INTERACTION BETWEEN APANTELES-RUFICRUS HAL AND METEORUS-RUBENS NEES ON LARVAE ON AGROTIS-IPSILON (HUFN)

The two internal gregarious parasitoids Apanteles ruficrus Hal. and Me teorus rubens Nees attack larvae of Agrotis ipsilon (Hufn.) and they n aturally co-exist during the period from end April to end May. The pre sent paper deals with the interaction between these two parasitoids. F irst and late 6th instar (3-day old) of A. ipsilon never attacked by e ither A. ruficrus or M. rubens. No sort of direct competition between the two parasitoids existed around 2nd, 3rd and early 6th instars, bec ause of the unique instar attacked by each. Fourth instar larva is ade quate for both parasitic species, but when being exposed simultaneousl y to females of both species, no progeny are obtained owing to the ear ly death of the host. Fifth instar of Agrotis larva is highly preferab le for Meteorus compared to Apanteles and thus, when being exposed sim ultaneously, the survivor is Meteorus. In nature the two parasitic spe cies were never obtained together from a 4th instar larva, and no Apan teles individuals were secured from 5th instar larvae.