Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/6/2011
Publication Date: 2/1/2012
Citation: Yocum, G.D., Rinehart, J.P., Kemp, W.P. 2012. Duration and frequency of the high temperature pulse affect survival of emergence-ready Megachile rotundata (Hymenoptera: Megachilidae) during low-temperature incubation. Journal of Economic Entomology. 105(1):14-19.
Interpretive Summary: Seventy percent of crops grown for human food production are dependent on pollinators. The value of this pollination service worldwide is estimated at 153 billion euros. This value does not include agriculture products that are not directly consumed by humans such as alfalfa that is used as an input for meat and milk production. Alfalfa is a major forage crop for livestock, with approximately 21.7 million acres harvested and 2.8 million acres seeded in the United States. The total value of the harvested alfalfa was 10.8 billion dollars and seed production was valued at 88 million dollars. The primary pollinator used in the production of alfalfa seed in North America is the alfalfa leafcutting bee Megachile rotundata. Ensuring the match between M. rotundata nest establishment and peak floral resources is critical in ensuring adequate pollination and healthy bee brood production. Timing M. rotundata nesting activity to coincide with alfalfa bloom is achieved by predicting the bloom date and then transferring the overwintering prepupae to 29 - 30 °C to initiate development on the appropriate date. If environmental conditions change so as to delay the bloom, managers will interrupt the spring incubation with a period of low-temperature incubation to slow the bees’ development. The aim of this investigation is to develop a more optimized low temperature regime to insure improved alfalfa pollination and brood production through better synchronization of bees with alfalfa bloom.
Technical Abstract: Synchronizing Megachile rotundata (F.) nesting activity with alfalfa bloom is essential for ensuring optimal pollination for alfalfa seed production. This is achieved by timing the initiation of spring bee incubation so that adults will emerge approximately two weeks before peak bloom. If weather conditions change so as to delay the bloom, bee managers will commonly expose the developing bees to a period of low-temperature incubation to slow their development. We have previously demonstrated survival during low-temperature incubation can be significantly increased by employing a fluctuating thermal regime (FTR) where the bees receive a daily pulse at 20 °C. A FTR incubation protocol is composed of a number of different components, such as the base and pulse temperatures, and the duration and frequency of the pulse. In this investigation, the effect of the duration of the pulse (20 °C) and the frequency of a pulse (60 minutes at 20 °C) on the survival of developing M. rotundata was examined. A pulse as short as five minutes at 20 °C increased survival of the developing bees as compared to the constant 6 °C controls. Increasing the pulse duration induced a further increase in tolerance. As with the pulse duration, increasing the pulse frequency from once weekly to twice daily had a significant effect on improving the bees tolerance to low-temperature incubation. This investigation further strengthens the argument that a FTR protocol is superior to using a constant low-temperature exposure for interrupting the spring incubation of M. rotundata.