A Thesis Submitted in Partial Fulfilment of the Requirements for the Degree of PhD in Life Sciences and Engineering of the Nelson Mandela African Institution of Science and Technology
Tomato leafminer [Tuta absoluta, Meyrick. (Lepidoptera: Gelechiidae)] is a notorious pest that causes massive losses in Solanaceae’s crops including tomato (Solanum lycopersicum L.). This study was conducted to evaluate the occurrence, damage incidences, host range, population dynamics and developed bio-control strategies for managing T. absoluta in Tanzania. Field surveys were conducted in thirteen tomato production regions of Tanzania by purposively sampling one region and one district from each region then three villages were randomly selected for field survey. Optima lures was deployed per plot (0.5 acre) and number of adult moths trapped were counted after 7 days. To identify host of T. absoluta, in each selected village number and types of crops damaged per plot were recorded. Ten plants per plot were randomly selected to determine the rate of T. absoluta damage per plant by counting number of damaged leaves/fruits per plant in each plot and expressed as percentage damage. However, botanical extracts against T. absoluta larvae was conducted in laboratory by using four plant species extracted by using organic solvents. Different concentrations of extract were tested against 10 second instar larvae of T. absoluta that were selected randomly. Mortality rate, pupation rate and adult emergence rate were recorded at interval of 24h. Results indicated that T. absoluta was present in 13 regions surveyed and proliferates in 12 host plants including tomato, potato, nightshade, pepper and some weed species particularly Solanum incanum. Population density of T. absoluta was high in Iringa compared to Arusha and Morogoro and the dry season exhibited higher number of T. absoluta than in rainy season in all regions surveyed. The study on T. absoluta management revealed that, the pest can be controlled by using locally available entomopathogenic fungi (Patent No. TZ/P/2018/000035), plant extracts from Bersama abyssinica stem bark, Commiphora africana leaves, Tergetes minuta seeds and Moringa oleifera essential oil from seeds and cultivation of four accessions of tomato landraces namely BKM-22, KGM-5, HSK-4 and HSK-38. Application of the developed bio–control strategies caused 60% to 80% mortality of adults and larvae of T. absoluta in the laboratory and open field conditions. The identified bio-control strategies and resistance tomato landraces are recommended for further analysis and for consideration as remedies against T. absoluta in tomato in Tanzania.