How insects decide what to eat and what to avoid

Washington, Apr 24 (ANI): A protein in sensory cells on the "tongues" of fruit flies enables them to detect a noxious chemical and, thereby influencing their decision about what to eat and what to avoid, reveals a Johns Hopkins team.

The study raises the possibility that the protein - TRPA1 - is a new molecular target for controlling insect pests.

"We're interested in how TRPA1 and a whole family of so-called TRP channels affect not just the senses, like taste, but also behaviour," says Dr. Craig Montell.

He claimed that when his team knocked out the TRPA1 sensor, the behaviour change - an alteration in food preference - was stark.

"This is the first TRP channel in insects that responds to a naturally occurring plant chemical known as an antifeedant, so now we have a target for finding more effective chemicals to protect plants from destruction by insect pests," he added.

"We already knew that TRP channels have these broad sensory roles, having previously discovered that the insect TRPA1 had a role in helping flies to detect small differences in sub-optimal temperatures within their comfort range. We wondered if it had any other sensory roles, so we went looking," said Montell.

First, the team genetically altered a normal TRPA1 gene. This experiment let them show that the protein was made in the fly's major taste organ (called the labellum) and trace its manufacture to a subset of sensory cells that respond to noxious chemicals.

The researchers then conducted a series of behavioural tests comparing the feeding of wild type flies to those of mutants in which the TRPA1 gene was knocked out - unable to manufacture the protein.

The team placed 50 to 100 flies that had been purposely starved for a day in a covered plate with 72 wells full of two concentrations of sugar water. The wells containing the high concentration of sugar water were laced with different bitter compounds, including quinine, caffeine, strychnine and aristolochic acid.

Surprisingly, most of the mutants avoided all but one of the bitter compounds - aristolochic acid, a naturally occurring chemical produced by plants to prevent themselves from being eaten by insects.

"To our surprise, it was looking at first like TRPA1 didn't have a role in responding to anything. The aristolochic acid was literally the last compound we tried. I certainly wasn't expecting that the TRPA1 would be so specific in its response," said Montell.

The team followed up with electrophysiology tests on both wild type flies and those lacking the TRPA1 gene.

They found that TRPA1 was required for aristolochic acid-induced activity by neurons, meaning it's essential for aristolochic acid avoidance.

"It's important to make this discovery in insects, not only because it's interesting to trace the similarities and differences through millions of years of evolution, but also because of the possible practical applications. By targeting this TRP channel, we might be able to prevent insects from causing crop damage," said Montell.

The study appeared in the online Early Edition of the Proceedings of the National Academy of Sciences (PNAS). (ANI)