Submitted to: American Bee Research Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 1/9/2006
Publication Date: 5/1/2006
Citation: Harris, J.W., Harbo, J.R. 2006. Vsh bees disproportionately remove varroa-infested hosts from the youngest age cohorts of pupae. American Bee Journal 146(5):448
Technical Abstract: Honey bees bred for high percentages of nonreproducing varroa mites hygienically remove mites with offspring from capped brood cells. This behavior is a form of varroa-sensitive hygiene (VSH). The objective of this experiment was to determine if VSH bees respond equally to varroa-infested pupae of different ages. Varroa-infested worker brood was placed into the center of the broodnest for each of 12 colonies (7 VSH bees and 5 controls) for 40 hours. An infestation rate was determined before and after the test period by sampling 235-300 capped brood cells. The ratio of number of infested pupae to number of uninfested pupae was compared between the initial and final infestation rates to calculate the removal rate for varroa-infested pupae from each comb. Removal rates were also estimated for each of 3 mutually exclusive age cohorts of pupae. Cohorts were defined by body color and eye pigmentation that are associated with different periods during the metamorphosis of worker bees. Cohort I included prepupae and white-eyed pupae in the range of 1- 4 days postcapping; cohort II included pink-eyed pupae and purple-eyed pupae without tanned joints on appendages (5 - 7 days postcapping); and cohort III included purple-eyed pupae with tanned joints on appendages and tan pupae with white wing pads (8 – 9 days postcapping). The final infestation rate for each cohort was determined by sampling pupae with morphological characteristics expected after 40 hours of development from the starting age. All removal rates were compared between stocks of bees using an analysis of variance with type of bee as a fixed effect and source of infested combs, source of bees, and the interaction of these two factors as random effects. Combs placed in control colonies had a 11 ± 24% (mean ± SD) reduction in number of varroa-infested pupae for all ages, while those placed in colonies of VSH bees had a 53 ± 21% reduction (P=0.0072). VSH bees removed significantly more varroa-infested pupae from cohorts I (P=0.041) and II (P=0.028) than controls (Table). The two types of bees did not differ in removal rates for cohort III (P=0.785). These results suggest that the stimuli which elicit hygienic removal of infested pupae from brood cells may be related to egg-laying by the mites or the appearance of mite offspring in brood cells, which coincide with the ages of pupae in cohorts I and II.