The inhibition of ecdysone signal pathway was the key of pyriproxyfen poisoning for silkworm, Bombyx mori

The role of neuropeptide prothoracicotropic hormone (PTTH) - Torso in pyriproxyfen-induced larval-pupal abnormal metamorphosis in silkworms

The neuropeptide prothoracicotropic hormone (PTTH) plays a key role in regulating ecdysone synthesis and promoting insect metamorphosis. Pyriproxyfen is a juvenile hormone analogue. We previously reported that pyriproxyfen disrupts ecdysone secretion and inhibits larval-pupal metamorphosis in silkworms. However, the specific molecular mechanisms by which pyriproxyfen interferes with ecdysone signaling remain to be elucidated. Herein, the RNA-seq analysis on the ecdysone-secretion organ prothoracic gland (PG) was conducted following pyriproxyfen exposure. A total of 3774 differentially expressed genes (DEGs) were identified, with 1667 up-regulated and 2107 down-regulated. KEGG analysis showed that DEGs were enriched in the MAPK signaling pathway, a conserved pathway activated by PTTH binding to Torso, which regulates the ecdysone synthesis. qRT-PCR results indicated a significant up-regulation in PTTH transcription level, while the transcription levels of torso and downstream MAPK pathway genes, Ras2, Raf and ERK, were down-regulated 24 h post-pyriproxyfen treatment. Consistent with these transcriptional changes, PTTH titers in the brain also increased following pyriproxyfen treatment. These results suggest that pyriproxyfen induces abnormal metamorphosis in silkworms by impairing PTTH-Torso signaling. This study enhances our understanding of the molecular mechanisms of pyriproxyfen-induced larval-pupal abnormal metamorphosis in silkworms, and also provides insights for developing detoxification strategies for juvenile hormone analog pesticides to non-target organisms.

Effects of pyriproxyfen on development and hormone of the aphis, Aphis craccivora (Hemiptera: Aphididae)

Pyriproxyfen (PPF) has been shown to affect the pupal stage and ecdysone levels in holometabolous insects, such as silkworms and mealworms. It remains unknown whether it affects hemimetabolous insects with their hormone levels in insects lacking a pupal stage. In this laboratory study, bioassays were conducted to investigate the effects of varying doses of PPF on Aphis craccivora Koch (Hemiptera: Aphididae). Ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was used to determine the types and titers of juvenile hormone (JH) and 20-hydroxyecdysone (20E). Additionally, the effects of PPF on A. craccivora reproduction and molting, as well as its influence on relevant gene expression, were examined. The results revealed LC50 and LC90 values of 3.84 and 7.49 mg/l for PPF, respectively, after 48 h of exposure. The results demonstrated a significant reduction in the titer of JH III and a significant increase in the titer of 20E following treatment with PPF. However, there was no significant decrease observed in the titer of JH III skipped bisepoxide (JH SB3). A sublethal concentration of PPF was found to inhibit Krüppel homolog 1 (kr-h1) gene expression and reduce aphid reproduction, but it did not significantly impact ecdysone receptor expression and aphid molting. The results of this study demonstrate that PPF exhibits a lethal effect on aphids, thereby providing an effective means of control. Additionally, sublethal concentrations of PPF have been found to inhibit the JH in aphids, resulting in a decline in their reproductive ability and achieving the desired control objectives.

JH degradation pathway participates in hormonal regulation of larval development of Bombyx mori following λ-cyhalothrin exposure

λ-Cyhalothrin (λ-cyh), a widely utilized pyrethroid insecticide, poses serious threats to non-target organisms due to its persistence nature in the environment. Exposure to low concentrations of λ-cyh has been observed to result in prolonged larval development in Bombyx mori, leading to substantial financial losses in sericulture. The present study was undertaken to elucidate the underlying mechanisms for prolonged development caused by λ-cyh (LC10) exposure. The results showed that the JH Ⅲ titer was significantly increased at 24 h of λ-cyh exposure, and the JH interacting genes Methoprene-tolerant 2, Steroid Receptor Co-activator, Krüppel-homolog 1, and JH binding proteins were also up-regulated. Although the target of rapamycin (Tor) genes were induced by λ-cyh, the biosynthesis of JH in the corpora allata was not promoted. Notably, 13 JH degradation genes were found to be significantly down-regulated in the midgut of B. mori. The mRNA levels and enzyme activity assays indicated that λ-cyh had inhibitory effects on JH esterase, JH epoxide hydrolase, and JH diol kinase (JHDK). Furthermore, the suppression of JHDK (KWMTBOMO01580) was further confirmed by both western blot and immunohistochemistry. This study has offered a comprehensive perspective on the mechanisms underlying the prolonged development caused by insecticides, and our results also hold significant implications for the safe production of sericulture.

Characterization and transcriptomic analyses of the toxicity induced by toosendanin in Spodoptera frugipreda

The fall armyworm, Spodoptera frugiperda, is a destructive agricultural pest that seriously threatens global food security. Insecticide resistance of this pest has gradually formed in recent years due to improper usage, and alternative methods are badly needed. Toosendanin (TSN) is a botanical compound with broad-spectrum insecticidal activities against many pests. However, the effects of TSN on S. frugiperda are still unclear. In this study, the growth inhibition phenomenon, including weight loss and prolonged developmental duration, in the larvae with TSN exposure was clearly observed. Compared to the control group, a total of 450 and 3314 differentially expressed genes (DEGs) were identified by RNA-Seq in the larvae groups treated with 10 and 20 mg/kg TSN, respectively. Furthermore, the DEGs involved in the juvenile hormone and ecdysone signal pathways and downstream processes, including detoxifying enzyme genes, chitin synthesis and metabolism genes, and cuticular protein genes, were found. Our findings suggest that TSN regulates the expression of key genes in juvenile hormone and ecdysone signal pathways and a series of downstream processes to alter the hormone balance and cuticle formation and eventually inhibit larval growth, which laid the foundation for the molecular toxicological mechanism research of TSN on S. frugiperda larvae.

Toxicity Tests for Chemical Pesticide Registration: Requirement Differences among the United States, the European Union, Japan, and China?

Pesticide registration is a scientific, legal, and administrative process that checks if a pesticide is safe and effective for its intended use before it can be used. The toxicity test is a key part of pesticide registration, which includes human health and ecological effect testing. Different countries adopt their own toxicity test criteria for pesticide registration guidelines. However, these differences, which may help accelerate the progress of pesticide registration and reduce the number of animals used, are yet to be explored and compared. Herein, we outlined the details and compared the differences between the toxicity tests in the United States, the European Union, Japan, and China. Some differences lie in the types and waiver policy, while others are in new approach methodologies (NAMs). On the basis of these differences, there is great potential for the optimization of NAMs during the toxicity tests. It is expected that this perspective can contribute to developing and adopting NAMs.