The tea grey geometrid Ectropis grisescens has long been a significant insect pest of tea plants in China. Two parasitoids, Parapanteles hyposidrae and Protapanteles immunis (Hymenoptera: Braconidae: Microgastrinae), are the most important parasitoids in the larval stage of E. grisescens. Yet, the potential of these two parasitoids for controlling the tea grey geometrid is not known. Here, we studied the parasitism performance of these two parasitoid species on different host densities under different temperatures as well as the interference effect of parasitoid density. The results showed that both parasitoid species, Pa. hyposidrae and Pr. immunis, exhibited a Type II functional response towards the tea grey geometrid E. grisescens at four tested temperatures. With increasing the density of E. grisescens larvae, the number of parasitized larvae increased until a maximum was reached. The highest number of hosts parasitized by Pa. hyposidrae or Pr. immunis reached 14.5 or 14.75 hosts d⁻¹ at 22 °C, respectively. The estimated values of instantaneous searching efficiency (a) and handling time (h) for Pa. hyposidrae or Pr. immunis were 1.420 or 3.621 and 0.04 or 0.053 at 22 °C, respectively. Pr. immunis performed better than Pa. hyposidrae under higher temperatures. The parasitism rate by a single female parasitoid decreased with increasing parasitoid density at different temperatures, resulting in a reduction of searching efficiency. The findings of this study showed that Pr.immunis could be a better effective biocontrol agent than Pa. hyposidrae against the tea grey geometrid.

The biological insecticide, Ectropis obliqua nucleopolyhedrovirus (EcobNPV), has been applied to control the major tea-pest Ectropis grisescens. Previously, the virus strain EcobNPV-QF4 showed higher a mortality rate (58.2% vs. 88.2%) and shorter median lethal-time (13.9 d vs. 15.4 d) on E. grisescens than the strain EcobNPV-QV. However, the mechanism of the difference in virulence between the two strains remains unclear. Using the leaf-disc method, we detected the virulence of the two strains on 3^rd-instar larvae, and found that median lethal-dose (LD₅₀) of EcobNPV-QF4 is 55-fold higher than that of EcobNPV-QV (4.35 × 10⁸ vs. 7.89 × 10⁶). Furthermore, fourteen larva transcriptomes of E. grisescens were subsequently sequenced at seven time-points after ingestion of the two virus strains, yielding 410.72 Gb of raw reads. Differential gene-expression analysis shows that 595, 87, 27, 108, 0, 12, and 290 genes were up-regulated in EcobNPV-QF4 at 0, 2, 6, 12, 24, 36 h and 48 h post ingestion (hpi), while 744, 68, 152, 8, 1, 0, 225 were down-regulated. KEGG enrichment showed that when the virus first invades (eats the leaf-discs), EcobNPV-QF4 mainly affects pathways such as ribosome (p-value = 2.47 × 10⁻²⁹), and at 48 hpi EcobNPV-QF4, causes dramatic changes in the amino-acid-synthesis pathway and ribosome pathway (p-value = 6.94 × 10⁻¹³) in E. grisescens. Among these, thirteen key genes related to immunity were screened. The present study provides the first ever comprehensive analysis of transcriptional changes in E. grisescens after ingestion of the two strains of EcobNPV.

Ectropis grisescens (Lepidoptera: Geometridae) is a destructive pest in tea plantations, leading to significant economic losses through defoliation. Existing control strategies, including chemical insecticides and biological agents, are often limited by environmental concerns, resistance, and variable efficacy. Recent evidence suggests that bacteria influence insect physiology and could be leveraged for pest management, but the postmortem microbial ecology of E. grisescens remains uncharacterized. In this study, we employed 16S rRNA sequencing to investigate temporal changes in the bacterial communities of E. grisescens cadavers at 0, 7, and 21 days following cryogenic mortality. Our results indicate a time-dependent decline in microbial diversity, while species richness initially increased before subsequent reduction. The dominant endosymbiont Wolbachia gradually diminished after host death, whereas Enterobacter remained abundant. Notably, non-dominant genera including Lysinibacillus and Sporosarcina exhibited a transient increase in abundance at day 7 before reverting to control levels by day 21. This study presents the first comprehensive analysis of postmortem microbial succession in a lepidopteran system, highlighting dynamic shifts in bacterial composition and offering potential avenues for microbiome-based pest management strategies.

Ectropis obliqua nucleopolyhedrovirus (EcobNPV) is an important biocontrol agent against Ectropis obliqua and E. grisescens. A previously isolated strain, EcobNPV-QF4, exhibits significantly higher virulence than the original strain EcobNPV-QV, yet the molecular basis for this difference remains unclear. Leaf-dipping bioassays demonstrated that EcobNPV-QF4 caused significantly higher larval mortality than EcobNPV-QV from 10 dpi onward, reaching 97.9% versus 33.8% at 16 dpi, and higher pupal mortality (100% versus 47.3%), confirming its superior virulence across both larval and pupal stages. To investigate the transcriptional dynamics underlying virulence variation, we performed a comparative time-course transcriptomic analysis of E. grisescens infected with either strain at 0, 2, 6, 12, 24, 36, and 48 h post-infection. The reliability of the RNA-seq data was validated by qRT-PCR for selected expressed genes. The results showed that, relative to EcobNPV-QV, the EcobNPV-QF4 strain exhibits a transcriptional strategy characterized by comprehensive and accelerated activation: the transcriptional initiation of its functional modules is globally advanced by approximately 6 h compared with EcobNPV-QV, and genes associated with midgut escape, virion assembly, and viral DNA replication are preferentially and coordinately expressed, resulting in a more synchronized transcriptional profile. Based on these findings, we hypothesize that the enhanced virulence of EcobNPV-QF4 is not attributable to a single factor but rather reflects a synergistic, multitiered acceleration of transcriptional progression that may compress the infection cycle and enhance viral dissemination efficiency. These findings provide critical insights into the molecular mechanisms that may underlie baculovirus virulence and provide a basis for future mechanistic studies.