Pest Management - Growing Organic Orchard Fruits - page 537

Bacillus thuringiensis
Bacillus thuringiensis (Bt) is found naturally in soil and on plants, and many
different subspecies or strains exist, some of which attack insects. It is very
important to know that not all strains attack all insects. Some strains are ef-
fective against caterpillars (moth and butterfly), while others attack beetles
or whiteflies. These products are generally nontoxic to mammals or birds, al-
though a very small percentage of people are allergic to B. thuringiensis in
large concentrations, and the bacteria can enter the human body through
wounds or contact with mucous membranes.
Bacillus thuringiensis products work only after an insect ingests them. A
crystalline protein produced by the bacteria attaches to the gut of the in-
sect, perforating the gut wall. The insects often stop feeding rather quickly
after ingesting the bacterium but may take several more days to die. Bacillus
thuringiensis products have a short lifespan in orchards and typically do not
remain effective for more than a few days after being applied to crops. Be
sure that the product you use is certified for organic programs (there are
some genetically engineered Bt products available), and be sure your product
is labeled for the specific pest you are trying to control. Resistance to B.
thuringiensis has been found in some populations of diamondback moth and
Colorado potato beetle, probably due to overuse of these bacterial insect-
icides. Use Bt products in rotation with other pesticides in an integrated and
diverse pest management program.
Beauveria bassiana
Beauveria bassiana is a soilborne fungus that is found worldwide and that
attacks some insects. Two strains are commonly used to control pests and
are made using fermentation to produce spores that are applied to plants in
sprays.
Pests for which B. bassiana products are registered include ants, aphids,
caterpillars, grasshoppers, mealybugs, thrips, weevils, and whiteflies. Infec-
tion usually occurs when the spray contacts an insect or the insect contacts
the spores left on plant surfaces after the spray dries. The spores germinate