INSECTICIDAL EFFECTS OF ACETONE, ETHANOL AND AQUEOUS EXTRACTS OF Azadirachta indica (A. Juss), Citrus aurantium (L.), Citrus sinensis (L.) AND Eucalyptus camaldulensis (Dehnh.) AGAINST MEALYBUGS (HEMIPTERA: PSEUDOCOCCIDAE)

Abstract

Mealybugs (Hemiptera; Pseudococcidae) are one of the noxious sucking pests infesting ornamental and horticulture crops including citrus. It is emerging as a severe threat to citrus industry in Indo-Pak region. This study determined in-vitro toxicity of different botanical extracts viz; neem (Azadirachta indica), sour orange (Citrus aurantium), sweet orange (Citrus sinensis) and eucalyptus (Eucalyptus camaldulensis) against adult females and 2nd instar nymphs of Drosicha mangiferae, a mealybug species regularly infesting citrus crop since last decade. Water, ethanol and acetone were used as extraction solvents. Leaf-dip and twig-dip methods were used for 2nd instar mealybug nymphs and adult female individuals, respectively. Five concentrations (0, 8, 16, 32 and 64%) of botanical extracts were bioassayed with four replications for each. Mortality of insects was observed at 24, 48 and 72 h post-treatment for nymphs and at 24 and 48 h post-treatment for adults. Data was subjected to probit analysis and two-way factorial ANOVA taking time and concentration as factors. Results revealed that the most toxic botanicals with minimum LC50 values against citrus mealybug adults were acetone extracts of A. indica and E. camaldulensis followed by ethanol extracts of C. sinensis seeds and C. aurantium leaves, while the most effective botanicals against 2nd instar mealybug nymphs were aqueous, ethanol and acetone extracts of A. indica and E. camaldulensis followed by ethanol extracts of C. sinensis peels and C. aurantium seeds. As expected, 2nd instar nymphs were found more susceptible to all extracts as compared to adult female individuals, most probably due to reduced penetration of botanical extract in adult insects due to powdery cushion on body. It is concluded that botanical insecticides can play a significant role in the management of insect/mite pests as being substitutes of toxic and hazardous synthetic chemicals. Particularly, neem (A. indica) and eucalyptus (E. camaldulensis) could be effective options against mealybugs and other hemipterous pests, and should be incorporated in the future pest management programs.