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that the re-stocking of the District of Columbia and its vicinity with 

 the apparently exhausted supply of Southern forms was due mainly to 

 flights induced by favoring winds, consists in the observed fact that 

 there was not a corresponding increase in the numbers of Southern 

 insects of other orders, such as beetles and bugs, insects of feeble 

 powers of flight as compared to moths. The harlequin cabbage bug 

 is an example of the less active fliers, as this insect was only slightly 

 more abundant than in the previous year, until very late in the season, 

 when injury occurred in some few localities. 



ATMOSPHERIC CONDITIONS DURING THE WINTER OF 1899 AND 1900 

 AND SUBSEQUENTLY. 



The condition of the weather at different periods of the year was 

 noted whenever it was thought that these conditions might affect 

 insect life. Some of the more important phenomena should be men- 

 tioned as a preliminary to remarks that will be made upon the effects 

 of these conditions in limiting the increase or decrease of the insects 

 under observation. 



No change worthy of mention which it was thought might affect 

 insects injuriously was noted during the winter months of 1899. 



December 24 the temperature reached a maximum of 53° F. dur- 

 ing the afternoon, and at this time several species of insects were 

 observed at work in addition to those which will later be mentioned 

 as affecting crucifers. That night, however, there was a considerable 

 fall in temperature, a little more than 10° lower than the average for 

 the day before, the minimum reaching 24°. 



During the next eleven days there was a considerable drop in the 

 temperature, snow falling and the ground remaining frozen until 

 January 6 or 7. At one time during this period the temperature 

 descended to 9°. On the 5th the days began to become warmer, but 

 the night temperatures continued quite low, as low as 15° on the date 

 mentioned. 



February 24, after a protracted rainy spell of several days' duration, 

 the storm cleared, the sun came out, and the thermometer reached a 

 maximum in the afternoon of 58° F. Search among grasses showed 

 several forms of insects in activity near the surface, and it is proba- 

 ble that many other insects were brought to the surface from their 

 hibernating quarters by these conditions. That night a severe wind- 

 storm with rain and snow came on, the temperature dropping by 6 

 a. m. of the following day to 9° F., remaining below the freezing 

 point for three days, but again attaining a maximum on March 1, of 

 59 c , similar to that experienced after the storm just specified. For 

 the next twelve days the temperature was scarcely below the freezing 

 point for more than a degree or two at any time until March 11, when 



4670— No. 30—01 5 



