Abstract
Bombus hypocrita and B. ignitus are promising candidates for use in commercial pollination of greenhouse crops and have the same four oviposition phases as B. terrestris. Queens of both species switch from laying diploid eggs to haploid eggs (Switching Point: SP) in Phase 3. The worker productivity of B. ignitus is higher than that of B. hypocrita. The duration of fertilized-egg oviposition of B. ignitus (1997: 47.5 days, 1998: 47.6 days) is about 10 days longer than that of B. hypocrita (1997: 37.1 days, 1998: 35.2 days), resulting in the difference in the duration of Phase 3 before SP between B. hypocrita and B. ignitus. However, there is no difference between the number of egg cells built per day of both species. The foundress B. hypocrita. queen produced progeny queens from fertilized eggs in Phase 2. However, progeny-queen production occurred only after Phase 3 in B. ignitus. These results suggest that B. hypocrita has flexible production of the reproductive caste, possibly as an adaptation to its distribution in the sub-arctic zone; B. ignitus is only distributed in the temperate zone and may not require such flexibility. This difference in reproductive strategy between the two species suggests that B. ignitus might be a better choice for early commercialization than B. hypocrita.
