Male calling song as a target for female mate choice and pest management in Queensland fruit flies

A project undertaken at the Department of Psychology, Macquarie University, and supervised by P Taylor

Across the animal kingdom, courtship rituals take on an astonishing range of forms as males ‘woo’ females with elaborate displays. Familiar examples include peacock tails, frog choruses … and even ourselves. Similar rituals are also common in smaller, simpler, animals, such as spiders and insects. Courtship behaviour, and especially the role of male displays in female mating decisions, has been one of the most prolific areas of study with the field of Behavioural Ecology. We are specifically interested in how female Queensland fruit flies (Q-flies) use male courtship displays when choosing a mate. In the late afternoon, groups of male Q-flies assemble on a plant, with each male occupying a leaf as a mating territory. The males release a pungent pheromone that attracts sexually receptive females to the group. These females may visit several males and eventually mate with one, or depart in search of better males elsewhere. Acoustic signals are prominent in the courtship of male Q-flies. Can these ‘songs’ provide females with reliable information to identify preferred mates?

As one of Australia’s most damaging horticultural pests, there are some additional benefits to understanding the importance of male courtship in the mating decisions of female Q-flies. As an environmentally benign management technique, the ‘sterile insect technique’ (SIT) has been employed to control Q-flies in the ‘Fruit fly exclusion zone’ (FFEZ) that covers parts of NSW, VIC and SA. Millions of male flies are reared in a special factory in Camden, run by NSW Agriculture. These flies are reproductively sterilized and released into the FFEZ. Released males that mate with wild females effectively prevent those females from producing offspring, as the sterile male sperm causes the embryos to fail. For SIT to work, wild females must accept the released sterile males as mates. We are interested in determining whether there are courtship differences between wild males and the released sterile males that might permit wild females to avoid mating with sterile males. Such ability in female Q-flies could effectively nullify SIT as a control method. By identifying some of the actual cues used by females when choosing mates, our results will help to ensure that rearing of released Q-fly males is directed toward those males with the greatest chances of being accepted as a mate by wild females.

The research involves two distinct phases. First, we are recording and analysing male songs to check for differences between wild and factory-reared types, and within each of these populations to check whether songs vary with characteristic male traits, such as body size. We will then play the songs back to females through loudspeakers to check whether females prefer the songs of certain males to others.

This work is being carried out at the Animal behaviour Research Group of Macquarie University. To ensure success of this program, Macquarie University has awarded supplementary funds to bring a leading expert in fruit fly acoustics, Dr Richard Mankin of US Department of Agriculture (Gainesville, Florida), to Sydney for a month to help with the refinement of techniques to be used in recording, analysing and playback of fly songs. Macquarie University has also awarded an addiional supplement to extend this research into a more thorough assessment of facotors influencing the sexual competition between wild and factory-reared male Q-flies.