SEASONAL HISTORY. 



41 



Table XVIII. — Complete life cycle of 19 grape root-worms at North East, Pa., reared 

 from eggs laid during 1908; adults emerged in 1909. 



Num- 

 ber of 

 indi- 

 viduals. 



Date of 



Number 

 of days 

 for the 



life 

 cycle. 



Hatch- 

 ing of 



Emer- 

 gence of 

 beetles, 

 1909. 





July 16 



...do 



...do 



...do.... 

 ...do.... 



July 20 



...do 



...do.... 

 ...do.... 

 ...do 



July 25 

 ...do 



July 9 

 July 10 

 July 13 

 July 15 

 July 17 

 July 7 

 July 8 

 July 10 

 July 11 

 July 30 

 July 26 

 July 27 



358 

 359 

 362 

 364 

 366 

 352 

 353 

 355 

 356 

 375 

 366 

 367 



19 



1 



G,810 



i 



SUMMARY. 



Average... 

 Maximum . 

 Minimutn . 



Days. 

 . 358.4 

 . 375 

 . 352 



SEASONAL VARIATIONS IN THE LIFE HISTORY OF THE GRAPE 



ROOT-WORM. 



In comparing the records for the time of emergence of the beetle 

 for the three consecutive years of 1907, 1908, and 1909 a marked 

 difference in the date of emergence will be found (fig. 16) . This varia- 

 tion is partly due to the relative lateness of the spring and partly to 

 the climatic conditions prevailing during the entire development of 

 the insect in the ground. 



The climatic conditions for the years 1906 to 1909, inclusive, have 

 been strikingly varied and, as will be seen, the life of the insect for 

 these years has been affected accordingly. The mean temperature 

 for 1906 was 1 degree above normal and the precipitation averaged 

 about 1 inch below normal^ August and September being particu- 

 larly dry and hot. Frost occurred June 11 and 12 and snow on 

 October 10, 11, and 12. The year 1907 was marked with an abnor- 

 mally low temperature, a late spring, and an early fall, with a rather 

 high precipitation for the summer months. The month of May was 

 the coldest on record during a period of eighteen years. In 1908, on 

 the contrary, the mean temperature was above normal and the 

 summer was marked by two periods of severe drought, the dry condi- 

 tions being especially felt during the end of August. In most respects 

 1909 (fig. 17) was nearer the average. 



Although 1906 was a favorable season, during which the larvse 

 attained a normal growth, yet owing to the late and cold spring of 

 1907 the emergence of the insect was very materially delayed and 



