Foraging behavior of Hippodamia variegata (Coleoptera: Coccinellidae) and Lysiphlebus fabarum (Hymenoptera: Braconidae), as the natural enemies of Aphis gossypii, under light and dark conditions

Light, as an environmental factor, affects the biology, physiology and behavior of insects. In this study, the feeding behavior of Hippodamia variegata and parasitism rate of Lysiphlebus fabarum were studied under light and dark conditions. Synchronous cohorts of different growth stages of H. variegata and female parasitoid wasps were produced and then they were singly introduced into experimental arena containing third instar nymphs of Aphis gossypii (20 nymphs for second instar larvae and female wasp; 30 nymphs for other growth stages of ladybird beetle) on a cucumber leaf. The results revealed that, although light did not influence foraging behavior of second instar larvae of the ladybird beetle, the number of killed aphids was significantly higher for fourth instar larvae by female and male adults of H. variegata during foraging in the light condition in comparison with the dark condition. The ratio of partial prey consumption (No. of partially consumed aphids to No. of aphids killed) was significantly greater in fourth instar larvae than in second instar larvae in the dark condition. Female adults displayed significantly more partial consumption of prey in the dark relative to the light condition. Moreover, in both light and dark phases, this ratio was higher in female adults than in males. The results revealed that female wasps parasitized fewer A. gossypii nymphs in the dark than in the light. Based on the acceptable performance of H. variegata in the dark condition, it can be said that in addition to the benefits of simultaneous application of the parasitoid wasp and the ladybird beetle during the day, aphid population decline continues at night.