bacillus thuringiensis shelf life

Paul Cherubini paulcher at
Thu Jun 25 04:50:57 EDT 1998

While we're dispelling myths about the ability of Bt to sterilize
forests, I would like to dispell some myths about conventional
insecticides as well. The public perception is that chemical
insecticides are the equivalent of a nuclear bomb to moths and
butterflies.  Farmers might wish this were true, but they know a single
insecticide application to an orchard or row crop for pest moth control
typically kills only 25-75% of the population.  So instead of having,
say 5000 moths/caterpillars per acre, your down to "only" 2500!

By the time a food crop gets to the produce section of a supermarket
around 95-99% of it has no detectable pesticide residues and the balance
has barely detectable residues, far below the federal tolerance (which
itself has a huge safety factor built into it) and many orders of
magnitude lower than the residue necessary to kill a moth or
caterpillar.  For this reason, I was amused the other day by the
suggestion that when buying parsley or carrots for Anise Swallowtail
caterpillars, one should buy only expensive "organically grown" produce!
A carrot or parsley farmer would be even more amused and probably would
wish he could show folks healthy moth caterpillars still munching on his
crops the day after a spraying.

Knowing the truth (limited killing power and short lived residues) about
both chemical and biological insecticides can be an advantage to a
butterfly farmer.  For example, two weeks ago I drenched my milkweed
plants with Ortho Malathion insecticide to kill a good percentage of the
ants, earwigs, spiders and other predators of monarch butterfly eggs and
caterpillars.  Then, just two days after spraying, I set a cage over the
plants and introduced several female monarchs inside the cage to have
them lay several hundred eggs.  Now, about ten days later, I have
several hundred almost full grown healthy monarch caterpillars.

Paul Cherubini

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