Effect of Insecticides on the Occurrence and Association of Whitefly, Aphid and Parasites on Cotton

Abstract

Observations in cotton field sprayed with insecticides showed that Aphis gossypii Glov. parsltlsm by Aphis gossypii Timberlake was very high in plots treated with fenvalerate. Triazophos and fenvalerate registered high populations of aphids which precluded the incidence of the whitefly Bemisia tabaci (Gennadius). Elimination of aphids by monocrotophos and methyl demeton provided a better habitat for B. tabaci . Positive association between the aphid and its parasite was seen in phosalone (r = 0.67), mineral oil (r = 0.52), endosulfan(r = 0.52), fish oil rosin soap (r = 0.51), methyl demeton (r = 0.50), neem oil (r = 0.48), fenvalerate (r = 0.48) and check (r = 0.65). Monocrotophos and triazophos had no association. The linear regressions showed that fenvalerate, phosalone and check plots permitted 96.9, 58.8 and 40.2 per cent parasitism respectively while only 13.8 to 31.5 per cent parasitism was observed in other insecticidal treatments. For occupation and development, there was a negative association between the aphid and whitefly in plots treated with phosalone (r = - 0.81), minerai oil (r = - 0.77), methyl demeton (r = - 0.72) and endosulfan (r = - 0.46).