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United States Department of Agriculture

Agricultural Research Service

Title: Fungicide Tests on Adult Alfalfa Leafcutting Bees Megachile rotundata (F.) (Hymenoptera:Megachilidae)

Authors
item Huntzinger, Craig
item James, Rosalind
item Bosch, Jordi - UNIV AUTONOMA BARCELONA
item Kemp, William

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 9, 2008
Publication Date: June 20, 2008
Citation: Huntzinger, C., James, R.R., Bosch, J., Kemp, W.P. 2008. Fungicide Tests on Adult Alfalfa Leafcutting Bees Megachile rotundata (F.) (Hymenoptera:Megachilidae). Journal of Economic Entomology. 101(3): 660-667

Interpretive Summary: Chalkbrood is a fungal disease of bee larvae causing significant mortality in the alfalfa leafcutting bee, a bee that is used extensively for alfalfa seed pollination in the U.S. Using laboratory bioassays, we previously demonstrated that fungicides can reduce chalkbrood levels in this bee. However, a control method employing the use of fungicides must not be harmful to adult bees. The toxicity of four fungicides, Benlate®, Captan®, Orbit™, and Rovral® to adult bees was evaluated using three different bioassays. In the first test, fungicides were applied to the bee’s thorax. In the second test, mimicking foliage residue, a piece of filter paper soaked in fungicide was placed on the bottom of a container of bees. The third test evaluated oral toxicity by feeding the bees fungicides incorporated into sugar-water. Both the topical and oral tests were sensitive and caused bee mortality while the filter paper test did not discriminate well among the fungicides. Toxicity was greater to males than to females. The use of fungicides for chalkbrood control is a logical choice, but caution should be used in how they are applied in the presence of bees.

Technical Abstract: Chalkbrood is a fungal disease of bee larvae caused by Ascosphaera aggregata. It causes significant mortality in the alfalfa leafcutting bee (Megachile rotundata), a bee that is used extensively for alfalfa seed pollination in the U.S. Using laboratory bioassays, we previously demonstrated that fungicides can reduce chalkbrood levels in this bee. However, a control method employing the use of fungicides must not be harmful to adult bees. The toxicity of four fungicides, Benlate®, Captan®, Orbit™, and Rovral® to adult bees was evaluated using three different bioassays. In the first test, fungicides were applied to the bee’s thorax. In the second test, mimicking foliage residue, a piece of filter paper soaked in fungicide was placed on the bottom of a container of bees. The third test evaluated oral toxicity by incorporating fungicides into a sugar-water solution that was fed to the bees. The filter paper test did not discriminate among the fungicides well, and the oral test resulted in the greatest mortality. Toxicity to males was greater than to females. The use of fungicides for chalkbrood control is a logical choice, but caution should be used in how they are applied in the presence of bees.

Last Modified: 10/24/2014
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