40 THE BEAN THRIPS. 
In the section around Compton, Cal., the adults were found to 
hibernate in small numbers on the underside of leaves of nasturtium, 
sugar beets, wild heliotrope, and other plants. They were also found 
Liberating in some numbers in dead leaves and rubbish. Wlien dis- 
turbed they were sluggish and made little effort to escape. 
Mr. P. K. Jones (in litt.) says that around Lindsay, Cal., the adults 
hibernate in numbers in the navel end of the Washington navel 
orange. He also stated that in midwinter he had taken this thrips 
along creek beds hibernating on the underside of leaves of wild rasp- 
berry and blackberry which were still on the plants. 
NOTES ON OCCURRENCE. 
Apparently the different methods of cultivation bear strongly on the 
abundance of these insects and consequent injury they may cause to a 
crop. In Los Angeles County, where clean cultivation is not strictly 
followed out, it begins to breed in the spring on the wild food plants 
and increases more and more until in August it has reached enormous 
numbers. Before this the native plants are, many of them, either 
matured or destroyed by the thrips, and as a result it spreads more 
and more to the cultivated crops and trees that serve as hosts. Dur- 
ing some years this occurs late in the season and very little real 
damage results, but if this insect should begin the year in fairly large 
numbers and under favorable conditions, great damage may result. 
In Ventura County, in October, 1910, the author made a careful 
examination of the entire bean-growing section and found that the 
bean thrips occurred in extremely small numbers on the little vege- 
tation remaining. At the same time it was extremely abundant 
around Compton. This condition seemed to be a direct result of the 
practice of the growers in Ventura of thoroughly plowing and culti- 
vating the fields within a short time after the beans are harvested 
and keeping them in perfect condition until the next crop is planted. 
This advantage is increased because there is very little waste space 
where weeds can grow up. Our investigations during the past two 
years have shown that this insect is not abundant on cultivated crops 
in the spring or early summer, but that after this period it increases 
more and more, and in certain years injures them so severely as to 
cause much loss. 
NATURAL CONTROL. 
BAINS. 
One of the largest factors in the destruction of thrips in some 
localities is the prevalence of hard, dashing rains. The author, 
while working in Florida with the greenhouse thrips, once observed 
