FIELD EVALUATION OF NATURAL AND SYNTHETIC INSECTICIDES AGAINST LEPTINOTARSA DECEMLINEATA SAY

Chemical control of Colorado potato beetle (CPB), Leptinotarsa decemlineata Say, has become difficult in Serbia because of its resistance to conventional synthetic insecticides (e.g. organophosphates, carbamates, pyrethroids). CPB resistance and ecological concerns require that conventional broad-spectrum insecticides be replaced by biorational and low-risk insecticides, i.e. synthetic and/or natural products with novel modes of action, effective against key pests but relatively safe for non-target organisms and the environment. The effectiveness of three natural products (abamectin, azadirachtin and spinosad), two synthetic products with novel modes of action (acetamiprid and metaflumizone) and one synthetic conventional insecticide (bifenthrin) against the 1st generation of CPB larvae was evaluated in field trials conducted in 2004 and 2005. In 2004, the mean number of CPB larvae before treatment ranged 13.2-20.2 per plant. Assessment 13-14 days after treatment (DAT) showed high efficacy of abamectin (94.8-100%; combined with adjuvant), spinosad (96-100%), metaflumizone (98.4-100%) and acetamiprid (100%). The efficacy of the botanical insecticide azadirachtin (53.5-83.5%) was estimated as satisfactory as its antifeedant activity prevented significant plant damage. Low efficacy was achieved by bifenthrin (41.3-64.5%), probably due to an intensive previous use of pyrethroids and a resulting CPB resistance. In 2005, lower doses of abamectin (9 g a.i./ha, combined with adjuvant) and spinosad (12 g a.i./ha) and a higher dose of azadirachtin (25 g a.i./ha) were applied to CPB infestation of 4.2-9.8 larvae per plant. Assessment 22 days after treatment showed high efficacy (97.8-100%) of these natural insecticides. The importance of these results for CPB control is discussed.