Wednesday, August 26, 2015

The new frontier in pest management - Bio Pesticides

Insecticides, fungicides, herbicides (weedicides), and nematicides can be broadly classified as pesticides.

Many widely used pesticides are synthetic products (Eg. DDT, Malathion, Diazinon, Antracol). A major problem posed by conventional synthetic pesticides is their toxicity to humans and other animals.

This has lead to renewed interest in the search for less toxic, natural substances – biopesticides.

What are biopesticides?

Biopesticides are certain types of pesticides derived from such natural materials as animals, plants, bacteria, and certain minerals.

For example, canola oil and baking soda have pesticidal applications and are considered biopesticides.

In 2014, there were more than 430 registered biopesticide active ingredients and 1320 active product registrations.

Biopesticides fall into three major classes: Microbial pesticides, Plant incorporated protectants (PIPS) and Biochemical pesticides.

  1. Microbial pesticides consist of a microorganism (e.g., a bacterium, fungus, virus or protozoan) as the active ingredient. Microbial pesticides can control many different kinds of pests, although each separate active ingredient is relatively specific for its target pest[s]. 
    • For example, there are fungi that control certain weeds, and other fungi that kill specific insects. The most widely used microbial pesticides are subspecies and strains of Bacillus thuringiensis, or Bt. 
    • Each strain of this bacterium produces a different mix of proteins, and specifically kills one or a few related species of insect larvae. While some Bt's control moth larvae found on plants, other Bt's are specific for larvae of flies and mosquitoes. The target insect species are determined by whether the particular Bt produces a protein that can bind to a larval gut receptor, thereby causing the insect larvae to starve.
  2. Plant-Incorporated-Protectants (PIPs) are pesticidal substances that plants produce from genetic material that has been added to the plant. For example, scientists can take the gene for the Bt pesticidal protein, and introduce the gene into the plant's own genetic material. Then the plant, instead of the Bt bacterium, manufactures the substance that destroys the pest. The protein and its genetic material, but not the plant itself, are regulated by EPA. 
  3. Biochemical pesticides include substances, such as insect sex pheromones, that interfere with mating, as well as various scented plant extracts that attract insect pests to traps. 
  4. ‘Botanicals’ are plant products used as biopesticides. Some of the best known examples are: Neeem(kohomba seeds, pyrethrum ( obtained from citronella) and citronella.


Azadirachtin

Azadirachtin is an insect growth regulator derived from neem ( "Kohomba ") tree seeds. Known to affect some 200 species of insects, azadirachtin disrupts insect feeding and inhibits its ability to molt as it changes from the pupa to adult stage.

An extract of the plant Dysphania ambrosioides (syn. Chenopodium ambrosioides) is used to control a number of sucking insect pests such as aphids, leafhoppers, whiteflies, and mites in citrus, grapes, tree nuts, and vegetables.

This product breaks down the pest’s exoskeleton, adversely affects its respiratory system, and interrupts its ability to navigate (find food).

Advantages of Biopesticides


  • No harmful residues detected 
  • Can be cheaper than chemical pesticides when locally produced.
  • Can be more effective than chemical pesticides in the long-term . 
  • Biodegradable 


Disadvantages of Biopesticides

High specificity: which may require an exact identification of the pest/pathogen and the use of multiple products to be used; although this can also be an advantage in that the biopesticide is less likely to harm species other than the target.

  • Often slow speed of action (thus making them unsuitable if a pest outbreak is an immediate threat to a crop such as an attack by locusts, and Brown plant hopper in rice). 
  • Often variable efficacy due to the influences of various biotic and abiotic factors (since biopesticides are usually living organisms, which bring about pest/pathogen control by multiplying within the target insect pest/pathogen)
  • Living organisms evolve and increase their resistance to biological, chemical, physical or any other form of control. If the target population is not exterminated or rendered incapable of reproduction, the surviving population can acquire a tolerance of whatever pressures are brought to bear, resulting in an evolutionary arms race. 


World Trade

It should be borne in mind, however, that the existing demand for biopesticides is not met by current production volumes, a situation only compounded by production costs generally above those of chemical products.

In most countries employing biological pest control strategies, biopesticides are purchased at considerably high prices (1 kg of Bt, for instance, can command a price of 10 to 30 dollars) or acquired from small local manufacturers selling their productions at 20 to 30 dollars per kg.

These figures are sometimes higher than those reached by chemical pesticides. Biopesticides represent a 200 million to 350 million US dollars/year market, amounting to less than 3 % of worldwide spending on agrochemicals (20 to 25 billion US dollars/year).

Although their higher price partially accounts for their lower market share, another factor undoubtedly contributing to this situation is the relentless advertising of large chemical corporations, which has dwarfed efforts to make the potential and advantages of biopesticides more widely known among prospective customers.

Cuba - a world leader

In no country has the application of biopesticides for phytosanitary purposes reached the level of organization, diversity and extension that exists in Cuba, according to the opinions of foreign specialists.

Until recently, Cuban agricultural production was based almost entirely on the conventional industrialised model characterised by a strong dependence on synthetic pesticides and fertilisers, fossil fuels and other Green Revolution inputs.

With the collapse of the socialist trading block in 1989, however, the country's access to the pesticides and other inputs it had relied on vanished almost overnight.

The simultaneous loss of most of the country's imported agricultural and industrial inputs, direct food imports, international markets and sources of foreign exchange resulted in a profound and continuing crisis for the Cuban people and government, a crisis amplified by escalation of the US government's long-standing economic and political blockade of the island nation.

By Ranjit Mulleriyawa
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