Toxicity of Neem Applied Alone and in Combinations with Bacillus thuringiensis to Colorado Potato Beetle (Coleoptera: Chrysomelidae)
Authors: Trisyono, Andi; Whalon, Mark E.
Source: Journal of Economic Entomology, Volume 92, Number 6, December 1999 , pp. 1281-1288(8)
Publisher: Entomological Society of America
Abstract:The toxicity of neem (Neemix, 0.25% azadirachtin [AI]) and combinations of neem and Bacillus thuringiensis was examined on 2nd instar of the B. thuringiensis susceptible (Bt-S) and resistant (Bt-R) strains of Colorado potato beetle, Leptinotarsa decemlineata (Say). Using a potato leaf-dipping method, the LC50 values of neem determined 2 d posttreatment to larvae of the Bt-S and Bt-R were 2.07 and 6.56 mg (AI)/liter, respectively. The LC50 values in both strains decreased significantly with increased exposure time. Cross-resistance between these toxins was not evident with a resistance ratio ranging from 1.3–3.2. Combinations of sublethal concentrations of neem (0.45 or 0.25 mg [AI]/liter) with a sublethal concentration of B. thuringiensis (0.74 mg [AI]/liter) to larvae of the Bt-S yielded an additive effect in larval mortality. In contrast, combinations of neem (0.78 or 0.43 mg [AI]/liter) and B. thuringiensis (319.8 mg [AI]/liter) resulted in a synergistic effect to larvae of the Bt-R strain. Sublethal concentrations of neem or B. thuringiensis applied separately or in combinations decreased the mean larval weight and retarded the larval growth of both strains. Our results suggest that neem is a potential insect growth regulator on larvae of the Bt-S and Bt-R and a possible B. thuringiensis resistance breaking compound. Field trials to determine the performance of neem in combination with B. thuringiensis on field populations of Colorado potato beetle are warranted.
Document Type: Research Article
Publication date: December 1999
- Journal of Economic Entomology is published bimonthly in February, April, June, August, October, and December. The journal publishes articles on the economic significance of insects and is divided into the following sections: apiculture & social insects; arthropods in relation to plant disease; forum; insecticide resistance and resistance management; ecotoxicology; biological and microbial control; ecology and behavior; sampling and biostatistics; household and structural insects; medical entomology; molecular entomology; veterinary entomology; forest entomology; horticultural entomology; field and forage crops, and small grains; stored-product; commodity treatment and quarantine entomology; and plant resistance. In addition to research papers, Journal of Economic Entomology publishes Letters to the Editor, interpretive articles in a Forum section, Short Communications, Rapid Communications, and Book Reviews.
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