Friday, July 15, 2011

Insects – Our Allies and Foes

Dr A 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.

4. Practical Pest Control at Home

Here are pest control techniques you can adopt at home.

1. To control furniture weevil and moths which destroy the felt and piano wood, place a teabag of well-dried and uncrushed black pepper in the piano chamber near the pedals. Paminta is a good repellant and has a pleasant smell.

2. Coconut trees whose shoots are destroyed by rhinoceros beetle (Oryctis rhinoceros) can be saved with ordinary sand. If the trees are low, sprinkle sand onto the leaf axils (angle between the leaf and axis from which it arises). Sand contains silica that penetrates the beetle’s conjunctiva, the soft part of the body where hard chitinous plates (hard outer membrane) are joined.

3. To control bean weevil (Callosobruchus maculatus), an insect that destroys stored beans, especially mungo), mix a little ash of rice hull (ipa’) and spread it in a way that sand kills the rhinoceros beetle.

4. To get rid of nematodes (microscopic elongated, cylindrical worms) in the soil, incorporate chopped or ground exoskeleton (skin) of shrimps into the soil, preferably mixing it with compost. Chitinase is formed which dissolves the cover of the egg and the body of the nematode. Use poultry dropping to reduce nematode population in farms and gardens.

5. To control the cucurbit (plants of the gourd family) fruit fly (Dacus cucurbitae), wrap the newly formed fruits of ampalaya and cucumber with paper bag. Bagging is also practiced on mango fruits. For ampalaya use newspaper (1/8 of the broadsheet) or used paper, bond size. Roll the paper into two inches in diameter and insert the young fruit, folding the top then stapling. Bagged fruits are clean, smooth and light green. Export quality mangoes were individually bagged on the tree.

6. To keep termites away from mud-plastered walls, incorporate termite soil (anthill or punso). To discourage goats from nibbling the trunk of trees, paint the base and trunk with manure slurry, preferably their own.

7. Raise ducks to eat snail pest (golden kuhol) on the farm. Chicken and birds are natural insect predators.

8. An extra large size mosquito net can be made into a mini greenhouse. Underneath, you can raise vegetables without spraying. You can conduct your own experiments such as studying the life cycle of butterflies.

9. Plants with repellant properties can be planted around the garden. Examples of these are lantana (Lantana camara), chrysanthemum, neem tree, eucalyptus, madre de cacao (Gliricida sepium), garlic, onions, and kinchai (Allium tuberosum).


10. To scare birds that compete for feeds in poultry houses, recycle old balls, plastic containers, styro and the like, by painting them with two large scary eyes (like those of owls). This is the reason why butterfly wings have “eyes” on them to scare away would-be predators. Hang these modern scarecrows in areas frequented by birds. To scare off birds in the field, dress up used mannequins. In some cases, the mannequin may be more effective than the T-scarecrow. Discarded cassette tape ribbon tied along the field borders scares maya and possibly other pests.

5. Insects as Food

One practical means of insect control is by harvesting them for food. This practice is not only confined among primitive societies but is still one of the most practical means of controlling insects. Anyone who has tasted kamaro’ (sautéed mole cricket – Gryllotalpa africana) would tell you it is as tasty as shrimps, lobsters or other crustaceans. After all, insects and shrimps belong to the same phylum – Arthropoda.

Locusts may destroy crops but, in a way, bring food to its victims. During a swarm, locust is harvested by the sacks and sold for food and animal feeds. The same goes for gamu-gamu (winged termites – Macrotermes) at the onset of the rainy season, or the salagubang (Leucopolis irrorata), another insect delicacy. Other food insects are the grubs of kapok beetle locally called u-ok, eggs and larvae of hantik (green tree ant), larvae of honeybee and cheese maggots.

When is a pest a pest?

When we see an insect, instinct tells us to kill it. We should not. A caterpillar is a plant eater, but the beautiful butterfly that emerges from it is harmless, efficient pollinator. Hantik ants make harvesting of fruits inconvenient because of their painful bite, but they guard the trees from destructive insects. Houseflies carry germs, but without them the earth would be littered with dead, undecomposed organisms. They are nature’s chief decomposers working hand in hand with bacteria and fungi. Termites may cause a house to crumble, but without them the forest would be a heap of fallen trees.

It is natural to see leafhoppers on rice plants, aphids on corn, bugs in the soil, grasshopper on the meadow, borers on twigs, fruit flies on ripening fruits. These organisms live with us under one biosphere. If we can think we can dominate them, we have to think again. They have been dominating the earth for billions of years, even before man appeared. Just one proof: the total weight of ants inhabiting the earth outweighs six billion human inhabitants.

There is no way to escape pesky creatures. Conflict arises only when their populations increase rapidly to overrun our crops, spoil our stored products, and threaten our health and welfare.

We have set certain thresholds of our co-existence with insects. As long as they do not cross that line, we can cohabit this planet peacefully with them. By so doing, we can ponder at the beauty of their wings, the mystery of the fire they carry, the music they make, the magnitude of their numbers, or marvel at the mystery of their presence.

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