The frequency of colonies that produce diploid males after brother‐sister (50%) and nephew‐niece (37.5%) matings proves that in B. terrestris the sex is determined by a single multi‐allelic sex locus. The diploid males which develop normally into adults make up 50% of the diploid brood. In the laboratory the growth rate of colonies with diploid males is influenced only slightly. Of 41 colony founding queens caught out of a natural population, all produced a colony without any diploid males. Therefore, the number of sex alleles in this population is estimated to be at least 24. This means that in commercial rearing systems for bumble bees, involving several generations, the occurrence of diploid males can largely be prevented by a good scheme for crossings.

The presence of both triploid males and females in Bombus terrestris was detected by distinct chromosome observation. These cytological features are novel among the higher Hymenopteran insects. We thus strictly applied the complementary sex determination (CSD) model previously proposed for Hymenopteran insects. Three out of 60 sibling queens that were mated with diploid males produced both triploid males and females, and founded colonies. The male to female ratio of the bees which emerged from the fertilized eggs of the queens was approximately 1 to 1. Thus we reconfirm that the sex in B. terrestris is determined by a single multi-allelic locus. The body size of the triploid males was smaller than that of the diploid and haploid males. We found hatched eggs laid by one triploid female (worker). One of these developed into a 3rd instar larva, however most of the triploid individuals were sterile.

The chromosomes of 21 species of Vespidae (consisting of 9 polistines and 12 vespines) were compared using an air-drying technique.The haploid number of the Polistinae ranged broadly (n=14, 22, 23, 26, 30, 31, and 34), while it was either n=25 or n=26 in the Vespinae. There were no karyological homologies (in terms of marker chromosomes) between these two subfamilies. Some phylogenetic relationships of social wasps were discussed, based on the karyological literature now available (32 species). We suggested that the three genera of Vespinae (Dolichovespula, Vespa, and Vespula) would have differentiated in two different ways from a common ancestor having 27 acrocentrics (n=27) by tandem fusion (the first genus with n=26) and by two centric fusions (the latter two genera with n=25).In the genus Polistes, the 5 subgenera (Fuscopolistes, Aphanilopterus, Megapolistes, Polistella, and Polistes) would have evolved independently toward increasing chromosome numbers since they started to separate from their ancestor having n=9-14.

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The European honeybee, Apis mellifera, has been introduced to all continents and their products like honey, propolis, royal jelly and beeswax are well known. However, its contribution is not restricted to such direct products but extends into a much wider area. For example, the economic value of seed production by pollination exceeds the above‐mentioned bee products. The application of F1 hybrid is increased to as much as 70% of commercial crops and flowers in Japan and honeybees are important pollinators in the F1 seed production. Incorporation into the large‐scale biodiesel fuel production system by culturing rape and sunflower seeds etc. is relied on because it is good to construct possible zero‐emission systems that reduce carbon dioxide and increase the rich by‐products like honey and royal jelly. Bees’ higher brain function and sophisticated social system of the colony opens new perspectives as a model system. Their individual ability to recognize even abstract concepts is comparable to that of higher primates. Rats or mice have no such ability. High performance learning ability of bees associated with proboscis extension reflex can be used to detect drugs at the airport. Function of the colony, on the other hand, is an excellent model for social physiology or a self‐organization system. After the whole genome of A. mellifera was read in 2006 by the world consortium, consisting of more than 90 institutions from all over the world, many molecular biologists are coming into bee world. Nobody has yet succeeded in the challenge to make transgenic honeybee, so far, because of the difficulty in controlling the reproductive system headed by the queen. However, if someone succeeded in a breakthrough we will have stingless honeybees and a disease‐resistant strain in the future.