Evidence of rapid spread and establishment of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) in semi-arid Botswana.
Background: Tuta absoluta (Meyrick), a major invasive pest of Solanaceous plants, was recently detected in Botswana. Abiotic and biotic factors, together with a suite of population demographic traits are likely key for species propensity and invasion success. First, we determined the movement of T. absoluta from its core detection centre to new invasion areas using pheromone baiting and established likely biotic dispersal drivers. Second, we measured thermal tolerance vis critical thermal limits and lower and upper lethal limits to determine how these traits shape population establishment. Results: We detected T. absoluta in all 67 pristine sites across nine districts of Botswana. Within-district trap catches varied between cultivated and wild hosts but were generally not statistically significant (P>0.001). We report three major wild host plants for T. absoluta as biotic dispersal drivers: Solanum coccineum (Jacq.), Solanum supinum (Dunal) and Solanum aculeatissimum (Jacq.). Solanum coccineum and S. supinum were omnipresent, while S. aculeatissimum distribution was sporadic. Thermal tolerance assays showed larvae were more heat tolerant, with a higher critical thermal maxima (CTmax) than adults (P<0.001), whereas the adults were more tolerant to cold with a significantly lower (P<0.001) critical thermal minima (CTmin) compared to larvae. The upper lethal temperatures ranged from 37-43°C, whereas the lower lethal temperatures ranged from -1 to -12°C for 0-100% mortality, respectively. In the light of prevailing environmental (habitat) temperatures (Thab), warming temperature (7.29°C) and thermal safety margin (22.39°C) were relatively high. Conclusion: Tuta absoluta may not be under abiotic physiological or biotic constraint that could limit its geographical range extension within Botswana. The ubiquity of wild Solanaceous plants with the bridgehead of year-round intensive monocultures of Solanaceous crops within a favourable climatic framework may mean that environmental suitability aided the rapid spread of T. absoluta.