Parasitism and mating of Diaeretiella rapae (Hymenoptera Aphidiidae) in an uncontrolled environment

Abstract

Parasitism and mating activities of Diaeretiella rapae were studied in a shadehouse under ambient environmental conditions during September (early spring) and November (late spring) Before collecting the data the parasitoid and its aphid host colonies were left to develop undisturbed on cabbage seedlings for 3 months in about 25 m² area The plants were highly infested with aphids (average 27225 aphids/plant) and parasitism by D rapae varied between 25 and 36 during the study period There was no significant change in parasitism rate during the 10week study period (P069) Adult parasitoids emerged from aphid mummies at a rate of more than 90 with a higher number of females than males The mean female/male parasitoid sex ratio was greater in the second 5week (late spring) than the early 5week period (early spring) (P<005) Mating activities of the parasitoids were observed at all times of the day It was found that 49 of the mating pairs comprised a male mounted on a female and 45 were male mounted on another male The malefemale mating was more prevalent during midday compared to morning and evening (P<005)