Abstract
In moths, sexual behavior combines female sex pheromone production and calling behavior. The normal functioning of these periodic events requires an intact nervous system. Neurotoxic insecticide residues in the agroecosystem could impact the normal functioning of pheromone communication through alteration of the nervous system. In this study we assess whether sublethal concentrations of the neonicotinoid insecticide thiacloprid, that competitively modulates nicotinic acetylcholine receptors at the dendrite, affect pheromone production and calling behavior in adults of three economically important tortricid moth pests; Cydia pomonella (L.), Grapholita molesta (Busck), and Lobesia botrana (Denis & Schiffermüller). Thiacloprid significantly reduced the amount of calling in C. pomonella females at LC0.001 (a lethal concentration that kills only 1 in 105 individuals), and altered its calling period at LC1, and in both cases the effect was dose-dependent. In the other two species the effect was similar but started at higher LCs, and the effect was relatively small in L. botrana. Pheromone production was altered only in C. pomonella, with a reduction of the major compound, codlemone, and one minor component, starting at LC10. Since sex pheromones and neonicotinoids are used together in the management of these three species, our results could have implications regarding the interaction between these two pest control methods.
Highlights
In lepidopterans, reproduction shows a periodic pattern related to the duration of the daily light and dark cycles and involves a complex series of behavioral and physiological events including chemical communication mediated by sex pheromones (Groot 2014)
Several studies report alterations of the normal perception of and response to chemical signals in insects treated with sublethal doses of insecticides (Haynes 1988; Tricoire-Leignel et al 2012). In this context of potential semiochemical and toxicological interactions in the agroecosystem, we explored the effect of sublethal doses of a neonicotinoid insecticide on pheromone production and release in three tortricid moths
C. pomonella called throughout the scotophase, G. molesta called from 4 h before the start of the scotophase to 0.5 h into the scotophase, and L. botrana called for 2.5 h starting at the beginning of the scotophase (Figure S3)
Summary
Reproduction shows a periodic pattern related to the duration of the daily light and dark cycles and involves a complex series of behavioral and physiological events including chemical communication mediated by sex pheromones (Groot 2014). Several factors influence calling behavior and pheromone production in moths (McNeil 1991; Raina 1993), including age (i.e., Webster and Cardé 1982; Gemeno and Haynes 2000; Kawazu and Tatsuki 2002; Mazor and Dunkelblum 2005; Ming et al 2007), mating status (i.e., Foster and Roelofs 1994; Delisle et al 2000; Mazo-Cancino et al 2004), and pheromone autodetection (Holdcraft et al 2016). Environmental stressors, such as sublethal doses of insecticides that intoxicate but do not kill the individual, could affect pheromone production and release (Haynes 1988; Tricoire-Leignel et al 2012), but this aspect has been tested in relatively few moth species.
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