49 



chemotropic agents for various Dipiera. Ethyl alcohol, in various 

 concentrations, exhibited little or no chemotropic properties, but 

 with the addition of small amounts of butyric, valerianic or acetic 

 acids it exercised a powerful attraction. Aqueous dilutions of the 

 above acids were not attractive, the respective esters probably 

 being the attractive agents in each case. The remaining sub- 

 stances utilised in these experiments were found to exhibit little or 

 no positive chemotropic properties. Out of considerably over 

 3,000 Diptcra attracted during the course of these observations, b\ 

 far the greater number pertained to one or other of the five families, 

 Rhypiiidcc, Mycetophilidcc, Sepsidcc, Muscidce and Anthomyidce. 

 As a general rule, members of both sexes of a species were 

 ;ittracted irrespective of the chemotropic agent employed. In the 

 majority of instances, males predominated over females, but in no 

 rase where the number of individuals of a species attracted 

 exceeded 20 was the disproportion greater than 2.9 males to 1 

 female. Rhyphus punctatus. Hylemyia strigosa and CaUiphora 

 erythrocephaia were the dominant species attracted. 



XXXI. J. Davidson. " Biological Studies of Aphis 

 rumicis L." Part 1. — " Description of the 

 Species and Life History." Bull. Entom. Res., 

 Vol. XI., 1921. 



'' Biological Studies of Aphis rumicis L." Part 

 II. — (a) "" Appearance of the Winged Forms ""; 

 (b) " Appearance of the Sexual Forms." Proc. 

 Roy. Dublin Soc, 1921. 



" Biological Studies of Aphis rumicis L." Part 

 III. — (a) " Reproduction of Aphis rumicis on 

 different Host Plants " ; (b) " Influence of Food- 

 Plants on the Characters of the Species " ; (c) " In- 

 fluence of Temperature and Humidity on the 

 Development of the Species." Annals of Applied 

 Biology, Vol. VIII., 1921. 

 The life history of Aphis rumicis is as follows : — 

 The ova are laid by sexual females on the winter host (Euony- 

 }uus) during September and October '^^ These hatch out in 

 March and April, and the Fundatrices produce the first viviparous 

 generation on the winter host. Eventually, w.v.'2> {migrantes) 

 develop, which migrate to the intermediate hosts, such as beans, 

 poppies, etc. On these latter plants, they produce a.v. (alienicola' 

 apterce). Eventually, w.v. (alienicolcr- alatce) are produced 

 which fly to other intermediate hosts, of the same kind or different 

 species, such as Chenopodium, Mangolds, Beet, Capsella bursa- 

 pastoris, Rumex, etc. This infestation of the intermediate hosts 

 continues throughout the summer months. 



In September, certain of the alienicolce apterce (sexiiparce 

 apterce) produce winged sexual males, and at the same period 

 certain of the cdienicolcc alcitcc (sexuparce cdatcc) which morpho- 

 logically resemble the earlier winged forms but are physiologically 

 different, fly back to the winter host, and there produce apterous 

 females. The males fly back from the intermediate hosts to the 

 winter hosts, the cycle being thus closed. 



(1) It is highly probable considering the wide distribution of Aphis rumicis that there are 



other winter ho«te. 

 (2> w.v. — \vin;.^pf1 vivipnrous fomalc: n.v.— apt* rous viviparous female. 



