# Patterns of Detoxification Enzyme Activities During the Selection of Phortica okadai Resistant to β-Cypermethrin Under Laboratory Conditions

## TL;DR

Researchers found that a species of fly, Phortica okadai, can develop resistance to the pesticide β-cypermethrin in the lab, with enzyme activity changes linked to this resistance.

## Contribution

The study identifies specific detoxification enzyme activity patterns associated with β-cypermethrin resistance in Phortica okadai under laboratory conditions.

## Key findings

- A P. okadai strain with 10.04-fold resistance to β-cypermethrin was developed after eight generations of selection.
- Resistance was associated with increased activity of GSTs, CarEs, and CYP450 enzymes in specific tissues.
- The intrinsic rate of increase decreased in the resistant strain, possibly due to mutations in detoxification genes.

## Abstract

In China, Phortica okadai is the only established vector of Thelazia callipaeda. β-cypermethrin is a pesticide commonly used for the control of agricultural pests that may pose a risk to P. okadai due to the potential development of pesticide resistance. A strain of P. okadai moderately resistant to β-cypermethrin (RS) was obtained after laboratory selection with a 10.04-fold increase in resistance (vs. the susceptible strain, SS). We compared the development duration and life table of the RS and SS, and the activities of carboxylesterases (CarEs), cytochrome P450 (CYP450), and glutathione S-transferases (GSTs) in different development stages and tissues of P. okadai in the RS and SS were measured. The results presented in this study provide critical baseline data for monitoring resistance evolution and optimizing vector control strategies against P. okadai.

After eight generations of laboratory selection with β-cypermethrin, a P. okadai strain was cultivated that displayed a 10.04-fold increase in resistance (RS) relative to the susceptible strain (SS), with an estimation of heritability (h2) of 0.34. Compared with the SS, the developmental duration of the eggs was significantly prolonged (p < 0.05); however, the pupal stage duration was shorter, with no statistically significant difference. Moreover, the levels of GSTs, CarEs, and CYP450 activity were notably higher in the RS than in the SS. In addition, the level of CarE and CYP450 activity in the RS was significantly higher in the midgut (MG), fat body (FB), and Malpighian tubules (MTs) compared to the SS; however, the GSTs showed no statistically significant difference in the MTs. These results suggest that P. okadai‘s resistance to β-cypermethrin could be selected rapidly and the decreases in the intrinsic rate of increase (r) observed in the RS are likely due to mutations in the detoxification enzyme genes under the strong selection pressure exerted by β-cypermethrin. The increased activity of GSTs, CarEs, and CYP450 was associated with β-cypermethrin resistance in the RS of P. okadai. The data reported herein provide a foundation for future studies on the mechanisms responsible for β-cypermethrin resistance in P. okadai.