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 onl}^ 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 setse 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 setse 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 waj^, 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 



