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

摘要

This study evaluated the functional and aggregational responses of 2nd and 3rd 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 3rd instar larvae displayed a higher rate of predation than the 2nd instar. The maximum attack rate (a) with lowest handling time (Th) was determined by r2 value which was found to be highest for 3rd instar larvae (r2 = 0.7308) followed by 2nd 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 3rd 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.