Observations in the biology and phenology of Aptesis nigrocincta (Hymenoptera: Ichneumonidae) parasitizing cocoons of the apple sawfly, Hoplocampa testudinea (Hymenoptera: Tenthredinidae) | [Observations sur la biologie et la phénologie d'Aptesis nigrocincta (Hymenoptera: Ichneumonidae) parasitant les cocons de l'hoplocampe Hoplocampa testudinea (Hymenoptera: Tenthredinidae)]
1999
Babendreier, D. ((Commonwealth Agricultural Bureau International Bioscience Centre Switzerland, Delémont (Suisse)))
The life history of Aptesis nigrocincta was investigated in laboratory and field experiments. Development from egg to adult is completed in 38.0 +/- 2.1 SD days for males and in 39.6 +/- 2.3 SD days for females. Females emerged without any mature egg and later in their life the eggload remained small (range from 0 to 8 mature eggs). Under laboratory conditions males of this species lived 50.6 +/- 17.9 SD days while females survived significantly longer (72.5 +/- 34.1 SD days). From field observations it could be ascertained that the phenology of this parasitoid is rather complicated with fractions of the population emerging directly, later in the same year and in the following year at different times. Three peak emergence times could be observed: a first one occurred during June, well synchronisized with the descending phase of the apple sawfly, a second one was observed during August and a third one in October. Males emerged about one or two weeks earlier than females. Hibernation takes place as mature larva in the cocoon or as adult (only females). In Switzerland two generations were observed. Rates of parasitism within single generations were variable, ranging from 12.1 to 39.7 / in the years of investigation. The impact of this bivoltine parasitoid accumulates on its univoltine host and A. nigrocincta is found to be the main mortality factor of apple sawfly cocoons in the present study
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