Laboratory assessment of lethal and sublethal side-effects supports a more benign profile of spinetoram compared to spinosad in the bumblebee Bombus terrestris.

BACKGROUND: This study was undertaken to identify potential side-effects of the novel naturalyte insecticide spinetoram in comparison with spinosad on the bumblebee Bombus terrestris L. We evaluated the potential lethal effects together with the ecologically relevant sublethal effects on aspects of bumblebee reproduction and foraging behaviour. Bumblebee workers were exposed via direct contact to wet and dry residues under laboratory conditions to spinetoram at different concentrations, starting from the MFRC and then different dilutions (1/10, 1/100, 1/1000 and 1/10000 of the MFRC), and compared with spinosad. In addition, we assessed the side-effects via oral exposure in supplemented sugar water.
RESULTS: Direct contact of B. terrestris workers to wet residues of spinosad and spinetoram showed spinetoram to be approximately 52 times less toxic than spinosad, while exposure to dry residues of spinetoram was about 8 times less toxic than those of spinosad. Oral treatment for 72 h (acute) indicated that spinetoram is about 4 times less toxic to B. terrestris workers compared to spinosad, while exposure for a longer period (i.e. 11 weeks) showed spinetoram to be 24 times less toxic. In addition, oral exposure to the two spinosyns resulted in detrimental sublethal effects on bumblebee reproduction. The no observed effect concentration (NOEC) for spinosad was 1/1000 of the MFRC, and 1/100 of the MFRC for spinetoram. Comparison between the chronic exposure bioassays assessing the sublethal effects on nest reproduction, with and without allowing for foraging behaviour, showed that the respective NOEC values for spinosad and spinetoram were similar over the two bioassays, indicating there were no adverse effects by both spinosyns on the foraging of B. terrestris workers.
CONCLUSION: Overall, the present results indicate that the use of spinetoram is safer for bumblebees by direct contact and oral exposure than spinosad and therefore can be applied safely in combination with B. terrestris. Another important conclusion is that the current data provide strong evidence that both spinosyns have no negative effect on the foraging behaviour of these beneficial insects. However, before making final conclusions, spinetoram and spinosad should also be evaluated in more realistic, field-related, situations for the assessment of potentially deleterious effects on foraging behaviour with use of queenright colonies of B. terrestris.

Jaar van publicatie:2011

Trefwoorden:Spinetoram, spinosad, microbial insecticide, spinosyns, bumblebees, Bombus terrestris, toxicity, direct contact, oral exposure, reproduction, foraging behaviour, IPM, ecotoxicity