Functional Response of Hippodamia variegata (Coleoptera: Coccinellidae) to Different Densitiesof Aphis gossypii (Hemiptera: Aphididae) in an Open Patch Design

Abstract

Functional response of the female ladybeetle, Hippodamia variegata (Goeze) (Col., Coccinellidae) to varying densities (5, 10, 20, 40, 60 and 80) of third instar nymphs of Aphis gossypii Glover was assessed in a growth chamber (25˚C, 65± 5% RH and a photoperiod of 16L: 8D h), on the black eyed bean, Vigna unguiculata (L.), in an open patch design. The logistic regression showed a type II functional response for female ladybeetles with the parameters (using Rogers’ model) as follows: a= 0.083±0.011h-1 and Th =0.197±0.040h. The mean time for the predator to be settled in a patch was 36.1±9.25, 26.8±5.81, 17.18±4.71, 8.5±2.12, 3.3± 0.88 and 0.8±0.35 minutes at densities of 5, 10, 20, 40, 60 and 80 third instar nymphs of A. gossypii, respectively. The settlement time decreased as prey density increased. The maximum theoretical predation (T/Th) for the females was 121.475. The proportion of female H. variegata that remained at the end of the experiment and their voracity were dependent on prey density. This may give an indication for the ability of the predator to persevere in the high pest infestations, and thus a high level of control could be expected. Keywords: Cotton aphid, Functional response, Hippodamia variegata, Predation, Settlement time.