Use of herbivore-induced plant volatiles as search cues by Tiphia parasitoids to located their below-ground scarabaeid hosts

Japanese beetle, Popillia japonica Newman, and oriental beetle, Anomala orientalis (both Coleoptera: Scarabaeidae) are considered invasive species and have been reported as key pests of urban landscapes in the Northeastern United States. Tiphia vernalis Rohwer and Tiphia popilliavora Rohwer (Hymenoptera: Tiphiidae) were introduced as biocontrol agents against these beetles. These parasitic wasps burrow into the soil and search for grubs. When a host is found, the wasp attaches an egg in a location that is specific for the wasp species. It is unknown if these wasps can detect patches of concealed hosts from a distance above ground and what role, if any, herbivore-induced plant volatiles play in their host location. This study evaluated the responses of female T. vernalis and of T. popilliavora to grub-infested and healthy plants in Y-tube olfactometer bioassays. Also the effect of root-herbivory on the composition of turfgrass (Poaceae) volatile profiles was investigated by collecting volatiles from healthy and grub-infested grasses. Tiphia wasps were highly attracted to volatiles emitted by grub-infested tall fescue (Festuca arundinacea Schreb.) and Kentucky bluegrass (Poa pratensis L.) over healthy grasses. In contrast, wasps did not exhibit a significant preference for grub-infested perennial ryegrass (Lolium perenne L.) as compared to the control plants. The terpene levels emitted by grub-infested Kentucky bluegrass and tall fescue were greater than that of control plants. Low levels of terpenes were observed for both test and control perennial ryegrass. The elevated levels of terpenes emitted by grub-infested Kentucky bluegrass and tall fescue coincided with the attractiveness to the tiphiid wasps. Here we provide evidence that plant exposure to root-feeding insects P. japonica and A. orientalis resulted in an increase of terpenoid levels in turfgrasses, which strongly attracts their above ground parasitoids.