INSECT ECOLOGY 365 



low atmospheric humidity, other stages are unfavorably affected; 

 (5) low atmospheric moisture might be developed into an efficient in- 

 secticide for certain species of stored grain insects. 



Eclosion. Moisture frequently determines the time of eclosion, 

 >r the emergence of an insect from the pupa. Hessian flies do not 

 erge from the puparia in dry weather, but issue in abundance after 

 ainfall in the proper season. When bred indoors, the flies do not 

 merge from dry soil, even though the temperature be favorable, but 

 merge shortly when the soil is moistened. 



Activity. Wet weather lessens the activities of insects exposed to 

 t. There are some exceptions, however. Larvae of the midges, Itoni- 

 idae, are all very sensitive to the presence of moisture, to which they 

 react positively. Larvae of the clover seed midge emerge from the clo- 

 ver heads usually in damp weather and often in large numbers when the 

 dants are wet with rain. Even when full grown and contracted in 

 eadiness to form the puparium, they revive and move about if mois- 

 ;ened with water. 



Oviposition. It has been found that with the house fly, when 

 emperatures are high or moderately high, increased humidity hastens 

 ;g-laying. This may be partially due to the effect of humidity on 

 .e food and breeding substances keeping them moist and attractive. 

 Bishopp, Dove, Parman.) 



Mortality. Changes in relative humidity produce striking changes 

 the mortality of Drosophila, the mortality increasing with a decrease 

 f humidity, the optimum humidity being 100 per cent. The effects 

 if low humidity on mortality are most marked with very young pupae, 

 hose covering permits a rapid evaporation of body moisture. After 

 few hours, when integumental changes making evaporation more 

 ifficult have set in, the effects of low humidity are correspondingly 

 ecreased. (A. Elwyn.) 



Hibernation. As a preparation for hibernation, the water content 

 of an organism is frequently reduced; as also in seeds or spores. Thus 

 the Colorado potato beetle loses about 30 per cent, of its gross weight 

 through the loss of water, which enables it to withstand a lower freezing 

 point and higher temperatures than if the protoplasm were not thus 

 condensed. (Tower.) As Sanderson notes, the time of emergence from 

 hibernation is controlled by moisture conditions as well as temperature, 

 or independent of temperature. Tower kept potato beetles for eight- 

 een months at a high temperature, but with a dry atmosphere, and 

 rey emerged as soon as normal moisture conditions were produced. 



