Journal of Economic Entomology (1999) 92, 1281-1288

Andi Trisyono and Mark E. Whalon (1999)
Toxicity of neem applied alone and in combination with Bacillus thuringiensis to Colorado potato beetle (Coleoptera: Chrysomelidae)
Journal of Economic Entomology 92 (6), 1281-1288
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.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Database assignments for author(s): Mark E. Whalon

Research topic(s) for pests/diseases/weeds:
biocontrol - natural enemies
control - general
Research topic(s) for beneficials or antagonists:
formulation/storage of bioagents

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Leptinotarsa decemlineata	Potato (Solanum tuberosum)
Bacillus thuringiensis var. tenebrionis (entomopathogen)	Leptinotarsa decemlineata	Potato (Solanum tuberosum)