7. Functional genomics and xenobiotic treatment

7.5. Applications and limitations

In honey bees, the genome is complex and many genes are not fully understood; indeed, over one third still are not functionally annotated (Walsh et al., 2022). Therefore, it can be difficult to know what particular genes control a trait or function, and RNAi is most commonly applied as a discovery tool in order to elucidate the roles genes play. There is also variability in responses of the knockdown effects. Factors such as genetic variation, environmental factors, and widespread off-target effects (Schulte et al., 2014), which are difficult to predict or control, sometimes making it challenging to replicate results.

Because of the haplodiploid system of sex-determination and complex mating strategy of honey bees, there is limited applicability to manipulate gene expression long-term (that is, to develop mutated lineages using CRISPR or transgenic techniques). Though there has been some success rearing transgenic queens (Schulte et al., 2014), those queens would need to mate with transgenic drones in order to establish a fully modified colony. Such an endeavor is exceedingly difficult and has not yet been achieved, but unmated queens can be stimulated to lay haploid eggs in microcolonies to yield genetically modified drones (Schulte et al., 2014). Moreover, ethical considerations of bee containment and risk of escape further inhibit widespread use of this technique.

The high efficiency of genetic modification by CRISPR, however, is making it increasingly feasible to avoid the need of creating a genetic lineage to produce large numbers of modified bees for experiments. Instead, embryos can be injected and reared in vitro in sufficient numbers to facilitate developmental studies (Roth et al., 2019). This method also poses virtually no risk of viable bees escaping into the environment. For these reasons, this seems to be the direction in which the field is headed, but studies on social phenotypes, such as the dance language or hygienic behavior, are not possible.