What Are The Harmful Effects Of Pests On Human Health And Economy?

Mostly, insects are more of a nuisance than a harm. Most may bite a human and cause itching and rashes. These are not harmful as such but they are bothersome.
However, some insects can actually harm humans or play a part in harming humans. Harmful insects are those which are poisonous when they bite. Examples include, fire ants, harvester ants, brown widow spiders, the hobo spider and the brown recluse spider.

Besides that insects may play a part in transmitting various diseases to humans. A very common example is the house fly. When it comes into contact with fecal matter, it (along with all the bacteria on it) sticks to its feet. Thus, when the fly next sits on something, it leaves a trail of fecal matter and its bacteria behind. If it comes into contact with food that we consume, we may ingest harmful bacteria. House flies are a common agent for cholera.

Other insects may act as vectors for a disease. This means they carry a pathogen in them. When they bite, this pathogen enters human blood, thereby causing disease.
Some insects and the diseases they may cause by acting as vectors are:

  Insect   Disease
Lice   Typhus
Anopheles mosquito   Malaria
Aedes mosquito   Dengue fever

Pests
Insects embrace with in their food habits almost every kind of organic material and thus become the greatest pests to man's food supplies. Insect pests cause the great loss to farm crops, gardens, stored food and property and affect the comfort and health of animals and man.
Crop Pests
Every cultivated plant has more than one insect pest and each important crop like cabbage worms, hoppers and potatoes beetles, chew and shallow the external parts of the plants. Grasshopper and locusts have invaded the green crop from the earlier days. Locusts on the warpath some times move on in swarms extending for many kilometres. Boll weevils spoil cotton before the harvest.
Sucking Insects such as plant bugs, aphids and scale possess extremely sharp, pointed beak like proboscis, which is thruster into the plant tissues to suck up their juices.
Plant pests
Bark beetles destroy lumber in the forests. Caterpillars and Japanese beetles kill millions of valuable shaded trees every year.
Stored grain pests
Borer in fruits, nuts and seeds attack them on field as well as in the store godowns. Grain weevils, flour beetles and moths damage stored cereals.
Household pests. Human food are eaten or spoiled by ants, crickets, cockroaches, and weevil sand fruit flies.
Domestic animal pests
Insects seriously injure Some times domestic animals.