74 Psyche [April 



effects which cause the insect to assume this position irrespective 

 of the immediate presence of the causative stimulus. 



One other explanation may be offered here: The aphid 

 possibly assumes this position for mechanical advantage, in the 

 way of bringing about optimum efficiency in the functions of the 

 sucking mouth-parts, and of minimizing the strain on the muscles 

 of the legs and other parts of the body which is occasioned by the 

 insect's having to remain in one position for considerable lengths 

 of time while feeding. 



The fact that the aphids turn around and resume feeding in 

 the reverse direction with respect to the plant when the tips of 

 the tansy on which they are situated are bent indicates that this 

 behavior of Macrosiphum has not been brought about as an 

 adaptation to any peculiarity in the structure of the host. 



The characteristic feeding position of Macrosiphum tanaceti 

 has also been observed by me in other species of Macrosiphum. 

 It is interesting to note that the aphids of other genera which I 

 have studied^ do not seem to exhibit this peculiarit5^ They 

 almost all indifferently assume any position while feeding. It 

 may be mentioned, as a possible explanation of this difference in 

 behavior, that these other aphids generally feed on the nether 

 surface of broad leaves, or are otherwise protected from the direct 

 rays of the sun. Thus the main stimulus which, as I have sug- 

 gested above, is probably responsible for the characteristic 

 position of the Macrosiphum species is suppressed in the case of 

 the other aphids. 



Summary of Section III. 1. Macrosiphum tanaceti appears 

 to be confined to a single host plant, Tanacetum vulgare. From 

 early in the spring until late in the fall in Boston and vicinity, this 

 aphid in diffierent instars is found feeding on the more succulent 

 portions of the plant, principally on the growing regions of the 

 stem. 



' 2. The head of the insect is directed toward the ground 



3Anoecia, Lachnus, Longistigma, Drepanaphis, Drepanosiphum, Myzus, Eriosoma, un- 

 identified aphids on Berberis vulgaris Linn., Celaslrus scandens Linn., Lythrum salicaria Linn., 

 Sherpherdia (Elaeagnus) argenlea Nutt., and Viburnum sp., and others. 



