Response of the braconid parasitoid Cotesia (=Apanteles) glomerata to volatile infochemicals: effects of bioassay set‐up, parasitoid age and experience and barometric flux

Abstract Upon initiating a research project on the role of volatile infochemicals in the tritrophic system Cotesia (= Apanteles ) glomerata (L.) ‐ Pieris brassicae (L.) ‐ cabbage, a bioassay was developed to investigate the response of C. glomerata. The bioassay should be effective in terms of high responsiveness and minimum variability and constructed through a comparative approach. Twenty seven treatments, organized in a factorial randomized block design, compared the effect of three bioassay set‐ups (glasshouse flight chamber, wind‐tunnel and Y‐tube olfactometer), three parasitoid age groups (1–2, 4–5 and 8–9 days old females), three pre‐treatment experiences (naive, damage experienced and oviposition experienced wasps) and the day‐to‐day effect on response of C. glomerata to clean cabbage (CC) and plant‐host complex (PHC) in a dual choice test. The best results with regard to the strength and consistency of response to the PHC were obtained in the glasshouse flight‐chamber by 4–5 days old female wasps with either damage or oviposition experience (94 and 90%, respectively). It is therefore recommended as a suitable bioassay for studying the role of volatile infochemicals in host‐habitat location by C. glomerata. A day‐to‐day variation in response was found in the glasshouse and wind‐tunnel. It was correlated with the direction of change in barometric pressure within the time period of the experiment, showing that steadily increasing atmospheric pressure yields a significantly higher response than steadily decreasing or fluctuating barometric flux. To control for the day effect it is suggested to conduct further experiments in a block design, having day as a block. Several aspects of the infochemical ecology of C. glomerata are discussed.