Role of host switching in the development of pesticide tolerance in Helopeltis theivora (Hemiptera: Miridae), the major pest of tea in India

The polyphagous pest Helopeltis theivora Waterhouse (Heteroptera: Miridae) is one of the major pests of tea [Camellia sinensis, (Theaceae)]. Duranta repens (Verbenaceae), an ornamental plant producing various allelochemicals, is used in many tea estates as hedge plant. This plant was earlier reported to be an alternative host of H. theivora. To gain an insight into the pest and host–plant relationships, the present work reports studies on host-based life-cycle traits, pesticide tolerance status and levels of detoxification enzymes, such as general esterases (GEs), glutathione S-transferases (GSTs) and cytochrome P450 (CYP450). Host switching in the development of pesticide tolerance in H. theivora was evident. While comparing the biology of this pest on the primary host (tea) and the alternative host (D. repens) it was found that total developmental period was higher in the Duranta-reared population, along with significantly higher nymphal mortality and significantly less fecundity. However, there was no significant difference in incubation period, hatchability, sex ratio, pre-oviposition period and adult longevity. Susceptibility of the Duranta-reared population against quinalphos (a commonly used insecticide) was 1.41 times less than the tea-reared H. theivora population. The host-based variation in the relative susceptibility against insecticide was corroborated by differential activity of the three major xenobiotic detoxifying enzymes mentioned above. GE, GST and CYP450 activities were 2.67-fold, 1.43-fold and 1.37-fold higher in the Duranta-reared population than in the tea-reared population, possibly signifying that host switching can play a role in the development of tolerance of H. theivora against insecticides.