Extracted from Bumble Bees and Cuckoo Bumble Bees of California by Thorp, R. (1983).
Bombus melanopygus edwardsii
Discussion. B. edwardsii belongs to the group of species which includes A. melanopygus, mtxtus, sitkensb, and sytvicola, and is most closely related to 5. melanopygus. It differs from melanopygus in having black, not red, hairs on metasomal terga 2 and 3.
In color pattern, J?, edwardsii most closely resembles £. bf/arius ("nearcticus" populations) and mtxtus. It differs from btfartus in having the scutellum entirely yellow and not interrupted by a broad V-shaped notch. It differs from mtxtus females in having black hair on the last two tergites instead of reddish or golden hairs. The males are easily separated, because the males of mixtus have unique brush-like fringes of hair on the inner faces of the basal antennal flagellomeres.
This species is remarkably uniform in color pattern, but may intergrade with B. melanopygus (see discussion under that species).
We have encountered 5 nests of this species. Three taken in Berkeley and El Cerrito were above ground (1.8 to 12.2 m) in old bird nests. Two oth¨ers (near Pope Valley, Napa Co., and near Santa Margarita, San Luis Obispo Co.) were underground in old rodent burrows. Nest associates included Vobtcetta larvae (Syrphidae) (Pope Valley) and Cratldus adults (Tenebrionidae) (Santa Margarita), the latter probably only incidental.
Discussion. B. melanopygus belongs to the group of species which includes B. edwardsii* mixtus, sitkensis, and sytvkota* and is most closely related to B. edwardsii. It differs from edwardsii in having red instead of black hair on metasomal tergites 2 and 3 and usually having black instead of yellow hair on tergites 4 and 5.
In color pattern it looks most like B. huntii and the Great Basin color form of California B. syivi-cola. It differs from both in having black hairs intermixed among the yellow hairs of the anterior scutum, which give the area a clouded appearance.
The principal color variation occurs in the amount of yellow hair replacing the black hair on metasomal tergites 4 and 5. An increase in yellow on these tergites is often accompanied by a decrease in the number of black hairs intermixed
on the anterior scutum. The resulting extreme looks like an edwardsU with red instead of black hair on tergites 2 and 3. Occasional males of this form are found in areas where edwardsU is abun¨dant and no females of melanopygus have been taken. These two taxa may be conspecific color forms. The area of overlap, northern California and west central Oregon, between edwardsU and melano¨pygus needs to be looked at more critically for signs of intergradation.
The nest biology of B. melanopygus is described by Johansen (1967) and Hobbs (1967b). Johansen (1967) found 11 of 14 colonies in surface nest boxes, which coincides with our observations on the above-ground nesting tendencies in B. edward¨sU. However, Hobbs (1967b) found four nests underground or at least with the entrance tunnel leading underground. The larvae of a sarcophagid fly, Brachkoma, fed on larvae and pupae of this bumble bee, and were considered the most destruc¨tive parasites found by Johansen (1967).
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