1018 ENTOMOLOGICAL SOCIETY. ^ 61 



only one food plant. Gillette (4) states definitely that M. cerasi lacks the 

 alternating food habit. On the other hand, Quaintance and Baker (5) claim 

 that it is migratory. How are we to account for these apparently conflicting 

 statements ? Is it possible that the species is partially monophagous and partially 

 migratory? Our observations and experiments prove that it is. Apterous forms 

 reside throughout the season on the primary host-cherry, and in addition alats, 

 produced during the summer, migrate to and establish colonies on a secondary 

 host. 



The cherry aphis apparently has an unique life cycle. Some plant lice with 

 the alternating food habit, e.g., Eriosoma lanigera, Prociphilus tessellata and 

 Myzus persicce occur at all times of the year on their secondary hosts, but, so 

 far as we are aware, no migratory aphid other than M. cerasi normally resides 

 on the primary host all year. If we were given to theorizing, we would suggest 

 that at the present time, the black cherry aphis is in the transitional stage 

 between the migratory type (e.g., A. avence,) and the more specialized monophagous 

 type (e.g., A. pomi). 



MiGRATORT Tests. 



In order to discover the secondary host a series of migratory experiments 

 Avere made with common plants belonging to the following genera : Agropyron, 

 Dachjlis., Poa, Polygomum, Rumex, Clieno podium, Ama/ranihus, Stella/riO', Silens, 

 Rammculus, Erysimum, Capsella, Lepidium, Brassica, Lohularia, PotentilM, 

 Prunus, Trifolium, Vicia, Medicago, Malva, Nepeta, Btachys, Verhascum, Flantago, 

 Cirsium, Arctium, Hieracium, Lactuca, Senecio, Aynhrosia, Aster, Sonchus, 

 Solidago. The migrants fed to some extent on cherry. Polygonum persicaria,^ 

 Ghenopodium album, Rumex acetosella, Stellaria medh, and Malva r\otundifolia, 

 but did not reproduce on these plants. Young were deposited on Polygonum 

 aviculare, Rumex crispus, Lohularia maritima, Verhascum thapsus, Flantago 

 lanceolata, P. major and Solidago sp., but they did not grow and soon succumbed. 

 Weak colonies developed on Brassica arvensis. Erysimum cheirantlioides and 

 Capsella hursa-pastoris* On Lepidium apetalum strong colonies were readily 

 established and were carried through to the end of -the season. 



Field Observations. 



In the field our search for migrants was rewarded by finding them and their 

 progeny on wild peppergrass, L. apetalum growing within two hundred yards 

 of an infested cherry orchard (first collection was made on July 9th, 1917). The 

 aphis was not taken on any other plant but in spite of this we are strongly 

 inclined to believe that other crucifers besides Lepidium serve as secondary hosts. 

 Next season, we hope to be able to prove this. 



The Egg. 



The minute, oval-shaped eggs {.Q>^ mm. x .33 mm.) change within a few 



days after being laid from watery green to black. They are deposited around 



the buds and on the rough bark of twigs and branches. They commence to 



hatch early in spring when the buds are swelling. In the cherry orchard (situated 



on the lake shore) which we had under observation this past season, the period 



of hatching extended from the 17th to the 24th of April. All the eggs hatched 



at least nineteen days before the cherry buds actually biarst. 



. — i 



*One colony on Erysimnm survived until autumn, at which time it gave rise to 

 return migrants and males. 



