Persistent Toxicity of Neem Derivatives to Green Leafhopper, Nephotettix virescens Distant (Cicadellidae: Homoptera)
Green house studies on the residual effectiveness of neem oil, Repelin and monocrotophos against rice green leaf hopper (GLH) nymphs conducted during September - October, 1990 and 1991 revealed that the residual effectiveness of the insecticides was dosage and exposure period dependent. The effectiveness of 1% neem oil persisted for six days but its persistence prolonged to nine days at 2% and 3–4% concentrations respectively. Similarly, Repelin remained effective upto six days and 6–9 days at 1 and 2% concentrations respectively. Monocrotophos at 0.07% concentration continued to cause mortality of the leafhopper for 21 to 24 days. The persistent toxicity (FT) values ranged from 90.51 to 191.58 for neem oil and Repelin at various concentrations as against 1741.60 for monocrotophos.