Do acoustic cues mediate host finding by Syngaster lepidus (Hymenoptera: Braconidae)?

Syngaster lepidus Brullé is a braconid solitary ectoparasitoid that attacks the larvae of the cerambycid beetles Phoracantha semipunctata and Phoracantha recurva . The beetle larvae are concealed under the bark of their Eucalyptus host trees feeding at the interface of the inner bark and the wood. Ovipositing female parasitoids search the bark surface and must first locate a host larva accurately, drill through as much as 1 cm of the bark in order to paralyze the larva beneath, and lay a single egg on the paralyzed larva. Female wasps were provided with logs infested with host larvae, in which the positions of the host larvae had been determined by X-ray imaging. The sequence of behaviors following the landing of a female wasp on an infested log was recorded on videotape and subsequently analyzed to provide a detailed description of the processes of host location and oviposition. Female wasps searched significantly more on log sections with active host larvae than inactive larvae. They also turned toward and moved in the direction of active larvae in response to sounds produced by feeding. While searching for hosts, female wasps stand on the log surface and walk towards the location of the larvae; while it is possible that they perceive both airborne sound and associated surface vibration, the vibration signals are probably more important in indicating direction and possibly distance to the host.