Cockroaches Lose Their Sweet Tooth

23 May 2013
Posted by Chris Smith.

In just 30 years cockroaches have evolved the ability to detect and avoid the traps commonly used to deal with them! Since the 1980s, the mainstay of cockroach control has been lures loaded with an insecticide-laced glucose bait that's impregnated onto a sticky surface. The sweet-toothed bugs would crawl inside and binge on a toxic feast, becoming stuck fast in the process. But now many of the insects - dubbed "glucose averse" - actively avoid such traps thanks to, it turns out, a switch in their taste detection system that has turned glucose from a treat into a deterrent. Writing in Science, North Carolina State University scientist Coby Schal and his colleagues recorded electrical signals produced by the tastebuds of both the new glucose-averse as well as traditional non-glucose-averse roaches when the insects were exposed to different flavours. Cockroaches have at least four different types of tastebuds, known as gustatory receptor neurones (GRNs). In normal "old school" cockroaches, GRN1 recognised sweet flavours, firing of a barrage of electrical spikes when glucose or fructose sugars were presented. GRN2, on the other hand, responded to the bitter taste of caffeine, which cockroaches are known to avoid. But, in the new glucose-averse insects, glucose only poorly stimulated the sweet-detecting GRN1 but triggered a salvo of activity in the normally bitter-responding GRN2. Fructose, on the other hand, triggered only GRN1, as expected. This shows that the animals have modified their taste receptor system so that they now register glucose as a bitter taste that they want to avoid. To find out how widespread this finding is, the researchers collected 19 wild-caught specimens from the field and tested them. Seven of them showed this altered behaviour. The team argue that the change has occurred through the strong selective pressure applied by the widespread use of glucose-baited cockroach traps. Insects with this adaptation would avoid the traps and live to breed another day, progressivly enriching the trait in the population...

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