Biological and behavioural responses of the sugarcane borer parasitoid Tetrastichus howardi to insecticides.

The pupal parasitoid Tetrastichus howardi (Olliff) (Hymenoptera: Eulophidae) parasitizes pupae of sugarcane stalk borers inside the stalk. Parasitoids currently used for applied biological control of sugarcane stalk borers target eggs and larvae, and T. howardi will add mortality to the pest stage with high survival. Nevertheless, insecticide applications required to control sugarcane borers and other sugarcane pests can affect T. howardi parasitism. Survival, walking, evasion and parasitism of T. howardi females were evaluated in response to the dry residue of insecticides from different chemical groups: chlorantraniliprole, bifenthrin, spinetoram, ethiprole, fipronil and thiamethoxam. Females of the parasitoid were confined on sugarcane leaves containing residues of the insecticides at 2, 24, 48, 72 and 96 h intervals after application, and survival monitored during the 96‐h period with subsequent determination of parasitism in the laboratory. Furthermore, female walking behaviour was observed individually using half‐treated arenas with insecticides. Chlorantraniliprole was compatible with T. howardi irrespective of residual intervals and studied variables. Other tested insecticides did not allow parasitoid survival up to 96 h of confinement on dry residues and, consequently, parasitism. Locomotory activity indicated that parasitoid females might avoid residues of spinetoram and ethiprole. Females were released in cages containing spinetoram and ethiprole‐treated sugarcane plants with the chance to move to untreated plants, parasitized pupae placed on either treated or untreated plants within a 24 h exposure period, which resulted in offspring production. Females observed for 10 min for walking behaviour in a half‐treated arena with chlorantraniliprole, ethiprole, fipronil, spinetoram, bifenthrin or thiamethoxam exhibited 100%, 73.3%, 70%, 66.7%, 10% and 0% survival after 24 h, respectively. Chlorantraniliprole was compatible with T. howardi through the bioassays conducted, and parasitoids showed the ability to parasitize their hosts on spinetoram‐ and ethiprole‐treated plants moving away from the treated environment. [ABSTRACT FROM AUTHOR]