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ATURAL1ST [Vol. XLIII 



Classification of Adaptations to Food 

 A plant-insect group— a group, that is, composed of 

 a plant and its insect visitants— is not, in fact, usually 

 marked, either as a whole or in any of its several parts, 

 by the presence of adaptive structures special to that 

 group. The structural adaptations of insects are, as a 

 rule, much too broadly shaped to fit them closely to any 

 one plant, and where such a fitting is found, it is clearly 

 due to some other than the structural factor. Such facts 

 bring us to a consideration of the whole subject of the 

 variations and classification of the adaptations of insects 

 to their food resources. 



These adaptations may be classed as structural, physio- 

 logical, psychological, synethic, 2 local, biographical and 

 numerical. All structural adaptations are, of course, 

 physiological, in a sense, but I use the word physiological, 

 as a matter of convenience, for functional adaptations 

 not based on obvious structural peculiarities, as where 

 an insect equally capable of feeding on the sap of two 

 plants, and readily availing itself of either, nevertheless 

 thrives and multiplies better on one than on the other, 

 the adaptation being evidently digestive or assimilative 

 rather than obviously structural. The San Jose scale, 

 for example, feeds readily on a great variety of trees and 

 shrubs, on some of which it thrives poorly and spreads 

 but little, while on others it multiplies enormously and 

 spreads with great rapidity. The word psychological 

 may be applied to cases of apparent choice or evident 

 inclination, as between the various available food plants 

 of the environment. Those fixed peculiarities of habit 

 or behavior which adapt an insect to one food plant or 

 class of food plants rather than to another we may call 

 synethic adaptations, in the absence of any existing word 

 applicable in this sense; local adaptations are those in 

 which the usual haunts and places of resort of an insect 

 species, however determined, bring it into common con- 

 tact with an available food plant, the frequency of this 



