Insects in the tropics have been found to be on the wrong side of global warming, says Kirtiman Awasthi Contrary to popular belief that global warming will lead to a population explosion in insects, a recent study claims otherwise. It says the phenomenon will lead to the extinction of insects in the tropical zone by the end of the century. There are two survival options: either they learn to adapt to the rising temperatures or migrate to higher latitudes, the authors say in the paper published in the May issue of Proceedings of the National Academy of Sciences. Insects in the temperate zones and the poles could, in fact, experience a dramatic increase in numbers, the study says. The reason for extinction, the authors say, is that as temperatures increase insects will not be able to perform physiological functions such as reproduction and locomotion. Since they are cold-blooded, they cannot regulate their body temperature. Classed as ectotherms, they operate in a specific temperature range called the critical thermal limit. As the temperature increases in this range, physiological activity increases. It reaches an optimum level and then declines sharply, say the researchers of the University of Washington, USA, who carried out the study. Tropical insects are already at the higher end of the critical thermal limit and hence the threat is imminent. Insects in colder regions may survive and proliferate because they are still at the lower end of the temperature range. For example, the pea aphid sampled at 52