38 
tions were unfavorable for the rapid increase of Allotria in 1908, 
which conditions would prove favorable for Aphidius and also 
unfavorable for its host, the Toxoptera. This infested area on the 
department grounds in Washington has proved to be of considerable 
interest, as the fluctuations of Toxoptera there, as well as those of its 
parasite Aphidius and the secondary parasite Allotria, must coincide 
with what is going on in similar places over the country, thus forming 
small secluded breeding areas where Toxoptera survives throughout 
the summer, more especially in the South. The area in question is 
a depression covered chiefly by bluegrass, occupying perhaps half an 
acre, surrounded on all sides except the south by shade trees (See 
PL II, fig. 2.) It is rather more moist and therefore cooler in summer 
than other portions of the grounds and in common with the rest is 
kept closely mown. An underground steam pipe which affords heat 
for a large number of greenhouses extends along the southern and 
eastern margins ; the ground above this pipe is always much warmer 
than the surrounding area during winter, the snow disappearing first 
and the grass in that location starting much earlier in spring. So far 
we have not found that these latter conditions have any influence 
in enabling the Toxoptera to breed viviparously during the winter. 
Even when the Toxoptera was excessively abundant here none could 
be found in the bluegrass-covered grounds only a few yards away, 
except in 1910, when it was quite numerous about the Washington 
Monument some four blocks away. Because of its isolation — there 
are no grain fields within miles on the Maryland side of the Potomac 
River and the department experiment farm at Arlington, Va., has the 
only grain for miles on the west side of the river — and because these 
last had never suffered from Toxoptera attack, this area became of 
too much importance as a convenient held of observation and experi- 
mentation to make an attempt at experimenting with the importation 
of great numbers of Aphidius desirable. There is every reason for 
believing that it is in similar favorable localities that Toxoptera 
passes the summer months in the southwestern portion of the country, 
where, as observations have shown, it is not able to withstand the 
high temperatures of the open fields. 
Toxoptera has been studied throughout the summer in the South- 
west with much difficulty, and not at all satisfactorily for the reason 
that we have been unable to keep it under continuous observation in 
the open fields. 
Except in cases of local outbreaks here and there over the country 
there has been no serious injury to grain crops by the " green bug" 
since 1907. Many additional localities for the species have been 
added since then, however, and it now appears to cover almost the 
entire United States, excepting perhaps New York and the New 
England States. (See fig. 4, p. 19.) 
