Determining suitable observation times for testing odor preferences of a parasitoid wasp, Cotesia kariyai, using a four‐arm olfactometer

Abstract Parasitoid wasps locate their hosts by tracking host‐related chemicals, such as herbivore‐induced plant volatiles (HIPVs). Attractiveness of HIPVs to parasitoid wasps has often been investigated using four‐arm olfactometers, but suitability of observation times for behavioral tests using olfactometers has received insufficient attention. In this study, we evaluated differences in results of two‐choice bioassays with multiple observation times in a four‐arm olfactometer. We found that odor preferences of the parasitoid Cotesia kariyai (Watanabe) (Hymenoptera: Braconidae) to host‐induced plant volatiles changed with time in a four‐arm olfactometer. These changes were detected only between 60–120 s from the start of experiments, and there were no changes in preference after 120 s. The gradual decrease in odor preference can be explained by habituation. It is necessary to consider habituation of parasitoid wasps to plant volatiles and to determine suitable observation times depending on the species, so that appropriate behavioral assays can be performed in a multi‐arm olfactometer or other equipment.