Effect of Sublethal Tebufenozide Applications on the Mortality Responses of Epiphyas postvittana (Lepidoptera: Tortricidae) Larvae Exposed to a High-Temperature Controlled Atmosphere

Abstract

First-, 3rd-, and 5th-instar Epiphyas postvittana (Walker) were exposed to a range of tebufenozide concentrations (0–200 ppm) incorporated into synthetic diet and their subsequent development and mortality responses were determined. Tolerance of tebufenozide increased with an increase in larval stage (1st instar < 3rd instar < 5th instar). Percentage of larval mortality increased with increasing tebufenozide concentration and exposure time. The highest mortality increase for 1st and 3rd instars occurred over tebufenozide concentrations of ≤3 ppm. No larvae first exposed to tebufenozide as 1st or 3rd instars survived to pupation if ingesting concentrations of ≥1.5 and 2.5 ppm, respectively. Although 5th instars ingesting tebufenozide displayed mortality earlier than more immature life stages, mortality was ≤85% regardless of tebufenozide concentration or exposure time because of early pupation. Tebufenozide consumption by any instar tested neither significantly delayed pupation nor resulted in an increase in the incidence of pupal deformities. Third and 5th instars were exposed to sublethal tebufenozide concentrations (0–3 ppm) for 7 and 2 d, respectively, and 5th-instar survivors of both instars subjected to high-temperature controlled atmosphere treatment (2% O2, 5% CO2, 40°C). Third instars ingesting 2 and 3 ppm tebufenozide were significantly more susceptible to the high-temperature controlled atmosphere treatment as 5th instars than larvae not exposed to tebufenozide. However, 5th instars that had ingested sublethal tebufenozide concentrations displayed the same mortality responses to high-temperature controlled atmosphere treatments as 5th instars not exposed to the insect growth regulator.