Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/9/2009
Publication Date: 4/1/2010
Citation: Yocum, G.D., Rinehart, J.P., West, M.S., Kemp, W.P. 2010. Interrupted Incubation and Short-Term Storage of the Alfalfa Pollinator, Megachile rotundata (Hymenoptera: Megachilidae): A Potential Tool for Synchronizing Bees With Bloom. Journal of Economic Entomology. 103(2):234-241.
Interpretive Summary: Alfalfa is a major forage crop for livestock, with 21.7 million acres harvested and 2.8 million acres seeded in the United States in 2007. The total value of the harvested alfalfa was 10.8 billion dollars and seed production was valued at 15 million dollars. Currently, alfalfa seed production is only economically viable with the use of managed pollinators, and the alfalfa leafcutting bee is the primary pollinator used in North America. One of the key elements to maximize seed production is synchronizing the nesting adult female bee activity with the onset alfalfa bloom. In anticipation of the alfalfa bloom, growers will move overwintering alfalfa leafcutting bees from storage to incubators to initiate development. Growers use a standard degree day model to predict the date of emergence. One problem with using a degree day model to synchronize alfalfa leafcutting bee emergence with the alfalfa bloom, is that once the spring incubation is started field conditions may change and thereby alter the timing of bloom. If the weather conditions change, causing alfalfa bloom to be delayed, growers will frequently delay the emergence of adult bees by lowering incubation temperatures. This exposure to low temperature can be stressful decreasing the bees ability to pollinate the alfalfa. The aim of this investigation is to develop a more optimized low temperature regime to insure improved alfalfa pollination through better synchronization of bees with alfalfa bloom.
Technical Abstract: Interrupting the spring incubation with short-term low temperature storage of the developing pupae and pharate adult stage of Megachile rotundata (F.) is a useful technique for synchronizing the emergence of this bee species with the peak alfalfa bloom. However, low temperature exposure can be stressful depending on the temperature, duration of exposure and the developmental stage exposed. To evaluate the effect of low temperature storage, after development was initiated by exposure to 29 ºC three developmental stages (eye pigment pupae, body pigment pupae, and pharate adults ready to emerge) were exposed to 6, 12 or 18 ºC for durations up to 28 days. The effect of delaying the termination of overwintering storage at 6 ºC from April to July (“April bees” and “July bees,” respectively) was also examined. The following observations were made: 1) All developmental stages examined of the April bees and July bees can be stored without harmful effects, as measured by percent survival, for 14 days at 12 ºC and above. 2) Increasing the overwintering storage at 6 ºC from April until July induced a delay in emergence for the body pigment pupae stored 12 ºC for 14 days and the ready to emerge adults stored at 6 ºC for 14 days. 3) The increase of overwintering duration also induced a decrease in the postemergence longevity of the ready to emerge adults stored at 6 ºC for 14 days. 4) Of the three storage temperatures examined, 18 ºC appears to be the optimal storage temperature for short-term storage of developing bees because of their slow but continuing development and the lack of increased mortality either during storage or after emergence.