Lecture 10 Abiotic factors on insect population
- Physical factors
- Nutritional factors
- Host associated factors
Physical factors
- Temperature, light, wind, soil conditions influence development, longevity,
reproduction and fecundity of insects
- Population density fluctuates depending on weather
- Extreme weather causes mortality of pests
Temperature
- Insects are poikilothermic - do not have mechanism to regulate body temperature
- Body temperature depends on environmental conditions
w Preferred or Optimum temperature is the temperature at which normal
physiological activities take place - insects survive at this temperature.
w Upper lethal limit - 40-50oC (even upto 60oC survival in some stored product
insects)
w Lower lethal limit - Below freezing point e.g. snow fleas
w The total heat required for completion of physiological processes in life - history
is a constant - thermal constant.
w At low temperature (winter) insect takes more days to complete a stage (larval or
pupal stage)
w At high temperature (summer) it takes less than to complete a stage.
w Some insects when exposed to extremes of temperature
w Undergo - Aestivation (during summer) or Hibernation (during winter)
w During this period, there is a temporary developmental arrest, metabolic activities
suspended. When temperature is favourable, they resume activity.
w Eggs undergo aestivation in summer
w Larva, pupa commonly undergo hibernation in winter
Influence of temperature on fecundity (egg laying)
Grasshopper lays 20-30 times more eggs at 32oC compared to 22oC
Oviposition of bed bug inhibited at 8-10oC
Other effects of temperature
- Early shoot borer of sugarcane attacks more high temp.
- Larval period of sugarcane internode borer
very short 16-24 days in summer
prolonged 141-171 days in winter
- Swarm migration of locust occurs at 17-20oC
- Physical factors
- Nutritional factors
- Host associated factors
Physical factors
- Temperature, light, wind, soil conditions influence development, longevity,
reproduction and fecundity of insects
- Population density fluctuates depending on weather
- Extreme weather causes mortality of pests
Temperature
- Insects are poikilothermic - do not have mechanism to regulate body temperature
- Body temperature depends on environmental conditions
w Preferred or Optimum temperature is the temperature at which normal
physiological activities take place - insects survive at this temperature.
w Upper lethal limit - 40-50oC (even upto 60oC survival in some stored product
insects)
w Lower lethal limit - Below freezing point e.g. snow fleas
w The total heat required for completion of physiological processes in life - history
is a constant - thermal constant.
w At low temperature (winter) insect takes more days to complete a stage (larval or
pupal stage)
w At high temperature (summer) it takes less than to complete a stage.
w Some insects when exposed to extremes of temperature
w Undergo - Aestivation (during summer) or Hibernation (during winter)
w During this period, there is a temporary developmental arrest, metabolic activities
suspended. When temperature is favourable, they resume activity.
w Eggs undergo aestivation in summer
w Larva, pupa commonly undergo hibernation in winter
Influence of temperature on fecundity (egg laying)
Grasshopper lays 20-30 times more eggs at 32oC compared to 22oC
Oviposition of bed bug inhibited at 8-10oC
Other effects of temperature
- Early shoot borer of sugarcane attacks more high temp.
- Larval period of sugarcane internode borer
very short 16-24 days in summer
prolonged 141-171 days in winter
- Swarm migration of locust occurs at 17-20oC
