Title: A laboratory technique to study the effects of Varroa destructor and viruses on developing worker honey bees Authors
Submitted to: Journal of Apicultural Research
Publication Type: Research Notes
Publication Acceptance Date: September 6, 2013
Publication Date: December 15, 2013
Citation: De Guzman, L.I., Khongphinitbunjong, K., Rinderer, T.E., Tarver, M.R., Frake, A.M. 2013. A laboratory technique to study the effects of Varroa destructor and viruses on developing worker honey bees. Journal of Apicultural Research. 52(5):262-264. Interpretive Summary: The effects of Varroa and deformed wing virus (DWV) on naturally developing L4 and newly sealed (NSL) larvae were assessed in the laboratory. Trial 1 used L4 and NSL inoculated with one Varroa with un-manipulated NSL served as controls. In Trial 2, only L4 larvae were used as hosts for the following treatments: a) one Varroa, b) two Varroa, c) no Varroa and fed 2 µl Deformed wing virus (DWV), d) one Varroa and fed 2 µl DWV, and control (no Varroa or DWV). All test brood (except Trial 1 control) was sealed with gel caps. Our results showed that about 80% of the Varroa reproduced. Regardless of Trial, Varroa reproduced normally with the lowest progeny per infested cell recorded in brood inoculated with one Varroa (3.1 ± 0.4 progeny) and those inoculated with 2 Varroa supported the highest progeny (5.8 ± 0.6 progeny). Likewise, test brood continued to develop to adulthood. Overall, newly emerged worker bees from the control groups were the heaviest (>100 mg) while those brood inoculated with 2 Varroa were the lightest (about 75 mg). Bee weights correlated negatively with the number of Varroa per infested host. Our data suggest that this gel cap technique did not cause adverse effect on Varroa reproduction and bee weights. It also avoids injuries to test bees because no larval manipulation is required. Brood removal by bees is also prevented.
Technical Abstract: Existing techniques for in vitro rearing honey bees and Varroa involve brood manipulation. In this laboratory study, we used larvae that were naturally developing in a comb as Varroa- and virus-inoculation hosts. In Trial 1, we used L4 larvae and newly sealed larvae (NSL) as hosts which were inoculated with one Varroa. Thereafter, each cell was sealed with a gel cap, which was cut from the bottom of a gelatin capsule. Un-manipulated NSL served as controls. Trial 2 used L4 (sealed with gel caps) as hosts with the following treatments: a) one Varroa, b) two Varroa, c) no Varroa and fed 2 µl Deformed wing virus (DWV), d) one Varroa and fed 2 µl DWV, and control (no Varroa or DWV). Fecundity of Varroa and weight at bee mergence were noted. Our results showed that about 80% of the Varroa reproduced. In Trial 1, Varroa inoculated in L4 (4.0 ± 0.3 progeny) and NSL (3.7 ± 0.4 progeny) groups had similar fecundity. However, workers from the control group (108.81 ± 0.91 mg) were heavier than from the NSL (96.2 ± 1.6 mg) group. Brood inoculated at the L4 stage (79.1 ± 2.1 mg) was lighter. In Trial 2, brood inoculated with two Varroa supported more progeny per infested cell (5.8 ± 0.6 progeny) than did brood with one Varroa (3.1 ± 0.4 progeny) or one Varroa and DWV (3.2 ± 0.4 progeny). Bee weights (mg) also differed significantly: control bees (101.2 ± 1.9) = bees having one Varroa (94.6 ± 3.5) = bees that had DWV (91.8 ± 2.6) > bees with DWV and one Varroa (80.9 ± 3.4) and bees with two Varroa (75.2 ± 2.5). Overall, bee weights correlated negatively with the number of Varroa per infested cell. The use of gel caps to seal brood naturally developing in their comb for laboratory studies has some advantages. This technique allows for the study of individual worker bee’s responses to inoculations with Varroa and viruses without the need to manipulate larvae, provision larval food or transfer brood to pupation plates. Loss of brood through hygienic behavior of bees is also avoided since test brood is kept in an incubator. This method also allows simplified tracking of individual bees.