An extended laboratory test to evaluate the effects of pesticides on bumblebees. Preliminary results

In recent years, several researches on the acute laboratory toxicity of pesticides to bumblebees have been carried. However, only a few researches on the toxicity of pesticides to bumblebees in semi-field and field-tests have bee conducted, and thus little information on this subject is available. The Italian Ministry of Agricultural Resources and Forestry financed the "AMA" Project (Ape-Miele-Ambiente) with the aim to intensify researches on toxicological impacts of pesticides on Apoidea. Within this project, we tried to develop an extended laboratory bioassay to evaluate the effects of insecticides and acaricides on bumblebees. In order to record the behaviour and mortality of bumblebee workers after exposure to plants sprayed with pesticides, special cages offering the bees ample flying space, were built. Prior being transferred into the cages, potted flowering cucumber (Cucumis sativus) plants were sprayed with different pesticides at the field rate. Three different classes of pesticides were tested: phosphorganics (chlorpyriphos-methyl, dichlorvos, dimethoate, heptenophos and quinalphos), azotorganics (ethiofencarb and imidacloprid) and pyrethroids (acrinathrin and bifenthrin). In a first test, in each cage, thirty bumblebees were put into contact with the plants 1 hour after the treatment. For the next three days, every 24 hours, abnormal behaviour and bumblebee mortality were recorded. In a second test, the introduction of the bumblebees into the cages was delayed up to 24 hours after the treatment; behaviour and mortality were recorded over the next two days. The cages were housed in a greenhouse and temperature was recorded throughout the testing period. Phosphorganics had the highest level of toxicity, especially dimethoate and quinalphos, whereas the lowest hazard was recorded for pyrethroids, for heptenophos and for ethiofencarb. Imidacloprid did not lead to high mortality rates, but interrupted the insects' activity for several hours. A consistent hazard decrease after delayed introduction was registered only for phosphorganics. The method seems to provide reproducible and useful results for the evaluation of pesticide toxicity. It may be used to reinforce results obtained from common laboratory toxicity tests (contact and oral), and may help to evidence repellence effects of pesticides. However, in order to standardise this testing method, several aspects require improvement, and climatic conditions, such as temperature and photoperiod, shoul