An invasive insect herbivore disrupts plant volatile-mediated tritrophic signalling

Abstract

Plants respond to insect attack by emission of volatile organic compounds, which recruit natural enemies of the attacking herbivore, constituting an indirect plant defence strategy. In this context, the egg parasitoid Trissolcus basalis is attracted by oviposition-induced plant volatiles emitted by Vicia faba plants as a consequence of feeding and oviposition by the pentatomid host Nezara viridula. However, this local tritrophic web could be affected by the recent invasion by the alien pentatomid bug Halyomorpha halys, an herbivore that shares the same environments as native pentatomid pests. Therefore, we investigated in laboratory conditions the possible impact of H. halys on the plant volatile-mediated signalling in the local tritrophic web V. faba-N. viridula-T. basalis. We found that T. basalis wasps were not attracted by volatiles induced in the plants by feeding and oviposition activities of H. halys, indicating specificity in the wasps' response. However, the parasitoid attraction towards plant volatiles emitted as a consequence of feeding and oviposition by the associated host was disrupted when host, N. viridula, and non-associated host, H. halys, were concurrently present on the same plant, indicating that invasion by the alien herbivore interferes with established semiochemical webs. These outcomes are discussed in a context of multiple herbivory by evaluating the possible influences of alien insects on local parasitoid foraging behaviour.

Keywords: Halyomorpha halys; Insect invasion; Multiple attack; Oviposition-induced plant volatiles; Trissolcus basalis.

Fig. 1

Response of Trissolcus basalis females to Vicia faba plant volatiles induced by Halyomorpha halys. Plant treatments: H. halys feeding and oviposition (Hh_F_O); H. halys feeding (Hh_F); unexposed (UX). n = number of replicates. Bars represent mean (±SE) of the time spent by wasp females in each arm of the Y-tube olfactometer over an observation period of 300 s (paired t tests)

Fig. 2

Response of Trissolcus basalis females to Vicia faba plant volatiles induced by concurrent infestation of Halyomorpha halys and Nezara viridula. Plant treatments: N. viridula feeding and oviposition (Nv_F_O); N. viridula feeding and oviposition and H. halys feeding (Nv_F_O + Hh_F); N. viridula feeding and H. halys feeding and oviposition (Nv_F + Hh_F_O); unexposed (UX). Bars represent mean (±SE) of the time spent by wasp females in each arm of the Y-tube olfactometer over an observation period of 300 s (paired t tests)