Tephritidae fruit flies (Diptera: Tephritidae) are regarded as important damage-causing species due to their ability to cause great economic losses in fruit and vegetable crops. Bactrocera minax and Bactrocera tsuneonis are two sibling species of the subgenus Tetradacus of Bactrocera that are distributed across a limited area of China, but have caused serious impacts. They share similar morphological characteristics. These characteristics can only be observed in the female adult individuals. The differences between them cannot be observed in preimaginal stages. Thus, it is difficult to distinguish them in preimaginal stages morphologically. In this study, we used molecular diagnostic methods based on cytochrome c oxidase subunit I and species-specific markers to identify these two species and improve upon the false-positive results of previous species-detection primers. DNA barcode sequences were obtained from 900 individuals of B. minax and 63 individuals of B. tsuneonis. Based on these 658 bp DNA barcode sequences of the cytochrome c oxidase subunit I gene, we successfully designed the species-specific primers for B. minax and B. tsuneonis. The size of the B. minax specific fragment was 422 bp and the size of the B. tsuneonis specific fragment was 456 bp. A series of PCR trials ensured the specificity of these two pairs of primers. Sensitivity assay results demonstrated that the detection limit for the DNA template concentration was 0.1~1 ng/µL for these two species. In this study, we established a more reliable, rapid, and low-cost molecular identification method for all life stages of B. minax and B. tsuneonis. Species-specific PCR can be applied in plant quarantine, monitoring and control of B. minax and B. tsuneonis.

Background Plant parasitic nematodes (PPNs) are responsible for causing many plant diseases and are extremely difficult to control at present. Currently, due to the negative effects of chemical agents on the environment and human health, the development of new biological pesticides has become an important part of plant nematode control. Nematophagous fungi refers to a class of fungi that kill plant nematodes. Notably, a large number of nematophagous fungi resources remain to be studied. The objective of our study was to use in vitro screening to identify nematophagous fungi and select strains that were highly active against nematodes, providing a primary research for the development and utilization of new nematophagous fungi. Results A new nematophagous fungal strain (GUCC2219) was isolated from cysts of possibly Globodera spp. and Heterodera spp., identified as Volutella citrinella. The hyphae of V. citrinella produced ring structures of variable size and exhibited predatory and nematicidal activity. The hyphal predation rates (in vitro) against three species of nematodes, Aphelenchoides besseyi, Bursaphelenchus xylophilus, and Ditylenchus destructor, averaged 59.45, 33.35, and 50.95%, respectively, while the fermentation broth produced by the fungus exhibited mortality rates of 100, 100, and 55.63%, respectively, after 72 h. Conclusion V. citrinella is a new strain with nematophagous properties, which are a novel discovery. At the same time, this is the first report of nematicidal and nematode predation activity in the genus Volutella.

Potatoes rank third in terms of human consumption after rice and wheat. Globodera spp. are significant pests of potato crop worldwide. Globodera rostochiensis was found in Weining County, Guizhou Province, China, in 2019. We collected soil from the rhizosphere zone from infected potato plants and separated mature cysts through simple floatation and sieving methods. The selected cysts were surface-sterilized, and the colonized fungi were isolated and purified. At the same time, the preliminary identification of fungi and fungi parasites on the cysts of nematodes was carried out. This study aimed to define the species and frequency of fungi-colonizing cysts of G. rostochiensis collected from Weining County, Guizhou Province, China, and provide a basis for the control of G. rostochiensis. As a result, 139 strains of colonized fungi were successfully isolated. Multigene analyses showed that these isolates included 11 orders, 17 families, and 23 genera. The genera Fusarium (with a separation frequency of 59%), Penicillium (11%), Edenia (3.6%), and Paraphaeosphaeria (3.6%) were the most frequently occurring. Among the 44 strains, 27 had a colonization rate of 100% on the cysts of G. rostochiensis. Meanwhile, the functional annotation of 23 genera indicated that some fungi have multitrophic lifestyles combining endophytic, pathogenic, and saprophytic behavior. In conclusion, this study showed the species composition and lifestyle diversity of colonized fungi from G. rostochiensis and demonstrated these isolates as potential sources of biocontrol agents. Colonized fungi were isolated from G. rostochiensis for the first time in China, and the taxonomic diversity of fungi from G. rostochiensis was clarified.

Plant-parasitic nematodes (PPNs) are significant pests that result in considerable economic losses in global crop production. Due to the high toxicity of chemical nematicides, there is a need to develop new strategies for nematode control. In this context, nematophagous fungi may offer a viable option for biological control. Two fungal strains (GUCC2212 and GUCC2232) were isolated from cysts of Globodera sp., identified as Neocosmospora stercicola. The fungal filtrates of the strains were evaluated for their nematicidal activity against three species of PPNs: Aphelenchoides besseyi, Bursaphelenchus xylophilus and Ditylenchus destructor. The fermentation filtrates of two strains exhibited substantial toxicity towards the evaluated nematodes, with mortality rates reaching up to 100% within 72 h. Concurrently, N. stercicola also demonstrated predatory and parasitic behavior. The eggs of Globodera sp. were parasitized by the two strains. N. stercicola represents a newly recorded species in China and a novel nematophagous species. In conclusion, the two strains of N. stercicola show promise as biocontrol agents for PPNs management.