Effect of increasing rate of insecticides on its selectivity for Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae)

Abstract

The present study evaluated the effect of different rates of chlorantraniliprole, chlorantraniliprole + lambda-cyhalothrin, spinosad, and chlorfenapyr on their selectivity for the pupae and adults of Trichogramma pretiosum. The negative effect of majority of the insecticides tested on most of the parasitoids was directly proportional to the rate of the insecticide applied. Chlorantraniliprole at a rate of 10 g a.i. ha-1 was classified as harmless (class 1) to both pupae and adults of the parasitoid. The effect of chlorantraniliprole at a rate of 20 to 50 g a.i. ha-1 varied from harmless (class 1) to slightly harmful (class 2) to the adults of T. pretiosum. Chlorantraniliprole 10 + lambda-cyhalothrin at 5 g a.i. ha-1 was classified as harmless (class 1) to the pupae and moderately harmful (class 3) to the adults of T. pretiosum. On the contrary, the highest rate of chlorantraniliprole 50 + lambda-cyhalothrin tested (i.e., 25 g a.i. ha-1) was classified as slightly harmful (class 2) to the pupae and harmful (class 4) to the adults of the parasitoid. Similarly, increasing the application rate of spinosad and chlorfenapyr also exhibited an increase in toxicity. Spinosad at a rate of 24 g a.i. ha-1 was classified as slightly harmful (class 2) and harmless (class 1) to the pupae and adults of T. pretiosum, respectively. Spinosad at 96 g a.i. ha-1 was classified as both moderately harmful (class 3) and harmful (class 4) to the pupae of the parasitoid. Chlorfenapyr at a rate of 192 g a.i. ha-1 was classified as both slightly harmful (class 2) and moderately harmful (class 3) to the pupae of T. pretiosum, whereas chlorfenapyr at 336 g a.i. ha-1 was categorized as slightly harmful (class 3) and harmful (class 4) to the pupae. These results indicate that an increase in the rate of insecticide affected T. pretiosum negatively. Therefore, higher insecticide rates should only be adopted when strictly necessary to control the target pest, because they might compromise the biological pest control process in the field.