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Evolution
The World of Darwin
Tobacco Budworm
Tobacco Budworm
During the 1960's, the tobacco budworm, the caterpillar of a night flying moth, became one of the most serious pests that cotton growers have ever had to face.

These caterpillars would eat the bolls, flower buds, and flowers of the cotton plant. In the process, they would cause millions of dollars worth of damage every year.

Growers promptly turned to organophosphate insecticides that penetrated the skin of the caterpillar and acted as a nerve poison. At first, this treatment seemed to be working, and one formulation of the insecticide killed about 60% of the budworms.

But 40% survived!

Fighting back, the growers turned to a different insecticide formulation that killed 70% of the budworms, but still some survived.

In the lower Rio Grande Valley, farmers applied different mixtures of organophosphates up to 25 times, and still the crop could not be harvested. The insecticide treatments did, however, kill all the spiders that normally ate the budworms.

Resistant budworms always survived, being more fit and better adapted to a now predator-free environment, no matter how laden it was with chemical poisons.

Incredible environmental pressure, exerted by the farmers and their poisons, ensured that within a few years there were millions of resistant budworms and no spiders. By 1969 the budworms had won, and 40 cotton gins were closed forever. Evolution had taken only 8 years and left economic disaster behind it.

A lesson learned Learning from the lessons of natural selection, some growers are now reverting to methods used 70 years ago and not putting new selection pressures on the insects.

Land is cultivated early, having been carefully cleaned to remove overwintering weevils. Short-season varieties of cotton are grown so as to outrun the pest problem, and spiders and other beneficial insects are encouraged, not killed indiscriminately. Insecticides are used on small areas only as a last resort, and only if a situation seems to be getting out of hand.

Such growers are no longer troubled by budworms.


BIOdotEDU
© 2001, Professor John Blamire