INTERSPECIFIC HOST DISCRIMINATION AND COMPETITION IN APOANAGYRUS (EPIDINOCARSIS) LOPEZI AND A(E)DIVERSICORNIS, PARASITOIDS OF THE CASSAVA MEALYBUG PHENACOCCUS-MANIHOTI

1. Choice experiments on interspecific host discrimination in A. lopez i and A. diversicornis were carried out on discs of cassava leaf conta ining four hosts (P. manihoti) that had been parasitized by the other species and four unparasitized hosts. 2. A. lopezi accepted both host types equally for oviposition, whereas A. diversicornis accepted fewer hosts that had been parasitized by A. lopezi than unparasitized ones. A. diversicornis is therefore capable of interspecific host discrimin ation, but such a capability was not demonstrated for A. lopezi. 3. Su rvival probability in singly pardsitized hosts was 0.85 for both paras itoid species. When the time interval between ovipositions was 2 h or less, survival in multiparasitized hosts was 0.68 for A. lopezi and 0. 17 for A. diversicornis, irrespective of priority. Increasing A. lopez i priority to 24 +/- 2 h did not increase A. lopezi survival. A. diver sicornis survival, however, increased to 0.43 when A. diversicornis wa s given 24 +/- 2 h priority. A. diversicornis eggs took 19 h longer th an A. lopezi eggs to hatch. This could explain the difference in compe titive abilities in multiparasitized hosts. 4. The observed difference in host selection behaviour between A. lopezi and A. diversicornis is in accordance with the different benefits of multiparasitism: A. lope zi gains more than A. diversicornis because of its superior within-hos t competitive abilities. 5. Neither species avoided multiparasitism co mpletely. The low survival probability of A. diversicornis in multipar asitized hosts may partly explain its failure to establish when introd uced into Africa as part of a biological control programme of P. manih oti.