118 



THE HOST PLANTS AND HABITS OF APHIS 

 RUM WIS LINN., WITH SOME OBSERVA- 

 TIONS ON THE MIGRATION OF, AND IN- 

 FESTATION OF, PLANTS BY APHIDESi. 



By J. DAVIDSON, M.Sc, F.E.S. 

 {Research Scholar in Agricultural Zoology, Board of Agriculture.) 



Introduction, 



The following experiraents are the first of a series of experiments 

 and observations on the habits and life-history of the Aphididae, which 

 the author hopes to carry out, with the hope that our knowledge of the 

 migratory habits of these insects, and the infestation of plants by them, 

 may be increased. 



The results obtained this season do not afEord sufficient data upon 

 which to base any definite explanations of these problems. Many of 

 the observations, however, have suggested certain lines of enquiry. 



In the latter part of this paper, the author has briefly discussed 

 some of the factors which may underly the questions of the migration 

 of Aphides and the infestation of plants by them. 



Some tentative suggestions as to the nature of these factors have 

 been made, with the hope that deeper enquiries into the habits of this 

 important family of insects may be stimulated. These suggestions are 

 based upon observations made in connection with these experiments. 



In September, 1912 {op. cit. below), Theobald published an interesting 

 paper dealing with the habits and life- history of Aphis rumicis, in which 

 this author describes a double life-cycle for this species. In one cycle 

 ova are produced by the sexuparae, in late Autumn, on Rumex plants. 

 These ova hatch out in Spring, and subsequently winged migrants are 

 produced on the Rumex plants. These migrants go, about June, to 



^ The species of Aphis used is the black aphis found in spring on Euonymus airopaeus 

 {Aphis euonymi). It is now eonaiderod as one of tiie many synonyms of Aphis rumicis, 

 vide Theobald, F. V. (I!tl2), Juuni. Bd. of Ayric. vol. xix. No G, Sept. 1912. pp. 4(iG-476. 



