Larvicidal activity and insecticidal mechanism of Chelidonium majus on Lymantria dispar.

Based on the broad spectrum of its biological activities, Chelidonium majus has been studied extensively in the medical field. However, few studies have focused on the insecticidal activity of C. majus, and the precise mechanism of its insecticidal activity. In the present study, larvicidal activity and insecticidal mechanism of C. majus on Lymantria dispar were investigated using bioassays, in vitro and in vivo enzyme activity assays, determination of the nutritional index, and gene transcription analysis. The results showed that alkaloids are the main insecticidal ingredients in C. majus. Among the five isoquinoline alkaloids, coptisine was present at the highest concentration (1624.23mg/L), while tetrahydrocoptisine showed the lowest concentration (0.47mg/L). Both the crude extract of C. majus (CECm) and the total alkaloids of C. majus (TACm) possessed a potent insecticidal activity toward L. dispar larvae. TACm had significant effects on the relative consumption rate, efficiency of conversion of digested food into growth, approximate digestibility, and approximate digestibility of L. dispar larvae. Enzyme activity assays suggested that both CECm and TACm displayed their strongest inhibitory activity to in vitro glutathione S-transferase (GST) and acetylcholinesterase (AChE), and showed the weakest inhibition of in vitro carboxylesterase (CarE). Moreover, CECm and TACm affected the in vivo activities of five enzymes. The in vivo activities of AChE and CarE in L. dispar larvae were inhibited significantly by CECm and TACm. Additionally, qRT-PCR analysis revealed that the transcription of the five enzymes was also affected by TACm. In conclusion, alkaloids in C. majus showed a prominent toxicity to L. dispar by reducing food intake, influencing nutritional indices, and affecting the activity and mRNA transcription of detoxifying and protective enzymes. This study provides novel insights into the insecticidal mechanism of C. majus.

Extensive Ace2 duplication and multiple mutations on Ace1 and Ace2 are related with high level of organophosphates resistance in Aphis gossypii.

Aphis gossypii (Glover) has been found to possess multiple mutations in the acetylcholinesterase (AChE) gene (Ace) that might involve target site insensitivity. In vitro functional expression of AChEs reveals that the resistant Ace1 (Ace1R) and Ace2 (Ace2R) were significantly less inhibited by eserine, omethoate, and malaoxon than the susceptible Ace1 (Ace1S) and Ace2 (Ace2S). Furthermore, in both the mutant and susceptible AChEs, Ace2 was significantly less sensitive to eserine, omethoate, and malaoxon than Ace1. These results suggested that both the mutant Ace1 and Ace2 were responsible for omethoate resistance, while the mutant Ace2 played a major role in insecticide resistance. The DNA copy number and transcription level of Ace2 were 1.52- and 1.88-fold higher in the ORR strain than in the OSS strain. Furthermore, the DNA copy number and transcription level of Ace2 were significantly higher than that of Ace1 in either OSS or ORR strains, demonstrating the involvement of Ace2 gene duplication in resistance. Thus, the authors conclude that omethoate resistance in cotton aphids appears to have evolved through a combination of multiple mutations and extensive Ace2R gene duplication.