Orientation of Navel Orangeworm (Lepidoptera: Pyralidae) Larvae and Adults Toward Volatiles Associated With Almond Hull Split and Aspergillus flavus.

The navel orangeworm Amyelois transitella (Walker, 1863, Lepidoptera: Pyralidae), a pest of California tree nuts, is associated with the fungus Aspergillus flavus, and previous research suggests these species are facultative mutualists. Because navel orangeworm larvae exhibit improved performance on diets containing this fungus, orientation toward hostplants infected with A. flavus may be adaptive. We conducted behavioral assays to determine if larvae respond to chemical cues produced by almond hull split and fungal infection. In petri dish arenas, larvae showed a preference for 1-octen-3-ol and 2-phenylethanol, volatiles characteristic of damaged plants, as well as methanolic extracts of almond meal with 1-octen-3-ol and the fungal volatile conophthorin. In contrast, larvae displayed aversion to ethyl benzoate, an inhibitor of fungal growth. When we assessed oviposition behavior relative to substrates with and without A. flavus, females laid almost twice as many eggs near inoculated surfaces. Moreover, an average of 63% of eggs laid near inoculated substrates were fertilized, compared with 24% of eggs near uninoculated sites. We also tested the hypothesis that unfertilized eggs are laid on nutrient-poor substrates to provide supplemental nutrition for larvae in an assay comparing larval survivorship in the presence and absence of unfertilized eggs. Neonates given eggs survived 2.5 times longer on an average than unprovisioned neonates (208.8 h vs. 85.2 h), indicating that this species may compensate with cannibalism for oviposition on lower-quality food sources. We conclude that larvae orient to probable host plant and fungal volatiles associated with hull split and document a possible strategy for larvae to establish on low-quality hosts.