4.4 and 4.5 pests and pesticides and impact of pesticides

In agroecosystems, thousands or millions of individuals of a single crop species are planted in a monoculture. 

To maximize growth of the desired crop, we try to eliminate organisms that we consider pests.

Pests are organisms that might compete with or damage crop species. Agricultural pests are plants and animals that reduce crop yield. 

There are no pests in nature! All organisms are simply producers and consumers within food webs.

Weeds are plant pests, mosquitoes are insect pests, and mice are rodent pests

In the forestry industry, spruce budworm, gyspy moths are examples of tree-infesting species

Colorado potato beetles feed on potatoes. If they find a potato field, they will begin feeding.

• One of the most common ways to control and eliminate pests is to use poison aka pesticides 

• There are many different kinds of pesticides. 

1. Herbicides are used on plants. 

2. Insecticides are used on insects, 

3. Rodenticides are used on rodents

4. Fungicides are used on fungi

• Natural pesticides do not last as long as man-made/synthetic pesticides - however, modern synthetic pesticides do not last as long as those developed 30+ years ago

Pesticides vary widely in the number of species they are able to control

Broad-spectrum pesticide: are toxic to a wide range of pests.

Narrow-spectrum pesticide: are toxic to only one specific pest. 

• Pesticides cause physical or biological harm to the pest organism 

• Pesticides can be applied directly by touching the target pest or indirectly. 

• Indirect example: herbicides sprayed on the soil, and taken through the roots of the weed, or insecticides sprayed on plant and later consumed by an insect

Pesticides have also helped control populations of biting insects such as mosquitoes, that spread diseases such as malaria

• Pesticides are often applied through aerosols or sprays onto fields, forests, and gardens. 

• A serious drawback of this is that some of the pesticides never reaches the target species, because it is carried away by the air or lands on the soil

• These pesticides then become potential sources of soil, air, and water pollution. 

• They can also harm other non-target species

  Pesticides often kill species they were not intended to kill. Since broad-spectrum pesticides control many different pests, they can kill non-damaging and sometimes beneficial organisms.

  
  

• One of the most serious side effects of pesticide use is the tendency to accumulate in individual organisms 

• This happens because some pesticides are not broken down or eliminated with other body wastes

• If an individual continues to eat food contaminated with the pesticide, it will accumulate in the body.

• All individuals are part of a food chain 

• As a result, toxins stored in the fats and oils of organisms at one trophic level are passed on to the organisms at the next trophic level 

• The higher up the food chain, the more concentrated the pesticides become - this process is called bioamplification

This is one danger associated with consuming food from the top of the food web

• When pesticides are used for long periods of time, some pest species may become resistant to the pesticide.

• This means that the pesticide is no longer able to control the pest

The pests that survive an application of a pesticide will reproduce, and pass on their resistance to future generations, causing that population to become highly resistant to a particular pesticide

• When pests develop resistance, farmers need to apply a greater concentration of pesticide OR switch to a different pesticide