Flies have more complex social lives than have really been appreciated by a lot of the field of fly behavioral neurogenetics. I wrote a little bit about this in another post: ‘How do Drosophila behave in the wild’, but it turns out in nature, Drosophila share their food substrates with lots of flies and other arthropods, and spend lots of time investigating and interacting with other flies (Markow, 2015).
Historically the only type of fly social behavior that was measured in the lab was courtship and aggression. More recently, Joel Levine studied social networks in flies (Jezovit et al, 2021) and high-content tracking methods (like Ctrax, Branson et al 2009) and behavioral classification of this tracking (using methods like JAABA, Kabra et al, 2013) has provided the opportunity to look at proximity, touching, and chasing pretty easily. As a result we are starting to gain a more holistic understanding of how social behavior looks like in the fly.
Given all of this, it shouldn’t be that surprising that isolation affects Drosophila behavior. Indeed, in order for wild-type male flies to show aggressive behaviors, they need to be isolated for a couple of days in advance. Early life isolation impacts social behavior (Bentzur et al, 2021) and isolation as an adult affects social behavior (Chen & Sokolwoski, 2022). Isolation has drastic effects on social dynamics in flies and the methods used to isolate the flies can affect these dynamics (Jezovit et al, 2021). However, these types of details are sometimes left out of methods in papers, so my guess is that lots of other behaviors are also impacted by isolation, but the effects haven’t necessarily been measured in a rigorous way.
So, is it OK to isolate your flies? I would argue that sometimes it is necessary, like with aggression where the flies aren’t really aggressive if you don’t isolate them. Sometimes you are studying individual differences between flies and you need to keep them isolated as adults so that you can keep track of them. I think the most important thing is to realize that this is one factor that could contribute to the behavior your are studying, and because of that you should keep detailed methods on your isolation procedures and include this when you publish your work so that later, when we know a lot more about the social behavior of flies, we can add this context to interpreting your results.