62 



THE SPRING GRAIN-APHIS OR ' ' GREEN BUG. ' ' 



During the summer of 1907, at Richmond, Ind., careful observa- 

 tions were made on 7 individuals of the summer forms, and in the fall 

 Mr. R. A. Yickery, of this bureau, made observations on 6 indi- 

 viduals, 3 of which proved to be males and 3 oviparous females. 

 In each case there were 4 molts. In the spring of 1908, 4 stem moth- 

 ers were found to molt 4 times only. In the spring of 1909 at Lafay- 

 ette, Ind., 1 stem mother was found to molt 4 times. Later on in the 

 summer, Mr. T. H. Parks, of this bureau, ran a series of experiments 

 with the summer forms and, of the 30 individuals under observation, 

 some of 'which were winged, he found that all without exception 

 molted 4 times. In the fall of 1910 several additional oviparous 

 females were found to molt 4 times only. This makes a total of over 

 50 specimens that came under our observation, under conditions that 

 would absolutely preclude error, and there was not a single excep- 

 tion — all molting 4 times. 



As it was found that the period between molts varied, experiments 

 were begun in the summer of 1907 at Richmond, Ind., in order to 

 learn how great the variation was when each individual was subjected 

 to the same conditions. 1 This experiment was carried on indoors 

 and all individuals were subjected to the same conditions. Table II 

 will show the variations. 



Table II. — Variation in the duration of the different instars in Toxoptera graminum. 



• 

 Individual. 



From, time 

 of birth to 

 first molt. 



From first 

 molt to sec- 

 ond molt. 



From sec- 

 ond molt to 

 third molt. 



From third 



molt to 

 fourth molt. 



A 



H. m. 

 38 35 

 40 15 

 50 20 

 45 

 44 30 



X H. m. 



28 29 



29 15 

 26 40 

 54 



32 35 



H. m. 

 31 37 



34 36 



35 48 

 40 



36 50 



H. m. 



39 40 



B 



34 37 



c , 



40 22 



D : 



64 



E 



39 37 







There is also considerable variation in the time from birth of 

 individuals to the fourth molt and the appearance of the first young, 

 as will be seen from Table III. Individuals in Table III are the 

 same as in Table II, with the addition of "F" and "lb\" 



Table III. — Variation in the time from birth of individuals to fourth molt and appearance 



of first young in Toxoptera graminum. 



Individual. 



From time of birth to 

 fourth molt. 



From time of birth until 

 first young appear. 



A 



Hours. 



143-144 

 143 

 153 

 153 

 204 

 195 



170-175 



Days. 

 5.9 

 5.9 

 6.3 

 6.3 

 8.5 

 8.1 

 7.1 



II. TO. 



144 35 

 148 

 164 

 165 

 246 

 205 

 « 175 



Days. 

 6.02 



B 



6.1 



c 



6.8 



D 



6.8 



E 



10.02 



F 



8.5 



163 



7.2 







i Proc. Ent. Soc. Wash., vol. 10, Nos. 1-2, pp. 11-13, 1908. 



Approximate. 



