PRESS BULLETIN No. 108.
FlMrida Agrlcullural Experiment Slallon.
THE WHITEFLY IN CHINABERRY AND UMBRELLA TREES.
BY E. W. BERGER.
It has been calculated by Professor P. H. Rolfs, that the whitefly popula-
tion, in midsummer, of a fully infested umbrella tree of medium size, bearing
about 20,000 leaves, may be 20,000,000 larvae. Dr. A. W. Morrill, basing his
calculations upon a tree of similar size, gives an estimate of about 11,000,000.
Both of these investigators, in order to be well on the conservative side, ac-
cepted the lowest figures of their calculations; whereas the average number
of insects per leaf, according to their actual counts, would have given some-
thing like 70 to 80 millions as the number of larvae per tree. From this last
estimate, it is evident that a large umbrella tree may harbor a hundred mil-
lions of whitefly larvae at one time. Allowing a dozen large umbrella trees
to a town, we may have upwards of 1,200,000,000 adult whiteflies coming out
of these trees during the latter part of summer.
WHAT BECOMES OF THE WHITEFLIES.
Careful observations have shown that these swarming millions of winged
whiteflies deposit only a comparatively small number of eggs upon the leaves
of the Chinaberry and umbrella trees at this time, but quit these trees and
deposit eggs upon evergreen food-plants, principally citrus, privet and cape
jasmine. Whether they do this instinctively, because the Chinaberry trees
lose their leaves in the fall and winter, so that the larvae from any eggs laid
on their leaves must die; or whether the leaves of these trees have developed
some repellent quality; or whether the quitting of these trees is caused by
overpopulation, does not affect the result. The fact is that these whiteflies
swarm about, and either fly or are driven by the wind for long distances,
many of them finding at last suitable plants on which to deposit their eggs.
Last summer the small citrus trees at the Experimee
from whitefly; but in August and September thousands
hovering about and depositing eggs, so that by the end of fa
trees were as heavily infested as citrus trees commonly become.
infested trees from which the whiteflies could have come were umbrel
in Gainesville about a mile away, so that the whiteflies had to travel atir
a mile. That many whiteflies must have gone farther out into the count
than the Experiment Station, can hardly be doubted, considering the great
numbers in which they were swarming about, not only on citrus trees, but on
other plants, on clothing, windows, and vehicles. The principal food plants in
February 13, 1909.
Gainesville and north Florida are Chinaberry and umbrella trees, there being
only enough citrus, privet and other evergreen food plants to bring about the
restocking of the deciduous trees every spring.
WHAT IS TO BE DONE.
That hundreds of millions of winged whiteflies may become matured on
Chinaberry and umbrella trees, and that these hordes of insects may swarm
for the distance of at least a mile, and perhaps several miles, from their
place of breeding is an established fact. Therefore these trees should be
destroyed before next spring, and before they become infested again by the
spring brood of whiteflies. They should be destroyed for three reasons.
1. Because these trees reduce the efficiency of all measures for the
control of the whitefly by one-half or more, or perhaps nearly nullify them,
by setting free swarms of whiteflies into the citrus trees at a time when the
fruit is maturing and it is most desirable to have the trees free from whitefly.
2. Because in newly infested localities "these trees are hastening the
dissemination of the whitefly into the non-infested groves. Besides the
spreading of the whiteflies from them through the air, teams are hitched un-
der such trees, and the vehicles become agents in carrying the insects into
other parts of the country, or to other Chinaberry or umbrella trees, under
which the team might again be hitched.
3. Because of the nuisance to man and beast from the myriads of
whiteflies which frequently fill the air in whitefly infested sections. That this
nuisance is principally due to the presence of Chinaberry and umbrella trees
is evident from the fact that it occurs in sections where there are Chinaberry
and umbrella trees, but where few or no orange trees are grown.
State papers please copy.