Altered heat nociception in cockroach Periplaneta americana L. exposed to capsaicin.

Some natural alkaloids, e.g. capsaicin and camphor, are known to induce a desensitization state, causing insensitivity to pain or noxious temperatures in mammals by acting on TRP receptors. Our research, for the first time, demonstrated that a phenomenon of pharmacological blockade of heat sensitivity may operate in American cockroach, Periplaneta americana (L.). We studied the escape reaction time from 50°C for American cockroaches exposed to multiple doses of different drugs affecting thermo-TRP. Capsaicin, capsazepine, and camphor induced significant changes in time spent at noxious ambient temperatures. Moreover, we showed that behavioral thermoregulation in normal temperature ranges (10-40°C) is altered in treated cockroaches, which displayed a preference for warmer regions compared to non-treated insects. We also measured the levels of malondialdehyde (MDA) and catalase activity to exclude the secondary effects of the drugs on these processes. Our results demonstrated that increase in time spent at 50°C (five versus one trial at a heat plate) induced oxidative stress, but only in control and vehicle-treated groups. In capsaicin, capsazepine, menthol, camphor and AITC-treated cockroaches the number of exposures to heat had no effect on the levels of MDA. Additionally, none of the tested compounds affected catalase activity. Our results demonstrate suppression of the heat sensitivity by repeated capsazepine, camphor and capsaicin administration in the American cockroach.

Pyrethroid residue dynamics in insects depends on the circadian clock.

Many factors may affect pesticide effectiveness against pests. One of the factors that should be considered is circadian rhythmicity. In this study, we evaluated daily variations in pyrethroid susceptibility in the house cricket, Acheta domesticus L. Crickets were exposed to a standard dose of ß-cyfluthrin at different times of a day, and pesticide residue levels were evaluated using gas chromatography. Results demonstrate that the time of pyrethroid disappearance is correlated with the circadian clock, with the highest decomposition rate at night. Furthermore, crickets also showed the highest resistance to the insecticide at night, expressed as a high survival rate. Moreover, ß-cyfluthrin induced significant changes in thermal preferences of intoxicated crickets. This is the first report showing that pyrethroid residue levels in the crickets' body depend on its circadian clock.