Behavioral Ecology Vol. 10 No. 2: 122-127
© 1999 International Society for Behavioral Ecology
Don't count your eggs before they're parasitized
contest resolution and the trade-offsduring patch defense in a parasitoid wasp
a Department of Crop Protection, University of Adelaide, Waite Campus, South Australia b Department of Applied Mathematics, University of Adelaide, South Australia
Address correspondence to S. A. Field, Department of Entomology, Hebrew University of Jerusalem, PO Box 12, Rehovot, 76100, Israel. E-mail: sfield{at}agri.huji.ac.il
Although aggressive conflicts over hosts occur among females in many species of insect parasitoids, few studies have examined the mechanisms by which these contests are resolved. In Trissolcus basalis, a parasitoid of pentatomid bug egg masses, females co-exploiting an egg mass (patch) encounter one another repeatedly and fight for possession of the patch. We investigated the resolution of pairwise contests by experimentally varying the release time of females and the size of the patch. Logistic regression showed that the female arriving first on the patch was more likely to win both the first agonistic encounter and to retain overall possession of the patch. This advantage to the first female suggests a resource-correlated asymmetry in favor of the first female, due to her having invested more offspring in the patch. Although escalations were more common when the asymmetry in arrival times was small, the majority of encounters within all contests were nevertheless resolved without escalated fighting, with the resident attacking and the intruder backing down. Thus contest resolution basically followed a "bourgeois" rule. Residents tolerated intruders more frequently when the patch size was larger and the second female was released later, illustrating the trade-off faced by residents between defending the patch and continuing to exploit it.
Key words: agonistic behavior, asymmetries, bourgeois strategy, egg parasitoid, Trissolcus basalis.