Functional and Aggregational Response of Chrysoperla sp. (carnea-group) (Neuroptera: Chrysopidae) on Brevicoryne brassicae (Linnaeus) (Hemiptera: Aphididae)

Abstract

This study evaluated the functional and aggregational responses of 2^nd and 3^rd instar larvae of Chrysoperla sp. (carnea-group) on medium sized aphids of Brevicoryne brassicae (L.). The functional response was investigated at prey densities of 2, 4, 8, 16, 32, 64 and 128 aphids per larvae and the studies revealed that behaviour of both the larval instars matched Holling's Type II functional response. The response curve exhibited a curvilinear rise to the plateau. The 3^rd instar larvae displayed a higher rate of predation than the 2^nd instar. The maximum attack rate (a) with lowest handling time (Th) was determined by r² value which was found to be highest for 3^rd instar larvae (r² = 0.7308) followed by 2^nd instar larvae (r²= 0.733). Numerical response (aggregational response) was investigated at varied density of prey, viz., 8, 16, 32, 64 and 128 aphids and varied density of predators, viz., 1, 2, 3, 4 and 5. The maximum aggregation response was observed at highest host density of aphids (128) with the maximum number of predators (5). The rate of attack (a) was highest for 3^rd instar larvae (2.32) at lowest predator density (1) and showed a downward trend with increase in predator densities due to intra-specific competition under conditions of food limitation.