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.
