Insects and temperature - A general theory

Insects are selected for slow development (but relatively fast growth) in spring, but for fast development in summer. These contrasting selection pressures explain five puzzling effects of temperature on insects: growth and development rates increase almost linearly with temperature; genetic variability in development rate is reduced at high (27 degrees C) temperatures; genetic variability in growth rate is reduced at low (15 degrees C) temperatures; development is very slow at the time of emergence after diapause, regardless of the temperature threshold for emergence; and growth is slow at low temperatures, but development is even slower. Insects use temperature to indicate time-of-season. Different species are geared differently to rising temperatures. Insect predators and parasitoids become more effective at high temperatures; and insect population dynamics are not stable in the conventional sense.