1909] Observations on a Gall Aphid 91 



ing black a few days after they were laid. They were generally 

 placed irregularly on the calyces and seed capsules and on the 

 small leaves of the upper branches. I examined many of the 

 large galls finding some eggs in them, but not nearly so many as 

 on the seed-heads. On October 21st I did find many eggs in 

 some frosted wilted leaves. The general instinct of the females 

 was plainly to carry the egg-laying as far up towards the seed- 

 bearing portion as possible. On Nov. i ith no more living aphids 

 of this species were found, for a freeze had killed all the Cheno- 

 podiiims. 



This habit of ovipositing on or close to the seeds is an instruc- 

 tive adaptation to the nature of the host. The winds and storms 

 of the winter of 1909 have broken off all the seed-heads and leaves 

 of the Chenopodimns, and at the time of writing (April) even the 

 bare stalks of the plants rarely remain standing. The seeds have 

 been distributed far and wide and many of the eggs of the aphids 

 must have been carried with them. The young stem-mothers 

 on hatching will be able to find their natural food easity avail- 

 able. Were most of the eggs laid on the leaves, they would be 

 so scattered by the winds that very few of the larvae could find 

 suitable food in the spring. Since most species of Chenopodiunt 

 and Atriplex are annual, the stem-mothers would suffer the same 

 mishap if the eggs from which they hatched had been laid on the 

 ground beneath the host. In October and November, 1905, at 

 Columbia, Missouri I observed the large red Macrosiphum rtid- 

 beckicB Fitch ovipositing in great numbers on the debris under one 

 of its hosts, a perennial goldenrod. In this case new shoots would 

 have come up in the spring around the old plants, and the larvse 

 on hatching would have found ready food. Here then, there was 

 no necessity of the mothers entrusting their progeny to the 

 capriciousness of the windy winter elements. 



The oviposition of our goosefoot aphid in the seed-heads 

 explains its world-wide distribution. Professor M. L. Fernald, 

 Harvard University, has written to me that Chenopodium album 

 is known to be an introduced plant from Europe, whence it has 

 followed the trail of the early American settlers. In Professor 

 Fernald's own explorations in the forests of Maine, New Bruns- 

 wick and Quebec this plant was never found except about settle- 

 ments. Atriplex patula is likewise recognized as an introduced 

 species. These plants are both common European garden weeds 

 whose seeds, with the eggs of their insect foes, could easily be in- 

 troduced with any rubbish into a new country. 



