SEASONAL ECOLOGY OF APHIDIUS-NIGRIPES (HYMENOPTERA, APHIDIIDAE), A PARASITOID OF MACROSIPHUM-EUPHORBIA (HOMOPTERA, APHIDIDAE)

Aphidius nigripes Ashmead is the most common parasitoid attacking the potato aphid Macrosiphum euphorbiae (Thomas) in eastern North America. In field and insectary experiments, >87% of A. nigripes prepupae succ essfully overwintered. Spring emergence occurred from mid-April to mid -May, the period during which diapausing M. euphorbiae eggs are hatchi ng on primary hosts. Data obtained from sticky traps indicate that bot h aphid and parasitoid enter the potato agroecosystem in early June, s uggesting that one or several generations occur on primary host plants in the spring. The number of males captured in sticky traps containin g virgin females indicated that the parasitoid is present in high numb ers throughout the potato growing season. Diapause in A. nigripes was observed from mid-August, when aphids had migrated back to their prima ry host plants. Our results do not support the hypotheses that inabili ty of the parasitoid to overwinter or host-parasitoid asyncrony explai n why A. nigripes does not appear to have any major regulating effect on M. euphorbiae in the potato agroecosystem.