Reduced mobility but high survival: thermal tolerance and locomotor response of the specialist herbivore, Pareuchaetes insulata (Walker) (Lepidoptera: Erebidae), to low temperatures

Abstract

Disentangling the responses of insects to variations in their thermal environment is central to our understanding of the evolution of temperature-dependent performance in these species. Here, we report results of experiments examining the effects of high (upper lethal temperature = ULT) and low (lower lethal temperature = LLT) temperature and exposure time on the survival of larvae and adults of a multivoltine, nocturnal moth species, Pareuchaetes insulata, a biological control agent whose impact on an invasive weed, Chromolaena odorata has been variable in South Africa. The influence of temperature and acclimation on locomotion performance of the moth was also investigated. Temperature and duration of exposure significantly affected survival of both adults and larvae of P. insulata with more extreme temperatures and/or longer durations proving to be more lethal. Third instar larvae and adults are both freeze intolerant and had LT50 of -5.9 and -4.7°C, respectively, after a 2 h exposure. Although cold acclimation was beneficial to the nocturnal larvae, temperatures below 10°C significantly reduce their locomotion activities. The average daily minimum temperatures in the coldest months at three locations in South Africa are over 5°C lower than those of Fort Lauderdale, Florida, USA, where P. insulata was originally collected. Our results suggest that lethal high or low temperatures at short timescales are trivial in explaining the variable performance of P. insulata, but reduced locomotion at sub-lethal temperatures may be an important driver of the population dynamics of the biocontrol agent (especially in winter months) and may consequently explain the low population levels of the moth because of possible reduced feeding by larvae during night-time low temperatures.

Assessment of pupal mortality in Hypena opulenta: An obstacle for establishment of a classical biological control agent against invasive swallow‐worts

“…Understanding the effects of winter temperatures on the survival of introduced biological control agents can help predict their population dynamics, as well as inform the release program to maximise their chances of success (Byrne et al, 2002; Guo et al, 2012; Uyi et al, 2017). For example, Duan et al (2020) studied cold‐induced mortality of Spathius galinae (Hymenoptera: Braconidae), a parasitoid biological control agent for emerald ash borer in North America.…”

Link between elevated locomotor activity and the spike bursting of antennal thermosensitive neurons in the carabid beetle Pterostichus oblongopunctatus

“…At unfavourably high temperatures (≥40 °C), we observed LA declines in P. oblongopunctatus. Reduced locomotion at very high temperatures has been observed in many insect species (Kjaersgaard 2010, Uyi 2017, Woods 2015, Dillon et al 2012, Anderson et al 2007. Kjaersgaard (2010) proposed that "a possible explanation for this could be that the exposure is so severe that any effect of thermal adaptation is effectively overridden by high thermal instability of the cells and membranes compromising the locomotor system and survival".…”

Developmental and reproductive performance of a specialist herbivore depend on seasonality of, and light conditions experienced by, the host plant

“…Outside the indirect effects of seasonality (low winter temperature: through host plant phenology and quality) on herbivore performance (in this study), recent studies suggest that direct and indirect effects of low winter temperatures can reduce the mobility, prolong development time and compromise other life history events or traits in P . insulata [ 56 , 57 ]. A combination of both direct and indirect effects of low winter temperatures (through direct effects and through host plant quality) may represent a double-blow for the insect during winter months, or in cold areas, and this may subsequently be detrimental for the populations of this insect in the field, particularly given its native-range climate.…”