Dirty Antennae Blind Insects To Their Environment

April Flowers for redOrbit.com – Your Universe Online

A new study, led by North Carolina State University, shows like self-absorbed teenagers, insects spend a lot of time grooming. This grooming, specifically antennal cleaning, is a common function of insects that removes both environmental pollutants and chemicals produced by the insects themselves.

Grooming helps insects maintain acute olfactory senses, the study shows, which are responsible for a host of functions such as food finding, sensing danger and locating a suitable mate. The study might also explain why some types of insecticides are more effective than others.

The team, including members from the Russian Academy of Sciences, found insects groom themselves incessantly. They wanted to explore the functions of this behavior, so they devised a simple set of experiments to understand what kind of materials insects were cleaning off their antennae. They also wanted to know where the material was coming from and the difference in functionality between groomed and ungroomed antennae.

The team studied the American cockroach, comparing groomed antennae to antennae that were experimentally prevented from being cleaned. Grooming cleans microscopic pores on the antennae that serve as conduits through which chemicals travel to reach olfactory sensory receptors. Cockroaches clean their antennae by using their forelegs to place the antenna in their mouths, and then methodically clean every segment from base to tip.

Both volatile and non-volatile chemical accumulations were found on the ungroomed antennae of cockroaches. More surprisingly, the team also found accumulations of a great deal of cuticular hydrocarbons — fatty, candlewax-like substances secreted by the roaches to protect them against water loss.

“It is intuitive that insects remove foreign substances from their antennae, but it´s not necessarily intuitive that they groom to remove their ℠own´ substances,” NC State entomologist Coby Schal says.

To test how well roaches picked up the scent of a known sex pheromone compound, along with other odorants, the team tested both groomed and ungroomed antennae, finding clean antennae respond to these signals much more readily.

To expand their research, the team also tested carpenter ants, houseflies and German cockroaches in the same manner. Flies and ants groom by rubbing their legs over their antennae to remove particulates, which the ants then ingest. The tests showed although they groom differently, the accumulations of cuticular hydrocarbons was greater on all these insects as well when antennae went ungroomed.

“The evidence is strong: Grooming is necessary to keep these foreign and native substances at a particular level,” Schal says. “Leaving antennae dirty essentially blinds insects to their environment.”

There could be pest control implications to these findings, as many insecticides are mists or dusts that could settle on the antennae. These substances should be ingested rather quickly due to constant grooming, making these forms of insecticides more effective than residual types which penetrate the thick outer cuticle.

The study can also be a caution to other research groups who use insects in their studies, Schal says. Gluing the insects mouth shut, as many studies do, to prevent feeding also prevents grooming. This may skew results because of sensory deprivation.

The results of this study were published online this week in the Proceedings of the National Academy of Sciences.

Image 2 (below): Electron microscopy images show ungroomed, groomed and cleansed roach antennae (A-C). Also shown are tiny, pheromone-sensitive sensilla on the antennae (D-F). Credit: Coby Schal/North Carolina State University



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