364 ENTOMOLOGY 



The heavy emergences apparently always have been during periods of 

 high barometric pressure. Trappings and observations indicate that 

 muscoid Diptera are most abundant during long periods with slight 

 variations in barometric pressure, provided, of course, temperature, 

 humidity and rainfall are favorable. 



Migration of the butterfly, Hypatus bachmani was observed during 

 the summer and fall of 1916 to take place after storms, which indicates 

 that the flights were during high barometric pressure. 



MOISTURE 



Moisture ranks with temperature as a highly essential condition of 

 existence. Moisture affects terrestrial animals most vitally through 

 evaporation, which will be considered beyond. v Here we may state 

 the effects of moisture without special reference to evaporation, but it 

 should be borne in mind that, in most of the phenomena discussed, 

 evaporation is an important factor. 



Metabolism. " Water plays a part in growth second in importance 

 to no other agent, so that in its absence growth cannot occur. As the 

 quantity is increased, growth is increased until an optimum is reached. 

 The amount imbibed does not, however, depend directly upon the 

 amount available, but rather upon the needs and habits of the 

 species/' (Dr. C. B. Davenport.) 



i. There is an optimum moisture for insect development. 2. This 

 optimum is not the same for different species. 3. The moisture which 

 may hasten the development of one species may retard the develop- 

 ment of another. (Bachmetjew.) Headlee adds that the rate of 

 metabolism in certain actively feeding insects with an abundant supply 

 of succulent food is not affected by large differences in atmospheric 

 moisture. He found that the green-bug, Toxoptera graminum, required 

 six days to pass from birth to maturity under a constant temperature of 

 80 F. and relative humidities of 37, 50, 70, 80 and 100 per cent. Pro- 

 fessor Headlee- found also that, with the angoumois grain moth and the 

 bean weevil (i) increase in atmospheric humidity means increase in 

 speed of metabolism as measured by length of life cycle; (2) the optimum 

 per cent, of atmospheric humidity is the highest which will not encour- 

 age a heavy growth of fungi; (3) 100 per cent, atmospheric humidity 

 destroys by encouraging the growth of fungi, and low atmospheric mois- 

 ture destroys directly probably by the extraction of water; (4) while 

 the egg stage of the bean weevil, at least, is most sensitive to the effect 



