Mating reshapes the waxy chemical coat on New World screwworm flies

Cuticular hydrocarbons are the waxes on an insect's outer surface. Their first job is to keep the animal from drying out, but the blend can also carry information about species, sex, age or reproductive condition ^[9].

The team's comparison turns on proportions. The same major compounds appeared in males and females, before and after mating. What differed was the amount of each in the mixture ^[12]. "We found that males and females carry many of the same hydrocarbons, but in distinctly different proportions," said Zain Syed, the University of Kentucky associate professor of entomology who led the study, published in the Journal of Medical Entomology ^[10][2]. "Mating further reshaped these chemical profiles, particularly in females," he said ^[11].

Measuring ratios across one fixed set of peaks is a sensible first design, because every group is scored against the same compounds ^[12]. How far the pattern generalises depends on the sample. The phys.org account of the paper does not report how many flies were measured, how old they were, or whether they were lab-reared or wild.

The thing this doesn't tell you is whether a male screwworm notices. A profile that changes after mating is a correlate of mating. It becomes a signal only when flies are shown to respond to it, and showing that takes bioassays with individual compounds ^[16]. The branched hydrocarbons that shifted most are the obvious first candidates ^[15].

A confirmed signal would matter most for the sterile insect technique. The U.S. eradicated screwworm in 1966 by rearing and sterilizing flies and releasing them. Wild females that mated with sterile males laid eggs that did not hatch ^[4]. The method depends on lab-raised males competing with wild males for those females ^[18]. Because females generally mate once ^[17], the first male to reach a wild female decides whether her eggs hatch ^[2].

Sixty years on ^[1], the pest is back in parts of Central America and Mexico ^[6], despite a barrier of sterile flies in Panama that had helped keep it out of cleared areas ^[5]. The CDC puts the current risk to people and animals in the U.S. at very low ^[8].

I think the paper is a careful description of the chemistry and a useful list of compounds to test. Until those tests run, the field advice stands: USDA tells animal owners to inspect wounds, watch for enlarging or foul-smelling sores and call a veterinarian if they suspect screwworm ^[20].