Physiological traits suggest limited diapause response in false codling moth, Thaumatotibia leucotreta (Lepidoptera: Tortricidae)

Abstract

The ability of a pest insect species to enter diapause, a physiological state of dormancy, has significant implications for population dynamics and pest management practises in agricultural landscapes. The false codling moth Thaumatotibia leucotreta is a major pest of deciduous and citrus fruit in southern Africa and a quarantine pest of international concern. Apart from an early field assessment that may have been compromised by taxonomic uncertainty surrounding cryptic developing life stages, no studies have investigated diapause induction within an experimental framework for this species, and none to date have used a suite of physiological traits potentially indicative of the diapause state. Here, we subjected larvae to cooling and shortening day length over a period of 14 days [Diapause Treatment (DT) group] relative to a similar-aged control (CON) group held at optimal rearing conditions (25°C, 12 : 12 L : D) and tested if physiological traits, including resting metabolic rate, body freezing temperature (=supercooling point, equivalent to the low-temperature mortality threshold) and body condition (body mass, body lipid and water content) varied in a direction that may be reflective of diapause induction. Mean metabolic rate in DT larvae was 0.044 ml CO 2 /h (mean mass: 52.7 mg), which was significantly higher than in CON larvae [0.025 ml CO 2 /h, mean mass: 51.5 mg (P = 0.04)]. Supercooling points were not statistically lower in the CON group than in DT larvae (DT:À15.6 AE 1.5°C; CON: À16.4 AE 2.8°C; P = 0.33). Measures of body size, body condition and resting water loss rates remained similar between groups. These results support the conclusion of early field observations that T. leucotreta does not undergo diapause that has significant implications for the management of the species.

Assessment of the probability of introduction of Thaumatotibia leucotreta into the European Union with import of cut roses

“…6°C facilitated the explanation of T. leucotreta occurrence records in western parts of Africa (Table 11 and Figure 11 ). However, the physiological aspect is of marginal relevance to predictions for EU climates, as the main constraint to T. leucotreta distribution in Europe is cold weather and the absence of dormancy in the pest (Terblanche et al., 2014 ).…”

“…Gutierrez and Ponti, 2013 ) that includes temperature‐dependent development (Figure 14 ), fecundity (Figure 15 ) and mortality functions (Figure 16 ). These biodemographic functions are fitted to experimental data (Daiber, 1979a , b , c ; Terblanche et al., 2014 , 2017 ; Sections 3.1.1 and 3.1.2 of this opinion). Experimental data for T. leucotreta from South Africa report low‐ and high‐temperature susceptibility and absence of diapause.…”

Recent insights into sublethal effects of pesticides on insect respiratory physiology

“…[49][50][51][52] Furthermore, larvae preparing for pupation have a higher resting metabolic rate than those not preparing for pupation. [53][54][55] The metabolic rate may also change due to parasitism of the larva as was shown for Manduca sexta L. 56 The metabolic rate of bumble bee queens depends on whether they are pre-or postwintered 57 and also on their task in the nest. 58 The second aspect that must be taken into consideration in respiratory studies is the individual properties of the subject.…”

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

“…False codling moth is a multivoltine agricultural pest of citrus and other fruit in southern Africa but with a broad host range (including macadamia nuts and cotton). Adults are active year‐round in agroecosystems and overwinter without diapause (Terblanche et al ., ). Although this species is relatively cold hardy, surviving well below 0 °C, the larvae are chill susceptible and subject to inoculative freezing (Boardman et al ., ).…”