Thermoperiodism synchronizes emergence in the alfalfa leafcutting bee (Hymenoptera: Megachilidae)

Authors: Yocum, George; Rinehart, Joe; Yocum, Ian; Kemp, William - Bill; GREENLEE, KENDRA - North Dakota State University

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/28/2015
Publication Date: 2/19/2016
Publication URL: http://handle.nal.usda.gov/10113/61955
Citation: Yocum, G.D., Rinehart, J.P., Yocum, I.S., Kemp, W.P., Greenlee, K.J. 2016. Thermoperiodism synchronizes emergence in the alfalfa leafcutting bee (Hymenoptera: Megachilidae). Environmental Entomology. 45(1):245-251.

Interpretive Summary: Alfalfa seed production in the northwestern United States and western Canada is heavily dependent upon the pollinating services of M. rotundata (F.) (Hymenoptera: Megachilidae). Insects commonly use the normal occurring light and dark cycle to synchronize their activities to the biotic and abiotic resources needed for development and reproduction. Megachile rotundata females nest in cavities either naturally occurring or in artificial nesting blocks. Because of the physical nature of the nest, M. rotundata brood may have limited to no exposure to photoperiodic cues in order to regulate important circadian (24 hour cycle) functions. Adult emergence of brood incubated under constant 29°C and darkness is arhythmic, emergence ocurred during the day and night. Exposing developing M. rotundata to a thermoperiod (a temperture treatment in which the temperture is elevated during the daylight period of day relative to the night time temperture) synchronizes emergence to the beginning of the high temperature phase of the thermoperiod and decreases the total number of days required for all adults to emerge. The amplitude of the thermoperiod regulates the timing of peak emergence in relationship to the increase in temperature. A thermoperiod amplitude of only 2°C is sufficient to synchronize peak adult emergence to take place during the rise in temperature. Increasing the amplitude of the thermoperiod to 6 or 8°C causes a positively correlated shift in peak emergence to later in the high temperature phase. Brood stored under constant 29°C and darkness for different durations (May/June early in the growing season or July/August late in the growing season) or under a fluctuating thermal regime (base temperature of 6°C and daily 1 h pulse of 20°C until September/November) maintain their capacity for entraining emergence timing by thermoperiodism. The possible management implications of these results would be improved mating success by concentrating adult emergence over a fewer number of days and during the time of day that would be most advantageous for mating.

Technical Abstract: Alfalfa seed production in the northwestern United States and western Canada is heavily dependent upon the pollinating services of M. rotundata (F.) (Hymenoptera: Megachilidae). Megachile rotundata females nest in cavities either naturally occurring or in artificial nesting blocks. Because of the physical nature of the nest, M. rotundata brood may have limited to no exposure to photoperiodic cues in order to regulate important circadian functions. Adult emergence of brood incubated under constant 29°C and darkness is arhythmic. Exposing developing M. rotundata to a thermoperiod synchronizes emergence to the beginning of the thermophase and decreases the total number of days required for all adults to emerge. The amplitude of the thermoperiod regulates the timing of peak emergence in relationship to the increase in temperature. A thermoperiod amplitude of only 2°C is sufficient to synchronize peak adult emergence to take place during the rise in temperature. Increasing the amplitude of the thermoperiod to 6 or 8°C causes a positively correlated shift in peak emergence to later in the thermophase. Brood stored under constant 29°C and darkness for different durations (May/June early in the growing season or July/August late in the growing season) or under a fluctuating thermal regime (base temperature of 6°C and daily 1 h pulse of 20°C until September/November) maintain their capacity for entraining emergence timing by thermoperiodism. The possible management implications of these results would be improved mating success by concentrating adult emergence over a fewer number of days and during the time of day that would be most advantageous for mating.