Single and multiple herbivory by host and non-host caterpillars on the attractiveness of parasitoids

What is it about?

It is well known that parasitoids are attracted to volatiles emitted by host-damaged plants; however, this tritrophic interaction may change if plants are attacked by more than one herbivore species. The larval parasitoid Cotesia flavipesCameron (Hymenoptera: Braconidae) has been used intensively in Brazil to control the sugarcane borer, Diatraea saccharalisFabricius (Lepidoptera: Pyralidae) in sugarcane crops, where Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae), a non-stemborer lepidopteran, is also a pest. Here, we investigated the ability of C. flavipes to discriminate between an unsuitable host (S. frugiperda) and a suitable host (D. saccharalis) based on herbivore-induced plant volatiles (HIPVs) emitted by sugarcane, and whether multiple herbivory (D. saccharalis feeding on stalk + S. frugiperda feeding on leaves) in sugarcane affected the attractiveness of HIPVs to C. flavipes. Olfactometer assays indicated that volatiles of host and non-host-damaged plants were attractive to C. flavipes. Even though host- and non-host-damaged plants emitted considerably different volatile blends, neither naïve nor experienced wasps discriminated suitable and unsuitable hosts by means of HIPVs emitted by sugarcane. With regard to multiple herbivory, wasps innately preferred the odor blend emitted by sugarcane upon non-host + host herbivory over host-only damaged plants. Multiple herbivory caused a suppression of some volatiles relative to non-host-damaged sugarcane that may have resulted from the unaltered levels of jasmonic acid in host-damaged plants, or from reduced palatability of host-damaged plants to S. frugiperda. In conclusion, our study showed that C. flavipes responds to a wide range of plant volatile blends, and does not discriminate host from non-host and non-stemborer caterpillars based on HIPVs emitted from sugarcane. Moreover, we showed that multiple herbivory by the sugarcane borer and fall armyworm increases the attractiveness of sugarcane plants to the parasitoids.

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