Predatory Efficiency of Menochilus sexmaculatus Fab . and Coccinella undecimpunctata Lin., (Coccinellidae: Coleoptera) on Alfalfa Aphid, Therioaphis trifolii (Monell.)

摘要

To evaluate predatory efficiency of Menochilus sexmaculatus Fab. and Coccinella undecimpunctata Lin.,(Coccinellidae: Coloptera) on alfalfa aphid Therioaphis trifolii (Monell) a laboratory experiment was conducted during winter 2000-2001 at Sindh Agriculture University, TandoJam, Sindh, Pakistan. The per day predatory efficiency of the zigzag beetle against 1st, 2nd, 3rd and 4th instars was worked out as 11.8, 26.8, 43.4 and 141.5, respectively and that of 11-spotted as 10.6, 18.4, 38.1 and 52.6 aphids. The per day efficiency for males of both zigzag and 11-spotted was 73.00 and 51.8, respectively; and that of the females it was 80.00 and 56.00 per day, respectively. The feeding rate per life stage of the zigzag beetle for all four instars was 86.5, 115.2, 164.9 and 948.1, respectively; and for the 11-spotted it was 55.10, 81.00, 175.20 and 278.80, respectively. The per stage for males of both these beetles rate was 2548.20 and 2930.00 respectively. And for the females it was 2800.00 and 3080.00 alfalfa aphids, respectively. Both the males of zigzag and 11-spotted beetles consumed 88.2 and 70 on 18th and 15th day and 60.5 and 58.3 aphids on 30th days of their age. Both the females consumed 99.21 and 77.4 on 18th and 21st day, respectively and 61.90 and 53.30 aphids, respectively on 30th day of their age. The voracity of both the beetles fluctuated as per aphid densities. The zigzag beetle: aphid ratio was 8.4: 10, 10.6:15, 11.2:20, 14.4:25, 17.0:30, 18.4:35, 23.8:40, 25:50 and 28:60 and that of 11-spotted it was 7.8:10, 9.2:15, 10.73:20, 12.4:25, 14.22:30, 16.6:35, 20.18:40, 21.93:50 and 24.26:60. The total consumption rate each of zigzag and 11-spotted was 19.49 and 15.30 aphids, respectively. The aphid population in control was worked out at zero predator that increased as 6.4, 7.2, 8.3, 9.4, 12, 12.8, 13.9, 14.68 and 14.8%.