52 PROTECTION OF PLANTS, 1917-18 



ANTS AND APHIDS. 



By Father P. Fontanel, S.J., St. Mary's College, Montreal. 



All naturalists who have studied ants or aphids have mentioned the in- 

 timate relations existing between these two groups of insects. I am quite ready 

 to admit, with Dr. Howard, that these relations constitute "one of the most 

 fascinating topics in the whole field of nature study." {The Insect Book, page 265). 

 Most writers see therein merely the manifestations of a marvellous instinct; 

 there are others, however, who try to deduce a proof for the existence of an intelli- 

 gence which would do honour to many specimens of the human species. 



From the economic point of view the interest lies in another direction. More- 

 over, I have ascertained that many persons are of the opinion that ants render a real 

 service to the plants. It is therefore worth while to examine the question closely 

 and to record some observations which are convincing and easily checked. 

 Such is the object of the following study. 



The plants examined with particular care were : Cineraria sp., Amaranthus 

 sp., Papaver sp., Malus sp., Dianthus sp.. Petunia sp., Rosa sp., Cerasus sp., 

 Prunus sp., Cucurbita sp., Acer negundo Linn., Cheiranthus sp. 



The observations were made on the following species of aphids : Aphis cardui 

 Lin., Aphis avenae, Rhopalosiphum dianthi, Rhopalosiphum nympheae Lin., 

 Aphis rudbeckiae Fitch., Hyalopterus arundinis Fabr., Aphis mali, Rhopalosi- 

 phum lactucae. Kalt. 



The determination of the greater number of species of aphids mentioned 

 above is due to the Department of Entomology of Ottawa and more especially to 

 Mr. Gibson and to Mr. Ross. I take the present opportunity to acknowledge 

 my indebtedness. 



This is the thesis which I wish to prove: Ants are injurious to plants through 

 their relations with the aphids; they are far more injurious, the smaller the plants are. 



Entomologists who have studied the insects from the economic point of 

 view could not avoid this question, and yet very few of them have made any 

 definite pronouncement. Mr. L. C. Miall, one of the most precise I know, merely 

 says :j"Ants often run about plants which are infested by aphids, and have been 

 seen to attack and drive off the aphis eaters." (Injurious and useful Insects, p. 

 157). This is not a very bold statement, for the ants might protect the aphids in 

 order to prey upon them afterwards at their leisure, just as a lion might protect 

 a lamb from a wolf. Mr. J. B. Smith in Economic Entomology, p. 127, goes 

 further "since they are of decided economic importance." 



