The green peach aphid, Myzus persicae Sulzer (Hemiptera: Aphididae), is an important sap-sucking pest of many crops, including Chinese cabbage, Brassinca oleracea L. The neonicotinoid insecticide thiamethoxam has been used as an effective insecticide to control M. persicae in cabbage fields. In this study, we assessed the effects of sublethal concentrations of thiamethoxam on demographic parameters of M. persicae. In leaf-dip bioassays, thiamethoxam showed a relatively high toxicity against M. persicae with an LC₅₀ of 6.80 mg liter⁻¹. The duration of the preadult stage was not significantly affected in the sublethal bioassay. Additionally, the longevity and adult preoviposition period were not significantly affected by sublethal thiamethoxam. However, sublethal thiamethoxam significantly increased fecundity (LC₁₀) and prolonged the total preoviposition period (LC₄₀). Consequently, the finite rate of increase (λ) and the intrinsic rate of increase (r_m) of aphids exposed to the LC₄₀ were significantly lower than those of control aphids, whereas the net reproductive rate (R₀) was higher, and the generation time (T) and the population doubling time (DT) were longer in the treated group. Based on these results, hormesis was induced by sublethal thiamethoxam in M. persicae, with the population growth of M. persicae negatively affected at higher sublethal concentrations of thiamethoxam. Therefore, our study indicated that the possible effects of thiamethoxam on aphids require further study to develop optimized integrated pest management strategies.

Brasenia schreberi, commonly known as watershield and referred to as 'Chun Cai' in Chinese, is a worldwide aquatic vegetable. It has long been regarded as health- promoting vegetable due to production of mucilage in young shoots, and thus has gained popularity in China. In September 2022, a leaf spot disease was observed at the National Aquatic Vegetable Germplasm Resource Nursery located in Wuhan, Hubei province, China. The disease occurred on watershield leaves. It started with the formation of leaf spots surrounded by halos.These spots ranged in color from yellow to brown and in diameter from 1 to 10 mm. Subsequently, the smaller spots merged, ultimately causing the entire leaves to turn black. Small brown- to black-colored sclerotia were produced on the underside of the diseased leaves. Disease incidence was 30% on average, and yield loss was approximately 15% on average. To isolate the pathogen, leaf tissues at the disease-healthy border area were excised into 5 × 5 mm pieces, these segments were immersed in 75% ethanol for 30 s, followed by immersion in 0.5% sodium hypochlorite for 30 s, and then rinsed twice in sterile water. After air-drying, the leaf pieces were incubated on potato dextrose agar (PDA) in darkness at 28°C for 3 d. Mycelia from the leaf pieces were transferred to new PDA plates for purification, three sclerotia-forming fungal isolates (Whcc-1, Whcc-3, Whcc-4) were finally obtained. They were incubated on PDA at 28°C for 4 to 14 d for observation of colony morphology. At 4 d after incubation (DAI), they grew rapidly with the average growth rate of 2.2 cm/d and formed colonies with whitish substrate mycelia and well-developed aerial mycelia and small white to light brown-colored sclerotia. At 10 to 14 DAI, the sclerotia gradually turned to black, 0.2 to 0.4 mm in diameter (0.26 mm on average, n = 50). These morphological characteristics matched description of Sclerotium hydrophilum (Bashyal et al. 2021). Molecular identification was done to further clarify the species identity of this fungus. Genomic DNA was extracted from isolates Whcc-1, Whcc-3, and Whcc-4. The internal transcribed spacer region of the ribosomal DNA (ITS-5.8S rDNA) and the small subunit ribosomal RNA gene (ssrRNA) were amplified using universal primers ITS1/ITS4 and NS1/NS6, as described by White et al. (1990). Sequence analysis revealed a high degree of similarity between the ITS-5.8S rDNA sequences from Whcc-1, Whcc-3, and Whcc-4 (GenBank Acc. No. OP782030, PP035994, and PP035995, respectively) and those of S. hydrophilum strain CBS201.27 (GenBank Acc. No. FJ231396), with similarities of 99.25%, 99.4%, and 99.25%, respectively. The ssrRNA sequences from Whcc-1, Whcc-3, and Whcc-4 (GenBank Acc. No. PP238401, PP261342 and PP261345) were found to be identical, displaying 100% similarity to the ssrRNA sequences of S. hydrophilum strain ZH11 (GenBank Acc. No. KC354147). Based on both morphological and molecular evidence, it can be inferred that Whcc-1, Whcc-3, and Whcc-4 belong to the species S. hydrophilum. Pathogenicity tests were conducted by inoculation of the mycelial agar plugs of Whcc-1, Whcc-3 or agar plugs of fresh PDA (control) on floating leaves of two watershield plants, 4 leaves (replicates) for each treatment. After inoculation, the treated leaves were sealed in plastic bags to maintain humidity, and grown under natural conditions (18°C to 28°C, with 8 hours of light daily). At 7 DAI, while control leaves remained healthy, the leaves inoculated with Whcc-1 and Whcc-3 leaves formed yellow- to brown-colored spots similar to those observed in the field surveys. S. hydrophilum was re-isolated from the leaf spots, thus verifing Koch's postulates. S. hydrophilum has a wide host range, infecting at least 19 genera of plants, including common rice and wild rice (Johnson et al. 1976), and water lily (Kernkamp et al. 1977). Moreover, it has been reported to infect rice in China (Punter et al. 1984; Zhong et al. 2018). To our knowledge, this is the first report of S. hydrophilum on watershield leaves in central China.

Trapa natans L., or water chestnut, is a currently globally distributed aquatic plant. The Yangtze River basin in China, a site origin of water chestnut (Fan et al., 2022), has extensive cultivation as a vegetable. In June 2021, a survey at the National Aquatic Vegetable Resource Garden in Wuhan, Hubei, China, revealed browning and wilting of water chestnut plants, with abundant white mycelia and brown to black sclerotia on leaves, indicative of southern blight (Sclerotium rolfsii). Field disease incidence a 1 ha area reached 70%, reducing fruit yield by 50%. About 10% of diseased plants showed blackening and rot from petioles to leaves. White sclerotial primordia and small brown to black sclerotia formed on the plant surfaces. By late August, symptoms exceeded 60%. To identify the pathogen, isolations were made from 243 sclerotial samples using 75% alcohol to disinfect, rinsed three times with water, and then incubated on potato dextrose agar (PDA) at 25℃. A total of 129 isolates were obtained, most of which exhibited characteristics of S. rolfsii. However, 21 isolates had sclerotia significantly smaller than those of S. rolfsii (1 to 1.5 mm in diameter). These isolates, cultured on PDA, produced abundant fluffy white aerial hyphae, 3 to 6 μm wide. Optimal mycelium growth was between 25 °C to 30 °C, with an average daily rate of 10 mm. White to light brown sclerotia appeared after 5 days and turned black within 10 to 14 days, averaging 0.34 mm in diameter (n=50). Some isolates produced a light brown pigment. These traits matched the description of S. hydrophilum (Bashyal et al. 2021). Isolates 221 and 238 were selected for molecular identification, with genomic DNA extracted from mycelia using the CTAB method. PCR amplification was conducted using ITS1/ITS4 and NS1/NS6 primers to target the internal transcribed spacer (ITS) and the small subunit ribosomal RNA gene (ssrRNA). Sequence analysis showed that the ITS sequence of isolate 221 (GenBank Acc. No. OR512512) had 99.84% sequence identity with S. hydrophilum Msh6 (GenBank Acc. No. FJ595946), and isolate 238 (GenBank Acc. No. PP035993) had 99.72% identity with S. hydrophilum Whcc-4 (GenBank Acc. No. PP035994). The ssrRNA sequences of both isolates (GenBank Acc. No. PP237261) had 99.69% identity with S. hydrophilum strain Hbq001 (GenBank Acc. No. KY995575), confirming their identification as S. hydrophilum. To assess pathogenicity, 16 water chestnut plants (cultivar Jia-yu Ling) at the rosette stage were placed individually in 32 cm diameter, 10 cm deep containers with fresh water. Eight plants were inoculated with 50 mature sclerotia from PDA cultures of isolates 221 and 238, and incubated at 25 °C for 14 days, with four plants per isolate. The remaining eight plants served as controls. Containers were covered to maintain 100% relative humidity at 25 °C to 32 °C for 3 days. This procedure was repeated twice. After 7 days, inoculated plants developed dark brown lesions on petioles that spread to leaves by 15 days post-inoculation. Fungi isolated from diseased leaves resembled isolates 221 and 238, fulfilling Koch's postulates. S. hydrophilum infecting at least 19 genera of plants, including rice (Zhong et al. 2018), wild rice, water lily (Kernkamp et al. 1977) and watershield (Fu et al. 2024). This is the first report of S. hydrophilum infecting water chestnut (T. natans) in central China, identifying it as a co-pathogen with S. rolfsii. Their combined presence may heighten plant mortality and threaten water chestnut cultivation.