Friday, December 11, 2009

Part 1 - Insects – Our Allies and Foes

Water strider is a swift, precise and fearless predator of
leafhoppers, ants and other insects that fall into the
water. Painting by Kathleen Mae Cangas 10, Summer
Art Workshop, SPUQC 2000

Abe V Rotor

Contrary to what many people think, most insects are extremely useful to mankind and the environment. Our world could not be any better without insects.

Without them, we would not have honey and silk, insect-pollinated fruits and vegetables, fish which feed on them, music they create on a warm summer night. Nor can we see the Monarch butterfly that meets us in the garden at sunrise in springtime.

On the other hand, we detest the presence of their destructive kin: the disease-spreading cockroach, ticks that spoil a dog’s lovely coat, caterpillars that defoliate our favorite trees, or simply the buzzing of a pesky mosquito that interrupts our prayers or good rest.

If these negative traits are not enough for us to take up arms against these pests, realize that the most ferocious animal on earth is not the lion or rhino, but the mosquito. Disease-carrying mosquitoes have caused, through the millennia, death and suffering to mankind. It is estimated that deaths due to mosquitoes alone surpasses that which all wars in history have caused. The mosquito’s most prominent victim, Alexander the Great, died of malaria at a young age on the banks of the Tigris-Euphrates Rivers, after a conquest that would have formed the biggest empire in the world.

So here are strategies of war against our insect enemies.

1. Natural Resistance

There is no substitute for natural resistance (those carried by the genes) in combating the pest. Where do these genes come from?

Even before scientists came to the conclusion that resistance (or susceptibility) is hereditary, farmers already adopted selectivity in plant breeding and animal husbandry, as the foundation of the first green revolution.

Evolution brought desirable genes together in a species. “Survival of the fittest,” Darwin’s general formula is the gradual pooling of these genes through time. It also explains why varieties and breeds native to a place are more resistant compared to their non-indigenous counterparts. Wittingly or not, man has caused the elimination of resistance genes. By making economically advantageous agricultural decision, man unwittingly has eliminated seemingly unimportant genetic characteristics. Many of the latter characteristics are carried by indigenous species.

In order to gain from this knowledge, one must look into the adoption of these two measures.

1. Choose plants and animals that are genetically adapted to the place. They have the natural resistance to pests and diseases, and can withstand unfavorable conditions prevailing in the area.

2. Maintain physiologic (involving healthy or normal functioning) resistance by enhancing soil nutrients and proper cultural practices. Healthy plants have less pest and disease problems. The same is true with animals. This leads us to the next practical technology.

2. Proper Cultural Practices

It is not only the season’s calendar that farmers plant or harvest their fields at the same. They have learned that by working collectively with the seasons, crop loss due to pest and diseases is minimized, since the damage they cause is thinly spread over larger area.

The fields are fallowed in the summer, giving the land time to “rest.” During this time the insect life cycle is severed and the buildup of its population is remotely possible. This practice is revived through cooperative farming, integrated with communal irrigation, mechanization, and collective marketing to provide economies of scale.

A key to control pests is to eliminate their breeding places. This is done by uprooting infected plants, or pruning affected parts, then burning them. To attract the potential pests, farmers plant trap crops ahead of planting time. The trap crop is then rouged and burned to eliminate the threat to the oncoming crop. Weeds need to be eliminated since they serve as alternate hosts.

3. Biological Control

As unsightly as cobwebs are, do not remove them. Destroying them will take away natural insect traps built by spiders. Inside warehouses, spiders prey on weevils and moths that destroy grains and other commodities. Those webs also trap pesky mosquitoes and flies at home. No echolocation device can avoid the fine web, making it an indigenous trapping devise, indeed.

On plants, the preying mantis snatches its victim with one deadly grasp. The spotted ladybug overruns a colony of aphids and has its fill, unless the red ants guarding the aphids come to the rescue. A nest of hantik ants up in the tree is an army of thousands. They swarm on intruders and large preys like caterpillars.

Under the microscope one can examine the unsuspecting Trichogramma. Mass production and dispersal of this parasitic wasp has benefited sugar and corn planters since its discovery in the 1950s. The University of the Philippines at Los Baños is mass-producing the parasite for dispersal in corn and sugarcane fields throughout the Philippines.

Bacillus thuringiensis or Bt, has become the most popular pathogens attacking Lepidopterous pests which include rice stem borers and corn borers. When the spores are applied as materials for inoculation, Bt can cause widespread pests elimination on the field.


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