Submitted to: Pesticide Biochemistry and Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/9/2011
Publication Date: 1/13/2011
Citation: Zhu, Y., West, S.J., Snodgrass, G.L., Luttrell, R.G. 2011. Variability in resistance-related enzyme activities in field populations of the tarnished plant bug, Lygus lineolaris. Journal of Pesticide Biochemistry and Physiology. 99(3):265-273. Interpretive Summary: Insecticide resistance monitoring is essential for resistance management of an economically important crop pest. Our study of enzymatic levels in field populations of the tarnished plant bug was the first time detoxification enzyme assays for building foundation for future monitoring studies. The forty-three locations represented plant bug populations across the Mississippi Delta region of the Mid-south. In general, activities of esterase and glutathione S-transferase showed greater variation than AChE among the 43 populations. Variations across populations from east to west or from north to south were low. In comparison with other reports, variable esterase and glutathione S-transferase activities among the populations were associated with variable resistance levels in different locations. Intensity of insecticide sprays appeared to be a driving force for resistance evolution. Crop rotation or landscape habitat might be other factor responsible for variable spray intensities and resistance levels in the plant bug. This study also explored potential use of inhibitors to suppress detoxification enzymes. Our data showed that many enzyme inhibitors were effective in suppression of detoxifying enzymes and could potentially be used as synergists for increasing the effectiveness of organophosphate insecticides. The results from this study provide valuable information for resistance monitoring and management organophosphate insecticides in the tarnished plant bug.
Technical Abstract: Widespread implementation of Bt crops for control of lepidopterous pests has reduced insecticide use and provided the tarnished plant bug the opportunity to become a serious pest on mid-South cotton. Organophosphate insecticides have predominantly been used against plant bugs in recent years due to the reduced efficacy of other insecticides. In this study, a biochemical approach was developed to survey enzymatic levels associated with organophosphate resistance levels in field populations of the tarnished plant bug. Forty-three populations were collected from the delta areas of Arkansas, Louisiana, and Mississippi. Three esterase substrates and one substrate each of glutathione S-transferase (GST) and acetylcholinesterase (AChE) were used to determine corresponding detoxification enzyme activities in different populations. Compared to a laboratory susceptible colony, increases up to 5.29-fold for esterase, 1.96-fold for GST, and 1.97-fold for AChE activities were detected in the field populations. In addition to the survey of enzyme activities among the populations, we also examined the susceptibility of major detoxification enzymes to several inhibitors which could be used in formulations to synergize insecticide toxicity against the target pests. As much as 52-76% of esterase, 72-98% of GST, and 93% of AChE activities were inhibited in vitro. By use of the biochemical approach, we measured enzymatic levels potentially useful in studying organophosphate resistance. Revealing variable esterase and GST activities among field populations may lead to a better understanding resistance mechanisms in the tarnished plant bug. This study also reports effective suppression of detoxification enzymes which may be useful in future insecticide resistance management program for the tarnished plant bug and other Heteropteran pests on Bt crops.