212 EXPERIMENTAL FARMS. 



64 VICTORIA, A. 1901 



In my last report considerable space was devoted to the Destructive Pea Aphis, 

 a new pest of the pea, of which no previous attack had been recorded in Canada. The 

 injury extended from all parts of the Maritime Provinces, through Quebec to the 

 western boundaries of Ontario, and the loss in many places was serious. Not only did 

 it occur in Canada, but much greater injury was caused by it in certain of the United 

 States, as Maryland, Delaware, ]^ew Jersey, Kew York, Connecticut, &c. Excellent 

 work has been done upon this insect in Maryland by its describer, Prof. W. G, John- 

 son, and in Delaware, by Prof. E. Dwight Sanderson, both of whom have published 

 bulletins on the subject. 



In Canada during the past season, although the Destructive Pea Aphis has occurred 

 throughout most of the districts visited by it last year, the numbers and injuries have 

 been decidedly less. It has been discovered in the United States that this insect 

 should perhaps be considered more particularly an enemy of clover than of peas. In 

 Canada the sj)ecies has been found only in small numbers on clover, and no perceptible 

 harm has either been observed or reported to this crop. Wherever the Destructive Pea 

 Aphis was obsei-ved, it was attacked to a very noticeable degree by parasitic enemies. 

 All of the species mentioned in my last report were found during the past season in 

 even greater abundance, and in addition to these with every outbreak the fungous 

 disease due to Empusa aphidis was more or less prevalent. At Ottawa by far the most 

 inveterate enemy of the plant-lice was the small orange larva of a species of Diplosis ; 

 these minute maggots, about one-tenth of an inch in length, crawled about on the 

 surface of the pea vines and worked very much in the same way as the larvaa of the 

 Syrphidae, or Hover Flies ; creeping up to an aphis they transfixed it and held it up, 

 raised from the surface, while they sucked out the juices of its body. The growth of 

 these little creatures was very rapid and there were several broods in the season. When 

 full grown these Diplosis larvse spun a minute cocoon on the stem of the pea plant, or, 

 falling to the ground, spun it there close to the surface, attaching several grains of 

 sand to the outside. This cocoon closely resembles that of the Wheat Midge, or the 

 tiny Cecidomyid Lasioptera vitis, of Osten Sacken, which emerges from the Grape 

 Vine Tomato Gall. The winter is passed by the larva inside the cocoon. The plants 

 iliost seriously attacked in Canada this year were late field peas, sweet peas in 

 gardens and the new crop plant known as the Grass Pea, which is being grown in some 

 districts on account of its exemption from the attacks of the Pea Weevil. Several 

 occurrences of the Destructive Pea Aphis were watched from the time they first 

 appeared this year at Ottawa, on July 27, until the time when permanent snow fell, 

 and a few specimens were found on clover by dicging up the plants from under the 

 snow. Parasites of several kinds were abundant throughout the season, and a 

 constant warfare was waged. No sooner did the aphis increase, and appear in large 

 numbers than the parasites appeared in greater numbers and brought them down 

 again suddenly almost to a point of total annihilation. However, at the end of the 

 season a few specimens of the aphis could be found wherever there were chance seedlings 

 of peas and upon late sweet peas, as well as the few mentioned above as found on 

 clover. The attacks of this insect upon the plants where it occurs are of a very perni- 

 cious nature, the plants soon becoming stunted, and the flowers, if produced, quickly 

 withering up. Sweet peas which were sown early and had made good growth stopped 

 flowering as soon as the insects appeared, and late sown plants were dwarfed and made 

 no further growth after the attack began. 



Last year the worst complaints of injury came from the Maritime Provinces. This 

 year Mr. Eobertson, the Superintendent of the Experimental Farm for the Maritime 

 Provinces, writes : * The Pea Aphis began its work this season in Nova Scotia just 

 about the same time as last year and it looked as if it was going to be just as destruc- 

 tiA'e ; but for some unaccountable reason it disappeared all at once, though not until 

 it had completely destroyed peas which were sown late or on poor ground, where they' 

 had a sickly growth to begin with. Such as had a strong and vigorous growth were 

 not much hurt. I did not notice any on clover.' 



