Are humans preventing flies from eavesdropping?
Today's world is full of background noise, whether it comes from a roaring river or a busy highway. High noise levels, whether human or natural, can affect animals' ability to listen and affect their interaction with other animals. A group of researchers from California Polytechnic State University studied how background noise affects the listening abilities of a parasitoid fly.
Ormia flies listen to cricket calls to find their hosts for their little ones. When found, flies lay their eggs on or near the cricket. The larvae hatch and bury themselves inside the cricket and eventually pierce and kill the host. As a result, the researchers hypothesized that noise could interfere with flies' eavesdropping, making it difficult for them to find their hosts.
The research was published in Royal Society Open Science, and used sticky fly traps near the speakers broadcasting cricket calls through a noise gradient. The results show that fewer parasitoid flies were caught near the speakers in noisier areas. Because parasitoids eventually kill their hosts, the results suggest that crickets could benefit from a call in noisy areas.
The study also found that traffic noise and natural ocean noise inhibit the orientation of flies relative to sound, suggesting that crickets could use sound as a parasitic shield in different sound landscapes. These results suggest that sound landscapes can influence the evolution of closely co-evolving host-parasitoid relationships.
There are still some questions for the authors: if parasitoid flies are less abundant in noise, would female flies have the same problem locating male cricket calls? Author Jennifer N. Phillips said, "Future work could examine whether female crickets have difficulty hearing and calling males in noise, which would represent a fitness cost for males trying to find a mate. This could compensate for the reduced risk of parasitism by flies. However, if crickets are able to adjust their call or their ability to find each other and the parasitoid fly does not, there may still be some advantage to the noise for crickets."
