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Title: Pre-release assessment of Gadirtha inexacta a proposed biological control agent of Chinese tallow (Triadica sebifera) in the United States

item WANG, Y - Chinese Academy Of Sciences
item ZHU, L - Chinese Academy Of Sciences
item XUE, G - Chinese Academy Of Sciences
item Wheeler, Gregory
item PURCELL, M - Commonwealth Scientific And Industrial Research Organisation (CSIRO)
item DING, J - Chinese Academy Of Sciences

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/24/2012
Publication Date: 9/7/2012
Citation: Wang, Y., Xhu, L., Xue, G., Wheeler, G.S., Purcell, M., Ding, J. 2012. Pre-release assessment of a noctuid Gadirtha inexacta (=Iscadia inexacta) proposed as a biological control agent of Chinese tallow (Triadica sebifera) in the United States. Biological Control.

Interpretive Summary: The weed, Chinese tallow, Triadica sebifera, is a weed of coastal prairies and forests in the southeastern US. Current management tactics, such as chemical and mechanical controls, are not sustainable solutions considering that Chinese tallow grows rapidly and produces a large number of seeds annually. Biological control is a permanent and cost-effective alternative means of Chinese tallow suppression. Surveys conducted in China discovered a promising caterpillar, Gadirtha inexacta that is being considered for biological control of this invasive weed. Results are presented that show this insect completed development on only three of the 46 plant species tested and all were close relatives of the weed that do not occur in the US. Additionally, field examinations conducted in China of the target weed and neighboring plants indicate the insect only occurred on the target weed. Impact studies indicate that single, and especially two generations, of larval damage significantly reduced seedling growth and increased mortality. These results indicate that this potential biological control agent shows promise for safe control of this weed in the US and will be tested under quarantine conditions on North American plants.

Technical Abstract: Native to China, Chinese tallow, Triadica sebifera (Euphorbiaceae) is an aggressive woody invader in the southeastern United States. The noctuid, Gadirtha inexacta, is a multivoltine herbivore attacking this plant in China. To evaluate its potential as a biological control agent in the United States, we conducted experiments on the host specificity and impact on the target weed in China. The host range was tested on 81 plant species in 20 families through no-choice larval development tests and field surveys. The results showed that G. inexacta could only complete development on T. sebifera, T. rotundifolia and Sapium chihsinianum, suggesting a narrow host range. Attack by G. inexacta larvae significantly reduced the growth of T. sebifera and the impact was greater when the plant was repeatedly defoliated and in shaded conditions. The plants were entirely defoliated after being repeatedly damaged in the treatments of the highest larval density (six larvae per seedling) in shade, causing 80% seedling mortality and the total biomass was reduced to 60% of the control. The results of this study suggested that G. inexacta is a potential biological control agent of T. sebifera though further tests on native North American species are needed.