Trissolcus japonicus foraging behavior: Implications for host preference and classical biological control

The brown marmorated stink bug, Halyomorpha halys, is an alien pest native to East Asia, which in the past two decades has invaded USA, Europe and other countries around the globe, causing severe economic losses and public nuisance. The Asian egg parasitoid Trissolcus japonicus is the most promising agent currently under study for the classical biological control of H. halys. The foraging behavior of this wasp was investigated in response to chemical traces – ‘footprints’ – deposited by its host H. halys and by a suboptimal predatory host species, the spined soldier bug, Podisus maculiventris. Motion tracking software (Ethovision) was employed to record and analyze the behavior of T. japonicus on stink bug-contaminated and on control substrates. Wasps exhibited a ‘motivated searching’ behavior (i.e. longer residence time, slower walking velocity, higher angular velocity and coverage of greater distances) in response to footprints originating from females and from males of both species compared to blank controls. However, this searching behavior was significantly more intense on H. halys footprints, compared to those of P. maculiventris. Moreover, T. japonicus significantly intensified its searching on footprints of all mobile nymphal instars of H. halys, but not on those of P. maculiventris nymphs. Additionally, the longevity of H. halys female trails was assessed, and footprints remained bioactive, eliciting a consistent searching behavior in the wasp for 72 h after initial deposition. A series of GC–MS chemical analyses revealed components of these trails, with n-tridecane and (E)-2-decenal found to be the most abundant, and probably the key components of the kairomone utilized by the wasp for short range host location. Solutions of the synthetic compounds were tested both together and singly. The blend of n-tridecane and (E)-2-decenal (4: 1) significantly prolonged the residence time of T. japonicus, as did n-tridecane alone. These results are discussed in the context of host preference and classical biological control.