Life table of the aphid parasitoid Aphelinus asychis (Walker)(Hymenoptera, Aphelinidae) parasitizing different age groups of Aphis gossypii Glover (Homoptera, Aphididae)Biologische Eigenschaften von Aphelinus asychis (Walker) (Hymenoptera, Aphelinidae) bei Parasitierung unterschiedlicher Altersstufen von Aphis gossypii Glover (Homoptera, Aphididae)

The current laboratory study was designed to evaluate developmental duration, pupal mortality, sex ratio, longevity, fecundity and host feeding behaviour of the aphid parasitoid Aphelinus asychis (Walker) (Hymenoptera, Aphelinidae) parasitizing different age groups of Aphis gossypii Glover (Homoptera, Aphididae) at 25 ± 1°C temperature, 60 ± 10% Rh and a photoperiod of 16:8 h (L:D). The results show that the development from egg to adult was significantly affected by host age. It was completed in 14.5 and 14.4 days in 1–2 day old A. gossypii-nymphs, 13.5 and 13.1 days in 4–5 day old nymphs as well as 12.3 and 12.2 days with adults as host for females and males, respectively. No significant differences of pupal mortality and percentage of females among host age groups were detected. The mean percentage of mortality parasitizing different host age groups varied between 23.6 and 26.8%. The sex ratio (♀♀:♂♂) of A asychis with 1–2 day old A. gossypii-nymphs as host was 1:0.9, with 4–5 day old nymphs 1:0.7 and with adult aphids as host 1:0.9. On the average of 32.8 days females lived slightly longer when parasitizing and host feeding on 1–2 day old aphid nymphs than with 4–5 day old nymphs or adults as host. Females lived significantly longer than males. The fecundity of A. asychis- females was highest parasitizing the first age group (232.3 eggs/♂), followed by adults (44.7 eggs/♂) and by the second age group (21.1 eggs/♂). Highly significant differences were also found in the total number of aphids consumed by host feeding. A. asychis host fed on 161.2 aphids of the first age group, followed by 87.9 aphids of the second age group and 42.7 adult hosts. The present study suggests that short developmental duration, high proportion of females, high longevity, high fecundity and host feeding as well as its preference for younger aphid hosts are properties that make A. asychis an interesting alternative for biological control of the cotton aphid in greenhouses.