Lethal and social-mediated effects of ten insecticides on the subterranean termite Reticulitermes speratus

Termites cause important economic losses worldwide and insecticides are largely used to control subterranean termites like Reticulitermes speratus Kolbe. However, few studies have documented the various effects that insecticides may have on termites, e.g., fumigation or colonial effects. Such knowledge would greatly help in optimizing termite management methods. Under laboratory conditions, we assessed toxicity of ten insecticides, i.e., chlorpyrifos, phoxim, carbofuran, propoxur, bifenthrin, cypermethrin, imidacloprid, fipronil, abamectin, and ivermectin, on R. speratus, and we documented possible insecticide transfer among termites, fumigation effect, and effect on termite colony. Abamectin, ivermectin, fipronil, and imidacloprid were effectively transferred among termite workers and induced high mortality in the receiving individuals, although the estimated LC50 values for these two insecticides were higher than those calculated for most of the others. Abamectin, ivermectin, phoxim, and chlorpyrifos showed strong fumigation effect, and ivermectin, fipronil (and to lesser extent abamectin) could lead to colony collapsing under laboratory conditions. Abamectin was the most efficient insecticide on R. speratus, being highly toxic through fumigation, highly transferable among individuals, and preventing colony to expand through abamectin-contaminated areas. Ivermectin showed similar properties but lacked the latter. Other insecticides showed various properties, either useful for preventing termite infestation or for colony suppression. The results may help in optimizing management of termites, although field experiments would need to document effects in practical situation.