2 BULLETIN 1008, U. S. DEPARTMENT OF AGRICULTURE. 



in recent times. In 1861 Wagner * by confining a female Hessian fly 

 with wheat plants secured a total of 83 eggs. He evidently carried 

 out other experiments, for he concludes that the number of eggs de- 

 posited by a female is more than 80 and less than 100. Koeppen 3 in 

 1889 stated that, according to Lindemann, a female may deposit up 

 to 200 eggs, but believed these figures too high and gave Haberlandt's 

 statement that the female deposits only from 40 to 50 eggs. 



The most careful observations up to the present time seem to be 

 those made by Enock. 4 He confined the female insects in cages with 

 barley plants, securing in one case a maximum of 158 eggs. He also 

 confined females singly in corked vials and secured in this way a 

 maximum of 130 eggs. The number of eggs he secured by these 

 methods ranged from 70 to 158, with an average for 10 cases of 113 

 eggs. He concludes that a single female lays from 100 to 150 eggs. 

 Although Lugger 5 dissected a female which contained 238 eggs, the 

 usual figures given since the date of the paper by Enock are based 

 on Enock's conclusion. This conclusion, however, resulted from an 

 insufficient number of experiments, and the methods used in obtaining 

 the counts will not give accurate results. The adults of the Hessian 

 fly are extremely sensitive to conditions of temperature and moisture. 

 The females normally oviposit at comparatively low temperatures and 

 when moisture in abundance is present. If these conditions are 

 reversed or if conditions are unsatisfactory in some other respect, 

 the females will die before depositing all their eggs. A new and 

 thorough study of the subject therefore seemed imperative. 



METHODS OF INVESTIGATION. 



For the reasons stated, the method of confining female Hessian 

 flies in vials and all other methods involving their confinement in 

 cages kept in the laboratory were rejected. Cages kept outdoors 

 at the usual times when adults are abroad were also dispensed with, 

 because any cage modifies natural conditions, more or less, and be- 

 cause it is difficult to secure accurate counts where eggs are scat- 

 tered over a number of plants. 



The writer is convinced that under normal conditions each female 

 deposits practically all of her eggs. It has been found that at the 

 time of eclosion each female contains her normal allotment of eggs 

 in a well-developed condition; in fact, it is possible to count all of 

 the eggs by dissecting the pupa stage. It seemed simpler and more 



2 Wagner, Balthasar. Observations on the New Gall-Gnat. Fulda, 1861. Trans- 

 lated In U. S. Entomological Commission,. Third Report Appendix II, B, 1883, p. [15]. 



3 Koeppen, F. T. Die Schaedlictien Insekten Russlands. St. Petersburg, 1880. 

 Translated in XL S. Entomological Commission, Third Report, Appendix IV, 1883, p. [41]. 



* Enock, F. The Life-History of the Hessian Fly, Cecidomyia Destructor, Say. 

 In Trans. Ent Soc. London, p. 332, 1891. 



B Lugger, O. The Hessian Fly. In Minn. Agr. Exp. Sta. Bui. 64, p. 552, 1890. 



