The best and cheapest is DDT. Widely slammed by the inaccurate and hysterical charges in Rachel Carson's Silent Spring, DDT was first banned and still is hard to make use of even though actual scientists studying Carson's charges found them to be unsubstantiated. She and the wacko environmentalists who followed her are thus responsible for between ten and thirty million deaths, mostly of children, mostly in Africa. This of course did nothing to reduce the population there, since the poor will always try to have enough children to ensure that some will be left alive to support them in their old age.

The link below, from junkscience.com, shows and documents how Rachel Carson's book Silent Spring was wildly inaccurate on DDT. Don't expect that to convince environmentalist wackos, though. It's their Bible and their religion. Especially repulsive is the quoted World Health Organization's attitude toward malaria--better, they said, that up to 40% of African children die of malaria than that they survive to breed. The fact is, however, that Africans try to have as many children as possible BECAUSE of the high child-mortality rates, so that at least some will survive to support the parents in their old age. In countries where child-mortality rates fall, people have fewer children, because they don't need so many to serve as "social security." http://www.junkscience.com/ddtfaq.htm

The two answers provided by another poster contain information that is not impartial or accurate. I discuss this at the end of my answer, which follows... Approximately two million people die from malaria every year and it is most common in less-developed countries. It is re-emerging in countries where it was believed to be eradicated. These cases involve people contracting malaria in their home country, not picking it up while visiting a country where malaria is common. This has serious medical implications. Unfortunately, drug companies have performed very little research and development on anti-malarial drugs. There is little profit in anti-malarial drugs for companies that must turn a profit for their shareholders and directors. An unfortunate circumstance, given, for example, the billions lavished on R&D for anti-depressants, such as the highly-profitable Prozac. Selling anti-malarial drugs to the poor is no way to run a for-profit, acpitalist business. This is a terrible consequence of the importance our society places on wealth generation. There are very few drugs available to treat malaria. Many are intended for use before entering a malarial region, rather than treating the disease after one has been infected (e.g., a drug for travellers, taken before exposure to malaria). The most widely used drug for treating malaria is chloroquine. All of these drugs are relatively expensive and not easily obtained by residents of regions where malaria is commonly found. If someone has an annual income of a few hundred dollars, the cost of anti-malarial drugs becomes a cruel joke. There is widespread, and growing, resistance to anti-malarial drugs like chloroquine and all have negative side-effects. Some anti-malarial drugs sold in developing countries are fakes, sold by the unscrupulous. One would hope that more R&D is being undertaken to improve the situation, but this is not the case. Perhaps when more people start dying of malaria in Europe and North America, the drug companies will consider it worth their while. This problem is not restricted to anti-malarial drugs. There are several drugs used to treat diseases usually found in developing countries that are too expensive for their target market or have been withdrawm from the market because of low sales, even when they have been generating profits - but profits that are not high enough. Large-scale use of insecticides against malaria have had mixed results. There is a wide body of scientific research on their use, much of it negative. DDT once enjoyed widespread use, but it and other related chemicals have been found to have serious problems. DDT is an organochlorine; other common pesticides include organophosphates and carbamates. All of these insecticides work as broad-spectrum insecticides: they kill both the good and the bad. When the insect populations rebound after the kill-off, they are often imbalanced: the previous population balance was destroyed and may not immediately reassert itself. This affects the predator / prey ratios, for example, and can have unforseen consequences. Because broad-spectrum insecticides have a kill rate of less than 100%, insects slowly build resistance to them as they are applied repeatedly over years or decades. This makes the insects harder to kill in succeeding generations. Organophosphates and carbamates have an advantage in that they break down fairly quickly in water or soil. They will, however, kill animals that ingest sufficient quantities immediately following a spray. Their impact on birds is far more severe than on mammals, as birds are up to one hundred times more sensitive as mammals to their effects. They also have a serious impact on amphibious and aquatic life. The situation is more severe with organochlorines, which include DDT. Organochlorines do not break down easily and can be found in the soil years after a spraying. This persistence not only helps insects become more resistant to them, but allows them to collect in the animals, birds, and amphibians living in the exposed area. Incredibly, animals living thousands of kilometres from areas where organochlorines have been sprayed have been found to harbour traces of the chemical. An application that was insufficiently strong to kill birds could still eventually lead to their deaths, because their bodies slowly accumulate the chemical over an extended period of time. Even if the chemicals do not kill animals themselves, they often leave the animals in a depressed physical condition, leading to higher death rates from illness, for example. Once thought safe over the short term, they became deadly over the long. The impact was greates on birds and animals at the top of the food chain, as they would ingest and retain the insecticides that their prey consumed. And so forth down the food chain. Some types of organochlorines are still used in some developing countries. There are dozens of documented instances of mass poisoning of birds from insecticides in Canada, the US, and elsewhere. The number of birds killed in these cases has been difficult to determine, but estimates have ranged from 500 to 20,000 in various cases. Observations indicate that birds can die within minutes of exposure to insecticides. Not all cases are reported, so it is difficult to estimate the overall extent of the problem. Not only are the sprayed areas affected, but neighbouring areas are at risk from overspray or from the spray drifting on the wind. Some pesticides on the market today are not broad spectrum poisons, but target individual species more closely. Some are not as lethal to birds or animals as the earlier chemicals. The synthetic pyrethroids used to control some insects are not as toxic to birds and animals, but are highly toxic to amphibious life and fishes. Bacteria agents have also been used successfully. So what is used on mosquitoes today? Larvicides - agents that attack the mosquito larva instead of the adult - include bacillus thuringiensis israelensis (Bti, a bacteriological control agent that is toxic to mosquito larvae), methoprene (a growth regulator that inhibits growth past the larval stage), and chlorpyriphos (an organophosphate that is being phased out for use near human populations). These are applied directly to the water in which the mosquitoes breed. The most common insecticide used on adult mosquitoes is malathion, a broad-spectrum organophosphate approved for ultra-low volume application. A number of non-chemical treatments are used to control mosquitoes. Most of these aim to control the wet areas in which mosquitoes breed. By controlling the number of places where the female mosquitoes lay eggs or that the larvae need for development, the mosquito populations can be sharply reduced. For areas where this type of control is difficult or impossible, people can limit their contact with mosquitoes by protecting their skin from bites, either with a physical barrier or with DEET. Mosquito netting around the bed provides a very effective barrier at night. Larvicides may also be used. Controlled spraying is possible, but repeated large-scale spraying has not been successful over the long term. If it was, areas would not need to be sprayed every year. ------------------------------------------------------------ Commentary: Another poster has heavily criticized the “inaccurate and hysterical charges” of Rachel Carson. I wonder if he has actually read this book and checked any of the references it contains or if he relies on the opinions of others. Carson’s book was sold in the popular press, but there are thousands of publications from the scientific community about the negative effects of pesticides. The source cited for the opposing viewpoint is the “Junkscience” website. This site is not an impartial third party. As a side note, in my professional life I have often performed work on behalf of clients as an impartial third party. I am familiar with the demands placed on the process: a high standard of personal and professional ethics. Results must be documented without observer bias or any preconceived notion of the outcome. I have been asked by certain clients on occasion to change or reword my reports, because the findings did not match their expectations. These requests have been politely declined. Junkscience does not meet any criteria I have ever seen to support any claim that it is an impartial third party. The individual running the website and writing the articles is affiliated with the Cato Institute, the Free Enterprise Action Fund, the Competitive Enterprise Institute, the National Centre for Policy Analysis, and the Fox News Channel. All of these are right-wing organizations with a clearly-defined political bias. "Cato officials have said they won't print any studies that come out favorably toward government programs. And right-wing think tank researchers have been fired for failing to follow the party line." [Brock, 2004] These organizations are deeply integrated with the Republican Party in the US, conservative industrial cliques, and the neo-conservative, neo-liberal, and libertarian ideologies promoted in these circles. These organizations collect any scientific reports that support their positions and commission research to prove the issues they support - answer first, research second, opposing viewpoints need not apply. I take issue with such organizations over their ethics, as their primary goal is to manipulate the public and move the discourse to their agenda.