Hazards of Imidacloprid Seed Coating to <I>Bombus terrestris</I> (Hymenoptera: Apidae) When Applied to Sunflower

Abstract

Seed coating treatments of sunflower by the systemic insecticide imidacloprid was suspected of affecting honey bees and bumblebees. The hypothesis raised was whether imidacloprid could migrate into nectar and pollen, then modify flower attractiveness, homing behavior, and colony development. Our greenhouse and field experiments with Bombus terrestris L. were aimed at the following: the behavior of workers foraging on treated and control plants blooming in a greenhouse, the homing rate of colonies placed for 9 d in a treated field compared with colonies in a control field, and the development of these 20 colonies under laboratory conditions when removed from the fields. In the greenhouse, workers visited blooming heads of treated and control plants at the same rate and the mean duration of their visits was similar. In field colonies, analysis of pollen in hairs and pellets of workers showed that in both fields 98% of nectar foragers visited exclusively sunflowers, whereas only 25% of pollen gatherers collected sunflower pollen. After 9 d, in the control and treated field, 23 and 33% of the marked foragers, respectively, did not return to hives. In both fields, workers significantly drifted from the center to the sides of colony rows. During the 26-d period under field and laboratory conditions, the population increase rate of the 20 colonies was 3.3 and 3.0 workers/d in hives of the control and treated field, respectively. This difference was not significant. New queens were produced in eight colonies in either field. The mean number of new queens per hive was 17 and 24 in the control and treated field, respectively. Their mating rate was the same. It was concluded that applying imidacloprid at the registered dose, as a seed coating of sunflowers cultivated in greenhouse or in field, did not significantly affect the foraging and homing behavior of B. terestris and its colony development.

Evidence for decline in eastern North American bumblebees (Hymenoptera: Apidae), with special focus on Bombus affinis Cresson

“…In particular, one group of persistent pesticides (the neonicotinoids) has been shown to be highly toxic to bees (EPA 1994;Marletto et al 2003) and has been implicated in bee declines in various regions in Europe (Tasei et al 2001). Its use in North America began in the early 1990s, before members of the subgenus Bombus were noted to be in decline, and thus this group of pesticides may be a substantial threat.…”

Impact of Currently Used or Potentially Useful Insecticides for Canola Agroecosystems on <I>Bombus impatiens</I> (Hymenoptera: Apidae), <I>Megachile rotundata</I> (Hymentoptera: Megachilidae), and <I>Osmia lignaria</I> (Hymenoptera: Megachilidae)

“…For example, although highly toxic by direct contact, the neonicotinoid insecticides are applied as seed treatments on canola, thus minimizing impact other than through possible minimal exposure to very low residues in nectar and pollen (Tasei et al 2001, Maus et al 2003, Cutler and Scott-Dupree 2007b. Conversely, although generally less toxic by contact, foliar applications of deltamethrin or spinosad could have immediate impact on foraging bees.…”

Ecotoxicity of Neonicotinoid Insecticides to Bees

“…59 Observations on foraging activity of Bombus terrestris revealed no difference regarding the presence of workers on blooming heads and the duration of their visits between imidacloprid-treated and control sunflowers. 32 Another member of the chloronicotinyl family, clothianidin appeared harmless when colonies of B. impatiens were exposed to the highest residue levels in pollen, 60 or when hives of Apis mellifera were exposed to flowering canola grown from clothianidin-treated seeds. 61 Although these studies showed the absence of effect of neonicotinoids on foraging of treated plants, perturbations of the foraging behavior on artificial feeder were revealed in other experiments.…”