We experience every year, during the warm season, a lot of problems related to our attempts to kill coackroaches, insects that are also responsible of the transmission of many human infectious diseases.

Scientists tell us they can also give other problems to humans: cause of they molt their skin, going from one nymph stage to the next and when they perform this action they can produce a huge accumulation of the skin left in the areas where we live. The dead skin can cause allergies and asthma.

Purdue University entomologists, who conducted laboratory tests about the effectiveness of a specific gel bait produced by DuPont and containinig the active ingredient 'Indoxacarb', have discovered some interesting informations, useful in the direction of a more effective control of this harmful insect.

Coackroaches are very difficult to control because of they multiply rapidly; they also hide in not easily accessible places and come out during the night, moving quickly in the darkness, along the walls, expecially in wet places; in this way they are able to visit our Kitchen, but also our bedroom while we are sleeping. They are really interested in those places where they can easily find plenty of food and water.

Taking advantage of their good knowledge about the cockroaches etology Purdue scientists have discovered, testing this gel bait that, as Grzegorz "Grzesiek" Buczkowski, assistant professor of entomology refers, a pest control bait will remain effective when it's transferred twice after the first killing dose. Passing the insecticide from one cockroach to the next is called 'horizontal transfer'.

The 'horizontal transfer' take place, in the first stage transfer, when cockroaches feed the nynphes after having been in a contamined place where are, or previously were, dying cockroaches. They recognize these place because in these locations other cockroaches leave some chemical compounds, called pheromones, with their feces. These compounds have the capability to influence other cockroaches' behavior. In this way this insects can be contamined by means of dying adults indoxacarb-containing excretions and then can transfer the insecticide taken from the feces, to their nynphes, killing them.

In the following stage transfer, other cockroaches die when feed on died nynphes.

The secondary mortality in the untreated cockroaches was significantly affected by the freshness of excretions, the presence of a different food and the duration of contact between the donors and the recipients. Then ingested indoxacarb was most effectively translocated when the recipients interacted with freshly symptomatic donors in the absence of alternative food. Some cockroache behaviors are involved in the horizontal transfer of indoxacarb: necrophagy, emetophagy, and ingestion of other excretions that originate from the donors.

The real interest for the results of this study is for both the stages of transfer, because the reaserchers observed an higher mortality in those insects that had been exposed to the insecticide through any other method. Not the same happened in the fourth stage of transfer, for this reason the test stopped at the third stage.

Buczkowski plans to investigate now tertiary kill with other cockroach baits and possibly looks at horizontal transfer of insecticides in natural settings rather than just in the laboratory.

The other researchers involved in this study were Gary Bennett, Purdue entomology professor, and Clay Scherer, global product development manager for DuPont Professional Products.

The Purdue Industrial Affiliates Program and DuPont funded this project. The Purdue faculty members involved in the research have no financial interest in DuPont or its insecticide Advion® Cockroach Gel.

The researchers report has been published in the June issue of the Journal of Economic Entomology.

Those further links could be usefull to deepen the issues about insect pheromones: