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

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.

Bacillus thuringiensis and Chlorantraniliprole Trigger the Expression of Detoxification-Related Genes in the Larval Midgut of Plutella xylostella

“…The LC 50 values for Bt-G033A, CL, and mixture insecticide (Bt + CL) were significantly higher in FOH-DBM and resistant strains (Bt-DBM, CL-DBM, and BtC-DBM) compared to SS-DBM strain. The resistance level of these DBM strains is different due to different generations of the strains from the results of our previous article ( Shabbir et al, 2021 ). The results revealed that Bt-G033A was the most toxic to all the DBM strains among the tested insecticides.…”

“…A high-resistant strain of DBM was collected from the Shijing county of Guangdong province in 2017 and named as FOH-DBM. Detailed information with respect to insecticide resistance of FOH-DBM is given in Supplementary Figure 1 and also discussed in our previous manuscript ( Shabbir et al, 2021 ). Later, this population was established in the greenhouse and reared on cabbage without exposure to insecticide.…”

“…Later, this population was established in the greenhouse and reared on cabbage without exposure to insecticide. The CL-DBM, Bt-DBM, and BtC-DBM strains were derived from FOH-DBM strain by two rounds of selection with CL, Bt (Bt-G033A), and mixture of Bt + CL, respectively ( Shabbir et al, 2021 ). The rearing conditions in the greenhouse were maintained at 25 ± 2°C, 70–80% RH, and a photoperiod of 16:8 h (L:D).…”

“…Compartment 1 was used for maintaining DBM larvae with no treatment; compartment 2 was used to rear DBM on cabbage plants treated with Bt 4,000X, 1.5 g (Bt powder), and 6 L water; compartment 3 was used to rear DBM on cabbage plants sprayed with mixture treatment of Bt and CL 2,000–1,000X, 3 g (Bt powder), and 6 ml CL into 6 L water; and in compartment 4, DBM was reared on cabbage plants sprayed with CL 300X, 20 ml (5% CL) plus 6 L water. In March 2018, these four compartments were treated again as following: compartment 1, no treatment applied; compartment 2, sprayed cabbage plants with Bt 8,000X, 1.25 g (Bt powder), and 10 L water; compartment 3, sprayed plants with 16,000–3,200X, 0.625 g (Bt powder), 0.125 ml (5% CL), and 10 L water; and compartment 4, treated with CL 1,600X and 6.25 ml (5% CL) plus 10 L water ( Shabbir et al, 2021 ).…”

Revealing the difference of α-amylase and CYP6AE76 gene between polyphagous Conogethes punctiferalis and oligophagous C. pinicolalis by multiple-omics and molecular biological technique

“…The CYP6AE76 activity was assessed according to the method reported by Qian et al [ 74 ] and Shabbir et al [ 75 ] with slight modification. A 125 μL of 2 mM p-nitroanisole (p-NA) solution and 50 μL (0.5 mg/mL) cytochrome P450 monooxygenase expressed in E. coli were added to each well of a microplate and mixed.…”