ON THE COEXISTENCE OF THE CASSAVA MEALYBUG PARASITOIDS APOANAGYRUS-DIVERSICORNIS AND APOANAGYRUS-LOPEZI (HYMENOPTERA, ENCYRTIDAE) IN THEIR NATIVE SOUTH-AMERICA

The encyrtid parasitoid Apoanagyrus diversicornis (Howard) (formerly k nown as Epidinocarsis divevsicornis) failed to establish itself in Afr ica where it was introduced, in addition to A. lopezi De Santis for th e biological control of the cassava mealybug, Phenacoccus manihoti Mat ile-Ferrero. Apoanagyrus lopezi is a better competitor and available e vidence suggests that competition prevents the coexistence. Yet, both parasitoid species were reared from P. manihoti in the same locality i n their native South America. Competition should prevent coexistence o n P. manihoti in South America as well as in Africa. We investigated h ow A. diversicornis persists in South America. The use of alternative hosts could explain its persistence. We aimed at finding possible alte rnative hosts for A. diversicornis that can serve as a refuge from com petition with A. lopezi. The existing information on the distribution of A. lopezi and A. diversicornis and their known hosts in South Ameri ca is reviewed. Candidate alternative hosts for A. diversicornis were selected and tested. Alternative hosts should at least be suitable for development of A. diversicornis and unsuitable for development of A. lopezi. Only Phenacoccus herreni Cox & Williams met these requirements . Phenacoccus madeirensis Green, P. solani Ferris and Ferrisia virgata (Cockerell) were unsuitable hosts for both species. In cages with con tinuous parasitoid populations under strong interspecific competition, A. diversicornis did significantly better if half the population of P . manihoti was replaced by P. herreni. This supports the hypothesis th at P. herreni can serve as an alternative host for A. diversicornis in South America and that its presence enhances coexistence of A. divers icornis and A. lopezi. Phenacoccus herreni is absent in Africa.