Efficiency of some chemical and biological insecticides on the cotton mealybug, Phenacoccus solenopsis (Hem.: Pseudococcidae), and some of its important natural enemies in field conditions

The cotton mealybug, Phenacoccus solenopsis Tinsley, is a potential pest that threatens green landscape in Ahvaz. In this study, the short-term and long-term effects of various insecticides (imidacloprid, diazinon, spinosad, Palizin^®, and azadirachtin) on the populations of cotton mealybugs and predatory ladybird beetles, Nephus sp. and Hyperaspis sp., as well as on the parasitism rate of cotton mealybug by Aenasius bambawalei Hayat, were investigated under field conditions. The results of the bioassay at 24 h after treatment showed that imidacloprid (84.6%), diazinon (84.1%), and Palizin^® (77.4%) significantly reduced the population of mealybugs compared to the control. The decrease effect of azadirachtin on the population density of cotton mealybugs 24 h after treatment was not significant (38.1% compared to the control). Furthermore, diazinin and azadirachtin had the greatest negative impacts (100% reduction compared to the control), and Palizin^® had the least toxicity to ladybirds, with no significant difference compared to the control treatment. The long-term effects of the tested insecticides showed that, compared with the other treatments, imidacloprid and Palizin^® had significant effects on reducing the pest population. Palizin^® and azadirachtin had the least effect on the parasitism activity of Aenasius bambawalei. Both imidacloprid and insecticidal soap were more effective at reducing the P. solenopsis population than were the other treatments, but due to the greater negative effect of imidacloprid than of insecticidal soap on natural enemies and the limitation of using insecticides in green landspaces, insecticide soap is suggested for use in IPM programs for this pest.