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

Abstract

AbstractIn this study, we explore the low-temperature thresholds of a pest of apple (Malus pumilaMiller; Rosaceae), the eyespotted bud moth,Spilonota ocellanaDenis and Schiffermüller (Lepidoptera: Tortricidae), in the context of spring frost.Spilonota ocellanaoverwinters 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 supercooling 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±0.2 °C for sixth instars. Larval weight increased with instar and was positively related to the supercooling point. As some insects are freeze tolerant and able to recover from freezing, we also exposed larvae to brief freeze events between −4.5 °C and −9.5 °C and found that the median lower lethal temperature, was −7.3±0.4 °C across all instars; indicating thatS. ocellanaspring instars are susceptible to freezing temperatures above their supercooling point. These low-temperature thresholds suggest that in the spring, S. ocellanalarvae are chill susceptible, and a hard frost (<−7 °C) would be necessary to cause significant larval mortality.