l9» 



NOTES AND ABSTRACTS. 743 



also acts as a water-absorbing and water-storing organ. The author 

 criticises the work of Schimper, Wettstein, and others. There is a useful 

 bibliography giving the more recent publications on the subject. 



G. F. S.-E. 



Aphis. — At the recent Congress of Economic Biologists held at 

 Birmingham a valuable paper was read by Mr. F. V. Theobald, entitled 

 " A Plea for the Study of British Aphides in connection with Cultivated 

 Plants." Mr. Theobald said that in 1904 plant-lice, or aphides, had been 

 more in evidence than in any year during the last quarter of a century. 

 Rare species were very plentiful, and common species swarmed. Many 

 could not be identified at all, and disappeared from the trees and plants 

 they, infested as rapidly as they apparently made their appearance. More- 

 over, in 1904 he observed several aphides migrating in vast swarms, aphides 

 that in previous years had been far from common in the locality. The 

 enormous reproductive power of these insects at certain times was well 

 known, but we know nothing of the causes that regulate the reproductive 

 phenomena ; why an excessive reproduction takes place now and again, 

 accompanied by a vast active migration— a so-called "blight." One 

 instance showing the unsatisfactory state of our knowledge in regard to 

 plant-lice and cultivated plants might be taken in the case of the Apple 

 aphides. The majority of writings by economic entomologists on Apple 

 aphis are, he said, valueless, because they treat two or three totally distinct 

 species as one. In 1902 Sanderson worked at the Apple aphides in 

 Delaware, and found that there were three common Apple aphides, viz. Aphis 

 pomi, Aphis sorbi, and the commonest aphis, a hitherto undescribed species 

 which Sanderson named Aphis Fitchii. With the object of seeing whether 

 if this new species was our common spring and autumn aphis, Mr. Theobald 

 made collections in various parts of the country, and found Sanderson's 

 species to be by far the commonest. This was very important, because 

 Aphis Fitchii was a well-known migrant. It fed on the Apple in spring 

 and early summer and was the cause of damaged buds, withered blossom, 

 and deformed fruits, but caused only very slight leaf curling. It left the 

 Apples in early summer and did not return until the autumn, when a 

 sexual brood was produced. He was inclined to believe that the Aphis 

 Fitchii migrated to Corn and Grasses. On the other hand, Aphis pomi was 

 permanent on the Apple, and was a great leaf-curler, producing a terribly 

 crumpled-looking leaf if allowed to work on unmolested. Aphis Fitchii 

 hatched much earlier than Aphis pomi, and commenced its attack before 

 the blossom was open. Spraying was of use in spring for this species ; 

 . it is not so, however, for Aphis pomi. It was, therefore, very important 

 to know what particular Apple aphis they had to contend with. It was 

 because they had not known what they had been giving advice upon that 

 v they got such varied results in spraying. Leaf-curling aphides were the 

 most 'difficult to cope with, because the curl protected the plant-lice from 

 any spray they chose to use. In fact, with such species as the Plum aphis 

 and the Currant aphis it was only a waste of time and money to do so 

 when the leaves were once deformed. A knowledge of the life-history of 

 an animal pest is most important, for it would show us where we could 

 attack it with some hope of success. 



