Superior basal and plastic thermal responses to environmental heterogeneity in invasive exotic stemborer Chilo partellus Swinhoe over indigenous Busseola fusca (Fuller) and Sesamia calamistis Hampson

Abstract

Lepidopteran stemborers are the most destructive insect pests of cereal crops in sub-Saharan Africa. In nature, these insects are often exposed to multiple environmental stressors, resulting in potent impact on their thermal tolerance. Such environmental stressors may influence their activity, survival, abundance and biogeography. In the present study, we investigate the effects of acclimation to temperature, starvation and desiccation on thermal tolerance, measured as critical thermal limits [critical thermal minima (CT min ) and maxima (CT max )] on laboratory-reared economic pest species Chilo partellus Swinhoe (Lepidoptera: Crambidae), Busseola fusca (Fuller) and Sesamia calamistis Hampson (Lepidoptera: Noctuidae) using established protocols. Low temperature acclimation results in improved CT min for B. fusca and C. partellus, whereas high temperature acclimation enhances the same trait for B. fusca and S. calamistis. Similarly, high temperature and starvation pretreatment improve CT max for C. partellus relative to S. calamistis and B. fusca. In addition, starvation and desiccation pretreatments improve CT min for all stemborer species. Furthermore, rapid cold-hardening (RCH) enhancs CT min for B. fusca and C. partellus, whereas rapid heat-hardening (RHH) improves the same trait for C. partellus. However, RCH and RHH impair CT max for all stemborer species. These findings show differential thermal tolerances after exposure to heterogeneous environmental stress habitats. Chilo partellus, of exotic origin, shows a higher magnitude of basal thermal tolerance plasticity relative to the indigenous African species S. calamistis and B. fusca. This indicates that C. partellus may have a fitness and survival advantage under climate-induced heterogeneous environments, and also have a greater chance for geographical range expansion and invasion success compared with the indigenous B. fusca and S. calamistis.

Cold hardiness of the South American tomato pinworm Tuta absoluta (Lepidoptera: Gelechiidae): both larvae and adults are chill‐susceptible

“…Improvement in cold hardiness following dehydration pre‐treatment may also indicate cross‐tolerance, 83 an indication of shared co‐evolved physiological resistance mechanisms between dehydration and cold stress. This result is in keeping with Mutamiswa et al 84 . who reported improved cold tolerance for Chilo partellus , Busseola fusca and Sesamia calamistis larvae following dehydration pre‐treatment.…”

Thermal plasticity in the invasive south American tomato pinworm Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae)

“…Tuta absoluta hardening experiments were performed using established experimental protocols for Diptera and Lepidoptera (e.g., Mutamiswa et al, 2018b). To assess the effects of RCH and RHH on T. absoluta physiological traits, hardening temperatures for the two developmental treatment stages (larvae and adults) were established through preliminary assays.…”

“…To assess the effects of RCH and RHH on T. absoluta physiological traits, hardening temperatures for the two developmental treatment stages (larvae and adults) were established through preliminary assays. Cold hardening temperature for larvae was derived from critical thermal minima (CTmin) (Hoffmann et al, 2003;Lee and Denlinger, 2010) and was defined as 6˚C below CTmin (Mutamiswa et al, 2018b) (Table 1). For adults, low hardening temperature was defined as 10˚C above the lower discriminating temperature, consistent with other studies (see (Table 1).…”

“…While several reports have documented significant ecological effects of RCH (Stotter and Terblanche, 2009;Basson et al, 2011;Mutamiswa et al, 2018b), RHH (Chidawanyika and Terblanche, 2011a;2011b;Mutamiswa et al, 2018b) and acclimation (Lagerspetz, 2006;Fischer et al, 2010;Chidawanyika and Terblanche, 2011a;Sgrò et al, 2016), little is known on phenotypic plasticity of T. absoluta and its thermal tolerance (Han et al 2018). Previous studies on T. absoluta have only focused on thermal requirements for development (Krechemer and Foerster, 2015; but see van Damme et al, 2015).…”

Fluctuating environments impact thermal tolerance in an invasive insect species Bactrocera dorsalis (Diptera: Tephritidae)

“…This is in keeping with Pieterse et al (2017) who reported a lack of plasticity in larval B. dorsalis. While phenotypic plasticity is nearly universal in insects (Whitman & Ananthakrishnan, 2009), and that it may facilitate invasiveness (Mutamiswa, Chidawanyika, & Nyamukondiwa, 2018b) and adaptation to changing environments (Chown & Nicolson, 2004), it may appear that it has little or no effect on the invasion edge of B. dorsalis (also see discussions in Pieterse et al, 2017).…”