Stimulatory and suppressive effects of novaluron on the Colorado potato beetle reproduction

The Colorado potato beetle, Leptinotarsa decemlineata (Say), is one of the most damaging insect pests of potato, Solanum tuberosum L. Novaluron is a relatively new benzoylphenyl urea insect growth regulator with good activity against this pest. Earlier studies revealed that feeding on potato foliage treated with novaluron induces reversible egg hatch inhibition in adult Colorado potato beetles. We investigated whether novaluron effects depend on physiological state of the beetles at the time of exposure. The following four treatments were created: young beetles unmated at the beginning of the experiment and feeding on potato foliage treated with novaluron, young beetles unmated at the beginning of the experiment and feeding on untreated foliage, older beetles mated at the beginning of the experiment and feeding on foliage treated with novaluron, and older beetles mated at the beginning of the experiment and feeding on untreated foliage. The beetles were exposed to the respective treatments for 5 d. After that, both young and older beetles feeding on novaluron-treated leaves were switched onto untreated leaves and monitored for another 5 d to test their ability to recover. Young beetles unmated at the beginning of the experiment produced more eggs after feeding on the treated foliage, possibly indicating the presence of a pesticide-induced homeostatic modulation. No such effect was observed in the older beetles. Regardless of beetle physiological state at the beginning of the experiment, eggs produced on treated foliage did not hatch. The beetles eventually resumed laying viable eggs after being switched onto untreated foliage, with the recovery being delayed by approximately 24 h in young beetles compared with older beetles. Our results corroborate that novaluron reduces fertility of treated adults.