Plants, growing in the wild or in cultivation, face numerous threats from insects, bacteria, viruses, and fungi, as well as from other plants. Biopesticides are inert substances or living organisms that can help protect plants from such threats. Chemical pesticides can offer similar protection but, by contrast, are neither alive nor made by living organisms.
A variety of chemicals produced by plants help ensure that parasites, predators, plant feeders, and herbivores seldom increase in number sufficiently to destroy the plant populations they prey upon. Chemicals found in very low concentrations in certain plants have been found to help keep locusts from feeding on those plants, and some trees produce nearly 1,000 different chemical compounds that help them resist herbivores and parasites.
Plant predators are themselves subject to attack by predators, parasites, and microbes, all of which can indirectly help protect a plant and therefore are also considered biopesticides. An oak tree may have about 100 species of insect herbivores feeding on it. In turn, there can be up to 1,000 species of predators, parasites, and microbes feeding on the herbivores. The microbes, parasites, and predators attacking the herbivore populations are considered “biopesticides,” as are any protective chemicals produced by the tree
Such living biopesticides play a vital role in agriculture and nature, helping to control insect pests, plant pathogens, and weeds. Numerous organisms, including viruses, fungi, protozoa, bacteria, and nematodes , as well as insects, such as parasitic wasps, can attack pest insects and weeds. In some cases, biologists search around the world to find natural organisms to help control an insect, a plant pathogen , or weed populations.
More than 95 percent of all crops have some degree of pathogen resistance bred into them, with resistance to fungi, bacteria, and viruses being most common. Most of this resistance was either added by farmer selection or plant breeder selection, rather than through genetic engineering. It is because of this natural resistance that has been bred into the crops that only 12 percent of the pesticides used in U.S. agriculture are fungicides.
Some viral resistance, however, has been bred into a number of crops through insertion of viral genes into the plant chromosomes. These genes may lead to the plant’s producing viral proteins—biopesticides of a sort—that hamper a virus’s own actions. This pathogen-derived resistance has been successfully used to protect Hawaii’s papaya crop from the devastating papaya ringspot potyvirus. The viral gene was inserted into the papaya genome using a “gene gun,” which shoots viral genes into papaya embryo cells.
Some crops (e.g. corn) are being engineered to contain both herbicide tolerance and the BT toxin. Generally, the use of herbicide-tolerant crops will likely increase the use of herbicides. This has the potential to increase environmental pollution since it might increase the farmers’ reliance on chemicals rather than mechanical and other means of weed control.
Biofuel, any fuel that is derived from biomass—that is, plant or algae material or animal waste. Since such feedstock material can be replenished readily, biofuel is considered to be a source of renewable energy, unlike fossil fuels such as petroleum, coal, and natural gas. Biofuel is commonly advocated as a cost-effective and environmentally benign alternative to petroleum and other fossil fuels, particularly within the context of rising petroleum prices and increased concern over the contributions made by fossil fuels to global warming. Many critics express concerns about the scope of the expansion of certain biofuels because of the economic and environmental costs associated with the refining process and the potential removal of vast areas of arable land from food production.
Types Of Biofuels
Some long-exploited biofuels, such as wood, can be used directly as a raw material that is burned to produce heat. The heat, in turn, can be used to run generators in a power plant to produce electricity. A number of existing power facilities burn grass, wood, or other kinds of biomass.
Liquid biofuels are of particular interest because of the vast infrastructure already in place to use them, especially for transportation. The liquid biofuel in greatest production is ethanol (ethyl alcohol), which is made by fermenting starch or sugar. Brazil and the United States are among the leading producers of ethanol. In the United States ethanol biofuel is made primarily from corn (maize) grain, and it is typically blended with gasoline to produce “gasohol,” a fuel that is 10 percent ethanol. In Brazil, ethanol biofuel is made primarily from sugarcane, and it is commonly used as a 100-percent-ethanol fuel or in gasoline blends containing 85 percent ethanol. Unlike the “first-generation” ethanol biofuel produced from food crops, “second-generation” cellulosic ethanol is derived from low-value biomass that possesses a high cellulose content, including wood chips, crop residues, and municipal waste. Cellulosic ethanol is commonly made from sugarcane bagasse, a waste product from sugar processing, or from various grasses that can be cultivated on low-quality land. Given that the conversion rate is lower than with first-generation biofuels, cellulosic ethanol is dominantly used as a gasoline additive.
The second most common liquid biofuel is biodiesel, which is made primarily from oily plants (such as the soybean or oil palm) and to a lesser extent from other oily sources (such as waste cooking fat from restaurant deep-frying). Biodiesel, which has found greatest acceptance in Europe, is used in diesel engines and usually blended with petroleum diesel fuel in various percentages. The use of algae and cyanobacteria as a source of “third-generation” biodiesel holds promise but has been difficult to develop economically. Some algal species contain up to 40 percent lipids by weight, which can be converted into biodiesel or synthetic petroleum. Some estimates state that algae and cyanobacteria could yield between 10 and 100 times more fuel per unit area than second-generation biofuels.
Economic And Environmental Considerations regarding biofuels
In evaluating the economic benefits of biofuels, the energy required to produce them has to be taken into account. For example, the process of growing corn to produce ethanol consumes fossil fuels in farming equipment, in fertilizer manufacturing, in corn transportation, and in ethanol distillation. In this respect, ethanol made from corn represents a relatively small energy gain; the energy gain from sugarcane is greater and that from cellulosic ethanol or algae biodiesel could be even greater.
Biofuels also supply environmental benefits but, depending on how they are manufactured, can also have serious environmental drawbacks. As a renewable energy source, plant-based biofuels in principle make little net contribution to global warming and climate change; the carbon dioxide (a major greenhouse gas) that enters the air during combustion will have been removed from the air earlier as growing plants engage in photosynthesis. Such a material is said to be “carbon neutral.” In practice, however, the industrial production of agricultural biofuels can result in additional emissions of greenhouse gases that may offset the benefits of using a renewable fuel. These emissions include carbon dioxide from the burning of fossil fuels during the production process and nitrous oxide from soil that has been treated with nitrogen fertilizer. In this regard, cellulosic biomass is considered to be more beneficial.