Influence of Moisture on Growth and Distribution 127 



humidities tend to improve survival, but the egg and pupa stages are 

 affected to only a slight extent by relative humidities up to 70 per 

 cent. However, at humidities above 80 per cent the viability of eggs 

 and pupae drops very sharply. 



When the moisture conditions of the environment become adverse, 

 the animals concerned either die or must migrate longer or shorter 

 distances to more favorable locations. Droughts greatly reduce the 

 occurrence of some species temporarily, or for long periods, by deci- 

 mating the population. Locomotor activity, as well as feeding and 

 other reactions, are controlled by humidity in certain animals, espe- 

 cially insects. It is known that in some instances increased activity 

 without orientation results from a change in moisture conditions; in 



40 



30 



20 



10 



100 

 90 



70- 



60- 



50- 



40 



30- 



20 



<■-•— -.^ Pupae 



^~- Larvae 





Eggs 



\\- 



Ti 



10 20 30 40 50 60 70 80 90 100 

 Relative humidity 



Fig. 4.16. Duration (upper) and survival (lower) of the indicated stages of 

 Tribolium confusum at different relative humidities under constant temperature 

 of 27°C (by permission from Animal Ecology by Chapman, 1931, McGraw-Hill 



Book Co.). 



