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Many essential oils have excellent insecticidal activity and have the potential to be developed as alternatives to chemical insecticides for pest control. Previously, we showed that β‐asarone, a major constituent of the essential oil derived from Acorus calamus L. (Acoraceae), has strong pesticidal activity against brown planthopper, Nilaparvata lugens (Stål) (Hemiptera: Delphacidae), the most notorious rice pest in Asia. Here, we report the first evaluation of the sublethal and transgenerational effects of β‐asarone on N. lugens. β‐Asarone significantly decreased female longevity, male longevity, fecundity, and hatchability of F0 generation individuals exposed to the LD30 and LD45 of β‐asarone relative to the acetone control. Moreover, compared with acetone, exposure to LD30 and LD45 of β‐asarone significantly shortened the duration of the egg stage, developmental duration of first instars, and female longevity of F1 generation individuals. Furthermore, the intrinsic rate of increase (r), finite rate of increase (λ), and net reproductive rates (R0) of insects treated with LD30 and LD45 of β‐asarone were significantly lower than those of insects treated with acetone. Compared with acetone, the fecundity and hatchability of F1 generation individuals were significantly decreased after exposure to β‐asarone at LD30 and LD45. These findings indicate the negative effects of sublethal doses of β‐asarone on N. lugens and provide novel information on the potential use of β‐asarone as a substitute chemical pesticide.

Replant disease caused by continuous cropping commonly occurs in yam with consecutive monoculture. However, little is known about how the continuous cropping of yam affects the rhizospheric soil bacterial community structure. In this study, the effects of continuous cropping on rhizospheric soil characteristics, bacterial diversity, and community structure were investigated in the Yongfeng yam fields under monoculture for 1, 5, 10, 15, and 20 years. Long-term monoculture caused soil acidification and increased the concentration of available potassium (AK) and available phosphorus (AP), and soil bacterial richness, but decreased the soil bacterial diversity. An exception was for the field under monoculture for 20 years as it showed the highest bacterial diversity. The relative abundance of beneficial bacteria, such as Proteobacteria, Actinobacteria, and Chloroflexi decreased while the relative abundance of harmful bacteria, including Gemmatimonadetes and Acidobacteria, increased with an extended continuous cultivation time. The networks varied among yams with different cultivation years and became complex with the increase in cultivation years. However, after time in monoculture, the bacterial network decreased gradually and existed stably. These changes in bacterial community composition and co-occurrence of networks may increase the potential risk of soil-borne disease and reduce the yield and quality of Yongfeng yam.

There is little information about nematode pests associated with yam in China. Between 2020 and 2021, surveys of yam fields were conducted to investigate the abundance and prevalence of plant-parasitic nematodes in major yam growing areas. A total of 110 bulk soil samples from the yam rhizosphere and 48 yam tubers were collected from seven counties in Jiangxi and Shandong provinces. Standard protocols were used to extract nematodes from soil and tubers and identified at the genus level. In this study, 16 species and 13 nematode genera were recorded. The five most prominent species on the yam rhizosphere according to mean population densities were Pratylenchus coffeae (291/individuals), Meloidogyne (262/individuals), Rotylenchulus reniformis (225/individuals), Merlinius (224/individuals), and Helicotylenchus dihystera (171/individuals). In the tubers, the three most prominent species were Pratylenchus coffeae (415/individuals), Meloidogyne (331/individuals), and Rotylenchulus reniformis (115/individuals). These species were verified with appropriate molecular analysis. The high prevalence of the ectoparasite (Merlinius spp.) on the rhizosphere of yam also revealed that Merlinius spp. May be more important to yam than previously thought. Morphological and molecular analyses further confirmed the identity of the species as Merlinius brevidens and were characterized for the first time on yam in China. Minor morphometrical differences (slightly longer body and stylet) were observed in Chinese populations of M. brevidens compared to the original description. Additionally, this study reveals that M. brevidens isolated from China showed a higher nucleotide sequence in the ITS region compared to M. brevidens populations from India. This finding provides baseline information on the nematode pest occurrence on yam in China and calls for effective management.