Resistance to monocrotophos in the coconut black-headed caterpillar: Outlining development of resistance in asynchronous populations

Monocrotophos has been the most frequently used insecticide in the management of coconut black-headed caterpillar, Opisina arenosella. Seven spatially segregated populations from Southern Karnataka, India with different records of insecticide applications were selected for the study. The population from Nittur was being continuously exposed to monocrotophos, while infested orchards from Arasikere, Kadur, Channapatna. Mandya and K R Pet taluks had only a past history of exposure to monocrotophos. The population from Mangalore was never exposed to the chemical. We discovered that Nittur population had 134 folds greater LC₅₀ value than the most susceptible one (Mangalore population). The results showed that Opisina can potentially develop populations resistant to monocrotophos. Considering that Opisina has discrete spatially segregated populations that are also asynchronous (which is uncommon among tropical insects), we make an attempt to provide a general framework to trace the developmenl of resistance in such populations.