Pumpkin fruit fly, Bactrocera tau, is a key pest in pumpkin orchards, causing serious economic damage. Impact of sucrose and protein on survivorship of adult males of Bactrocera tau has been studied in the present study. Flies fed optimal diet (Sucrose and Protein in 3:1 ratio), and only sugar from the day of eclosion demonstrated mortality of only 7.33% and 1.33% respectively in 4 days. However, flies fed only protein, and starved from the day of eclosion showed mortality of 100% and 99.6% respectively in the same time period. At the same time, change of dietary habit of flies from optimal diet to protein as well as optimal diet to no food on 7^th and 11^th day resulted no survivorship, or 100% mortality, for both cases in 4 days. Number of adult flies died for the change of optimal diet to sugar on 7^th day and 11^th day in the study period was insignificant. Study demonstrated the absolute requirement of carbohydrate in the adult diet, and insignificant capability of conversion of lipids to metabolic energy.