author(s)
Aijaz Ahmad Sheikh, NZ Rehman and Ritesh Kumar

abstract
Changing environment demands organisms to change in order to survive. Organisms respond to their environments by making different types of adaptations. Adaptations are essentially a product of natural selection. As populations are subjected to vagaries of climate, the genetic characteristics that are well suited to the environment are selected. Insects are found in a wide range of environment experiencing extremes of biotic as well as abiotic factors. To survive the environmental extremes, to escape or alleviate adversities of environment, insects have evolved a number of physiological, behavioural and morphological adaptations. Behavioural responses include burrowing into substrate and being active only through a restricted period of the day. Furthermore, insects may feign death, a response termed thanatosis. It is obvious that at least some of the colours and patterns (Crypsis and Mimicry) serve a defensive function by offering a degree of protection from predators and to adapt in the environment. As a group, insects have limited ability to regulate their body temperature and have thus required a range of strategies to support life in thermally stressful environments (low as well as high temperature), including behavioural avoidance through migration and seasonal changes in cold tolerance. With respect to cold stress, insects have traditionally been divided into two main groups: freeze tolerant and freeze avoiding, although this simple classification is underpinned by a complex of interacting processes, i.e. synthesis of ice nucleating agents, cryoprotectants, antifreeze proteins and changes in membrane lipid composition and the change in membrane permeability, reduction in transpiration rate and synthesis of heat shock proteins help the insects to thrive under high temperature conditions. Thus it may be said that adaptations (physiological, behavioural and morphological adaptations) have played a leading role in insects to become the most dominant organisms on the earth’s surface.