Modelling time‐varying low‐temperature‐induced mortality rates for pupae of Tuta absoluta (Gelechiidae, Lepidoptera)

Abstract

In a series of laboratory experiments, acclimated pupae of Tuta absoluta were exposed to various constant low temperatures in order to estimate their maximum survival times (Kaplan–Meier, Lt99.99). A Weibull function was fitted to the data points, describing maximum survival time as a function of temperature. In another experiment at −6°C, the progress of mortality increasing with exposure time was identified. These values were fitted by a sigmoidal function converging asymptotically to 100% mortality for very long exposure times. Analysing mortality data from the maximum survival experiment by a generalized linear model showed a significant common slope parameter (p < .001) that reveals parallelism of the survival curves at each temperature if a log time axis is used. These curves appear stretched (time scaled) if plotted with a nonlogarithmic time axis. By combining these mathematical relations, it was possible to calculate a species‐specific ‘mortality surface’ which exhibits mortalities, depending on temperature and duration of exposure. In order to accumulate hourly mortalities for courses of varying temperatures, an algorithm was developed which yields mortality values from that surface taking into account the attained mortality level. In validation experiments, recorded mortalities were compared against modelled mortalities. Prediction of mortality was partially supported by the model, but pupae experiencing intensely fluctuating temperatures showed decreased mortality, probably caused by rapid cold hardening during exposure. Despite this observation, mortality data converged to distinct levels very close to 100% depending on the intensity of temperature fluctuations that were characteristic for different types of experiments. The highest mortality limit occurred at intensely fluctuating temperatures in laboratory experiments. This constituted a benchmark that was not reached under various field conditions. Thus, it was possible to identify temperature limits for the extinction of field populations of Tuta absoluta pupae.

Supercooling capacity and cold tolerance of the South American tomato pinworm, Tuta absoluta, a newly invaded pest in China

“…When the exposure duration was longer than 4 h, the pupal stage recorded the lowest Ltemp 90 compared to the other life stages, indicating a higher cold tolerance capacity of pupae during long-term low temperature stress. This is consistent with the results reported by Kahrer et al (2019), who found that T. absoluta pupae were the most frost-resistant compared to other developmental stages of the species at − 4 °C. However, results from Van Damme et al (2015) showed that adults had the highest cold tolerance compared to larvae and pupae at 5 °C, but the survival was not significantly influenced by its developmental stage at 0 °C.…”

“…It was assumed that the low temperatures during winter in newly invaded areas would prevent invasive species from successful overwintering (Kahrer et al 2019). Xinjiang is one of the regions in China that suffer very harsh winter, with the lowest temperatures recorded between − 10 and − 30 °C (Hu 2014). Consequently, understanding the cold tolerance of T. absoluta is crucial for evaluating its dispersal potential in this province.…”

“…However, the survival of T. absoluta under temperatures below 0 °C has not been studied. In another study, the maximum survival times (Kaplan-Meier, Lt 99.99 ) of T. absoluta pupae were determined at − 10, − 8, − 6, − 4, − 2, 0, + 2 and + 4 °C, but not for other life stages (Kahrer et al 2019).…”

Impact of low temperature and host plant on Tuta absoluta

“…During adverse weather conditions (for instance during winter), abiotic factors are unfavorable and tomato plants become scarce forcing SATP to adopt diverse strategies to survive (Nyamukondiwa et al., 2013; Van Damme et al., 2015; Machekano et al., 2018; Cherif et al., 2019; Kahrer et al., 2019; Tarusikirwa et al., 2020; Campos et al., 2021). These strategies have been extensively studied, including facultative diapause and survival of pupae in temperatures below critical thresholds for SATP development (Van Damme et al., 2015; Kahrer et al., 2019; Campos et al., 2021). Prior studies have not provided information on the survival of SATP at 4 °C for various exposure periods on alternative host plants.…”

Biological invasion risk assessment of Tuta absoluta: mechanistic versus correlative methods

“…8). e Temperaturedependent mortality (data from Van Damme et al 2015;Krechemer and Foerster 2015;Martins et al 2016;Kahrer et al 2019) with the line indicating the fitted polynomial function used in the model…”