8.2. Maintaining drones under in vitro laboratory conditions
Similar to queens, drones should be maintained in the laboratory with workers collected off brood frames. Preferably, these workers should come from the same colony as the drones to facilitate the latter’s acceptance. Additionally, attention must be paid to the type of nutrients provided to caged drones and workers because of the potential importance of protein to development of tissues, including gonads (Jaycox, 1961). Unlike queens, multiple drones can be kept in the same cage, and at a 2:1 drone:worker ratio (Jaycox, 1961; Huang et al. 2012). This will ensure that drones survive at least until they reach maturity, approximately 8-9 days post-emergence (Jaycox, 1961). If caged individuals die during the experiment, one should consider maintaining this drone:worker ratio by adding or removing workers.
Because of the affinity of the parasitic mite Varroa destructor to drones, researchers must also consider the influence of parasitism during development when designing experiments. Drones should be maintained in conditions previously recommended for adult workers because they exhibit a similar thermo-preference (Kovac et al., 2009). However, future studies should evaluate alternative temperature and feeding regimes when evaluating drone reproductive traits because of the sensitivity of sperm production. For example, Jaycox (1961) recommended that drones be kept between 31 and 34° C, and suggested that drones can be caged without workers when appropriate feeding devices provide honey rather than sucrose because of drones’ difficulty to invert sugars. General methods for maintaining drones more appropriately in the laboratory urgently needs development because of their greater sensitivity to in vitro conditions (Tanner et al., 2012b).