Dissertation (MSc. Chemistry)Tomato leafminers, Tuta absoluta pose a control challenge due to resistance against many chemical pesticides including abamectin. In this study, new pesticide was developed by heating mixture of abamectin with neem oil at1:1 ratio. The heating of this mixture resulted to formation of a new compound which is highly biopotent than its constituent substances. This was confirmed by TLC spot formed at Rf 0.43. A leaf dip bioassay method was used to test toxicity against T. absoluta. Bioassay was carried out outside laboratory settings under uncontrolled conditions where percentage corrected mortality and LC50 for each pesticide was determined. Mortality was assessed after every two days for a week (six days). New pesticide had better performance than abamectin, neem oil or mixture of abamectin and neem oil. The highest mean corrected percentage mortality and LC50 reached with abamectin was 79% and 363 ppm respectively. Neem oil had LC50 of 2089 ppm and 61% as corrected mean percentage mortality at highest concentration. The mixture of abamectin and neem oil without heating had LC50 of 251 ppm with 88% mean corrected percent mortality while the new insecticide had LC50 151 ppm with mean corrected percentage mortality of 93% at highest concentration after six days. This is evidence that neem oil improves abamectin performance. Tuta absoluta is better controlled when farmers apply formulation of pesticide containing neem oil before tomato plants shown sign of infestation. This is to say apply pesticides even when there is no sign of damage. Timing is an important factor in leafminers control.