BACKGROUND: Balancing the safety and efficiency of chiral pesticides can help protect pollinators. We evaluated the stereoselective behavior, bioactivity, toxicity and exposure risk of the chiral insecticide pyriproxyfen in a citrus nectar system. RESULTS: Density functional theory (DFT) and ultra-performance liquid chromatography tandem mass spectroscopy (UPLC-MS/ MS) were applied for absolute configuration appraisal and chiral analysis validation, respectively. The recoveries ranged from 72.3% to 100.5% with an relative standard deviation (RSD) ranging from 1.2% to 9.7%. In a field trial, we determined insecticide half-lives in citrus leaves and flowers, which were 7.0 and 8.6 days for R-(+)-pyriproxyfen, and 11.7 and 14.7 days for S-(−)-pyriproxyfen, respectively. We found that the bioactivity of R-(+)-pyriproxyfen was 3.39 and 2.37 times higher than S-(−)-pyriproxyfen against Unaspis yanonensis and Diaphorina citri nymphs, respectively. S-(−)-pyriproxyfen had 3.8 times higher acute toxicity than R-(+)-pyriproxyfen on Apis mellifera L., and its exposure risk was moderate based on the hazard quotient.CONCLUSION: The phenomenon of stereoselective degradation and biological effect demonstrated that the high-risk stereoisomer of S-(−)-pyriproxyfen degraded more slowly than R-(+)-pyriproxyfen, but R-(+)-pyriproxyfen with better efficiency for target. Therefore, an increased duration of R-(+)-pyriproxyfen activity on citrus was beneficial for efficacy. Our results could guide the scientific application and evaluation of chiral pesticides on nectar plants.

A bacterial pathogen strain was isolated from susceptible tissue of Hongyang variety kiwifruit in Zhongfeng Town, Ziyuan County, Guilin City, Guangxi, China. Due to the relatively single variety of kiwifruit in Guangxi, the control technology of fruit farmers is backward, and the climate is humid, which is suitable for the growth of pathogenic bacteria, resulting in frequent occurrence of diseases. In this study, the pathogen strain was identified on the basis of morphological, physiological and biochemical tests, 16S rRNA , PCR detection with specific primers, and Biolog analysis. The results showed that a tobacco allergic reaction could be induced by inoculation with the pathogenic bacteria, Additionally, brown necrotic plaques appeared on kiwifruit leaves, necrotic phloem lesions appeared, and wounds on kiwifruit branches turned brown. The characteristics identified by morphological, physiological, biochemical and Biolog identification were similar to those caused by Pectobacterium sp. Through 16S rRNA sequence analysis and PCR identification with specific primers, bands with a size corresponding to target bands, indicating that the pathogen was Pectobacterium carotovorum subsp. actinidiae . This is the first report of kiwifruit canker disease caused by Pectobacterium carotovorum subsp. actinidiae in Guangxi, China. In addition, through this study, a preliminary understanding of the pathogen has been obtained, which will lay the foundation for the prevention and control of the disease in the future.

Eleven new tetracyclic quassinoids, picrachinensin A−K (1−11), along with six known congeners, were isolated from the stems and leaves of Picrasma chinensis. Their structures were elucidated by integrated multiple spectroscopic techniques, singlecrystal X-ray diffraction analysis, and electronic circular dichroism. Notably, compounds 3 and 4 are a pair of undescribed epimers, and 8 and 9 are unusual quassinoids with a hydroxymethyl group at C-13. Biologically, compound 7 exhibited insecticidal activity on both adults and larvae of Diaphorina citri Kuwayama even more effectively than the positive control (abamectin), with an LD 50 of 55.69 mg/L for adults and a corrected mortality rate of 30.42 ± 2.78% for larvae (100 mg/L). According to preliminary structure− activity relationship investigations, the hydroxymethyl at the C-13 position of quassinoids was beneficial for their insecticidal activity. In addition, compounds 1, 4, and 12 exhibited excellent neuroprotective effect against H 2 O 2 -induced oxidative injury on SH-SY5Y cells, with more potent activity than the positive control (Trolox), and all the compounds exhibited no cytotoxicity to SH-SY5Y and BV-2 cells at the indicated concentrations.

β-Carbonic anhydrase (βCA) is very important for plant growth and development, but its function in immunity has also been examined. In this study, we found that the expression level of Solanum lycopersicum βCA1 (SlβCA1) was significantly upregulated in plants treated with Xanthomonas euvesicatoria 85-10. The protein was localized in the nucleus, cell membrane and chloroplast. Using tomato plants silenced with SlβCA1, we demonstrated that SlβCA1 plays an active role in plant disease resistance. Moreover, we found that the elicitor PopW upregulated the expression of SlβCA1, while the microbe-associated molecular pattern response induced by PopW was inhibited in TRV-SlβCA1. The interaction between PopW and SlβCA1 was confirmed. Here, we found that SlβCA1 was positively regulated during PopW-induced resistance to Xanthomonas euvesicatoria 85-10. These data indicate the importance of SlβCA1 in plant basic immunity and its recognition by the Harpin protein PopW as a new target for elicitor recognition.