Efficiency of vibrational sounding in the parasitoid Pimpla turionellae is affected by female size

Abstract

The pupal parasitoid Pimpla (=Coccygomimus) turionellae L. (Hymenoptera: Ichneumonidae) attacks a broad range of lepidopteran pupae. The variation in host size translates into substantial differences in size among adult parasitoids. Pimpla turionellae shows a strong host size-dependent sex allocation, which indicates that parasitoid body size influences sex-specific effects on fitness costs. We tested whether the body size of females affects their capacity to locate hosts by vibrational sounding. We investigated parasitoids from three size categories with respect to their ability to find artificial hosts (cigarette filters) in cylinders made of thin or thick paper (20 or 65g/m2, respectively). Using laser Doppler vibrometry, we measured vibration signals produced by large and medium-sized females during vibrational sounding. Large females produced vibrations of a higher intensity than, but a similar frequency to, their smaller conspecifics. The parasitoid's ability to locate a hidden host model by vibrational sounding also improved with size. This indicates that parasitoid size is an important factor in determining the female's host-searching success. We discuss the results in relation to the parasitoid's behavioural ecology.