of the Dacini tribe. Its pre-imaginal survival was strongly variable between the host-species, or even null on Bactrocera cucurbitae (Coquillett) which encapsulated its larvae. Fopius arisanus overcame the immune response of B. zonata and probably of other host-species. We hypothesized that the host-parasitoid interactions rely on generic mechanisms, shared by numerous Tephritidae. We moreover show that F. arisanus responded to synomones from numerous botanic families. This generalist behaviour might even lead it to habitats which are not host for Tephrititdae. It responded to kairomones from the feces and egg masses of Tephritidae, but did not to egg masses of S. cal citrans. Its innate reaction to visual stimuli was also few specialised, since it discriminated only between achromatic informations. The flight of females towards host habitat was mainly regulated by age and egg load: 6d old females have a very high potential fecundity and egg production, keeping apparently the foraging motivation constant until their death. Inside the laboratory, F. arisanus behaves innately as a very polyphagous endoparasitoid specialised on Tephritidae. We discuss the appropriateness of this behaviour in its highly variable original environment. We consider particul arly the " errors" generated by this generalist behaviour. Finally, we discuss about the use of this parasitoid in classical biological control programmes.
La famille des Tephritidae comprend de nombreux ravageurs des cultures fruitières d'importance majeure. Leur contrôle nécessite des outils de lutte utilisables dans un contexte de développement durable de l'agriculture, telle que la lutte biologique. Fopius arisanus (Sonan) été introduit fin 2003 à La Réunion afin d'y limiter les populations des huit espèces de Tephritidae d'importance économique. Cette étude regroupe les travaux menés sur le comportement de sélection de l'hôte des femelles de F. arisanm. Elles parasitent toutes les espèces locales de Tephritidae nuisibles , mais préfèrent les espèces de la tribu des Dacini. Elles répondent à des infochimiques variés. Ce comportement généraliste peut les amener sur des fruits ou des Tephritidae non hôtes. Nous supposons que les interactions hôte-parasitoïde sont modelées par des mécanismes génériques. Nous discutons de l'adéquation entre ce comportement et la variabilité de son environnement originel.