Scientists Say Sustainable Agriculture
is Superior

ECOLOGISTS AGREE: WE'RE NO SMARTER THAN NATURE
6 August, BioMedNet News

Corporate models of farming took it on the chin at the Ecological Society of
America conference earlier this month, as participants railed at heavy
pesticide use as an unsustainable practice for agriculture.
Traditionally, most ecologists have been reluctant to apply their
understanding of natural systems to the much-simplified artificial
ecosystems that farm fields represent. But ecologists at the symposium on
ecology and agriculture felt no such hesitation. "The more effectively
insects are killed, the more effectively they evolve resistance," said
University of Illinois entomologist May Berenbaum.

Berenbaum honed in on the central irony of chemical usage: The strategies
currently used in pesticide application - application of insecticides to
large areas for prolonged periods of time every generation, with the goal of
destroying every last bug - are a perfect recipe for natural selection of
evolution resistance. More than 500 arthropod species are known to have
evolved resistance to insecticides and more than 140 weed species to
herbicides thus far. Higher doses of the chemicals are being used with less
effect every year, says Matt Liebman of Iowa State University.

Some insects have shown behavioral changes along with changes in physiology.
For instance, Illinois farmers held the corn rootworm at bay for 30 years by
rotating crops, planting corn in a given field one year and soybeans the
next. The corn-munching rootworms would lay their eggs, which would
overwinter in the field. Come spring, the rootworm larvae would hatch into a
sea of soybeans, and promptly starve to death.

Recently, however, the bugs have evolved two ways of dealing with their
predicament, Berenbaum says. Some fly to nearby soybean fields and lay eggs
there, and others stay dormant for two winters instead of one, waiting to
hatch in the "correct" year.

Using chemicals to fight insects that eat plants is nothing new: Plants
themselves have been at it for millions of years. But, Berenbaum says,
plants conduct their chemical warfare differently, and more effectively.
Rather than broadcast a chemical wantonly in every direction before an
insect is even on the scene, many plants conserve their defenses until they
are attacked, and limit their toxins to specific sites. They also boast a
complex arsenal of many chemicals, whereas humans often rely on one at a
time.

Berenbaum studies wild parsnip plants and the webworms that devour the
plant's flowers and fruit. The plants defend themselves with a battery of
different furanocoumarins, so webworms choose plants with lower
furanocoumarin concentrations. In the co-evolutionary arms race between
plant and insect, Berenbaum has found that the plants produce many fruit
lacking seeds, which pack only one-third as many furanocoumarins as seeded
fruits. The webworms eat the seedless fruit of no value to the plant, while
the fruit with seeds survives. Seedless fruits thus serve "as decoys that
divert webworms away from viable fruit," said Berenbaum.

The plant's strategy may appear to cut into its immediate yield, but "plants
are less concerned with maximizing yield than they are with maximizing
reproductive output" in the long term, she said. That's a lesson Berenbaum
thinks humans need to take to heart: Farmers and their crops both share the
same goal but "plants are in it for the long haul, and don't spend a lot of
time and energy in revenge mentality."

The next frontier - crops bioengineered with genes to fight insects - may be
no more immune from the forces of evolution. "We have every reason to
believe that resistance will be a problem with transgenic crops," said
Berenbaum. As Bt-corn and Roundup-ready soybeans occupy more fields, cases
of resistance have already popped up.

What then is the solution? Berenbaum suggests using the decoy principle in a
different way: Mixing in non-crop plants might lure insect pests away from
crops and onto the decoy species, a strategy now practiced to lure lygus
bugs off cotton and onto alfalfa. "One of the best hopes for resistance
management is to diversify the landscape," Berenbaum said.

Liebman echoed many of Berenbaum's concerns and solution and says that in
crop rotation, as compared to monocultures, weeds decreased in 82% of cases
and increased in only 3%. Following the other presentations, Harvard
University's Richard Levin suggested that pesticide practices may indeed
change. "The chemical dependency we have now is a brief successional stage
in the history of agriculture, and we're already passing out of it," he
said.