NATURAL CONTROL. 41 
that crotons, which in the greenhouse were infested with thousands 
of thrips and which in. June were placed outside and subjected to 
the Florida summer rains, when examined in September were so free 
from this insect that it was almost impossible to find specimens. 
California, with its long dry season, does not obtain the same 
benefit, but even there the rains may reduce attacks of the bean thrips 
to some extent. On February 7, 1911, the writer observed a pea 
field that had from 5 to 8 adults on every plant. After this date 
there was a severe rain of several days' duration, and when the 
field was again examined, on April 1, it was almost impossible to 
find the thrips. Mr. Graf, writing from Puente, Cal., on October 6, 
1911, noted that the larvae were much scarcer than a week earlier, 
probably owing to a rainfall of one-half inch. Mr. Wildermuth, 
at Tempe, Ariz., wrote on October 5, 1911 : 
A search in the patch of alfalfa back of the office, where thrips had been 
very numerous for several weeks, failed to reveal very many thrips to-day. 
The heavy rain of yesterday and last night was probably responsible for 
washing them off. 
In California, then, late rains in the spring may greatly diminish 
the numbers of this insect, or early rains in the fall destroy many 
that otherwise would enter hi- 
bernation. 
NATURAL ENEMIES. 
Fig. 10. — The bean thrips : Prepupae parasit- 
A ffreat deal of attention has ized b ^ Thrtpoctmus russeiu. Much en- 
° . . j, larged. (Author's illustration.) 
been given to the subject of 
natural enemies and some information obtained on this important 
feature of insect control. 
In the fall of 1910 the larva of this thrips was discovered to be 
parasitized (see fig. 10) by a minute hymenopteron. This was de- 
scribed by Mr. J. C. Crawford as Thripoctenus russelli (see fig. 11). 
During 1911 this parasite was observed to work extensively in Los 
Angeles County on the bean thrips and seemed to destroy large 
numbers. Some collections of thrips larvae gave as high as 70 per 
cent killed by the parasite. For a full account of this parasite the 
reader is referred to Technical Series 23, Part II, Bureau of Ento- 
mology, United States Department of Agriculture. 
During 1911 the larva of a green lacewing fly (Ohrysopa cali- 
fornica Coq.) was commonly observed feeding on the larva of this 
thrips. As this insect was observed so engaged in several localities 
in Los Angeles County, and in noticeable numbers, it probably kills 
a large number of thrips. 
The larva of a syrphid fly (Sphwrophoria sulphuripes Thomson) 
was also observed on numerous occasions feeding on the larva of 
