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New Zealand Plant Protection 63 (2010): 283

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

R. Kant, M.A. Minor, S.A. Trewick and W.R.M. Sandanayaka


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 10-week study period (P=0.69). 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 5-week (late spring) than the early 5-week period (early spring) (P<0.05). 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 male-female mating was more prevalent during midday compared to morning and evening (P<0.05).

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