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.

Trichogramma wasps, egg parasitoids widely used to control lepidopteran pests, have long eluded in-depth molecular mechanistic studies due to their minute size and genetic tool scarcity. While previous RNAi efforts were restricted to T. dendrolimi, we developed the first cross-species RNAi system for both T. dendrolimi and the previously intractable T. ostriniae. Temporal expression profiling identified white and laccase 2 as stage-specific RNAi targets, peaking during prepupal/pupal stages, which were tested across species and developmental stages using microinjection and soaking dsRNA delivery methods. Survival analysis prioritized soaking for T. dendrolimi prepupae/pupae, while microinjection was essential for T. ostriniae to bypass prepupal mortality during soaking. Concentration-dependent RNAi targeting the white gene achieved 85.61% transcript reduction in T. dendrolimi via soaking and 89.36% in T. ostriniae via microinjection at 2000 ng/μL, correlating with 64.06% and 32.09% white-eyed pupae, causing a significant reduction in eye pigments. For the laccase 2 gene, soaking at 2000 ng/μL induced 88.35% transcript reduction in T. dendrolimi and 73.31% in T. ostriniae, leading to incomplete cuticle tanning and sclerotization. This study resolves the long-standing challenge of genetic manipulation in Trichogramma wasps, providing a universally applicable framework to decipher parasitoid–host interactions at the molecular scale, which is useful for sustainable pest management strategies.

Background The parasitoid insect Trichogramma dendrolimi can successfully 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 focused mostly on ecological characteristics, so the molecular mechanism of diapause in T. dendrolimi is mostly unknown. In this study, we compared transcriptomes of diapause and non-diapause T. dendrolimi to identify genes involved in the development of diapause. Results Transcriptome sequencing was performed using different samples, including diapause prepupae, pupae after diapause, normal prepupae, and pupae. This initially yielded a total of 87,022 unigenes with an average length of 1,604 bp. By removing redundant sequences and those without significant BLAST hits, a non-redundant dataset was generated, containing 7,593 sequences with an average length of 3351 bp. Among the differentially expressed genes, 1,204 were specifically expressed during the diapause stage, and 820 were significantly up-regulated. The result of GO enrichment analysis revealed that binding, oxidation−reduction process, and ribosome biogenesis were significantly affected. Ten genes were selected for validation using a quantitative real-time PCR (qPCR). The changes showed the same trend between the qPCR and RNA-Seq results. Based on previous studies and our data, several genes were identified to be involved in diapause, including UDP-glucuronosyltransferase; Glutathione-S-transferase, ATGs, zinc finger protein genes, cell cycle-related genes, Trehalase, trehalose transporter, hsp68, p53, and DNA damage-regulated gene 1 (pdrg1), and genes related to lipid metabolism were also included. Conclusions In this study, we generated a great amount of transcriptome data from T. dendrolimi, providing a resource for gene function research. The diapause-related genes that we identified establish a valuable basis for future studies on the molecular mechanisms of diapause, not only for T. dendrolimi, but for other species as well.