Assessing the Single and Combined Toxicity of Chlorantraniliprole and Bacillus thuringiensis (GO33A) against Four Selected Strains of Plutella xylostella (Lepidoptera: Plutellidae), and a Gene Expression Analysis

Muhammad Zeeshan Shabbir,Ling He,Fei Yin,Jie Zhang,Zhen-Yu Li,Changlong Shu

doi:10.3390/toxins13030227

Abstract

Concerns about resistance development to conventional insecticides in diamondback moth (DBM) Plutella xylostella (L.), the most destructive pest of Brassica vegetables, have stimulated interest in alternative pest management strategies. The toxicity of Bacillus thuringiensis subsp. aizawai (Bt GO33A) combined with chlorantraniliprole (Chl) has not been documented. Here, we examined single and combined toxicity of chlorantraniliprole and Bt to assess the levels of resistance in four DBM strains. Additionally, enzyme activities were tested in field-original highly resistant (FOH-DBM), Bt-resistant (Bt-DBM), chlorantraniliprole-resistant (CL-DBM), and Bt + chlorantraniliprole-resistant (BtC-DBM) strains. The Bt product had the highest toxicity to all four DBM strains followed by the mixture of insecticides (Bt + Chl) and chlorantraniliprole. Synergism between Bt and chlorantraniliprole was observed; the combination of Bt + (Bt + Chl) (1:1, LC50:LC50) was the most toxic, showing a synergistic effect against all four DBM strains with a poison ratio of 1.35, 1.29, 1.27, and 1.25. Glutathione S-transferase (GST) and carboxyl-esterase (CarE) activities showed positive correlations with chlorantraniliprole resistance, but no correlation was observed with resistance to Bt and Bt + Chl insecticides. Expression of genes coding for PxGST, CarE, AChE, and MFO using qRT-PCR showed that the PxGST and MFO were significantly overexpressed in Bt-DBM. However, AChE and CarE showed no difference in the four DBM strains. Mixtures of Bt with chlorantraniliprole exhibited synergistic effects and may aid the design of new combinations of pesticides to delay resistance in DBM strains substantially.

Highlights

The diamondback moth (DBM), Plutella xylostella (L.) (Lepidoptera: Plutellidae), is a major pest of Brassica vegetables, reported in more than 80 countries, and causes severe damage to vegetable crops in China and wherever it occurs [1,2,3,4,5,6]
The Bacillus thuringiensis (Bt)-DBM and Bt + chlorantraniliprole (BtC)-DBM strains showed a moderate level of resistance to chlorantraniliprole, with a resistance ratio of 24.2- and 27.3-fold, respectively (Table 1)
The LC50 value of Bt-DBM was 16.29 mg L−1, showing an 18.7-fold resistance level compared to field-original highly resistant (FOH)

Summary

Introduction

The diamondback moth (DBM), Plutella xylostella (L.) (Lepidoptera: Plutellidae), is a major pest of Brassica vegetables, reported in more than 80 countries, and causes severe damage to vegetable crops in China and wherever it occurs [1,2,3,4,5,6]. The evolution of resistance to a wide range of insecticides, and subsequent spray failures, have been reported for P. xylostella, including Bt products [1,4,8,9]. Mechanism of resistance can involve higher levels of detoxifying enzymes or metabolic resistance, reduced penetration and changes in the target sites due to mutations [10,11,12]. The common mechanisms of metabolic resistance to insecticides include enhanced carboxyl-esterase (CarE), glutathione S-transferases (GST), and cytochrome P450 monooxygenase (MFO) activity [13,14,15]. The correlations between detoxifying enzymes and insecticide resistance have been reported extensively [4], including the overexpression of enzymatic detoxification involved in resistance in P. xylostella [9]

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Conclusion