Single dose of insecticide can kill 3 cockroach generations

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Washington, June 24 : Scanning and killing hidden cockroaches will not be a tricky task any more, thanks to Purdue University entomologists, who have developed a pest-killing gel bait, a single dose of which can kill three generations of cockroaches as they feed off of each other and transfer the poison.

Grzegorz "Grzesiek" Buczkowski, assistant professor of entomology said that this is the first time that scientists have shown that a pest control bait will remain effective when it's transferred twice after the first killing dose. Such passing of insecticide from one cockroach to the next is called horizontal transfer.

"Our findings are exciting because cockroaches are difficult to control since they multiply so rapidly. They are especially bad in urban housing, and they can cause health problems," said Buczkowski.

He said that it's difficult to find and rid areas of the insects because cockroaches come out at night and live in inaccessible places. They invade places where they easily can find plenty of food and water. Besides, cockroaches are attracted to where other cockroaches are by a chemical compound, called pheromones, that animals secrete and which influences other cockroaches' behaviour.

In the new study, the scientists used German cockroaches, the most common household species in the United States, to test a DuPont product with the active ingredient indoxacarb. While the researchers only studied indoxacarb, Buczkowski speculated that other insecticides may also have three-generation horizontal transfer kill capabilities.

When the insecticide was first transferred from a dying adult to the youngest stage nymphs, it was found that an average of 76 percent of these cockroaches also succumbed to the indoxacarb-containing excretions from the dying cockroaches.

In the third stage of transfer, or tertiary kill, an average of 81 percent of the adult male cockroaches that ate the dead nymphs' bodies also died. Both statistics were taken 72 hours after the insects were exposed to a cockroach already affected by indoxacarb.

Buczkowski said that the mortality of cockroaches at the fourth level, three times removed from the original insecticide dose, was not much higher than for those insects that hadn't been exposed to the insecticide through any method.

Other than attracting more cockroaches with the pheromones in their feces, the insects may also cause other problems.

"Cockroaches molt their skin as they go from one nymph stage to the next, and there is a huge accumulation of the skin left in the areas where they live. The dead skin becomes airborne and causes allergies and asthma. It's really the biggest problem with cockroaches," said Buczkowski.

The study is published in the June issue of the Journal of Economic Entomology.

ANI

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