Abstract
The prevailing use of neonicotinoids in pest control has adverse effects on non-target organisms, like honeybees. However, relatively few studies have explored the effect of sublethal neonicotinoid levels on olfactory responses of pest insects, and thus their potential impact on semiochemical surveillance and control methods, such as monitoring or mating disruption. We recently reported that sublethal doses of the neonicotinoid thiacloprid (TIA) had dramatic effects on sex pheromone release in three tortricid moth species. We present now effects of TIA on pheromone detection and, for the first time, navigational responses of pest insects to pheromone sources. TIA delayed and reduced the percentage of males responding in the wind tunnel without analogous alteration of electrophysiological antennal responses. During navigation along an odor plume, treated males exhibited markedly slower flights and, in general, described narrower flight tracks, with an increased susceptibility to wind-induced drift. All these effects increased in a dose-dependent manner starting at LC0.001 - which would kill just 10 out of 106 individuals - and revealed an especially pronounced sensitivity in one of the species, Grapholita molesta. Our results suggest that minimal neonicotinoid quantities alter chemical communication, and thus could affect the efficacy of semiochemical pest management methods.
Highlights
Animals moving in fluid media locate odorous resources by upwind orientation, which consists of maintaining their heading against flow[1]
Sex pheromone research has permitted the development of environmentally-sound semiochemical pest management methods, such as monitoring, mass-trapping and mating disruption (MD), which exploit the response of males to synthetic sex pheromone[8]
We recently found that topical application of the neonicotinoid thiacloprid (TIA) substantially reduced pheromone release behaviour in females of three tortricid moth species [Cydia pomonella (L.), Grapholita molesta (Busck) and Lobesia botrana (Denis & Schiffermüller); from here on “CP”, “GM” and “LB”, respectively], starting at the lethal concentration LC0.001 which kills only 10 in 106 individuals[25,22]
Summary
Animals moving in fluid media locate odorous resources by upwind orientation, which consists of maintaining their heading against flow[1]. This strategy in itself does not guarantee finding an odor source because flow direction and intensity change through time, producing a shredded and relatively discontinuous odor plume which can be lost. Mate finding in moths and other insects is facilitated by sex pheromones, typically produced by females and detected by males from relatively long distances, of perhaps tens or hundreds of meters[5]. The chemical and temporal attributes of the odor plume are detected by highly specific and sensitive pheromone receptor cells located on the antennae, and their responses are integrated in the antennal lobe and higher brain centers[6]. We speculate on the consequences of our findings in the context of pest management programs that combine the use of insecticides and sex pheromones
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