Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/12/2010
Publication Date: 2/20/2011
Publication URL: handle.nal.usda.gov/10113/49130
Citation: Lv, J., Wilson, L.T., Beuzalin, J.M., White, W.H., Reagan, T.E., Way, M.O. 2011. Impact of Cotesia flavipes (Hymenoptera: Braconidae) as an augmentative biocontrol agent for sugarcane borer (Lepidoptera: Crambidae) on rice. Biological Control. 56:159-169. Interpretive Summary: The larva is the destructive life stage of the sugarcane borer moth. The larvae damage crops belonging in the grass family, i.e. rice, corn, grain sorghum, and sugarcane. Controlling these larvae frequently relies on insecticides, but these are expensive to apply and there can be environmental issues associated with insecticides following their use. An alternative to insecticides is biological control or the practice of using beneficial insects to keep populations of the sugarcane borer below economically damaging levels. However, more times than not, beneficial insects do not reach sufficient numbers in fields to control the pest until it is too late, e.g. economic damage has occurred. One approach to solving this problem is to rear beneficial insects for release into the field. In this way, numbers of beneficial insects can be established in the field early in the season and in numbers sufficient to control the borer. However, this approach is also expensive and may not always provide sufficient control. In this paper the authors report research evaluating the basic parasite biology, the economics of rearing, and the expected control from the parasite Cotesia flavipes. These results are needed when determining if a biological control agent would be an appropriate candidate for artificial rearing and release. Research findings reported indicate that the targeted biological control agent would not be an appropriate candidate for release. It would be more expensive to rear than to use current insecticides and would not provide the needed control. The paper also provides information important for researchers working in the area of biological control as it provides an appropriate model for researchers that are evaluating other potential biocontrol agents.
Technical Abstract: In an effort to find an appropriate biological control agent for release in rice, a 2-year field cage experiment was conducted in Beaumont, Texas to estimate parasitism of sugarcane borer, Diatraea saccharalis (F.), by Cotesia flavipes (Cameron). The effective search rate was 0.0049 square meter ground area (2.21 tillers) per day per parasitoid. A lab experiment showed the number of host parasitized per female per day reached a maximum (0.933) at 28 'C. Parasitized larvae recovered from the field experiment produced an average of 27.9 ± 19.1 (mean ± s.d.) parasitoids, with a 2.57:1 sex ratio. A cohort-based age-structured model was developed to simulate the population dynamics and economic impact of sugarcane borer and C. flavipes in rice, as affected by overwintering larval density, timing and rate of parasitoid aerial release, and year-to-year climate (temperature and rainfall). The results suggest the cumulative seasonal damaging larval density (3rd or later instars) is negatively correlated with winter temperature, while maximum parasitoid density and maximum proportion parasitized are positively correlated with the cumulative seasonal damaging larval density. Cotesia flavipes was most effective when released 40 or 50 days after rice planting, with simulated yield loss reduced by up to 50.9% when the release rate was 10 females (14 males + females) per square meter. The maximum simulated economic benefit ($118.03 per ha) is ca. 8.7% of that provided by insecticide-based control, which occurred when the release rate was 1 female (1.4 males + females) per square meter. The inability of C. flavipes to provide economic control in temperate-subtropical areas is due to its high rearing cost, a low effective search rate, a low maximum number of hosts parasitized per female, and failure of the parasitoids that emerge in the spring to find hosts. The biocontrol capability of Trichogramma galloi Zucchi was also simulated. When the number of T. galloi released resulted in a cost equal to the insecticide-based control, this species has the potential to provide up to 94.6% egg parasitization. The maximum economic benefit provided by T. galloi was $1128.75 per ha, ca. 83.2% of that provided by insecticide-based control. Trichogramma galloi show the potential to be effective in augmentative biocontrol of the sugarcane borer in rice in subtropical-temperate climatic regions.