102 THE REPORT OF THE [ No. 19 



relief He believed fungous diseases, especially Empusa aphidis, are one of the factors 

 which will bring about the temporary dis»ppearance of the pest. 



Mr. Galloway said the point in regard to the appearance and disappearance of forms 

 holds good in fungous attacks also, the most striking example bsing the potato blight. 

 The same holds good in the passing of the Russian thistle. These things come and go 

 and come again, and the principle holds good with fungous disaases as well as with 

 insects 



Papers were read by Mr. B. T. Galloway on " Progress in the Treatment of Plant 

 Diseases in the United States," and by Prof. Webster on " Meteorological Influences on 

 the Hessian Fly." These were retained for publication elsewhere. The meeting then 

 adjourned to the Central Park to inspect Mr. South wick's spraying outfit. 



On reassembling in the afternoon an elaborate and valuable paper was presented by 

 Messrs. E. D. Sanderson and C. L. Penny, of the Delaware Experiment Station, on 

 " Hydrocyanic Acid Gas as an Insecticide on Lovv Growing Plants." The results of their 

 experiments proved that this method of treatment is practicable, but, owing to its cost, 

 only for plants of some considerable value and for relatively small areas. Under many 

 circumstances it could be used to much better advantage than any other means of com- 

 bating a pest, and often might be found effectual where no other method of extermina- 

 tion were possible. 



Mr. Sanderson then presented a paper, "Notes from Delaware," in which he re- 

 ported upon the most noticeable attacks of the year in that State, and dwelt particularly 

 upon the destructive green-pea louse, which had already been under discussion. After 

 giving an account of the various parasites which preyed upon the insect, he said : 



" The enemies of the lice appear too late to prevent the bulk of the injury, and as 

 the same was true last year, it seems impossible to place any dependence upon them. It 

 seems evident, however, that the lice are attacked by a parasite while still in crimson 

 clover (parasitized lice were also common on red clover), but are not parasitized until 

 they have been on peas for some time. Is it not possible the sudden appearance of the 

 lice last year may have been due to the sevtre winter, which killed off' the parasites and 

 other enemies which usually hold the lice in check on the clover and so reduce their num- 

 bers that but few of them spread to peas ?" 



" The very sudden appearance of this new species last year was a unique entomo- 

 logical surprise. Where it came from was a question. It would seem to me that the 

 original food plant of the pest was clover and probably crimson clover. It is true that 

 crinoson clover is not grown in the North where the louse was found destructive last 

 year, but it is entirely possible that it may have spread from sections in which crimson 

 clover is grown to red clover in these localities, but have been held in check by its para- 

 sites, and remained unnoticed. Furthermore, the insect enemies of red clover have at 

 various times received study without this species having been previously noted. On the 

 other hand, there seems to be good evidence that the louse has been on crimson clover 

 for several years. One of our best farmerp, Mr. Frank Bancroft, of Camden, Del., tells 

 me that he has seen whit he judges to be the same louse on crimson clover for at least 

 six or seven years. In 1890 crimson clover grown upon an experimental plot at the 

 Delaware Station became so badly infested with a plant louse that it was feared it would 

 be killed. Professor Beckwiih's notes state (May 11, 1890) that thfse were exterminated 

 by a fungous disease, and the clover was not seriously icjured. Upon looking over the 

 station collection I found specimens of N. destructor which unfortunately were without 

 any label, but were among mateiial which was unquestionably collected prior to 1896. 

 Upon correspociding with Professor Beckwith he intormed me that he distinctly remem- 

 bered preserving specimens of the aphis in question. As h's accession catalogue shows 

 no such specimens to have been numbered, though by no means conclusive, the evidence 

 is at least strongly circumstantial that Nectarophora destructor occurred in injurious 

 numbers on crimson clover as early as 1890." 



" As regards remedies, 1 have practically nothing new to offer. It evidently is im- 

 portant to plant crimson clover as far from peas as possible, and to turn it under as early 

 as practicable." 



