Mass rearing and biological characteristics of Aphidophagous predators, Coccinella septempunctata Linnaeus, 1758 and Hippodamia variegata (Goeze, 1777) (Coleoptera:Coccinellidae) on some aphid species (Hemiptera:Aphididae)

Laboratory studies were conducted to investigate the biological characteristics of aphidophagous predators Coccinella septempunctata L. and Hippodamia variegata (Goeze) using some species of aphids. The results revealed that the total developmental period of Aphis gossypii Glover fed C. septempunctata (14.59±0.30 days) was significantly lower compared to Aphis nerii Boyer de Fomscolombe fed C. septempunctata (18.66±0.33days). Voracity of different growth stages of C. septempunctata manifested that maximum number of A. gossypii (231.56±11.43) and A. nerii (72.47±5.87) was consumed by adult female. The total developmental period of H. variegata fed on A. gossypii and A. nerii was respectively 12.20±0.18 and 12.29±0.16 days. Mean daily voracity of H. variegata showed that the adult female consumed the highest number of A. gossypii (123.76±11.56) and A. nerii (52.93±4.87). The Manly's preference index of C. septempunctata towards various ratios of A. gossypii and A. nerii indicated that the adult male, female and the 4th instar larvae showed feeding preference for A. gossypii over A. nerii. The Manly's preference index calculated for the adult male and 4th instar larvae of H. variegata revealed that both the predators did not significantly discriminate between A. gossypii and A. nerii. Conversely, the adult female showed significantly greater preference for A. nerii than A. gossypii (P = 0.0001). The cubic logistic regression analysis of the data revealed type II functional response for C. septempunctata and H. variegata. The parameter estimates of adult male, female and 4th instar larvae of both the aphidophagous predators calculated through Holling's disc model and Rogers' equation revealed that the highest attack rate (a), shortest handling time (Th) and maximum capture rate (T/Th) was exhibited by adult female. Comparison of functional response curves of adult male, female and 4th instar larvae revealed that that all the three predators, especially female exhibited a more vigorous response at lower densities and that maximum consumption of prey at all the densities offered was shown by female followed by 4th instar larvae. Investigations on the cannibalistic behavior of C. septempunctata and H. variegata revealed that eggs and younger larvae proved more vulnerable to cannibalism and that the cannibalism was inversely related to the availability of aphids. The adult lady birds and 4th instar larvae of both the species consumed considerably higher number of eggs even in the presence of aphids. Results on the IGP of eggs of H. variegata by adult male, female and 4th instar larvae of C. septempunctata revealed that at 0 aphid density heterospecific egg consumption was maximum, however, considerable number of eggs were also consumed at 30 and 80 aphid densities. Consumption of 1st and 2nd instar larvae was also higher in the absence of aphids but intermediate at 80 aphid densitiy and greatly reduced or almost negligible at 350 aphid density. The same sequence was also true for the IGP of C. septempunctata by H. variegata adult male, female and 4th instar larvae. Results on the preference of C. septempunctata and H. variegata towards conspecific or heterospecific eggs revealed that both the aphidophagous coccinellids showed higher degree of preference for egg cannibalism (conspecific eggs) over IGP (heterospecific eggs).