False codling moth Thaumatotibia leucotreta (Lepidoptera, Tortricidae) larvae are chill‐susceptible

Abstract

This study reports on the low temperature tolerance and cold hardiness of larvae of false codling moth, Thaumatotibia leucotreta. We found that larvae have mean critical thermal minima (lower limits of activity) of 6.7°C which was influenced by feeding status. The effects of low temperature exposure and duration of exposure on larval survival were assessed and showed that the temperature at which 50% of the population survives is −11.5 ± 0.3°C after 2 h exposure. The supercooling point (SCP, i.e., freezing temperature) was investigated using a range of cooling rates and under different conditions (feeding and hydration status) and using inoculative freezing treatments (in contact with water or orange juice). The SCP decreased significantly from −15.6°C to −17.4°C after larvae were fasted for 24 h. Twenty‐four hour treatments at either high or low relative humidity (95.9% or 2.4%) also significantly decreased SCP to −17.2°C and −18.2°C respectively. Inoculative freezing (by water contact) raised SCP from −15.6°C to −6.8°C which could have important implications for post‐harvest sterilization. Cooling rates did not affect SCP which suggests that there is limited phenotypic plasticity of SCP during the larval life‐stage, at least over the short time‐scales investigated here. In conclusion, larvae of T. leucotreta are chill‐susceptible and die upon freezing. These results are important in understanding this pest's response to temperature variation, understanding pest risk status and improving post‐harvest sterilization efficacy.

An invitation to measure insect cold tolerance: Methods, approaches, and workflow

“…Most authors currently choose cooling rates that compromise between ecological relevance and time investment; generally 0.1 to 0.5 °C/min (e.g. Boardman et al, 2012;Crosthwaite et al, 2011;Renault et al, 2004;Sformo et al, 2011). It is clear that the rate of temperature change does affect the response of the insect (this has also been vigorously discussed in the context of high temperature tolerances, e.g.…”

“…This is most relevant to species expected to overwinter in moist conditions, and ice formation can be inoculated by placing an animal in contact with a moist substrate (e.g. Boardman et al, 2012;Koštál and Havelka, 2000), applying ice (e.g. Layne et al, 1990), or applying a known ice nucleator, such as silver iodide (e.g.…”

“…Chill susceptibility is sometimes referred to as chilling-or cold-intolerance. For example, the larvae of the false codling moth, Thaumatotobia leucotreta (Lepidoptera: Tortricidae), freeze between -13 °C and -22 °C but are killed by brief exposures between -8 °C and -12 °C (Boardman et al, 2012). Chill susceptibility is not a strategy per se, but represents the impact of cold on a majority of insects, particularly those that are not at all cold-hardy, and including many insects from the tropics or in temperate areas during the growing season.…”

Physiological and molecular mechanisms associated with cross tolerance between hypoxia and low temperature in Thaumatotibia leucotreta

“…Larvae of false codling moth T. leucotreta (Meyrick) (Lepidoptera, Tortricidae) were obtained from Cedar Biocontrol Insectary, XSIT (Pty) Ltd, Citrusdal, South Africa and maintained in the laboratory in 5 L containers in an incubator (±25°C, L:D 12:12 h; YIH DER growth chamber, model LE-539, SCILAB instrument CO Ltd., Taiwan OR) (Boardman et al, 2012). Fourth to fifth instar larvae were placed individually in 1.5 mL tubes with air holes for the duration of the experiment, and were fasted for 24 h prior to experimental pre-treatment in an attempt to remove the confounding effects of gut contents.…”

Agathis bishopi (Hymenoptera: Braconidae) as a Potential Tool for Detecting Oranges Infested with Thaumatotibia leucotreta (Lepidoptera: Tortricidae)

“…Considerable research has been recently undertaken to develop more robust management options for T. leucotreta such as screening for resistant cultivars (Love et al 2014), and improved preharvest (Li and Bouwer 2012;Coombes et al 2013;Opoku-Debrah et al 2013) and postharvest (Johnson and Neven 2010;Boardman et al 2012) control measures. Although considerable success has been recorded in the preharvest and postharvest control of T. leucotreta, limited research has focused on developing improved technology for postharvest detection of infested fruit, particularly in the packhouse where fruit is sorted and packed for export.…”