THE PEA APHIS WITH RELATION TO FORAGE CROPS. 27 



to control, or at least hold in check, the aphides, and a little later, 

 usually depending on the climatic conditions, the aphidid fungus 

 (Empusa aphidis) becomes prevalent, so much so, in fact, that the 

 plant-lice are often apparently completely exterminated. However, 

 as the weather conditions become more favorable for the aphis and 

 less for the fungous disease and the aphidid parasites, the few sur- 

 vivors are soon able to cover the plants with their progeny, so that 

 by September we ordinarily find them again abundant on clover and 

 late garden peas. 



Farther north the insect does not seem to appear in injurious num- 

 bers until later — that is, not until about July. The following records 

 of injury for 1899 recorded by Dr. Chittenden (1900) illustrate this 

 statement. The first record was for Gloucester County and Ports- 

 mouth, Va., on May 17; Maryland, May 23; Newark, Del., June 2; 

 East Hampton, Conn., July 3; Long Island, N. Y., July 7: Orono, 

 Me., July 28; Ontario and Nova Scotia, Canada, August 9. 



GENERATION EXPERIMENTS. 



We have carried on generation experiments with this species 

 through two years (1912 and 1913) at La Fayette, Ind., and the fol- 

 lowing notes were made at La Fayette, except as indicated. The 

 same general methods, as well as the cages and rearing shelters, here- 

 tofore used by the writer and described and figured in Technical 

 Series Bulletin No. 25, Part II, of the Bureau of Entomology, have 

 been adopted. The writer here expresses his appreciation of the 

 services rendered by Messrs, C. W. Creel and A. F. Satterthwait, both 

 of the Cereal and Forage Crop Insect Investigations, who attentively 

 cared for the experiments during the absences of the writer in 1912 

 and 1913, respectively. 



In 1913 eggs began to hatch on March 31 and from that date until 

 January, 1914, there was obtained, out of doors, a maximum of 19 

 generations, no sexual forms being produced in the first-born genera- 

 tion series. On the other hand, following down " the last-born of the 

 last-born" generation series, a minimum of 7 generations was obtained, 

 the last generation consisting of males. The last generation, in this 

 case, was really the twelfth generation from the egg, for a break in 

 the first series of last-born generations made it necessary to substi- 

 tute with the last-born of a later generation. Thus we obtained an 

 average of 13 generations for the year. (See Table II.) 



