HEAT RETENTION DURING INCUBATION IN NESTS OF THE ALFALFA LEAFCUTTING BEE (HYMENOPTERA, MEGACHILIDAE)

Temperatures within polystyrene, paper, and wooden nests of the alfalf a leafcutting bee, Megachile rotundata (F.), were monitored during inc ubation at 30.0-degrees-C. In the polystyrene and paper nests, tempera tures began to increase 10 d after the start of incubation and continu ed to rise until adults emerged. Temperatures reached 35.1-degrees-C i n the polystyrene and 37.2-degrees-C in the paper, while the wood nest s never exceeded 30.6-degrees-C. Compared with air temperature degree- days, cells in the center of the polystyrene nests accumulated up to 2 8 more degree-days after 20 d, whereas those in the paper accumulated 32 more degree-days. In polystyrene nests, heat units increased toward the center holes, reaching a maximum at the fifth row toward the cent er. Emergence was also monitored from polystyrene blocks, wooden board s, and loose cells. Females emerged 2.1 d later from polystyrene block s compared with wooden boards and the emergence period was lengthened by 2.5 d. Because of the increased temperatures and the prolonged emer gence period experienced with these materials, we recommend that fille d polystyrene and paper nests not be incubated but be stripped of thei r cocoons as they were designed.