THE MIGRATION OF THE FLY LARVAE 323 



until they reach the tip, then turn and move downward. The 

 larvae may die while on this ascending migration but apparently 

 never try to change the direction of progress. 



5. The rate of migration is extremely variable and seems to 

 be influenced by individual differences rather than physical 

 factors. The average time required by 205 larva hatching 

 from eggs laid normally to move one millimeter was about four 

 and one-half minutes, with extremes of one-half minute and 

 seventy -five minutes. The average time required by 119 larvae 

 hatching from eggs deposited in an inverted position to move 

 one millimeter was about three and one-half minutes, with 

 extremes of two-fifths of a minute and forty-six minutes. 



6. The mortality of migrating larvae is greatest when the 

 eggs are laid in an inverted position. Twenty-three per cent 

 of the larvae hatching from eggs laid normally died on migra- 

 tion, while fifty-seven per cent of the larvae hatching from 

 eggs deposited in an inverted position perished. 



7. When the eggs are deposited normally, the per cent of 

 mortality increases with the distance of the egg from the ligule. 

 When the eggs are laid in an inverted position, the mortality 

 increases with the distance of the egg from the tip of the leaf. 



LITERATURE CITED 



Packard, A. S. The Hessian Fly — Its Ravages, Habits and the Means of Pre- 



1883 venting Its Increase. U. S. Dept. Agri., Ent. Comm. 3rd Rept., 

 pp. 198-248. 

 Enock, F. The Life-history of the Hessian Fly, Cecidomyia destructor, Say. Trans. 



1891 Ent. Soc, London, for 1891, pp. 329-366. 

 Osborn, H. The Hessian Fly in the United States. U. S. Dept. Agri., Div. 



1898 Ent., Bui. 16 (n.s.), pp. 7-57. 

 Felt, E. P. Cecidomyia destructor, Say. N. Y. State Mus., Bui. 53, pp. 705-730. 



1902 

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1902 1-24. 



Garman, H. The Hessian Fly in 1902-1903. Kentucky Agri. Expi. Sta., Bull. 



1903 111, pp. 213-224. 



Gossard, H. A., and Houser, J. S. Hessian Fly. Ohio Agri. Exp. Sta., Bui. 



1906 177, pp. 1-39. 

 Webster F. M. The Hessian Fly. U. S. Dept. Agri., Bui. of Ent., Cir. 70, pp. 



1906 1-16. 

 Forbes, S. A. The Hessian Fly in Illinois, 1910. Univ. 111. Agri. Exp. Sta., 



1910 Cir. 146, pp. 1-4. 

 Headlee, T. J., and Parker, J. B. The Hessian Fly. Kans. Agri. Exp. Sta., 



1913 Bui. 188, pp. 83-138. 

 Dean, G. A., and Nabours, R. K. A New Air Conditioning Apparatus. Journ. 



1915 Ec. Ent., 8:107-111. 

 Webster, F. M. The Hessian Fly. U. S. Dept. Agri., Farmers' Bui. 640, pp. 



1915 1-20. 



