PARASITE, APHIDIUS TESTACEIPES. 121 
present for weeks in a field with no visible indication of their presence. 
Yet only a few warm days are required to bring about their final 
development, whereupon the presence of the more or less globular, 
leathery, brown bodies of the parasitized host first begin to attract 
attention and thus actually reveal the presence of the Aphidius, 
which has already been established there. 
An excellent illustration of this is afforded by an occurrence of 
Toxoptera in eastern North Carolina, observed by Mr. L. M. Smith. 
In a small field of oats near Newport, wingless viviparous female 
Toxoptera and young were found in destructive abundance with no 
indication whatever of the presence of Aphidius. Yet when speci- 
mens of the pest submitted by Mr. Smith reached Washington, some 
o t f them were beginning to change color from the presence of Aphidius 
larvse within their abdomens. Again, when Mr. C. N. Ainslie visited 
Wellington, Kans., April 1, 1907, he observed no trace of the presence 
of Apliidius, but upon returning to this same locality on April 10 he 
found them present. Only a few of the Toxoptera had yet become 
dark brown, but a large number showed the orange color that told 
the story of their parasitism. Therefore all statements made in 
previous publications relative to the lack of parasites, or to the 
extent to which they occurred in any field or locality, must be under- 
stood as applying only to either the adults or to the browned cocooned 
bodies of the host insects, and are not in any sense to be considered 
as indicating the extent to which these host insects were carrying 
obscured Aphidius larvae about with them in their bodies to develop 
adults whenever there were a few sufficiently warm days. 
EFFECTS OF WET WEATHER OX THE DIFFUSION OF APHIDIUS. 
There is another element affecting the diffusion of this most 
efficient of natural enemies of Toxoptera, namely, protracted rains. 
When it is raining the parasite simply will not take wing at all or 
move about in a way to be affected by winds. This element will 
not admit of tabulation for the reason that a thunder shower followed 
by warm, bright sunshine tends to make these, as well as all winged 
insects, more -active after the storm has passed. Thus, the amount 
of precipitation really means little, while a slow, drizzling, protracted 
rain (though the total precipitation may be much less) will keep the 
parasite in seclusion much more effectively. Hence it is that not 
only a comparatively high temperature accompanied by winds is 
essential, but the weather must also be fair and sunny. 
In British East Africa Toxoptera is worse during seasons when 
there is much wet weather, and in the Orange Free State outbreaks 
of the pest seem to be also associated with similar meteorological 
conditions during spring. 
