Pretreatment induced thermotolerance in lightbrown apple moth (Lepidoptera: Tortricidae) and associated induction of heat shock protein synthesis

Abstract

The use of heat treatments for disinfestation purposes is becoming widespread. The efficacy of such treatments may be influenced by exposure of insects to a range of temperatures in the environment before heat treatment disinfestation. We exposed 5th-instar light brown apple moth (Epiphyas postvittana Walker) to a range of temperatures and durations in hot air before treatment, and examined the effects of these conditions on mortality in a 43 °C hot-water treatment and on the induction of heat shock protein synthesis. Insect thermotolerance increased substantially with increased pretreatment temperature and duration the time until 99% mortality increased from 23.0 min with no pretreatment, to 37.4 min after 8 h at 35°C. Long periods at temperatures before treatment as low as 28°C increased thermotolerance, and periods as short as 15 min increased thermotolerance at higher temperatures. Correlated with this increased thermotolerance was the de novo synthesis of several proteins observed by radiolabeling with [35S]-methionine. Commercially available monoclonal antibodies of broad species cross reactivity to known heat shock proteins (HSP25, HSP60, HSP70, and HSP90) bound to constitutive forms of these proteins in Western blots but were not induced as a result of heat pretreatment. A protein of M(r) 78 kDa was the predominant protein synthesized, which is in agreement with a recent report of a new class of heat shock proteins in the Lepidoptera. These data indicated that thermal conditions experienced by insects before disinfestation can greatly influence thermotolerance.