Field ecology and behaviour of the egg parasitoid Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae)

Abstract

The ecology and behaviour of Trissolcus basalis (Wollaston), a parasitoid of the eggs of the horehound bug Agonoscelis rutila (F.) and numerous other species of pentatomid bug, were studied in the field over two years near Adelaide, South Australia. The adult bug population declined sharply early in summer due to the combined effects of senescence of host plants, egg predation and parasitism by T. basalis and a sympatric species, Trissolcus ogyges (Noble). Hyperparasitoids of T. basalis were recorded for the first time in South Australia. Competition among female parasitoids for access to host egg masses differed widely between the two years (same season), and females displayed adaptations to competition. They patrolled host egg masses when alone and defended them aggressively in direct contests with conspecifics. These observations reinforce previous laboratory work, and suggest further avenues of research on the behavioural strategies used by T. basalis during defence of egg masses.