The sunflower moth, Homoeosoma electellum (Hulst), and banded sunflower moth, Cochylis hospesWalsingham, are important insect pests of cultivated sunflower, Helianthus annuus L., in North America. We tested whether females and larvae of the two species were able to differentiate between different phenological stages of sunflower heads, as well as whether females of the two species could detect the presence of conspecific larvae in heads. Sunflower moth adult females laid more eggs on R5-stage than R2-stage sunflower heads, and also on covered R5-stage heads as compared to covered R2-stage heads. In contrast,C. hospes laid more eggs on R2-stage heads than R5-stage heads, but there was no differentiation between the two when the heads were covered. In a bioassay testing, the preferences of neonate larvae of H. electellum and C. hospes to R2-stage and R-5-stage head tissues of both species exhibited preferences to the head stage they typically feed on (that is, H. electellum larvae preferred R5 florets to R2 involucral bracts, whereas, C. hospes larvae preferred R2 involucral bracts to R5 florets). Finally, both H. electellum and C. hospes females exhibited ovipositional preferences to uninfested sunflower heads over heads infested with conspecific larvae, suggesting that females could detect infested heads, possibly by a change in chemical signal. This study demonstrates the importance of chemical stimuli in the preferences of these two species to sunflower phenological stages.
Key words: Sunflower, Homoeosoma electellum, Cochylis hospes, involucral bracts, chemical stimuli.
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