July i, 191S 
True Nature of Spinach-Blight 
11 
favorable weather, and may feed on many plants during their life. For 
this reason heavy infestations of this species within localized areas in a 
given field are rare. R. persicae has a tendency to congregate and, 
except during periodic outbreaks, are abundant only in more or less 
restricted areas within a field. As might be expected, the alate forms 
are the more active disseminators of spinach-blight. 
Conditions which lead to a large production of alate females are in¬ 
directly responsible for the epidemics of blight which may follow. The 
production of alate females of M. solanifolii occurs throughout the winter 
months, and counts made at various times during the season showed that 
the ratio of alate to apterous forms was 4.12 to 1 for 2,500 individuals. 
Alate females of R. persicae are less numerous than the apterous form, 
except during a severe outbreak; under normal conditions the ratio of 
abundance of the two forms in the order mentioned is 1 to 47.41 for 2,500 
individuals. Counts made at the time of an outbreak showed that the 
two forms were about equally abundant. 
From its ability to withstand lower temperatures Macrosiphum solan¬ 
ifolii does not undergo the numerical fluctuations which occur with 
Rhopalosiphum persicae. The latter species occurs in great abundance, 
usually two or three times during the winter. Severe epidemics of spin¬ 
ach-blight often follow within a few weeks in the areas of heavy infes¬ 
tation. 
FOOD PLANTS OF MACROSIPHUM SOLANIFOLII AND RHOPALOSIPHUM' 
PERSICAE 
Rhopalosiphum persicae attacks nearly all vegetable crops, as well as 
many weeds, shrubs, and trees. Over 60 species have been listed as its 
food plants, and undoubtedly there are others which are yet unknown. 
Dr. Edith M. Patch, 1 in reporting her studies of M. solanifolii , gave a 
list of 20 plants which served as its food. In our studies of the species 
under southern conditions it has been found to be more cosmopolitan in 
its feeding habits than was hitherto supposed. The question of the- 
relationship between the food plants of both R. persicae and M. solanifolii 
to spinach-blight has entailed a great amount of work which is as yet 
unfinished; hence, aside from mentioning that spinach is the most im¬ 
portant fall and winter food plant of both species in this region, the 
findings in this connection are reserved for a later publication. 
DIRECT INOCULATIONS WITH THE JUICE FROM BLIGHTED PLANTS 
VIRUS INOCULATIONS 
Blighted plants were collected from a field of young spinach and 
brought to the laboratory, where they were mashed in a mortar and the 
juice strained through a cloth. With a flamed needle the first row of 
1 Patch, Edith M. pink and grbkn aphid op potato. Maine Agr. Exp. Sta. Bui. 242, p. 205-233, 
fig. 47-49. 1915- 
