Impact of Cotesia flavipes (Hymenoptera: Braconidae) as an augmentative biocontrol agent for the sugarcane borer (Lepidoptera: Crambidae) on 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) on rice. A lab experiment showed that the number of hosts parasitized per female per day reached a maximum (0.961) at 28 °C. Parasitized larvae recovered from the field experiment produced an average of 27.9 ± 19.1 ( x ¯ ± s.d.) parasitoids, with a 2.57:1 (female/male) 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. C. 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 and 4 males m−2. The maximum simulated economic benefit ($59.48 ha−1) is ca. 6.7% of that provided by insecticide-based control, which occurred when the release rate was 1 female and 0.4 males m−2. 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 spring emerging parasitoids to find hosts.