Polymorphic adaptive insecticidal resistance in Rhynocoris marginatus (Fabr.) (Het., Reduviidae) a non-target biocontrol agent

Rhynocoris marginatus (Fabr.) is a polymorphic reduviid predator inhabitating tropical rainforests, semi-arid zones, scrub jungles and agro-ecosystems and predates upon insect pests. It exists in three different morphs; (1) with black connexivum (niger); (2) with red connexivum (sanguineous); and (3) with black and red banded connexivum (nigrosanguineous). Insecticides used to manage insect pests affect non-target biocontrol agents such as R. marginatus . Hence laboratory experiments were conducted to evaluate the adaptive polymorphic resistance of the morphs of R. marginatus to the toxic effects of three insecticides, namely, dimethoate, methylparathion and quinalphos, with each in five concentrations. The 50% lethal concentration (LC₅₀) values clearly indicated that methylparathion was the most toxic insecticide followed by quinalphos and endosulfan to all three morphs. Among the three morphs, the niger was the most resistant and the sanguineous was the most sensitive.