Mutual Interference and Spatial Distribution of Infestations in Two Sympatric Trichogramma Species: T. brassicae Bezdenko and T. cacoeciae Marchal (Hymenoptera: Trichogrammatoidea)

Two Trichogramma brassicae females exploiting a large patch of hosts (Ephestia kuehniella Zeller eggs) exhibit clear mutual interference with a reduction in infestation efficiency, without effect on sex allocation but with clear overlapping of their infestation sites. When they exploit unevenly distributed hosts ( six patches of equal size), interference occurs but with lower intensity. Their infestation sites overlap significantly, suggesting some interattraction between them. On unevenly distributed hosts, two T. cacoeciae females do not interfere in parasitizing efficiency and their respective infestation sites are randomly distributed: they look as if they were indifferent to each other. One female T. brassicae and one female T. cacoeciae simultaneously exploiting unevenly distributed hosts do not interfere in parasitizing efficiency, but they avoid each other and partially succeed in spatial sharing of host patches. Spatial interactions between females could contribute to optimization of host exploitation. When females are able to discriminate hosts, spatial interactions appear as complementary to host-marking strategies, whereas in heterospecific associations where host discrimination does not work, they avoid multiparasitism and constitute an alternative strategy to ineffective host marking. (C) 1991 Academic Press, Inc.