Biopesticides are used in the protection against pests. They occur naturally and are derived from plants, animals and microorganisms. Although biopesticides only account for a relatively small portion of the pesticide market, they have several benefits over chemical pesticides and conventional farmers are switching to these in high numbers to take advantage. Here we look at some of the different types that they can opt for and present some particularly common examples of each.
Biopesticides fall into three main classes – biochemical pesticides, microbial pesticides and Plant-Incorporated-Protectants (PIPs).
Biochemical pesticides
These are natural substances that, although difficult to classify, impede processes such as mating, growth and development of the pest.
Originating in neem tree seeds, Azadirachtin is a well-documented example of a biochemical pesticide. It has growth inhibitor and antifeedant properties impeding normal functioning of the neuroendocrine and alimentary systems of several insect species including fleas, mosquitos and flies.
A synthetic compound can be regarded as a biochemical pesticide if it is structurally much like that of the natural substance. This is the case with S-Methoprene, an Insect Growth Regulator (IGR), which can be against many insects including mosquitos. It imitates the natural juvenile hormone and, as a result, interferes with normal development. Although the effect is not instant, in most cases it stops adult mosquitos emerging from pupae.
Microbial pesticides
These are defined by the United Stated Environmental Protection Agency (EPA) as “certain types of pesticides derived from such natural materials as animals, plants, bacteria, and certain minerals”. Although able to control many different types of pests, they are very specific in their actions.
The bacterial type of microbial pesticide is generally taken into the pest by means of swallowing or absorbing. They then go on to parasitize the host. Insects can be targeted by numerous bacteria; however, the most common example is the use of subspecies and strains of Bacillus thuringiensis, or Bt. Each strain manufactures a different concoction of proteins that’s kills one, or a small group of, related species. One strain may act of moth larvae whilst another on mosquito larvae, for example.
Viruses from the highly specialized family Baculoviridae can be used a biopesticides. They act on many different insects and some arthropods.
Fungal pesticides – another type of microbial pesticide – do not need to be ingested by the target pest. Instead, contact is sufficient. These types of pesticides generally exist as fungal spores and are applied by spraying – much like that of chemical pesticides. Beauveria bassiana HF23 is a fungal pesticide which specifically targets house fly in poultry houses and chicken manure pits. This has been shown to be highly unlikely to have toxic effects on humans, animals or the environment.
Plant-Incorporated-Protectants (PIPs)
PIPs are substances that a plant produces to protect themselves from pests – they can produce these due to genetic material that are added to the plant. PIPs can protect plants from viruses, bacteria or make them insect resistant. For example, the genetic material for the bt pesticidal protein can be inserted into the plants own DNA. The plant, rather than the Bt bacterium, can then synthesize the compound that will kill the pest. Plants producing PIPs are sometimes referred to as genetically modified (GM) or genetically engineered (GE) due to the added genes. Common examples of crops incorporating this method are soy, cotton, soybeans and potatoes
In effect, the plant makes its own pesticide. This enables farmers to use less pesticides on their crops. This is particularly important due to the vast environmental implications of chemical pesticide use.
