133 



eration notably increased in size. Jaiuiary 30. Winged apiiis of sixth 

 generation appeared this morning. January 31. First young of the 

 seventh generation appeared; also second winged specimen of the sixth 

 generation. February 4. I^iaced stalk of corn in this pot. Anotiier 

 winged female in tiiis lot. Fel^ruary o. More winged ones ap{)earing. 

 February 8. Crushed a winged louse and found it full of young. Feb- 

 ruary 18. Eighth generation under this bell glass now appearing. All 

 these are progeny of wingcid parents except tliose of one wingless female. 

 Number seems to be diminishing. March 5. Plant-lice increasing and 

 growing slowly. March 8, Number decreasing very much. March 

 ]]. Ninth generation has appeared since last observation. A consid- 

 erable number of plant-lice in good condition, March 19. This lot 

 fairly numerous, with one winged specimen. With this day tiie exp<;ri- 

 ment closed. This series of observations is, on the whole, coiLsistent 

 and satisfactory, and establishes quitti d(;finitfily the appearance of nine 

 successive generations between November 13 and March 11 at intervals 

 ranging from twelve Uj twenty-two days, with an average of seventeen. 

 Differences in apparent interval are in some cases due to the death of 

 tlie oldest of a generation without reproduction. The conditions under 

 wiiich these insects were maintained being of course far from the opti- 

 mum, their rate of multiplication was small and the total number 

 a[jpearing very few. In this, as in other cases, the parent did not long 

 outlive the reproductive maturity of her oldest young. 



Experiment 7. An isolated win/jed fent/de placed on wheat under a 

 bell glass November I'i. — November 16. Winged female dead, but a 

 young louse feeding on the wheat. From this time forward growth 

 and reproduction proceeded steadily but slowly, with some interruption 

 from an attack of fungous disease, until February 14, at which time the 

 pot and covering bell-glass were placed outdoors to test the effect of a 

 change of conditions. On the 16th fewer insects were alive, and but 

 few of these were wingless. No further examination was made until 

 March 4, by which time everything had died — seemingly a week or so 

 before. Careful search of IIkj earth and {slants yielded /lo trace of plant- 

 louse eggs. 



The foregoing data confirm our ignorance more than they incnjase 

 our knowledge, showing, as they do, the failure of all attempts to find 

 or produce a bisexual generation or an alternative food plant of Aphis 

 mavlis, or to learn how and where it normally passes the winter. Its 

 willingness to feed on winter wheat and ability to breed freely on tliat 

 plant, its indisposition towards grass or the foliage of the apple, and the 

 natural frequency of successive generations, are the principal other 

 facts evident from these observatioas. 



