Recently, the Biohazard and Safety Team from the School of Life Sciences, Nanchang University, published a research article entitled "Differential cellular and humoral immune responses of the Asian citrus psyllid Diaphorina citri to its ecto- and endoparasitoids" in Journal of Pest Science (SCI Zone 1 Top in Agricultural and Forestry Sciences, a leading journal in the field of entomology and pest science (JCR Q1)), an authoritative journal in the field of entomology. This study is the first to reveal the effects of two dominant parasitoid wasp species of the Asian citrus psyllid (Diaphorina citri) on the host's humoral and cellular immunity.

Citrus is one of the most economically important fruit crops in southern China. Huanglongbing (HLB), known as the "cancer of citrus," is naturally transmitted by the Asian citrus psyllid (Diaphorina citri). Currently, chemical control remains the primary strategy for managing D. citri. However, the long-term and excessive application of chemical pesticides has led to environmental pollution, threats to human health, and increased pest resistance. Therefore, exploring effective green pest management measures for D. citri is particularly crucial.

Parasitoid wasps are classified into endoparasitoids and ectoparasitoids based on their parasitic modes. Endoparasitoids lay eggs inside the host's body, where the larvae hatch and feed on the host's internal tissues and hemolymph for development. In contrast, ectoparasitoids deposit their eggs on the host's surface, with larvae feeding on nutrients externally. Parasitoid wasps regulate hosts through multiple mechanisms, including manipulating the host's immune response to ensure successful parasitism and the normal development of their offspring, ultimately leading to the death of the host pest and effective control of the pest population. Tamarixia radiata (an ectoparasitoid) and Diaphorencyrtus aligarhensis (an endoparasitoid) are key components of biological control for D. citri. They can effectively suppress D. citri populations in natural environments and show considerable promise for practical application. Nevertheless, there have been no previous reports on the effects of these two parasitoid wasp species on the immune response of D. citri.

Figure 1: Parasitism of D. citri nymph by T. radiata or D. aligarhensis.

This study is the first to describe the morphological characteristics of five types of hemocytes in the hemolymph of D. citri nymphs. It was found that parasitism by T. radiata resulted in a significant reduction in the number of adherent hemocytes of the host; after a transient decrease in the proportion of prohemocytes, the proportion of granulocytes increased. In contrast, parasitism by D. aligarhensis only slightly altered the hemocyte distribution of D. citri.

Figure 2: Hemocytes in citrus psyllid hemolymph.

Figure 3: Changes in the different hemocyte types after parasitism.

Detection of the expression of immunity-related genes in the Imd, JAK/STAT, Toll, and PO pathways of D. citri after parasitism showed that both parasitoid wasp species significantly affected these pathways, but the magnitude and temporality of the effects differed. At 24 and 48 hours after parasitism by Tamarixia radiata, the immune genes of D. citri remained significantly affected; whereas at 48 hours after parasitism by D. aligarhensis, the expression levels of the relevant genes in D. citri had returned to basal levels or were slightly downregulated. These findings supplement our understanding of the mechanisms underlying the cellular and humoral immunity of D. citri and fill the gaps in the research on the interaction mechanisms between the immune systems of D. citri and its parasitoid wasps.

Figure 4: Effect of T. radiata parasitism on the immune pathways of D. citri nymphs.

Figure 5: Effect of D. aligarhensis parasitism on the immune pathways of D. citri nymphs.

This research provides an important theoretical and experimental groundwork for the effective control of Diaphorina citri—thereby blocking the transmission of Huanglongbing—by regulating the immune system of Diaphorina citri in future studies. Paper link: https://doi.org/10.1007/s10340-025-01998-9

Master's students Zhuo Yu and Liwen Feng from Nanchang University are the first authors of the paper, and Associate Professor Bin Wan is the corresponding author. Professor Bin Xia from the School of Life Sciences, Nanchang University, and Researcher Jean-Luc Gatti from the University of Côte d’Azur, France, provided important support and guidance for the research and manuscript writing. Graduate students Mohao Xiong, Wenfeng Hu, Jun Zhong, and Cong Zhang also participated in the study. This research was supported by the National Natural Science Foundation of China (Grant Nos. 32460702 and 32102204) and the Natural Science Foundation of Jiangxi Province (Grant No. 20224BAB215021).

In recent years, The Biological Disasters and Safety Team at Nanchang University has focused on key pests such as Diaphorina citri (the vector of citrus Huanglongbing) and the citrus red mite (Panonychus citri). The team has collaborated on tackling key scientific issues related to the development and application of biological control using natural enemies and novel RNAi-based biopesticides.