A Calendar of Incubation for Alfalfa Leafcutting Bees

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Cocoons are placed in incubation trays and are allowed to warm up slowly over several days at room temperature. The incubator temperature is then increased to 30ºC. Count “day 1” of incubation as the first day at which they are at 30ºC. This calendar of incubation assumes continual cool storage at 5ºC prior to incubation, and continual incubaton at 30ºC. Degree-Days are the number of degrees above the base temperature for development (15.7ºC) for a day. At 30º, 14.3 degree days (D.D.) are accumulated each day.

Day 1 Cocoons are at 30ºC. All are in the prepupal stage. Black lights and water traps are in place. (fig. 1)
Day 3 Pteromalus undergo their final molt into the pupal stage.
Day 7 Place dichlorvos into the incubator at the recommended rate of 3/4 strip per 1000 cu ft. If the incubator is only partially full use a lower rate.
Day 8 Leafcutting bees begin to undergo their final molt into the pupal stage. At this stage they are very sensitive to temperature fluctuations so maintain an even temperature – no cooling and holding at this time!
Day 8-9 First Pteromalus begin to emerge. If the vapona is working they should die in the trays rather than making it to the water trap. 150 D.D.
Day 9-12 Pteromalus continue to emerge. (fig. 2)
Day 10 Leafcutting bee larvae pupate – white pupa stage. 148 D.D.
Day 12 Pink eye stage. 165 D.D.
Day 13 Dark eye stage. 190 D.D. Remove the dichlorvos strips. Actively air the incubator thoroughly and completely, using an exhaust fan and circulating fans, for 24-48 hours. Maintain the 30º temperature if possible and desirable. (fig. 3)
Day 14-15 Leafcutting bee pupae continue to darken in color. If cooling occur-red during airing after vapona removal bring the incubator temperature back to 30ºC for continuation of development. (fig. 4)
Day 14-15 Native leafcutting bees Megachile relativa emerge. This may cause concern to the new beekeeper that the timing is off and the bees are beginning to emerge several days early. These bees are larger, and the female has orange hairs on the abdomen. (fig. 5)
Day 14-22 At any time during this period, if incubation must be slowed due to weather or bloom, the cocoon temperature can be lowered to 10-15ºC for up to two weeks. This virtually stops development. Once the temperature is increased development resumes until the hatch is complete. Remember that the bee temperature must at 10-15ºC, not just the air temperature.
Day 16 Early hatching pupae (mainly males) are completely dark in color; later hatchers (mainly females) are darkening. (fig. 6)
Day 18-19 Males begin to emerge. Remember that the bees are very susceptible to high temperatures! 265 D.D.
Day 21-22 Females begin to emerge. Male emergence peaks. Second generation Pteromalus begin to emerge. 307 D.D. (fig. 7)
Day 23-24 Female emergence peaks. 336 D.D.
Day 23-24 Trays are taken to the field for adult bee release once the females are 75% hatched. Trays may be returned to the incubator for completion of female hatch under controlled temperature conditions, then taken to the field again after two or three days.
Day 28 Hatch is virtually complete at 30ºC.