Residual toxicity and biological effects of neem (Azadirachta indica) oil against cotton mealybug, Phenacoccus solenopsis Tinsley (Sternorrhyncha: Pseudococcidae)

In the present study impact of different neem oil concentrations having been investigated on the development, longevity, fecundity and mortality of Phenacoccus solenopsis under ambient laboratory conditions using leaf and surface treatment bio-assay trials. Neem oil at 25000 and 30000 ppm on Hibiscus leaves killed 53% and 60% 2 instar cotton mealybug nymphs, respectively after 24 h treatment which was significantly greater (P less than 0.05) than control. Neem oil at higher concentrations (20000, 25000 and 30000 ppm) adversely affected the duration for cocoon formation, pupal period, male longevity and shortened the male adult life duration and the longevity of mated and virgin females as compared with other treatments. However, neem oil concentrations did not have any significant effect on the oviposition and post-oviposition periods of females. Female fecundity and eggs per batch decreased by 73% and 50%, respectively when they were reared at 30000 ppm neem oil concentration as compared to those reared on untreated leaves. The detrimental effects of neem oil concentrations on cotton mealybug were sustained for three months under ambient laboratory conditions. The present work has shown that the neem oil solution can be stored up to three months under shade conditions without deteriorating its effectiveness.