Fruit production is one of the fastest growing sectors in Botswana. As one of the agricultural sectors, fruit production is very crucial as it contributes immensely towards income generation and employment opportunities, especially for vulnerable rural livelihoods. Despite all the benefits, one of the biggest hurdles in the fruit production industry is disease and insect pests. Chief among these insect pests is the Bactrocera dorsalis (Hendel) (Diptera: Tephritidae). Bactrocera dorsalis is a worldwide economic insect pest of fruit and vegetables that has spread its geographical range to many African countries including Botswana. It was first detected in Botswana in 2010 in the Chobe district. However its spread and establishment around the country following its first detection is largely unknown. Furthermore despite this pest being of economic importance and a biosecurity threat, its response to prevailing Botswana microclimates and global change remained unknown. My study therefore investigated (i) presence and (ii) seasonal population dynamics of B. dorsalis in Botswana. Furthermore I investigated the thermal tolerance of B. dorsalis by measuring its different thermal low and high temperature activity traits vis a vis Critical thermal limits (CTLs), Lethal temperature assays (LTAs), and Supercooling points (SCPs), in order to understand how temperature largely impact this specie’s activity and thus population dynamics, abundance and consequently invasive potential. My seasonal monitoring results indicate that B. dorsalis is now established in the Chobe district, (its first area of detection) as shown by its continued presence all year round and high average monthly trap catches (<0.1) as compared to other districts. . Furthermore the insect pest has been detected in other districts south of Botswana, including Kgatleng, Kweneng, South-east, and Southern. This indicated that since 2010, the insect pest has spread down south of the country, with potential negative effects on fruit industries in those areas. Nevertheless, records of this insect pest in some of the areas (South-East and Kgatleng) were erratic, symbolizing that the areas did not have ‘resident breeding populations' for B. dorsalis but rather repeated introductions from ‘endemic’ or highly infested areas. Laboratory thermal activity experiments showed there was an improvement in critical thermal maxima (CTmax) at higher ramping rate across all the two developmental stages, indicating the lack of potential to shift high temperature tolerance for the two developmental stages at short timescales. The average high temperature of activity (CTmax) for adults and larvae were 46.16°C and 45.23°C respectively. However, there was an improved critical thermal minimum (CTmin) for larvae at slower ramping rate, indicating potential to improve low thermal tolerance at slower ramping rates, otherwise termed rapid cold hardening, the average low temperature for activity (CTmin) for adults and larvae 9.10°C and 7.3°C respectively. The results for lower- and upper lethal temperature assays (LLTs and ULTs respectively) revealed a reduction is survival at all the developmental stages as severity and duration increased, affirming the notion mortality is a function of temperature duration and severity. The ULTs and LLTs for adults, larvae and pupae ranged from 39-45, -6– 4°C; 38-41, -4–2°C and 39-45, -8–4°C respectively at 0.5 to 4hrs treatments. Pupae were the most temperature tolerant compared to other mobile stages. The SCPs of B. dorsalis developmental stages were -16.5 (adults), -16.6 (pupae) and -12.18˚C (larvae). SCP’s were significantly affected by developmental stages with pupae and adults having relatively depressed SCPs compared to larvae. General microclimatic temperatures recorded here versus experimentally derived thermal limits to activity imply that both high and low temperatures may not limit B. dorsalis establishment in the short term, and that the species may thrive upon introduction to the thermal environments investigated. The results of this study are of major implications to the management and enforcement of quarantine regulations of B. dorsalis. Knowledge of thermal biology is highly critical in the development of phytosanitary measures as well as in the forecasting of its ability to spread and establish in novel areas. This data may help in the development of mechanistic models of B. dorsalis invasion potential.

Theses (MSc-Biological Sciences, Applied Entomology) )----Botswana International University of Science and Technology, 2017