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Abstract

Aggressive defence of host patches has been reported in many parasitoid wasps, but rarely examined in quantitative detail. One aspect of interest is that foraging female parasitoids do not simply consume resource patches, they invest offspring in them. Therefore, patch defence in parasitoids can involve not only resource defence prior to oviposition, but also postoviposition defence of offspring (maternal care). In this paper, the time-structure and sequence of pairwise agonistic contests between females of the parasitoid Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae) are analysed. Three main periods were evident in contests. In the first period, both females exploited the patch with no aggression. After the initiation of fighting, they entered a ‘contest period’, during which resident and intruder roles became clearly resolved. The resident then usually guarded the patch for up to several hours before leaving. This signalled the beginning of the third period, in which the intruder returned to superparasitise the patch. During the contest period, resident behaviour initially reflected the trade-off between exploiting fresh hosts, and defending those it had already parasitised from the intruder, which persistently returned to the patch to try and oviposit, with some success. However, when the patch became fully parasitised, both resident and intruder switched to a ‘waiting game’, in which they sat motionless for extended periods, the resident on the patch and the intruder at a distance. These stand-offs were punctuated by occasional aggressive patrolling by the resident, and cryptic returns to the palch by the intruder. This waiting game appears to be an informational war of attrition, suggesting a conceptual basis for modelling patch-leaving decisions using evolutionary game theory.