ARS | Publication request: A fluctuating thermal regime improves survival of cold-mediated delayed emergence in developing Megachile rotundata (Hymenoptera: Megachilidae)

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 23, 2011
Publication Date: August 1, 2011
Citation: Rinehart, J.P., Yocum, G.D., West, M.S., Kemp, W.P. 2011. A fluctuating thermal regime improves survival of cold-mediated delayed emergence in developing Megachile rotundata (Hymenoptera: Megachilidae). Journal of Economic Entomology. 104(4):1162-1166.

Interpretive Summary: Like many agricultural products in the United States, the production of alfalfa seed is heavily dependant on insects for pollination. Instead of using honeybees, the majority of this crop is pollinated by the alfalfa leafcutting bee Megachile rotundata, making it a highly managed species. In the spring, growers remove overwintering bees from cold storage and incubate them in preparation for the start of alfalfa bloom. However, during this incubation period, field conditions can alter the timing of bloom, thus causing the bees to be ready before the crop. Previously, we reported that this species can be cold stored for brief periods after incubation has been started, thus giving growers flexibility in the timing of adult bee emergence. In this paper, we demonstrate that fluctuating thermal regimes (FTR) can be used to give growers more flexibility by increasing the “shelf-life” of bees prior to emergence. While constant temperatures can be used to store bees for up to one week with no decrease in survival, properly staged bees can be stored for up to six weeks without a significant decrease in percent emergence. Hence, we expect fluctuating thermal regime protocols to become a valuable tool for managers of this important alternative pollinator, especially when timing nesting activity with peak bloom to maximize effectiveness.

Technical Abstract: A significant concern in the commercial application of the alfalfa leafcutting bee Megachile rotundata (F.) for pollination is synchronizing bee emergence and activity with peak crop bloom. Previous studies have demonstrated that the commerical spring incubation of this species can be successfully interrupted by low temperature storage, thereby slowing development and giving producers flexibility in timing emergence to weather conditions or crop bloom. In this study we demonstrate that the implementation of a fluctuating thermal regime, during which bees are given a daily one hour pulse of high temperature, markedly increases the “shelf-life” of individuals of this species. While constant temperatures can be used to store bees for up to one week with no decrease in survival, properly staged bees can be stored for up to six weeks without a significant decrease in percent emergence. Hence, we expect fluctuating thermal regime protocols to become a valuable tool for M. rotundata managers, especially when timing nesting activity with peak bloom to maximize effectiveness.