|Cooper, William - Rodney|
Submitted to: Journal of Insect Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/24/2011
Publication Date: 10/20/2011
Citation: Cooper, W.R., Kinney, L.R. 2011. Chestnut species and jasmonic acid treatment influence development and community interactions of galls produced by the Asian chestnut gall wasp, Dryocosmus kuriphilus. Journal of Insect Science 11:140. Interpretive Summary: American chestnut was once a dominant canopy tree in Appalachian forests prior to the introduction of the fungus that causes chestnut blight. Chinese chestnut is a commercially important nut crop that is resistant to the blight. Efforts are underway to transfer blight resistance from Chinese chestnut to American chestnut for restoration purposes. Both chestnut species are attacked by insect pests, many of which are not native to the U.S. and are poorly understood. One of these pests is the Asian chestnut gall wasp, which manipulates the growth of chestnut to produce complex growths (galls) that provide food and shelter to the young of the gall wasp. Jasmonic acid is a plant chemical involved in defense against insects and pathogens, and in regulation of certain plant growth and nutritional processes. These plant responses can be activated by application of jasmonic acid, and diminished by application of a jasmonic acid inhibitor. We examined the effects of application of jasmonic acid or its inhibitor on the growth of chestnut galls, survival of gall inhabitants, and attack by natural enemies. Jasmonic acid treatment on Chinese chestnut galls increased gall size, defenses, and survival of gall inhabitants, but the inhibitor had no effect. Jasmonic acid treatment on American chestnut galls had no effect, but application of the inhibitor reduced gall size, defenses, and gall wasp survival. Although jasmonic acid activates defenses against many insect herbivores, our results suggest that it may benefit gall wasps by increasing gall defenses and quality. Overall, Chinese chestnut galls were more often attacked by natural enemies (parasites) than American chestnut galls. This suggests that the common parasitoid of the Asian chestnut gall wasp may not be an effective natural enemy on American chestnut galls.
Technical Abstract: Jasmonic acid (JA) is a plant-signaling compound involved in defenses against insects and pathogens, and in the regulation of nutrient partitioning. Gall wasps (Hymenoptera: Cynipidae) induce the formation of structures (galls) on their host plants which house immature wasps and provide them with nutrition and protection. The goal of our study was to investigate the affects of JA manipulations on gall development and defenses. We treated Dryocosmus kuriphilus galls on American (Castanea dentata) and Chinese (C. mollissima) chestnuts with JA or a JA-inhibitor, diethyldithiocarbamic acid (DIECA), and measured the effects of these treatments on gall characteristics and defenses. Chinese chestnut galls treated with JA had greater volume and dry weight, thicker schlerenchyma layers, and fewer external fungal lesions compared with controls. Galls from both chestnut species that were treated with JA contained a lower proportion of chambers that were empty, and elevated tannin levels compared with controls. The effects of DIECA on galls were generally opposite from those of JA. American chestnut galls treated with DIECA had lower dry weight and fewer feeding punctures caused by the lesser chestnut weevil, Curculio sayi, compared with controls. Galls from both chestnut species that were treated with DIECA were smaller with more external fungal lesions compared with controls. Compared to American chestnut galls, Chinese chestnut galls had increased parasitism rates and fewer gall wasps. Our study is the first to investigate the effects of JA on an insect gall, and indicates that JA treatments benefit gall wasps by increasing gall quality and defenses.