Laboratory Studies of Honeybee Larval Growth and Development as Affected by Systemic Insecticides at Adult-Sublethal Levels

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Abstract
The effects of two systemic insecticides, carbofuran and dimethoate, at concentrations sublethal to adult worker honeybees (<1·25 μg/g food) on larval growth, pupation success and acetylcholinesterase (AChE) activity were investigated in worker larvae reared on royal jelly (RJ) in the laboratory. Larvae initially exposed to either insecticide at 5 μg/g RJ at a late age (e.g. 96 h) gained weight more slowly than control larvae and died relatively early. Insecticide concentrations of 1·25 μg/g rarely disrupted growth of larvae first exposed at 72–96 h of age. Concentrations sublethal to adults sometimes rcduced mature weights of larvae first exposed at an early age (44 h). Rcduced numbers of potentially viable pupae resulted when these larvae were exposed to carbofuran at 1·25 μg/g or dimethoate even at 0·313 μg/g. As activity of AChE in homogenstes of untreated larvae was highly variable, AChE activity does not appear to be as reliable a criterion for detecting insecticide poisoning of larvae as reduction in larval weight. Results suggested that long-term exposure of honeybee larvae to insecticide-co n laminated diets at concentrations not immediately lethal to worker adults may cause significant hidden damage to colonies.