Effects of neem on oviposition and egg and larval development of Mamestra brassicae L: Dose response, residual activity, repellent effect and systemic activity in cabbage plants

 A commercial extract of neem (NeemAzal-T) and a simple extract of pulverised seeds extracted in warm water were tested against the cabbage pest Mamestra brassicae L. Gravid cabbage moth females were given a choice between sprayed and unsprayed plants for oviposition during nine days. Second instar larvae were caged on plants and exposed to a series of neem concentrations (leaf dip assay) and to neem applied to the roots (systemic uptake). Residual activity of NeemAzal-T was tested by caging 2nd instar larvae on plants that had been sprayed with neem solutions 1 h to three weeks in advance. Oviposition was reduced to half the number of eggs per plant by the neem treatment. The number of eggs that hatched was not affected by the neem treatment, but development of these larvae was strongly inhibited and all larvae in the neem treatment died within two weeks without reaching 2nd instar. The concentration of the active ingredient azadirachtin-A (the azadirachtin component in NeemAzal-T) needed to protect plants from damage by 2nd instar larvae was 8 μg ml−1. The lethal doses for 2nd instar larvae were determined by probit analysis to be 6.2 and 17.2 μg ml−1 for LC50 and LC95, respectively. NeemAzal-T protected plants from damage for at least three weeks if applied before oviposition, or at least two weeks if applied against 2nd instar larvae. In these studies, neem inhibited oviposition, larval development and feeding, and greatly increased mortality.