The role of detoxification enzymes in the susceptibility of Brevipalpus californicus exposed to acaricide and insecticide mixtures

Worldwide used bio-insecticides Cry1Ac toxin has no detrimental effects on Episyrphus balteatus but alter the symbiotic microbial communities

Hoverflies, capable of abilities providing dual ecosystem services including pest control and pollination, are exposed to insecticidal proteins from transgenic plants via pollen and prey aphids. However, the effects of such exposures on hoverflies have never been adequately assessed. Here, we investigated impacts of the most widely used biotoxin Cry1Ac on a representative hoverfly species Episyrphus balteatus through food chain transmission and active toxin exposure. The results showed Cry1Ac can be transmitted into E. balteatus through feeding on Aphis gossypii reared by Bt insect-resistant cotton variety expressing the Cry1Ac toxin, but the biological parameters of E. balteatus including survival rate, growth, development, reproductive capacity, and detoxification-related gene expression, were not significantly affected. Furthermore, the exposure to high-dose Cry1Ac toxin (500 μg/mL) resulted in slight increase of 16.67 % in the activity of detoxification and antioxidant enzyme catalase in E. balteatus and inhibited the egg hatching, partially inducing stress responses. Notably, the exposure to Cry1Ac toxin disrupted the microbiota homeostasis in E. balteatus, and the relative abundances of three dominant symbiotic bacterial genera (Cosenzaea, Wolbachia, and Commensalibacter) in E. balteatus exhibited a 10 % ~ 40 % fluctuation under Cry1Ac toxin stress. Taken together, these results suggest Cry1Ac toxin is not lethal to E. balteatus, but it poses a potential threat to its endosymbiotic bacteria.

Comparative toxicity and enzymatic detoxification responses in Spodoptera frugiperda (Lepidoptera: Noctuidae) to two insecticides

The fall armyworm (FAW), Spodoptera frugiperda Smith (Lepidoptera: Noctuidae), poses a significant threat to food security, necessitating effective management strategies. While chemical control remains a primary approach, understanding the toxicity and detoxification mechanisms of different insecticides is crucial. In this study, we conducted leaf-dipping bioassays to assess the toxicity of quinalphos and beta-cypermethrin·emamectin benzoate (β-cyp·EMB) on S. frugiperda larvae. Additionally, we assessed the response of alterations in CarE, GST, MFO, and AChE activities to sublethal concentrations of these insecticides over various treatment durations. Results indicated that β-cyp·EMB exhibited higher toxicity than quinalphos in S. frugiperda. Interestingly, the highest activities of GST, CarE, MFO, and AChE were observed at 6 h exposure to LC10 and LC25 of β-cyp·EMB, surpassing equivalent sublethal concentrations of quinalphos. Subsequently, GST and CarE activities exposure to β-cyp·EMB steadily decreased, while MFO and AChE activities exposure to both insecticides was initially decreased then increased. Conversely, two sublethal concentrations of quinalphos notably enhanced GST activity across all exposure durations, with significantly higher than β-cyp·EMB at 12-48 h. Similarly, CarE activity was also increased at various durations. Our research has exhibited significant alterations in enzyme activities exposure to both concentration and duration. Furthermore, Pearson correlation analysis showed significant correlations among these enzyme activities at different treatment durations. These findings contribute to a better understanding of detoxification mechanisms across different insecticides, providing valuable insights for the rational management of S. frugiperda populations.

Synergistic action and mechanism of scoparone, a key bioactive component of Artemisia capillaris, and spirodiclofen against spider mites

BACKGROUND

Plants have numerous defensive secondary metabolites to withstand insect attacks. Scoparone, which is extracted from the medicinal plant Artemisia capillaris, has potent acaricidal effects on Tetranychus cinnabarinus. Spirodiclofen, derived from a tetronic acid derivative, is a potent commercial acaricide that is extensively used globally. However, whether scoparone has synergistic effects when used in conjunction with spirodiclofen and the underlying synergistic mechanism remains unclear.

RESULTS

Scoparone exhibited a potent synergistic effect when it was combined with spirodiclofen at a 1:9 ratio. Subsequently, cytochrome P450 monooxygenase (P450) activity, RNA-Seq and qPCR assays indicated that the enzyme activity of P450 and the expression of one P450 gene from T. cinnabarinus, TcCYP388A1, were significantly inhibited by scoparone and spirodiclofen + scoparone; conversely, P450 was activated in spirodiclofen-exposed mites. Importantly, RNAi-mediated silencing of the TcCYP388A1 gene markedly increased the susceptibility of spider mites to spirodiclofen, scoparone and spirodiclofen + scoparone, and in vitro, the recombinant TcCYP388A1 protein could metabolize spirodiclofen. Molecular docking and functional analyses further indicated that R117, which is highly conserved in Arachnoidea species, may be a vital specific binding site for scoparone in the mite TcCYP388A1 protein. This binding site was subsequently confirmed using mutagenesis data, which revealed that this binding site was the sole site selected by scoparone in spider mites over mammalian or fly CYP388A1.

CONCLUSIONS

These results indicate that the synergistic effects of scoparone and spirodiclofen on mites occurs through the inhibition of P450 activity, thus reducing spirodiclofen metabolism. The synergistic effect of this potent natural product on the detoxification enzyme-targeted activity of commercial acaricides may offer a sustainable strategy for pest mite resistance management. © 2024 Society of Chemical Industry.

Impact of Neem Seed Extract on Mortality, Esterase and Glutathione-S-Transferase Activities in Thai Polyvoltine Hybrid Silkworm, Bombyx mori L

Neem, a biopesticide, offers a safer alternative to the synthetic insecticides commonly used in mulberry cultivation, which can harm silkworms. This study aimed to investigate the effects of Thai neem seed extract on all instar larvae of the Thai polyvoltine hybrid silkworm, Bombyx mori L., Dok Bua strains, focusing on the mortality rate and the activities of esterase (EST) and glutathione S-transferases (GST) enzymes. Acute toxicity was assessed using the leaf-dipping method. Results showed that the mortality rate tended to be higher in younger instars than in older ones. The first instar larvae exhibited the highest mortality rate at 94%, whereas the LC50 was highest in the third instar at 5.23 mg L-1 at 72 h. This trend aligns with the activities of EST and GST, which were evaluated in the whole bodies of the first instar larvae and the midgut tissue of fifth instar larvae. As the extract concentration increased, EST activity decreased while GST activity increased in both the first and fifth instar larvae. These findings highlight that neem extract is toxic to all instar larvae, with GST playing a crucial role in detoxification, particularly in the whole body of the Thai polyvoltine hybrid silkworm.

Construction, Pesticidal Activities, Control Effects, and Detoxification Enzyme Activities of Osthole Ester/Amide Derivatives

Pesticide research and development has entered an era of safety, efficiency, and environmental friendliness. Discovery of effective active products directly or indirectly from plant secondary metabolites as pesticide candidates has been one of the current research focuses. Herein, two series of new ester and amide derivatives were prepared by structural modifications of a natural coumarin-type product osthole at its C-4' position. Their structures were characterized by IR, mp, ¹H NMR, and HRMS. Confirmation of steric configuration of seven compounds was based on single-crystal analysis. Against Tetranychus cinnabarinus Boisduval (Acari: Tetranychidae), (2'E)-3'-ethoxycarbonylosthole (4b) and (2'E)-3'-(n)hexyloxycarbonylosthole (4e) exhibited 3.2 and 3.1 times acaricidal activity of osthole, and particularly, they also showed 2.4 and 2.2 times control efficiency on the 5th day of osthole. Against Aphis citricola Van der Goot (Homoptera: Aphididae), (2'E)-3'-(p-CF₃)benzyloxycarbonylosthole (4w), (2'E)-3'-benzylaminocarbonylosthole (5f), and (2'E)-3'-phenylethylaminocarbonylosthole (5g) showed 1.9-2.1-fold aphicidal activity of osthole. Furthermore, the changes in two detoxification enzyme [carboxylesterase (CarE) and glutathione S-transferase (GST)] activities over time in treated T. cinnabarinus were investigated. These results can pave the foundation for future design and preparation of osthole derivatives as botanical agrochemicals.

Impact of diseases and pests on premature fruit drop in sweet orange orchards in São Paulo state citrus belt, Brazil

BACKGROUND

Despite technical improvements in the citrus chain and leadership in orange production achieved in the past decades, premature fruit drop remains a major component of crop loss in São Paulo state citrus belt, the largest sweet orange production area in the world. The present study aimed to determine, during five consecutive seasons, the impact of the diseases and pests on premature fruit drop in the orange belt.

RESULTS

Fruit drop due to the main diseases and pests averaged approximately 11.0%, which corresponded to approximately 63% of the annual fruit drop. The average fruit drop rate due to fruit borer and fruit flies combined was 4.0%, Huanglongbing (HLB) 3.3%, black spot 2.6%, leprosis 1.0% and citrus canker 0.3%. The average amount of fruit drop (million 40.8 kg boxes) and value of crop losses (million US$ dollars), in five seasons, were 12.7 and 66.2 for fruit borer/fruit flies, 11.0 and 57.9 for HLB, 8.1 and 42.2 for black spot, 3.1 and 15.6 for leprosis, and 0.9 and 4.9 for citrus canker, respectively.

CONCLUSION

Fruit borer and fruit flies (combined), HLB, black spot, leprosis and citrus canker are, in this order, the main diseases and pests in the orange belt of São Paulo state. All of these causes significantly increased the overall fruit drop rate in the evaluated seasons. The results will contribute to the development of the Brazilian citrus industry, while showing to other citrus-growing regions the potential that diseases and pests have to jeopardize production. © 2022 Society of Chemical Industry.