72 THE SPRING GRAIN-APHIS OR i ' GREEN BUG.' 5 



is 43 days, the minimum 1 day, the average being 12.6 days; the 

 maximum for those born after the middle of August is 45 days and 

 the minumum 5 days, the average being 24 days, while the average 

 for the entire season is 16 days. 



In Texas the difference between summer, spring, and fall is still 

 more marked, December and January being about the same as the 

 summer months. Mr. Urbahns found that during December and 

 January the maximum reproduction period was 19 days and the 

 minimum 2 days, the average being 8 days; during April and May 

 the maximum was 30 days and the minimum 4 days, the average 

 being 16.8 days; during June, July, and August the maximum was 

 16 days and the minimum 4 days, the average being 8.4 days; during 

 September, October, and November the maximum was 28 days and 

 the minimum 3 days, the average being 17 days. The average for the 

 entire season was 13.9 days. 



LONGEVITY. 



At Richmond and La Fayette, Ind., Toxoptera lives for a much 

 longer period in the spring and fall than in the summer. In fact, in 

 the summer it often survives a shorter time than is required for it to 

 reach maturity in the spring and fall. 



Those born from the latter part of March to the last week in May 

 live from 15 to 78 days, the average being 43 days; those born from 

 the first week in June to the middle of August live from 9 to 57 days, 

 the average being 24 days; those born from the middle of August on 

 through September live from 12 to 75 days, the average thus being 40 

 days. The average length of life for the whole viviparous breeding 

 season is 35 days. These averages are not made up from the maxi- 

 mum and minimum alone but every individual in the line of first- 

 born of the continuous generation experiments is considered. 



Mr. Urbahns found that in Texas the spring grain-aphis lived much 

 longer in spring and fall than in summer. In fact, in the summer it 

 was difficult to keep it alive at all, it being necessary to keep the cages 

 in the shade. 1 He also carried on some reproduction experiments in 

 December and January, and in these two months found that it lived 

 from 25 to 39 days, averaging 34 days. In April and May it lived 

 from 13 to 47 days, averaging 35 days; in June, July, and August it 

 lived from 10 to 30 days, averaging 17 days; in September, October, 

 and part of November it lived from 11 to 56 days, averaging 28 days; 

 the average for the season (from March to November) was thus 26 

 days. 



In making up these averages only whole numbers are used, frac- 

 tional parts of a day not being considered. Also, all individuals 

 upon which we had complete observations were considered. 



i Ante, p. 47. 



