Pollinator of the Month: Indiscriminate Cuckoo Bumble Bee (Bombus insularis)
There are four species of Psithyrus (cuckoo bumble bees) found in Calgary; they are the Ashton's cuckoo bumble bee, indiscriminate cuckoo bumble bee, Fernald's cuckoo bumble bee, and Suckley's cuckoo bumble bee. All four species are native to Calgary.
Cuckoo bumble bees are considered obligate brood parasites or social parasites. Female cuckoo bumble bees emerge fertilized in the spring. They then enter another bumble bee nest and kill or immobilize the host species queen and lay their own eggs. Once the eggs of the cuckoo bumble bee hatch, the larvae are taken care of by the host species workers. The adults of the species are reproductive males and females, no workers exist. This differs from the typical life cycle of other bumble bees.
As a result of being social parasites cuckoo bumble bees lack a worker caste and no longer develop pollen baskets (corbicula), making them completely dependent on their host species for survival. Despite not having pollen baskets they are still considered pollinators, however they are only visiting flowers for their own nourishment thus the pollination behaviour of cuckoo bumble bees differs from other bumble bees which may negatively impact plant reproductive success.
Cuckoo bumble bee populations may be threatened by decline in their host species populations, however while cuckoo bumble bees have negative impacts on the survival of the host species they likely do not contribute to population decline of their host species. . For the indiscriminate cuckoo bumble bee (Bombus insularis) their host species include yellow-fronted bumble bee, Nevada bumblebee, tricolored bumblebee, and golden northern bumble bee.
To identify the indiscriminate cuckoo bumble bee (Bombus insularis) look for a yellow top of the head and yellow area in front of the wings (scutum). The area behind the wings (scutellum) can be yellow or black. The area between the wings (alar) is black. The abdomen is divided into six sections (tergites). The first and second sections are fully black; the third section is usually black with yellow being sometimes near the bottom and sides of this section; the fourth and fifth sections are black in the middle with yellow on the sides. The tergites never have any white hairs on them.
Indiscriminate cuckoo bumble bees have been found pollinating fireweed, asters, goldenrods, common basket flowers, and narrow leaf hawkweed.
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