Mature larvae of the codling moth, Cydia pomonella L. (Lepidoptera: Olethreutidae), exit the fruit and seek sites suitable for pupation. Spinning cocoons in such sites, larvae produce a complex, cocoon-derived blend of volatiles recently shown to attract and/or arrest both conspecific larvae and the prepupal parasitoid Mastrus ridibundus Gravenhorst (Hymenoptera: Ichneumonidae). Here we report components of this blend that constitute the pheromone of fifth-instar C. pomonella larvae. Thirty-one two-choice olfactometer experiments showed that a blend of synthetic (E)-2-octenal, (E)-2-nonenal, sulcatone, and geranylacetone, in combination with either 3-carene and/or three saturated aldehydes (octanal, nonanal, decanal), elicited behavioral responses from C. pomonella larvae. In on-tree experiments with corrugated cardboard bands as pupation sites for larvae affixed to tree trunks, and with laboratory-reared larvae released onto such trees, more larvae cocooned in those halves of cardboard bands baited with cocoon-spinning conspecific larvae, or with synthetic pheromone components, than in unbaited control halves of the bands. With the larval aggregation pheromone identified in this study, there might be an opportunity to manipulate C. pomonella larvae in commercial fruit or nut orchards.
Traditionally, studies of sexually size-dimorphic birds and mammals report that the larger sex is more sensitive to adverse environmental conditions during ontogeny. However, recent studies in avian species that exhibit moderate size-dimorphism indicate that the smaller sex may be more sensitive to poor rearing conditions. To better understand sex-specific sensitivity in a passerine exhibiting moderate size-dimorphism, we examined growth, cell-mediated immunity (CMI) and survival of European starling Sturnus vulgaris nestlings following an experimental reduction of maternal rearing ability (via a feather-clipping manipulation). Contrary to conventional theory, daughters showed reduced growth in both body mass and measures of structural size in response to the maternal treatment. In contrast, sons showed no reductions in any of these traits in relation to the treatment. No sex-specific differences in nestling CMI were found for either group, although CMI of nestlings raised by manipulated mothers were higher than those of control nestlings. Finally, fledging sex ratios did not change from those at hatching indicating that neither sex appeared differentially sensitive to the maternal treatment in terms of mortality. These results reveal that variation in the quality of the rearing environment can have significant effects on the smaller sex of a passerine exhibiting moderate dimorphism and as such support recent studies of species with small-moderate sexual size-dimorphism. Combined results suggest that sex-specific effects of environmental variation on nestling development may be both context-(i.e., brood size, resource level, hatching order) and temporally-(when during development they occur) specific. Furthermore, more studies are needed that examine multiple traits at several developmental stages and then follow the sexes over the longerterm to examine potential effects on fitness.
Insect aggregation pheromones are defined as chemical substances produced by members of one or both sexes that induce members of both sexes to form aggregations (Borden 1984). Aggregation pheromones are typically emitted by and attract adult insects. Interestingly, larvae of the codling moth, Cydia pomonella L. (Lepidoptera: Olethreutidae), seeking pupation sites will aggregate in response to pheromone produced by cocoon-spinning conspecific larvae (Duthie et al. 2003). Such aggregations may be part of a mating strategy in which protandrous males are arrested by sex pheromone emanating from mature female pupae, thus allowing mating to ensue as soon as a female moth ecloses (Duthie et al. 2003). The cocoon-derived pheromone also attracts the specialist prepupal parasitoid Mastrus ridibundus Gravenhorst (Hymenoptera: Ichneumonidae), which “eavesdrops” on pheromonal communication of cocoon-spinning larvae (Jumean et al. 2004).
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