Thermal limits to survival and activity in two life stages of false codling moth Thaumatotibia leucotreta (Lepidoptera, Tortricidae)

Abstract

The present study examines life stage‐related variation in the thermal limits to activity and survival in an African pest, the false codling moth Thaumatotibia leucotreta (Lepidoptera, Tortricidae). Thermal tolerance, including the functional activity limits of critical thermal maxima and minima (CTmax and CTmin respectively), upper and lower lethal temperature, and the effect of heat and cold hardening (short‐term acute plasticity), is measured across a diverse range of low or high temperature stress conditions in both larvae and adults. We also report the sum of inducible and cognate forms of the amounts of heat shock protein 70 (HSP70) as an explanatory variable for changes in thermotolerance. The results show that the larvae have high variability in CTmax and CTmin at different ramping rates and low levels of basal (innate) thermal tolerance. By contrast, the adults show high basal tolerance and overall lower variability in CTmax and CTmin, indicating lower levels of phenotypic plasticity in thermotolerance. HSP70 responses, although variable, do not reflect these tolerance or survival patterns. Larvae survive across a broader range of temperatures, whereas adults remain active across a broader range of temperatures. Life stage‐related variation in thermal tolerance is most pronounced under the slowest (most ecologically‐relevant) ramping rate (0.06 °C min–1) during lower critical thermal limit experiments and least pronounced during upper thermal limit experiments. Thus, the ramping rate can hinder or enhance the detection of stage‐related variation in thermal limits to activity and survival of insects.

Rate dynamics of ectotherm responses to thermal stress

“…Our results demonstrate that the commonly expected direction of response characterized by an improvement of CTLs (higher CT max , lower CT min ) with the increasing rate of temperature [36][37][38][39][40]. A strong species-specific response for both CT max and CT min , independent of body size (unlike the situation found in interspecific analyses [24]), reveals four different thermal tolerance response patterns to the increasing exposure time (i.e.…”

Effect of short-term high-temperature exposure on the life history parameters of Ophraella communa

“…Ophraella communa overwinters and expands its distribution mainly in the adult stage 9 , suggesting that adults are better able to tolerate environmental stress than other stages. Mobile adults likely experience a greater range of thermal microclimates, and greater variability in tolerance or greater basal (innate) tolerance might be expected 28 . The greater mobility of larvae and adults compared to other stages allows them to search for low-temperature microclimates to reduce thermal injury through behavioural thermoregulation 71 , which increases the thermal tolerance of larvae and adults in the field.…”

“…The effects of thermal stress depend on the frequency, amplitude, and duration of the stress 26 . Meanwhile, the effects of thermal stress differ based on which life stage experienced the heat stress 28 . Both basal tolerance and plastic responses contribute to the ability of ectotherms to counter heat stress 29 .…”

“…Behavioural thermoregulation allows mobile stages (like larvae and adults) to escape lethal temperatures, and less mobile stages (like eggs and pupae) thus have to cope with and tolerate more extreme conditions than mobile stages 30 . According to this principle, immobile stages are expected to show higher basal thermotolerance than mobile stages 28 – 30 . Any developmental stage of insect species with relatively short generation periods may experience heat stress in the field, thus the population sizes of these species may be affected.…”

Cold treatment enhances low‐temperature flight performance in false codling moth, Thaumatotibia leucotreta (Lepidoptera: Tortricidae)

“…Immediately after collection, all moths were irradiated with 150 Gy in a panoramic cobalt‐60 source (double encapsulated C132 type 78 source; dose rate at 3.75 Gy/min) in a temperature‐controlled room (15 ± 1 °C), after which they were kept at 25 °C for 20 min before they were either cold‐treated overnight at 2 ± 1 °C for 16 h in an environmental chamber (Binder climate chamber, KBW 240 Binder, Tuttlingen, Germany) or kept as a control group at 25 ± 1 °C in a temperature‐controlled room (confirmed using a temperature data logger, 101A, MadgeTech). A cold‐treatment temperature of 2 °C was chosen to ensure that moths were kept below their critical thermal minimum (CTmin) (∼6 °C) (Terblanche et al ., ) but above sub‐zero temperatures to prevent ice formation. The chosen treatment temperature was deemed appropriate, as the current handling and transportation temperatures of the SIT operation have been associated with poor recapture counts under both warm and cold environmental conditions (Boersma & Carpenter, ; Stotter & Terblanche, ).…”