Cold tolerance of the spring-feeding larvae of the eye-spotted bud moth, Spilonota ocellana (Lepidoptera: Tortricidae)

Swain, J.A., Judd, G.J.R., and Cory, J.S. 2017. Cold tolerance of the spring-feeding larvae of the eye-spotted bud moth, Spilonota ocellana (Lepidoptera: Tortricidae). The Canadian Entomologist, 149: 291–299.

Abstract

In this study, we explore the low-temperature thresholds of a pest of apple (Malus pumila Miller; Rosaceae), the eye-spotted bud moth, Spilonota ocellana Denis and Schiffermüller (Lepidoptera: Tortricidae), in the context of spring frost. Spilonota ocellana overwinters as a larva, resuming activity and feeding early in the growing season when it could be vulnerable to unexpected freezing temperatures. We determined that the mean super-cooling point of spring instars did not differ for larvae within or outside leaf-shelters and ranged from -9.1 ± 0.2 °C for fourth instars, to -7.9 ± 21 0.2 °C for sixth instars. Larval weight increased with instar and was positively related to the super-cooling point. Since some insects are freeze tolerant and able to recover from freezing, we also exposed larvae to brief freeze events between -4.5 to -9.5 °C and found that the median lower lethal temperature, was -7.3 ± 0.4 °C across all instars; indicating that S. ocellana spring larval instars are susceptible to freezing temperatures above their super-cooling point. These low temperature thresholds suggest that in the spring, S. ocellana larvae are chill-susceptible, and a hard frost (< -7 °C) would be necessary to cause significant larval mortality.

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