What specialized structure do female Yellowish Cuckoo Bumblebees lack compared to standard bumblebees?

Corbiculae

The defining structural difference between the Yellowish Cuckoo Bumblebee females and standard, non-parasitic bumblebees lies in the complete absence of corbiculae. Corbiculae are specialized structures found on the hind tibia of worker and queen bumblebees that actively provision their young. These structures function as pollen baskets, smooth and concave areas fringed with stiff hairs designed specifically for collecting and transporting large loads of nectar and pollen back to the nest. Because cuckoo bumblebees are social parasites, the parasitic female does not engage in foraging or rearing young; this labor is entirely delegated to the host colony whose nest she invades. Consequently, the anatomical apparatus required for that provisioning task—the corbiculae—is never developed in the parasitic female.