INTERSPECIFIC INTERFERENCE BETWEEN APOANAGYRUS-LOPEZI AND APOANAGYRUS-DIVERSICORNIS, PARASITOIDS OF THE CASSAVA MEALYBUG PHENACOCCUS-MANIHOTI

The parasitoids Apoanagyrus lopezi De Santis and A. diversicornis (How ard) (Hymenoptera: Encyrtidae) have been introduced into Africa for th e biological control of the cassava mealybug Phenacoccus manihoti Mati le-Ferrero (Homoptera: Pseudococcidae). We have studied competition be tween these species to investigate if they can coexist. Here we report on the influence of the simultaneous presence of non-conspecific adul t females on searching efficiency on patches. Wasps of either species foraged on discs of cassava leaf with mealybugs, while at the same tim e different numbers of non-conspecifics were also depleting the patch. Patch area per parasitoid and number of hosts available to each paras itoid were equal in all treatments. In both species, the presence of o ther foragers clearly affected several aspects of the parasitoids' beh aviour. Patch residence time increased with the number of non-conspeci fics in A, diversicornis. In both parasitoid species, the proportion o f hosts left unparasitized after the patch visit decreased with increa sing numbers of females on the patch. The proportions of super- and mu ltiparasitism did not change with the number of females. Both species produced more offspring during a patch visit in the presence of more n on-conspecifics. These behavioural changes did not, however, lead to a change in the offspring production rate on patches. A. diversicornis produced offspring at a rate three times that of A. lopezi when one A. lopezi and one A, diversicornis foraged simultaneously. This is the f irst report of an aspect of interspecific competition where A. diversi cornis has an advantage over A. lopezi. Interference between adult fem ales thus promotes coexistence of the two species on P. manihoti.