Submitted to: Naturwissenschaften
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/10/2004
Publication Date: 1/15/2005
Citation: Jumean, Z., Unruh, T.R., Gries, R., Gries, G. 2005. Mastrus ridibundus parasitoids eavesdrop on cocoon-spinning codling moth, Cydia pomonella, larvae. Naturwissenschaften. 92: 20-25. Interpretive Summary: Codling moth, the proverbial worm in the apple, remains the most important pest of apples and pears worldwide. Many studies have investigated chemical communication in this insect in order to understand this pest and discover methods to control it. This work shows that a coevolved parasitic wasp of codling moth cues in on chemical signals used by the larvae to aggregate in cocooning sites. While this aggregation behavior is not fully understood, it is clear that the wasp takes advantage of the signal to find its prey. The chemical signal may someday be used to attract the parasite and enhance parasitism of codling moth in orchards.
Technical Abstract: Cocoon-spinning larvae of the codling moth, Cydia pomonella L. (Lepidoptera: Olethreutidae) employ a pheromone that attracts or arrests conspecifics seeking pupation sites. Such intraspecific communication signals are important cues for illicit receivers such as parasitoids to exploit. We tested the hypothesis that the prepupal C. pomonella parasitoid Mastrus ridibundus Gravenhorst (Hymenoptera: Ichneumonidae) exploits the larval aggregation pheromone to locate host prepupae. In laboratory olfactometer experiments, female M. ridibundus were attracted to 3-day-old cocoons containing C. pomonella larvae or prepupae. Older cocoons containing C. pomonella pupae, or larvae and prepupae excised from cocoons, were not attractive. In gas chromatographic-electroantennographic detection (GC-EAD) analyses of bioactive Porapak Q extract of cocoon-derived airborne semiochemicals, ten compounds elicited responses from female M. ridibundus antennae. Comparative GC-mass spectrometry of authentic standards and cocoon-volatiles determined that these compounds were 3-carene, myrcene, heptanal, octanal, nonanal, decanal, (E)-2-octenal, (E)-2-nonenal, sulcatone, and geranylacetone. A synthetic 11-component blend consisting of these ten EAD-active compounds plus EAD-inactive (+)-limonene (the most abundant cocoon-derived volatile) was as effective as Porapak Q cocoon extract in attracting both female M. ridibundus and C. pomonella larvae seeking pupation sites. Only three components could be deleted from the 11-component blend without diminishing its attractiveness to M. ridibundus, which underlines the complexity of information received and processed during foraging for hosts. Mastrus ridibundus obviously eavesdrop on the pheromonal communication signals of C. pomonella larvae that reliably indicate host presence.