Introduction
Name: JIANG Zi-Ru
Location: Nagoya University, Japan
Email: ziru.jiang[at]gmail.com ；jiang.ziru.n8[at]f.mail.nagoya-u.ac.jp
Research Achievements and Results
Title: Flora of fungi associated with an ambrosia beetle (Euwallacea interjectus (Blandford)) attacking fig tree, tree-pathogenic risk of the fungi, and predatory behavior of a natural enemy of the beetle
An ambrosia beetle, Euwallacea interjectus (Blandford) (Coleoptera: Curculionidae: Scolytinae), was found in the fig trees infested with fig wilt disease and occurred extensively as a suspected vector of plant pathogenic fungus, Ceratocystis ficicola, in Japan (Kajitani 1996, 1999). C. ficicola causes serious wilt disease in many fig orchards in Japan. Ambrosia beetles have specialized structures termed mycangia (fungus-carrying organ), special fungal symbionts (fungal spores or hyphae) are contained and allowed to proliferate in their mycangia. The adult and larva feed on fungal mycelia which are inoculated into the xylem and develop on the walls of the galleries tunneled in the sapwood by the colonizing adult females. Details of the structure and location of mycangia are important for a complete understanding of ambrosia beetles’ biology. However, the real way by which E. interjectus declined fig tree was still unknown. My PhD research work mainly focused on exploring the location and structure of mycangia and fungal symbionts of adult female E. interjectus.
Project 1. Mycangia and fungal symbionts of E. interjectus
This previous study showed C. ficicola was most frequently isolated from the beetle’s elytra as compared to other body parts. However, the role of mycangia in transmitting the pathogenic fungi has never been investigated, more information on the location and structure of mycangia of E. interjectus is necessary to improve the understanding of vectoring this fungal pathogen. In my study, I non-destructively examined the morphology of mycangia for adult female E. interjectus using micro-CT. Paired mycangia were first observed on typical CT cross-sections of the head. Each mycangium, ovoid in shape, was located in tissues just posterior to emarginated notch of eyes, adjacent to pharynx (Jiang et al., Entomological Science, 2019).
For further studies on the fungal symbionts of E. interjectus, I identified and compared the fungal symbionts between wild and rearing E. interjectus. Isolated fungi were identified based on morphological characteristics and DNA sequence data.
Regardless of the wild and rearing populations, Fusarium sp. is closely associated with female adults of E. interjectus. The present research showed C. ficicola is not transmitted via mycangia of E. interjectus (Jiang et al., Poster Presentations, 2018, 2019).
Project 2. The role of mycangial fungi of E. interjectus in fig wilt disease
In order to verify the role of the mycangial fungi (Fusarium sp.), I used three kinds of inoculation treatment (T1: Fusarium sp., T2: C. ficicola, T3: Fusarium sp. + C. ficicola) for fig saplings. As a control, sterilized toothpicks were also inserted into the saplings. As an initial external symptom, the saplings in T2 and T3 started wilting around 12 days after inoculation, and all of the saplings finally died. The wilting speed of fig saplings inoculated with Fusarium sp. + C. ficicola was 7 days faster than that with C. ficicola. No wilt symptom was observed on T1 and the control.
To evaluate water-transporting function in the main stems, I did xylem sap-conduction test by injection of acid fuchsin solution and observed xylem discoloration turning brown (necrosed tissue) near the inoculation site in all of the treatments including the control 28 days after inoculation. The longitudinal range of the discoloration extended in T3 (40 cm) was much longer than that in T2 (30 cm), in terms of the upward distance from the inoculation site. These facts suggest that Fusarium sp. may be a potential causal agent of xylem dysfunction in fig tree, although it did not seem to directly kill the tree.
Project 3. Earwig preying on ambrosia beetle: Evaluating predatory process and prey preference
In the laboratory, I set up a test arena, then observed and recorded behavioral interactions between A. marginalis and E. interjectus. The result shows that A. marginalis is actually a predator of E. interjectus and other species of ambrosia beetle, indicating its high potential for use in effective pest control in the field. The predators strongly select their prey depending on prey size, rather than sex or beetle species (Jiang et al., Poster Presentations, 2019; Jiang and Kajimura, 2020).
More Information
For more information, please click on the following websites
ORCID iD: https://orcid.org/0000-0003-1378-1646