In the late 1970's the ash whitefly invaded Southern California. With no natural predators, their population exploded. Between the buildings at my school there were so many whiteflies in the air that it literally looked like a heavy ash fall from brush fires. (In a different climate I would have said, "snow flurries".) A number of trees at the school died as a result of the ash whiteflies. Citrus trees were especial hard hit. The lower sides of leaves, like this tangelo were completely covered with larvae and pupae, frequently causing them to curl and turn yellow.
This photo shows the size of adult ash whiteflies, much smaller than the giant whiteflies . Over years the small birds like the California bush tit discovered their nutritional value, and species specific parasitic wasps were imported. Gradually the pest was brought under "control". This was the worst case I could find when I wanted pictures for this page.
sticky honeydew exuded
by the larval whiteflies drips onto the upper surface of lower leaves.
The sooty mildew, any of several species of black fungus, find
this a most favorable situation. Dust also sticks to the sticky
mess, and with the thick, black growth, blocks out most of the
light for photosynthesis.
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