Host finding and host discrimination ability in Anaphes nitens Girault, an egg parasitoid of the Eucalyptus snout-beetle Gonipterus scutellatus Gyllenhal

Abstract

We investigated host finding and host discrimination ability in Anaphes nitens, a solitary egg parasitoid that attacks a gregarious host, the egg capsules of the Eucalyptus snout-beetle, Gonipterus scutellatus. In a first experiment, females were assigned to three treatments: no experience, one experience on an unparasitized egg capsule or one experience on a parasitized egg capsule. We combined this variable with three types of hosts: unparasitized, previously parasitized by the experimental female, or parasitized by conspecifics. Females were observed in a no-choice test, and results indicate that: (1) naive females can discriminate but do not refrain from superparasitism, (2) previous experience and the type of egg capsule affect host acceptance and visit duration, and (3) there is no evidence of self-discrimination. The acceptance of parasitized hosts decreased from 90% for the inexperienced females at their first encounter with the host, to 45% for the experienced females, and visit duration from 17.2 to 9.2 min. In a second experiment, a choice test was performed to assess A. nitens preference towards hosts of different age. Females oviposited preferentially in very young hosts. A field experiment tested the ability to find new hosts within the window of vulnerability of the egg capsules, by manipulation of the time that hosts were exposed to parasitism. Results showed that parasitoids need one day to discover the hosts and that parasitism does not increase after three days. We conclude that A. nitens biocontrol success is due to its ability to find fresh hosts, and to its discrimination ability, even if the female is inexperienced. 2003 Elsevier Inc. All rights reserved.