External costs are not fully factored into the problem. So everyone in the chain from farm to table benefits. The food costs less, the farmer produces more, and the quality is "higher." Because the grower can produce more the grower earns more. A specific dollar cost to environmental damage is not factored in. A specific cost to human health is not factored in. However, such issues are mostly too complex. Look at the battle over cigarette usage. Now consider a product that is no more than 1/100 as toxic (either because the acute toxicity is lower, or because the dosage is lower). We cannot prove that cigarette use causes cancer -- all we have is a correlation that shows up again and again. That is not proof in the same way that a mathematician can prove a theorem.

The other issue is that non-pesticide approaches are often (not always) less effective. Another issue is that people keep moving pests and diseases around. So a crop may have very low pesticide usage today, but tomorrow someone that came through some far off land brings a new disease. The choice is to abandon that crop or increase pesticide use. A new alternative is to genetically modify the crop. This is a faster alternative to classical plant breeding programs, and in a few cases can take advantage of genes that are not a natural part of the genetics of the modified crop. GMO crops are not accepted in many places. A great example of this in the United States is the introduction of Citrus greening (Huanglongbing) into Florida, then Texas, and California.

Finally, the alternatives to pesticide use are not simple. In many cases it is difficult to turn any profit from their development. This leaves this approach for governmental organizations and universities. These approaches take a great deal of time to develop, and there are relatively few people to do the work. Furthermore, there is an enormous amount of work to do. So I can make an insecticide and use it on corn, potatoes, beans, rice, avocados, apples, carrots, leeks, and hundreds of other crops. It still kills insects. An organic gardening approach that works for carrots does not work for apples. In biology, each crop is unique and each pest is unique. The organic mulch that works for apples may not have the right blend of nutrients for corn.

Of course part of the problem is that we grow monocultures. If people could only eat what they could grow .... at least some of our pest problems would disappear. However, the very fabric of our society would need to change to make this possible, and I just don't see that happening. The problem gets worse if one is not vegetarian. So, without using the internet, how many square feet of pasture is needed to sustainably rear a cow to maturity? I don't know, but I suspect that my 0.4 acre plot is way too small. That is also a trick problem, because one cow is not sustainable. Pushing the cost of producing calves onto a farmer is not allowed unless you include all the external costs in rearing and transportation.

Dear Eva,

The answer to your question is economic and behavioural, here you can find a fine one

http://ageconsearch.umn.edu/bitstream/48363/2/WP53.pdf

Dear Eva Dust

 You are right, international company's interest in huge income from chemicals and their derived, Not only the little income from alternative, but also the disadvantages for most of it over the level of their advantages, laid to limitation of their uses. By the time it will take places, it was discussed during conference 2015. Damascus Syria

Regards

Prof. Houda Kawas

External costs are not fully factored into the problem. So everyone in the chain from farm to table benefits. The food costs less, the farmer produces more, and the quality is "higher." Because the grower can produce more the grower earns more. A specific dollar cost to environmental damage is not factored in. A specific cost to human health is not factored in. However, such issues are mostly too complex. Look at the battle over cigarette usage. Now consider a product that is no more than 1/100 as toxic (either because the acute toxicity is lower, or because the dosage is lower). We cannot prove that cigarette use causes cancer -- all we have is a correlation that shows up again and again. That is not proof in the same way that a mathematician can prove a theorem.

The other issue is that non-pesticide approaches are often (not always) less effective. Another issue is that people keep moving pests and diseases around. So a crop may have very low pesticide usage today, but tomorrow someone that came through some far off land brings a new disease. The choice is to abandon that crop or increase pesticide use. A new alternative is to genetically modify the crop. This is a faster alternative to classical plant breeding programs, and in a few cases can take advantage of genes that are not a natural part of the genetics of the modified crop. GMO crops are not accepted in many places. A great example of this in the United States is the introduction of Citrus greening (Huanglongbing) into Florida, then Texas, and California.

Finally, the alternatives to pesticide use are not simple. In many cases it is difficult to turn any profit from their development. This leaves this approach for governmental organizations and universities. These approaches take a great deal of time to develop, and there are relatively few people to do the work. Furthermore, there is an enormous amount of work to do. So I can make an insecticide and use it on corn, potatoes, beans, rice, avocados, apples, carrots, leeks, and hundreds of other crops. It still kills insects. An organic gardening approach that works for carrots does not work for apples. In biology, each crop is unique and each pest is unique. The organic mulch that works for apples may not have the right blend of nutrients for corn.

Of course part of the problem is that we grow monocultures. If people could only eat what they could grow .... at least some of our pest problems would disappear. However, the very fabric of our society would need to change to make this possible, and I just don't see that happening. The problem gets worse if one is not vegetarian. So, without using the internet, how many square feet of pasture is needed to sustainably rear a cow to maturity? I don't know, but I suspect that my 0.4 acre plot is way too small. That is also a trick problem, because one cow is not sustainable. Pushing the cost of producing calves onto a farmer is not allowed unless you include all the external costs in rearing and transportation.

This is an obvious question comes to everyone's mind . But scientific reason for not using alternatives to pesticides in great areas/landscapes is that, in large crop field if we don't use pesticides and go for other management practices and unfortunately a few of insect pests survived successfully, they will damage the crop vigorously. And in large field controlling a small patch of land is not possible and also not cost-effective.  

Dear Eva

Using alternatives to pesticides is attractive.  However, it comes with a cost beyond the financial, although monetary cost is an important factor in most countries where profit margins for many or even most farmers are so tight that we see farmers abandoning the industry in large numbers because they cannot make ends meet.

The main problem with so called alternatives, as Tim has pointed out, is that they are generally less effective, which in the intensive cultivation cycle to which we are tied makes it impossible to produce sufficient food for our enormous population.  Reduce the human population to 17th century numbers and all might be well but that is not going to happen short of a Malthusian pandemic of huge proportions.

Another aspect of the wish towards more "natural" pest control is that it too largely depends upon chemicals, just chemicals derived from plants.  True, those chemicals were evolved to deter pest insects and even disrupt their biology but interestingly many of them have similar modes of action and binding sites to those used by synthetic pesticides.  So if an insect is resistant to a pesticide it is quite possible it could also either be resistant or else quickly develop resistance to the natural alternative.  In general these natural alternatives need to be used at much higher dose levels than the synthetics, which also comes at a cost financially, ecologically (you need to take up much more land in growing the plants - or use other natural resources for synthesising the nature identical versions), and on the crops  (many of these alternatives can result in phytotoxicity if over used).

One final problem is that the evidence for activity of some alternatives has been "hyped up" by people with their own vested interests.  For example, in my field of ectoparasitology there are huge and widepread claims for some natural materials like neem limonoids without a shred of real evidence in support of those claims. Any activity of formulations containing those chemicals on insects that cannot eat it are more likely due to the other chemicals in the formulations used.  But most people interested in the sphere are either not sufficiently knowlegeable about formulation pharmacology or else have their own axes to grind, so the possible charlatans have not been shown up.  Of course there is evidence that neem has an anti-feedant effect on caterpillars and other phytophagous insects but that has practical limitations.

I must emphasis that I am not saying that use of alternative approaches has no value only that it has limitations that need to be considered before being applied in any real life situation. There is a long step between the laboratory bioassay and the field test, and even further between field test and farmer use.  Generally speaking most options do not bridge that gap but could perhaps be applied to specialised circumstances like greenhouse crops or private horticulture, which would be one small advance since most gardens are actually small nature reserves and contain much more biodiversity than any agricultural set up.

It might be because they are not yet approved in larvae scales in terms of persistence, biological efficacy and real operational costs.

To expand on a point Ian brought up.... There is a perception that natural products are safe, or at least safer. To those people I would like to introduce a range of safe natural products: cyanide, strychnine, aflatoxin, ricin, tetrodotoxin, coniine, nicotine. The last one is sold in the USA as an insecticide under the trade name Black Flag. Of course these products are environmentally safe when encountered at the doses present in the environment. However, this dose is not suitable for our use in agriculture. So we concentrate the toxin (or synthesize it), and then it is no longer a benign product. It does not matter if the cyanide came from almonds or was made in a chemistry lab.

Even "safe" products like Bt (Bacillus thuringiensis: https://en.wikipedia.org/wiki/Bacillus_thuringiensis) are not environmentally benign when applied to large areas of forest for gypsy moth control. https://www.academia.edu/2268564/Long-term_evaluation_of_the_effects_of_Bacillus_thuringiensis_kurstaki_gypsy_moth_nucleopolyhedrosis_virus_product_Gypchek_and_Entomophaga_maimaiga_on_

That said, if B. thuringiensis is left in the habitat where it evolved, then it is environmentally benign.

We could probably do just fine if we cut agricultural production in half. However, I don't hear many people volunteering for death by starvation. Most countries will not (or can not) adopt China's approach of government mandated family size. However, until we can manage our population growth globally, we are faced with ever increasing environmental issues.

The scientific reason to why alternatives to pesticides are not used in great areas is not only as outlined by Ian and Tim above, but also the vast gap in human appreciation of Integrated Pest Management (IPM) where numerous ecological issues must be taken into account. The ecological web of "creatures" is far more complex than already addressed and is a continuously evolving and dynamic issue which outstretches human knowledge.