EXPERIMENT STATION BULLETINS. 247 



THE DESTRUCTIVE PEA-LOUSE. 



(Nectarophora pisi Kalt.) 



In May, 1899, an outbreak of this insect in the state of Maryland, attracted the 

 attention of all interested in the industry of pea growing. Since that time, the trouble 

 has spread to New York, Delaware, North Carolina, New Brunswick, Nova Scotia, 

 Ontario, Ohio, and Wisconsin. Michigan has been the recipient of just enough damage 

 to make it seem advisable to sound this warning note. In Maryland, the loss in 1899, 

 most of which was ascribed to this insect, was estimated at three million dollars, and 

 the injury as a whole seems to be becoming more widespread, rather than otherwise, 

 although the condition is becoming better in the parts originally invaded. Prof. 

 Sanderson, in his admirable account of this pest, considers it identical with the 

 European pea-louse, which has been known and dreaded for many years, and which is 

 called the "green dolphin."* The appearance of the destructive pea-louse closely 

 conforms to that of most plant-lice. It is a large-sized green louse either winged or 

 wingless, the latter form predominating. It feeds upon clover and vetches, besides peas 

 and is said to feed also upon various other plants. It is said to pass the winter on 

 clover, greatly preferring crimson clover to all others. 



Michigan has, thus far, escaped with comparatively slight losses, but the pest is in 

 Ontario, Ohio and Wisconsin, and has already done some damage here. We can hardly 

 hope to escape scot-free. The insect has been found here at Saginaw, Cheboygan, Sault 

 Ste. Marie, Gladstone, Petoskey, Harbor Springs, Alpena, Ludington, Charlevoix and 

 Lansing. 



Specimens collected in the vicinity of Traverse Bay by the writer were identified as 

 the green pea-louse, but in order to be certain it was thought best to send them to 

 Prof. Sanderson, who kindly compared them with material from other localities and 

 pronounced them identical. The damage in all these places was slight. At Harbor 

 Springs, most of the damage was done to sweet peas in 1900. At Ludington, the damage 

 seems to have been restricted to a small area, and at Charlevoix, only one field was at 

 all seriously injured. The rest of the localities named had merely a small infestation 

 except Alpena, the details of which infestation I do not know. 



In reply to a letter Messrs. D. M. Ferry & Co., of Detroit, write the following in 

 part: "We would say that we have grown peas in Michigan for the past twenty years 

 or more and there have been few years when one or more of our crops have not been 

 injured to a greater or less degree by lice which we thought were the common 'green fly' 

 so often seen in green-houses. At the same time, the pest has never been so serious a one 

 as to materially affect the average yield, and we have thought that the natural enemies 

 of the insect, such as the common 'lady-bugs' and unfavorable weather conditions (for 

 the lice) could be depended upon to keep them in check. The past year we saw one 

 crop which was badly infested and the plants practically destroyed in part of the field. 

 At that time there were a great many lady-bugs at work and when we visited the field 

 some weeks later, the lice had disappeared and we harvested a fair crop on all but a 

 small part of the field where the lice were the worst." 



The above letter shows that the pea-louse is not a new insect in our State and that, 

 at least up to the end of 1900, it had not become serious. It is. however, coming nearer 

 and nearer, gradually closing in on us and in a State like Michigan, where clover is so 

 freely grown, I repeat, we cannot hope to entirely escape. 



It seems best therefore, under the circumstances, to make known the best methods of 

 combatting the pest in order to anticipate. It is hoped that any outbreak of this or 

 in fact any other insect, will be immediately reported to the entomologist in order to 

 make it possible to carry on experiments on our own account and in our own State. 

 It often happens that a measure which may prove perfectly satisfactory in one district 

 is of comparatively little use in another. In order to get the best results it is necessary 

 to compare the different methods in our own State under existing conditions of weather 

 and soil taking into account cost of insecticides, cost of labor, price obtained for the 

 product, etc. 



* Twelfth Annual Report Delaware College. Agricultural Experiment Station for 1900, p. 175. 



