Background: The parasitoid wasp, Trichogramma dendrolimi, can enter diapause at the prepupal stage. Thus, diapause is an efficient preservation method during the mass production of T. dendrolimi. Previous studies on diapause have mainly focused on ecological characteristics, so the molecular basis of diapause in T. dendrolimi is unknown. We compared transcriptomes of diapause and non-diapause T. dendrolimi to identify key genes and pathways involved in diapause development. Results: Transcriptome sequencing was performed on diapause prepupae, pupae after diapause, non-diapause prepupae, and pupae. Analysis yielded a total of 87,022 transcripts with an average length of 1604 bp. By removing redundant sequences and those without significant BLAST hits, a non-redundant dataset was generated, containing 7593 sequences with an average length of 3351 bp. Among them, 5702 genes were differentially expressed. The result of Gene Ontology (GO) enrichment analysis revealed that regulation of transcription, DNA-templated, oxidation-reduction process, and signal transduction were significantly affected. Ten genes were selected for validation using quantitative real-time PCR (qPCR). The changes showed the same trend as between the qPCR and RNA-Seq results. Several genes were identified as involved in diapause, including ribosomal proteins, zinc finger proteins, homeobox proteins, forkhead box proteins, UDP-glucuronosyltransferase, Glutathione-S-transferase, p53, and DNA damage-regulated gene 1 (pdrg1). Genes related to lipid metabolism were also included. Conclusions: We generated a large amount of transcriptome data from T. dendrolimi, providing a resource for future gene function research. The diapause-related genes identified help reveal the molecular mechanisms of diapause, in T. dendrolimi, and other insect species.

Trichogramma dendrolimi is one of the most successfully industrialized Trichogramma species used to control agricultural and forestry pests in China. However, the molecular mechanisms underlying its host recognition and parasitism remain largely unknown, partially due to the limited genome information of this parasitoid wasp. Here, we present a high-quality de novo assembly of T. dendrolimi through a combination of Illumina and PacBio sequencing technologies. The final assembly had a length of 215.2 Mb and contains 316 scaffolds with a scaffold N50 size of 1.41 Mb. Repetitive sequences with a length of 63.4 Mb and 12,785 protein-coding genes were identified. Significantly expanded gene families were identified to be involved in the development and regulatory processes, while remarkably contracted gene families were involved in the transport processes in T. dendrolimi. The olfactory and venom-associated genes were identified in T. dendrolimi and 24 other hymenopteran species, using uniform methods combining BLAST and HMM profiling. The identified venom genes of T. dendrolimi were enriched in antioxidant activity, tricarboxylic acid cycle, response to oxidative stress and cell redox homeostasis. Our study provides an important resource for comparative genomics and functional studies to interpret the molecular mechanisms underlying host recognition and parasitism of Trichogramma species.

Trichogramma dendrolimi Matsumura is widely used as a biological control agent of many lepidopteran pests. Diapause has been used as an effective method to preserve the Trichogramma products during mass rearing production. However, it currently takes at least 70 days to break diapause, and we tested whether gradually increasing the temperature instead of using constant temperature could reduce the time of diapause termination and offer a higher flexibility to Trichogramma producers. The diapause termination rates of individuals kept at different conditions were measured, and five groups for which diapause termination rate reached the 95% were selected to test five biological parameters, including the number of eggs parasitized, the parasitism and emergence rates, the female sex ratio, the wing deformation rate, and the parasitoid longevity. Compared to the currently used procedure (70 days at 3 °C), treatments with at least two different temperatures resulted in higher parasitism and emergence rates while keeping the other parameters constant. The treatment that consisted of at least two different temperatures preceded by only 55 days of induction period had the highest population trend index, meaning that the population under these conditions grows more rapidly. Our results demonstrate that gradually increasing temperature allows T. dendrolimi to complete diapause earlier than at present while increasing its potential pest control capacity and providing additional flexibility in mass production of T. dendrolimi.

Frogeye leaf spot (FLS), caused by Cercospora sojina, is a significant disease affecting soybean crops economically. Seed inspection plays a vital role in reducing the incidence of this disease. However, limited research has been conducted on the fast and accurate identification of C. sojina in soybean seeds. In this study, we developed a rapid diagnostic method to detect C. sojina in soybean seeds using loop-mediated isothermal amplification (LAMP) assays. A software application called K-mer Elimination by Cross-reference was utilized to identify specific sequences belonging to C. sojina. The LAMP primer set designed based on the selected specific sequence proved to be highly specific, distinguishing C. sojina from other common soybean pathogens and two maize pathogens of the Cercospora genus. The primer set exhibited remarkable sensitivity, detecting sixteen copies per reaction, which is approximately 1,000 times more sensitive than conventional PCR. The LAMP assays were applied for direct inspection of soybean seeds, revealing that twenty of the thirty tested soybean varieties were contaminated with C. sojina, with contamination rates ranging from 10% to 60%. The seeds of TongNong 943 and JiNong 38 had the highest contamination rate at 60%. Seeds coated with fungicide showed a reduced disease incidence, as demonstrated on PDA medium and in soil pots. In summary, our results indicate that rapid seed diagnosis using LAMP assays can effectively screen out seeds carrying C. sojina, providing a preventive strategy in managing FLS disease.