PARASITISM BY APHIDIUS-ERVI (HYM, APHIDIIDAE) - PREFERENCE FOR PEA APHID AND BLUE ALFALFA APHID (HOM, APHIDIDAE) AND COMPETITION WITH A-SMITHI

The pea aphid Acyrthosiphon pisum (Harris) and the blue alfalfa aphid A. kondoi Shinji are pests of alfalfa Medicago sativa L. worldwide. Th e parasitoid Aphidium ervi Haliday attacks both species and A. smithi is host specific to pea aphid Experiments were conducted to determine the preference of A. ervi for A. pisum and A. kondoi at three densitie s of hosts using the percentages of parasitism and superparasitism, an d the distribution of eggs among hosts as criteria. Also examined was the outcome of competition between the two parasitoids when exposed to the same hosts. A. ervi attacks more A. pisum when provided alone (no choice test) and when provided together in equal numbers with A. kond oi (choice test). There was no significant difference in the number of progeny produced by either parasitoid when a female of each species w as introduced simultaneously into the same test unit containing A. pis um hosts. The effects of the pathogen Pandora neoaphidis on this compe tition is reviewed.