Abstract: The aim of this study was to determine the effects of Trichogramma ball color on the temperature and the emergence rate of Trichogramma chilonis inside the ball under the condition of sun exposure. In this study, the temperatures inside Trichogramma balls of different colors were measured under sun exposure or shade in sugarcane fields at varying air temperatures. The temperature and the emergence rates of T. chilonis inside Trichogramma balls of different colors were measured at an air temperature of 31℃ in sun exposure. And the percentages of the emerged T. chilonis flying out of the Trichogramma balls of different colors were also observed. Under sun exposure, the temperature inside brown balls is the highest, followed by red balls and white balls. The temperature in the balls is higher than the ambient temperature. Under sun exposure and air temperature of 23 ℃—31 ℃, the temperature outside the ball did not exceed 38 ℃, whereas the temperature inside the ball rose sharply after 5—10 minutes under sunlight. The temperatures inside the white, red and brown balls were 0 ℃—11.2 ℃, 1 ℃—12.5 ℃ and 1.5 ℃—20.2 ℃ higher than the temperature outside the balls, respectively. Multivariate analysis of variance indicated that the air temperature, the Trichogramma ball color and the time of sun exposure had significant effects on the temperature inside the ball. Under shade in the sugarcane fields, there were no significant differences between the temperatures inside the white and red balls and the ambient temperature. The temperature inside the balls could rise to more than 45 ℃ when the balls were exposed to sunlight for 5 minutes at an air temperature of 31 ℃, but the emergence rate of T. chilonis inside the balls showed no significant difference compared with that of T. chilonis held at 26 ℃ in the laboratory. The emergence rates of T. chilonis inside the red and brown balls were significantly lower than that inside the white balls when exposured to sunlight for over 10 minutes, and the emergence rates of T. chilonis inside the balls decreased significantly when the exposure to sunlight exceeded 30 minutes. No emergence of T. chilonis were recorded when the balls were exposed to direct sunlight for more than 60 minutes. Two factors analysis of variance showed that both the time of direct sunlight exposure at high temperature and the color of Trichogramma ball had significant effects on the emergence rates of T. chilonis inside the ball. The ball color had no significant effect on the percentage of the emerged T. chilonis inside the ball flying out of the ball. These results shed light on improving the field release technology of Trichogramma and determining suitable temperature and ball color for the release Trichogramma ball.

Key words: Trichogramma chilonis, solarization high temperature, Trichogramma release ball, plant protection unmanned aerial vehicle