Insect growth regulating and antifeedant effects of neem extracts and azadirachtin on two aphid species of ornamental plants

Leaf disc choice test bioassay demonstrated that formulated neem seed extra cts were highly deterrent and growth regulatory to rose aphid, Microsiphum rosae (L.) and Chrysanthemum aphid, Macrosiphoniella sanbornii (Gillete). E ffective concentrations to produce 50% feeding deterrence was 0.80 and 0.84 % respectively for 2nd instar nymphs irrespective of bioassay duration. The disruption of aphid feeding was related to the presence of azadirachtin co ncentration in the extract. The toxicity on contact from the leaf surface o r via topical application due to azadirachtin was significantly different a nd topical treatment was at least 7 times more effective for both species. Thus growth regulatory effects of azadirachtin were influenced by the host plant and the stage of treatment. Field evaluation with formulated neem ext racts revealed the effect to be more of growth regulatory nature thereby sh owing that azadirachtin is a physiological toxin for aphid species. Neem se ed extracts reduced the population of aphid on respective host plants signi ficantly, EC50 values being 0.88 and 0.96% for M. rosae and M. sanbornii re spectively.