Davidson — Biological Studies of Aphis rumicis L. 30o 



I wish to express my thanks to Ur. A. D. Imms for the helpful sugges- 

 tions he has given nie during tlie progress of the experiments, and to 

 Mr. Ward Cutler for his criticism when writing the paper. 



(a) Fundatrix Generation on Euonymus. 



Young aphids (1st instar), which hatched out from ova of Aphis rumicis, 

 from Euonymus, were reared on young twigs of Eiconymus europaeus, which 

 were kept in wet sand in the laboratory. They all developed into a. v. ? 2 , 

 being the adult Fundatrices. 



In six experiments it was found that Fundatrices became adult in 8 to 10 

 days after birth, and commenced to produce young within 2 to 4 days after 

 the last moult. The young in all cases were apterous viviparous females. 



(b) The First Viviparous Generation on Eiconymus europaeus. 



The offspring of the Fundatrices are the first viviparous generation. In 

 these experiments, individuals of the first viviparous generation born between 

 April 13th and 18th, 1914, became adult in 9-11 days after birth. In all cases 

 they gave rise to a. v. ? 2 , and the first young were produced in seven instances 

 on the same day that the last moult took place. In the remaining cases, the 

 first young were produced in 1 to 3 days after the last moult. They were 

 grown on twigs of Euonymus in wet sand. 



(c) Successive Viviparous Generation reared on Euonymus. 



Small Euonymus bushes, about a foot high, were grown in pots and 

 infected as I'equired, each plant being covered with a muslin bag. Observa- 

 tions were made as recorded below. It should be noted that when winged 

 forms are transferred to a new plant there is often great difficulty in getting 

 them to settle down on the plant, and several days may elapse before they 

 produce young on it. Sometimes, out of as many as fifteen winged forms, 

 only two or three will settle down and produce on the plant, the remainder 

 collecting in the top of the muslin cover. By restricting the space round the 

 plant, this difficulty can be somewhat overcome. 



Euonymus A. — 11. 4. 14. Infected with two Fundatrices reared from ova 

 on Euonymus. 23. 4. 14. Adult w. v. ? 9 present ; only a few a. v. 2 2 

 present. 



Euonymus Aj. — 23. 4. 14. Infected with 4 w. v. ? $ , 1st v. gen. from A. 

 12. 5. 14. Plant is not making young growth and is " woody." Aphids small 

 size, restless, and wandering over the plant ; some immature w. v. $ ? pre- 

 sent, but majority are a. v. ? ? , some a. v. ? ? adult. 



Euonymus A.2. — 25.4.14. Infected with 3 w. v. ? ?, 1st v. gen. from A. 



2q2 



