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

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 planthost 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.