Abstract:  During the last decades, Zaprionus indianus, a warm adapted drosophilid species has invaded and expanded its boundaries in the Indian subcontinent. Z. indianus has successfully invaded because of its high adaptive flexibility and extreme physiological tolerance. A comparison of developmental thresholds of Z. indianus (warm specialist) and D. melanogaster (cosmopolitan) during pre-adult and adult life stages at extreme temperatures showed significant difference in mortality and threshold temperature between both species. To test for variation in stress resistance and survival in preadult/adult stages over winter, Z. indianus populations were initiated from temperate and tropical sites in India. The hatchability of eggs and adult survival of these populations were monitored in field cages at a temperate location and under constant laboratory conditions, until all adults died. Total hatchability and survival showed significant difference with latitude, due to high hatchability and survival by temperate in northern populations as compared with  southern populations. Egg to adult viability experiment indicated that eggs laid in low temperature conditions developed successfully to the adult stage when the temperature became moderate. This study is evident for climatic adaptation in immature stages and stress tolerance in adults that may provide seasonal protection to the species. When climate warming scenario was considered, i.e., temperature increase of 0.6℃, a slight increase in temperature could cause a significant increment in population viability and a decrease in developmental duration. These results explain why Z. indianus can easily cross barriers and is able to adapt to new environment.

Key words: Zaprionus indianus, life stage, climatic adaptation, physiological tolerance, climatic warming