72 
Psyche 
[April 
Macrosiphum tanaceti feeds on the growing regions of the 
stem, on which different instars of this species are found in large 
numbers from early spring until late in the fall in Boston and 
vicinity. The more succulent portions of the petioles are also 
feeding places for the later nymphal instars and the adults, 
although they are found here only occasionally. While the 
aphid is feeding, its head points toward the ground, the antennae 
are directed lateroposteriorly with reference to the body, and the 
legs are spread apart. The haustellum is at right angles with the 
body or inclined somewhat anteriorly. The labium, which 
serves as the sheath for the rest of the mouth-parts, except the 
labrum, remains straight. No posterior bending is observed at 
the point of junction of any two labial segments, which is a charac- 
teristic feeding habit of the members of a closely allied order 
the Heteroptera. The latter group resorts to this contrivance in 
order to enable the setae to penetrate deeper into the plant tissues. 
In Macrosiphum tanaceti the tips of the setae apparently do not 
go far beneath the epidermis of the plant, perhaps reaching only 
a small portion of the cortical layer. This supposition is based 
on the fact that in all the specimens examined while in the act of 
feeding it was found that the setae protrude less than a millimeter 
beyond the distal end of the labial sheath. 
The position assumed by the insect while feeding is in- 
teresting. It is not easy to see why the insect should prefer to 
remain in that seemingly uncomfortable posture in which the 
abdomen is situated uppermost. The following experiments 
were conducted in order to find out the possible explanation for 
this peculiar habit: 
Growing tips of Tanacetum vulgare, with numerous tansy 
aphids in different instars feeding on them, were carefully bent 
down without injuring the plants and were made to remain in 
this position by fastening them with strings. In this way, the 
aphids, without being disturbed, are reversed in their position, 
now with the head uppermost. These experiments were per- 
formed in the morning when it was still cool, at noon, when the 
sun was very bright and the temperature was about 32° C. (90° F.) 
and in the evening when it was almost dark. The results in all 
