Bombus ignitus

Bombus ignitus exhibits a size dependent division of labor. An aforaging gene, Bifor, has been isolated in B. ignitus. Bifor expression negatively correlated with size, with higher levels of expression found in the smaller nurses. Foragers are larger in size and have lower levels of Bifor expression.[10]

Bombus ignitus is monandrous; the queen mates with only a single drone to form a colony. All workers and new queens, as a result, are descendants of the queen and a single drone.[4] This monandrous behavior decreases the amount of genetic variation present in a single colony relative to that of a polygynous or polyandrous species.

Both the queen and workers possess the ability to reproduce. The queen suppresses the reproductive actions of workers through increased aggressive action against reproductively active workers and destruction of eggs laid by workers. In colonies still dominated by the queen, the vast majority of drones are derived from the queen. In colonies where the queen has died, roughly half the drones are born from workers.[4]

Bombus ignitus, like many bees, exhibit Haplodiploidy. Diploid queens produce diploid workers and new queens from fertilized eggs. Haploid drones are produced from unfertilized eggs, laid by either the queen or workers.[4] All sperm produced by a drone is identical, containing its exact haploid DNA. Variation arises from females, who produce genetically variant eggs through meiosis. Sex is determined under a single-locus complementary sex determination (sl-CSD) system, where multiple alleles at a single locus determine the sex of an individual. Sex locus heterozygotes develop as females, while hemizygous and homozygous eggs develop as haploid and diploid males.[11]

As the queens of B. ignitus mate with only one male, the workers are more closely related to other workers (with whom they share an average of seventy five percent of their genes with) than to the queen (who they only share half their genes with). With respect to male offspring, workers are more closely related to the sons of other workers, sharing an average of 37.5 percent of their genes with them, than the sons of the queen, who they only share 25% of their genes with.[4]

Worker policing, manifested through aggressive actions against fertile workers and removal of the eggs of workers, has been observed in colonies of B. ignitus. Similarly, reproductive workers have been observed taking aggressive behavior against founding queens. These include eating the eggs laid by the queen and laying eggs themselves, as well as attacking the queen herself. In an analysis of seven B. ignitus colonies, the survival rate of colony founding queens was 72%. These queens had damaged wings or bodies, which suggests numerous conflicts with workers.[4]

Bombus ignitus is currently used for agricultural pollination in China and Japan.[3] The species has been chosen as a reliable species for commercial mass-production in Korea, though issues of diapause management must still be addressed. B. ignitus was chosen over the already established bumblebee, Bombus terrestris, for fear of competition or genetic contamination by mating with native bumblebee species.[12]

The protein BiVSPI, Found in the venom of B. ignitus, has been identified as a serine protease inhibitor. BiVSPI exhibits antimicrobial functions, and has been found to inhibit the growth of Gram-positive bacteria and fungi.[13] The cDNA of four antibacterial peptide genes - apidaecin, hymenoptaecin, abaecin, and defensin - were isolated and cloned from B. ignitus.[14] Synthesized abaecin has been shown to inhibit the growth of Gram- negative bacteria, but had little inhibitory effect towards the growth of Gram-positive bacteria.[15]