Plants produce diverse secondary compounds as natural protection against microbial and insect attack. Most of these compounds, including bitters and acids, are sensed by insect gustatory receptors (Grs). Although some organic acids are attractive at low or moderate levels, most acidic compounds are potentially toxic to insects and repress food consumption at high concentrations. At present, the majority of the reported sour receptors function in appetitive behaviors rather than aversive taste responses. Here, using two different heterologous expression systems, the insect Sf9 cell line and the mammalian HEK293T cell line, we started from crude extracts of rice (Oryza sativa) and successfully identified oxalic acid (OA) as a ligand of NlGr23a, a Gr in the brown planthopper Nilaparvata lugens that feeds solely on rice. The antifeedant effect of OA on the brown planthopper was dose dependent, and NlGr23a mediated the repulsive responses to OA in both rice plants and artificial diets. To our knowledge, OA is the first identified ligand of Grs starting from plant crude extracts. These findings on rice–planthopper interactions will be of broad interest for pest control in agriculture and also for better understanding of how insects select host plants.

S. pupariae is a newly discovered species of parasitoid wasps. Research into its development, behavioral genetics, and molecular mechanisms provides valuable insights for improving integrated pest management strategies. Quantitative real-time PCR (qRT-PCR) is the most commonly used method for analyzing gene expression. This method requires the identification of stable reference genes to accurately evaluate transcriptional level variations. In this study, eight candidate reference genes (TUB, TBP, RPS18, GAPDH, 18S rRNA, RPL32, Actin, and EF1-α) were identified and evaluated for their suitability as reference genes. Gene expression levels across different developmental stages were analyzed using three software tools, GeNorm, NormFinder, and BestKeeper, and the online tool RefFinder. The overall ranking of reference gene stability was as follows: RPS18 > 18S rRNA > RPL32 > GAPDH > Actin > TUB > TPB > EF1-α. Ultimately, RPS18 was determined to be the most stable reference gene.

Sclerodermus guani is the most extensively studied and widely used parasitoid wasp for controlling forest trunk-boring pests in China, with temperature being a key environmental factor affecting its development and reproduction. Against the backdrop of global climate change, the frequency of heat stress on parasitoid wasps is increasing. Therefore, studying their adaptability to heat stress is of great significance for breeding heat-tolerant strains. The findings of such research may help improve efficiency in rearing this wasp and provide guidance for its use in pest control. This study investigated the thermal adaptability of the wasp at temperatures ranging from 21 to 33 °C. The results showed that temperature significantly affected its parasitism capacity and behavior. As temperature increased, female wasps searched for and stung hosts more actively, and their pre-oviposition period decreased, as well as their developmental duration. The reproductive fitness of the wasp also varied significantly with temperature, with the most favorable temperatures being 27 °C and 30 °C. Both low and high temperatures were detrimental to its reproduction, and the difference in the number of female offspring was significant. The experimental results indicate that S. guani has higher reproductive fitness at 27–30 °C. Therefore, it is recommended that this parasitoid wasp be reared indoors at 27–30 °C and released for pest control in forests when the temperature is above 24 °C.

Sclerodermus sichuanensis, a parasitic wasp, plays a significant role in wood-boring forest pest control in China. Research has shown that the photoperiod significantly affects the development and reproduction of parasitic wasps. However, the effects of the photoperiod on S. sichuanensis have not yet been reported. This study investigates the impact of different photoperiods on the developmental duration and reproduction of S. sichuanensis. The wasps were reared under four photoperiod conditions: 0L:24D, 8L:16D, 16L:8D, and 24L:0D. The results show that increased light duration shortened the egg, larval, and pupal stages, with the total developmental period decreasing by up to 17 days. The number of offspring was highest in the 8L:16D and 16L:8D treatments, while constant light (24L:0D) led to a significant decrease in offspring numbers. The parasitism rate and pre-oviposition period were also affected by light exposure, with the longest pre-oviposition period observed in complete darkness. These findings indicate that the photoperiod plays a crucial role in regulating the development and reproductive efficiency of S. sichuanensis, suggesting that appropriate light conditions could enhance the efficiency of its use in pest control.

Sclerodermus guani Xiao et Wu, Sclerodermus sichuanensis Xiao, Sclerodermus pupariae Yang et Yao, and Sclerodermus alternatusi Yang are four species of Sclerodermus that have been found in China on longhorn or buprestid beetle hosts. These parasitoids are of great importance to forest management because they control certain forest pests. Knowledge of their developmental differences is important for maximizing their use in bio-control programs, yet little about them is known. This study compared their number of offspring and developmental biology. There were significant differences in the four parasitoids’ egg, larval, pupal, and total developmental stages. The F₂ male offspring of each parasitoid emerged approximately one day ahead of the female. Additionally, there were differences in the number of F₂ male and female offspring, as well as in the sex percentage, among the four parasitoids. Compared to the other three wasps, S. alternatusi had a significantly lower F₂ female percentage of 67.07%, which was notably less than that of the other wasps (over 90%). The total F₂ offspring number and F₂ female offspring number of S. guani were the greatest. Sclerodermus alteratusi produced a larger percentage of winged females (5.66%) compared to S. pupariae (3.98%), and no winged females developed from S. guani or S. sichuanensis. Almost all individuals survived the 30-day experiment, the survival rate decreased to about half after 120 days at 12 °C, and there was no difference between the species. The biological differences between the four wasp species analyzed in this study will help improve the effectiveness of mass-rearing them for the biological control of forest pests.