COMPARATIVE DEVELOPMENT AND COMPETITIVE ABILITY OF DIBRACHYS PELOS (HYMENOPTERA: PTEROMALIDAE) ON VARIOUS POTENTIAL HOSTS

Dibrachys pelos (Grissell) is an occasional gregarious ectoparasitoid of Sceliphron caementarium (Drury). We report the second record of this host association, collected in western Nebraska, and present results of laboratory experiments on host suitability and utilization. When D. pelos was reared alone on prepupae of 6 possible hosts, 4 proved entirely suitable: the mud dauber wasps Sceliphron caementarium and Trypoxylon politum Say, and two of their parasitoids, a velvet ant, Sphaeropthalma pensylvanica (Lepeletier) and a bee fly, Anthraxsp. On these hosts D. pelos completed development in 2-4 weeks, with average clutch sizes of 33-57, of which 24.7% were males. The other two hosts tested, the flesh fly Neobellieria bullata (Parker) and the leaf-cutter bee Megachile rotundata (Say), proved marginal, with very few adult progeny produced. When reared on these same 6 hosts with the addition of a competing parasitoid, Melittobia digitata Dahms, D. pelos fared poorly, being the sole offspring producer in at most 30% of the trials (on Anthrax hosts) and failing to prevail at all on T. politum hosts. Comparative data on host conversion efficiency indicated that M. digitata was more efficient than D. pelos on every host except Anthrax.