A female Homona magnanima moth. Image credit: Hiroshi Arai (CC BY 4.0)
Bacteria, viruses and other microbes are often thought of as external threats – but some also live inside animals, where they can be passed from mother to offspring. These types of microbes are commonly carried by insects and have various strategies for manipulating reproduction so they can spread through a population more easily.
One striking example is male killing, in which microbes selectively kill the male offspring of infected mothers during development. This results in a predominately female population, which can continue transmitting the microbe to future generations. Here, Arai et al. investigate whether Wolbachia – a group of bacteria that infect more than half of all insect species – employ a universal male-killing strategy, or whether they have evolved different mechanisms tailored to specific hosts.
The team focused on a region of the Wolbachia genome that encodes multiple candidate genes involved in male killing. First, Arai et al. explored whether a Wolbachia gene called Hm-oscar is responsible for male killing in the moth Homona magnanima. They found that over activating Hm-oscar in embryos not infected with Wolbachia increased male mortality, reproducing the effects of male killing, leading to a female-biased sex ratio. Further experiments confirmed that Hm-oscar exerts this effect by inhibiting masculinizer, a key gene necessary for male development.
Next, Arai et al. tested another gene called wmk, which Wolbachia use to kill the male offspring of fruit flies. However, manipulating this gene in H. magnanima had no impact on male survival, suggesting that Wolbachia use different male-killing genes in different insect species.
Understanding how Wolbachia affect insect reproduction sheds light on how bacteria interact with different host species. This knowledge also has practical applications. For instance, male-killing strategies could be leveraged for pest control to reduce populations of harmful insects without using pesticides. Future research may uncover additional Wolbachia genes involved in reproductive manipulation and explore their potential use in managing insect populations.
