Kaori Yara

Disarming the Jasmonate-Dependent Plant Defense Makes Nonhost Arabidopsis Plants Accessible to the American Serpentine Leafminer

Loss of jasmonate-dependent plant defense converts nonhost plants to host plants that are accessible to leafminers, and demonstrates a role for jasmonate in regulating host plant suitability of herbivores. Here, we analyzed the interaction between Arabidopsis (Arabidopsis thaliana) and the American serpentine leafminer (Liriomyza trifolii), an important and intractable herbivore of many cultivated plants. We examined the role of the immunity-related plant hormone jasmonate (JA) in the plant response and resistance to leafminer feeding to determine whether JA affects host suitability for leafminers. The expression of marker genes for the JA-dependent plant defense was induced by leafminer feeding on Arabidopsis wild-type plants. Analyses of JA-insensitive coi1-1 mutants suggested the importance of JA in the plant response to leafminer feeding. The JA content of wild-type plants significantly increased after leafminer feeding. Moreover, coi1-1 mutants showed lower feeding resistance against leafminer attack than did wild-type plants. The number of feeding scars caused by inoculated adult leafminers in JA-insensitive coi1-1 mutants was higher than that in wild-type plants. In addition, adults of the following generation appeared only from coi1-1 mutants and not from wild-type plants, suggesting that the loss of the JA-dependent plant defense converted nonhost plants to accessible host plants. Interestingly, the glucosinolate-myrosinase defense system may play at most a minor role in this conversion, indicating that this major antiherbivore defense of Brassica species plants probably does not have a major function in plant resistance to leafminer. Application of JA to wild-type plants before leafminer feeding enhanced feeding resistance in Chinese cabbage (Brassica rapa), tomato (Solanum lycopersicum), and garland chrysanthemum (Chrysanthemum coronarium). Our results indicate that JA plays an important role in the plant response and resistance to leafminers and, in so doing, affects host plant suitability for leafminers.

Influence of the introduced parasitoid Torymus sinensis (Hymenoptera: Torymidae) on T. koreanus and T. beneficus as indigenous parasitoids of the chestnut gall wasp Dryocosmus kuriphilus (Hymenoptera: Cynipidae) on chestnut trees in Nagano Prefecture, Japan

We describe here the parasitoid wasps Torymus sinensis Kamijo and T. beneficus Yasumatsu & Kamijo (early-spring and late-spring strains), which are introduced and indigenous natural enemies of the chestnut gall wasp Dryocosmus kuriphilus Yasumatsu, an invasive chestnut pest in Japan. We recently discovered specimens of T. koreanus Kamijo, endemic in Korea, among Torymus parasitoids collected from D. kuriphilus galls in a Japanese chestnut orchard. In this study we compare the composition of Torymus parasitoids emerging from D. kuriphilus galls before and after the release of T. sinensis. Before the release of T. sinensis, early-spring and late-spring strains of T. beneficus predominated (58.3 and 20.8% of specimens collected). However, a few years after the release, both T. beneficus strains had been almost completely displaced by T. sinensis. In contrast to the rapid decrease in T. beneficus, T. koreanus did not decrease drastically before and even after the release of T. sinensis (approximately 10–20% of specimens collected). These results suggest that not a few T. koreanus were present in the Japanese chestnut orchard investigated at least several years after the release of T. sinensis, although both the T. beneficus strains were rapidly displaced by T. sinensis during this period.

Distribution and population structure of two phylogroups of the parasitoid Encarsia smithi (Hymenoptera: Aphelinidae) in tea fields infested with the invasive camellia spiny whitefly Aleurocanthus camelliae (Hemiptera: Aleyrodidae) in Shizuoka Prefecture, Japan

A recent study revealed that two phylogenetic groups of the parasitoid Encarsia smithi (Hymenoptera: Aphelinidae) can attack the camellia spiny whitefly Aleurocanthus camelliae (Hemiptera: Aleyrodidae), an invasive pest of Japanese tea fields. Type I was introduced in 1925 from China to Japanese citrus orchards to control the citrus spiny whitefly A. spiniferus, but it has also recently appeared in several tea fields. Type II, presumably introduced accidentally, was also found in many tea fields. However, little is known about distribution and their relative importance as a biocontrol agent in tea fields. To investigate these aspects, we developed specific PCR for the two groups using a variation in their nuclear ribosomal DNA’s ITS region. We then surveyed their distribution in 23 tea fields in Shizuoka Prefecture, Japan, from 2013 to 2015 using this specific PCR. We found that both types were distributed, sometimes coexisting, in many tea fields during 2013–2015, although the population structure of these types varied with the field, year and season. These results suggest that A. camelliae can be controlled unintentionally by accidentally introduced exotic natural enemies (Type II) and/or Type I species originally introduced to control other invasive pests such as A. spiniferus.