Oct. 22. I92I Hopkins Host-Selection Principle 191 



HISTORICAL 



Very few references to the adaptation of insects to their host plants 

 or the variation in their selection of host plants can be found. The 

 most important paper dealing with the subject is that by Pictet.^ This 

 author shows by several examples, (Ocneria) Porthelria dispar for 

 one, that caterpillars of the second and third generations may be made 

 to change their preferred food plants and that the adults reared from 

 them exhibit changes in size and coloration. This paper is reviewed, 

 and supplemented with reports of corresponding observations, by 

 Schroder,^ who in a previous article ^ showed that even nidification (in 

 Gracilaria stigmatella F.) and habits of feeding, combined with 

 changes in reproduction (in the beetle Phratora vitellinoe L.). can be 

 changed and that these acquired characters are transmitted spontane- 

 ously from the third generation. 



In 1907 and 1908 Paul Marchal ^ succeeded in transferring numerous 

 specimens of Lecanium corni Bouche from the peach (Amygdalus 

 persica Linn.) to the black locust {Rohinia pseudacacia Linn.). 

 Eggs hatched and larvae developed on the new host plant, spreading out 

 over the leaves in large numbers, and in the fall migrating from the leaves 

 to the wood for hibernation. In the summer of 1908 the insects com- 

 pleted their development and had then the large size, deep coloration, 

 and characteristic appearance of the insect described by Douglas as L. 

 robiniarum, the attacks of which on the black locust had been severe 

 in several European localities. This indicated that L. robiniarum was 

 only a race of L. corni, resulting from individuals that had become 

 transferred in some manner from the peach to the introduced American 

 black locust. Dr. Marchal found great difficulty in reestablishing on 

 the peach individuals of L. corni produced on the black locust. 



There are other records showing the acquired adaptation of certain 

 species to new host plants, similar to those here cited. The practical 

 application of such phenomena, however, has, so far as can be ascer- 

 tained, first been recognized by Dr. A. D. Hopkins (referred to on p. 189 

 of this article) and presented by him in concrete form. 



In a paper prepared by M. Joseph Capus ^ on a nematode disease of 

 peas in the Gironde and read by Paul Marchal at the session of July 10, 

 19 1 8, of the French Academy of Agriculture there is a record of injury to 

 peas by a fungus (Fusarium vasinfectum var. pisi van Hall, considered as 

 the conidial form of Necosmopora vasinfecta E. F. Smith, accompanied by 



1 PicTET, Arnold, influence de l'alimentation et de l'humidite sur la variation des papillons. 

 In Mem. Soc. Phys. et Hist. Nat. Genfeve, v. 35, fasc. i, p. 45-127, pi. 2-5. 1905. 



2 Schroder, Chr. die literatur uber die FARBtmo der insekten des jahres 1905. In Ztschr. 

 Wiss. Insektenbiol., Bd. 3, p. 162-164. i907- 



3 i'BER experimentall erzielte instinktvariationen. In Verhandl. Deut. Zool. GeseU., 



Jahresversamml. 13, p. 158-166. 1903. 



* Marchal, Paul, le lecanium du rohinia. Compt. Rend. Soc. Biol. [Paris], t. 6s, p. 2-5. 1908. 



^ Capus, Joseph, and Marchal, Paul, sur la maladie vermiculaire des pois dans la gironde. In 

 Compt. Rend. Acad. Agr. France, t. 4, no. 25, p. 712-716. 1918. 



