It is difficult for us in 1992 to appreciate the food problems which occurred in the 19th century. Fresh eggs, milk, vegetables and fruit were seen only in the season of production, and even then had to be cleaned of slugs, maggots, and rotted portions. Flour was often contaminated by insects and rodents. In winter, cereals and potatoes were staple, made more exciting by salt meat, cheese, pulses, honey and some dried fruit.

Crop yields then were less than half of those today, being limited by poor varieties, lack of soil nutrients, weed competition and damage by birds, rodents, insects and fungi in the fields and barns. The growing understanding and use of fertilizers was one major improvement during that century, but the main impact on yields was the advent of pesticides, without which yields even now would be reduced by about 40% (W.F.J Cuthberston, Chemistry in Britain 27, (11) 1010, 1991.)

The use of specific chemicals as pesticides did not begin recently. Copper arsenate was introduced as an insecticide around 1870, and Bordeaux mixture in the 1880s (by then the Irish potato famine caused by Phytophthora infestans had already taken its toll). Lead arsenate came into use in the 1900s and aryl mercury seed dressings and dithiocarbamate fungicides in the 1930s. The 1940s, stimulated to some extent by the needs of the Second World War, saw the introduction of organophosphorus insecticides and chlorinated hydrocarbons. (DDT, lindant) and the pheno-oxyacetic acid selective herbicides (MCPA, 2,4-D and 2,4,5-T). These had substantial benefits at the time, the first by controlling fleas and lice (and the human diseases which they vectored) on servicemen, and the second by removing broadleafed weed competition from cereals. More recently we have become aware of the accumulation of DDT in animal tissues, especially at the end of the food chain, and its very slow decomposition. The carcinogenic effects of dioxin (2,3,7,8- tetrachlorodibenzo-p-dioxin or TCDD) which is often present in minute quantities as an impurity in 2,4-D and 2,4,5-T (Agent Orange) was brought to our attention by the use of these chemicals as defoliants in Vietnam. There are other pesticides which initially solved serious pest or disease problems but were later found to have undesirable side-effects.

On the whole, now, we have learned to consider such dangers and avoid them, although I witnessed published invitations for tenders for large tonnages of DDT for cotton in Tanzania as recently as the mid-1980s. Slow-metabolizing pesticides used in the Third World not only affect those countries adversely, but also are taken up by migrant birds which return north, bringing the pesticide with them to reduce egg viability and nesting success.

The present relationship between pesticide usage and world food supply has been well-assessed by David Pimental, professor of insect ecology and agricultural sciences at Cornell University (Chemistry in Britain 27 (7) 646, 1991). He puts present world population at 5.3 billion people, increasing at a quarter million per day; about 1.5 billion are currently malnourished. I have tried to estimate the cost (or rather, the value) of the food eaten, but this is difficult. A laborer in East Africa earns about U.S 50 cents/day and, from this and the food grown in his "shamba", he feeds his family; not very well, as you might guess!

In first world countries, the minimum wage ranges around $30/day, so maybe we can assume that an average family of four persons manage to eat on $10-15/day. With these two widely different figures, and assuming that most of the world population does not enjoy First World conditions, we might guess that the value of the food eaten by the human race is about $2000 billion per year.

Now, some more information from Profesor Pimental. About 98% of world food comes from land sources, so let us focus on them. About 35% of crops are estimated to be lost to pests in the U. S (Table 1):

Table l: Percentage of losses in crops to pests in the U.S.A.

DateInsectsDiseasesWeedsTotalCrop Value($ billion)

It's eye-opening to learn that $150 billion worth of crops are still lost to pests in the field, but after harvest a further 20% of crops are lost during transport and storage, i.e. about half of the potential food supply is lost to pests (some $250 billion worth per year in the USA). I would guess that losses to pests in Third World countries are substantially more than 35%, but even using Cuthbertson's figure of 40%, the cost of world losses to pest would be $1.330 billion.

About 2.5 million tons of pesticides are applied world-wide annually; of this, some 50-60% are herbicides, 20-30% are insecticides and 10-20% are fungicides, the total value being about $16 billion. Yet pesticides are used on less than one-third of cropland, and most are used on high-value crops such as cotton, fruit, vegetables and rice. It is even more eye-opening to have Professor Pimental tell us that less than 0.1% of pesticides reach and kill their target, the other 99.9% being available to affect non-target pests, soil, water and atmosphere. The amount of pesticides used in the USA has more than doubled since 1960, and their potency has increased, e.g. the kill achieved in 1945 by 2lb/acre of DDT is obtained with 0.1lb/acre of relatively safe pyrethroids. Fortunately, yields are increasing due to better varieties and greater use of fertilizer and irrigation. Losses to pests are still enormous, and tend to increase due to:

1. destruction of natural enemies of the pests;
2. an increase in resistance of pests to pesticides;
3. movement away from crop rotation towards mono culture;
4. lowering of Federal Drug Administration tolerance for insect parts in food;
5. increased use of aircraft for application, causing loss of pesticide;
6. less tillage, leaving more crop residues to harbor pests;
7. herbicide use altering the physiology of crops, making them more vulnerable to insect attack.

Pesticides have many significant undesirable side effects, some due to our own carelessness. 500,000 accidental poisonings and 10,000 deaths occur annually world-wide from pesticides, although the United States has fewer such poisonings per unit weight of pesticide than other parts of the world. Professor Pimental has collected data on estimated annual losses and costs in the USA:

1. the poisoning of domestic animals and destruction of meat and milk contaminated by pesticides costs $15 million;
2. destruction of natural enemies of pests by pesticides leads to further outbreaks which cost a further $150 million to control;
3. killing honeybees and wild bees cuts honey production and crop pollination by $150 million;
4. drifting of pesticides applied by aircraft affect adjacent crops and forests costing $75 million;
5. losses of wildlife and fish cost $15 million;
6. the government program to regulate pesticide us costs $150 million to administer;
7. monitoring wells and groundwater for pesticides costs $1,200 million.

There are other effects which are difficult to cost, such as loss of soil microfauna and microflora, and chronic health problems such as some cases of cancer and allergies. If all environmental and social costs were assessed, the total annual cost to the USA is $2-4 billion annually. Let's just summarise those annual figures:

Value of food eaten in the world......$2 000 billion
Food crop losses to pests (world).......$l 330 billion
Cost of pesticides used (world)..............$16 billion
Cost of side-effects (USA).......................$4 billion

Professor Pimental states that pesticide use could be reduced by half without any reduction in food supply, but this would involve using them only when necessary and also adopting non-chemical alternatives. He estimates that food production costs would rise by 0.5 to 1% - but these would probably be offset by benefits to public health and the environment. Some people believe that production costs would increase substantially, and so they would, for certain crops: Frank Garner, editor of "Florida Grower and Rancher" states in the August, 1992 edition, " ... The American farmer, the world's leading agricultural producer... will be called upon to meet increasing demands of growing world population with fewer chemicals and more constraints on his use of land and water ... farming is the only business that buys retail and sells wholesale ... a farm implement which costs more than 20 times what it did 40 years ago now helps produce a crop which sells for 3 times what it did then."

In south Florida, for example, unsprayed mango or avocado trees would have much lower yields and unsightly fruit, while papaya fruit can hardly be produced without insecticide. However, possibly safer insecticides could be used in some crops, spraying cycles lengthened and biological controls used where feasible. The public seems willing to accept reduced food cosmetic standards, and the presence of soft-bodied insect parts in some processed foods is harmless.

It is interesting that both Professor Pimental and Frank Garner advocate rotating pesticides to reduce build-up of resistance, planting resistant varieties, monitoring pests before spraying, improved application techniques and utilization of non-chemical pest control methods.

Professor Pimental calls for more research and cooperation to achieve this which means corresponding funding to do it. It would seem to me that this ever-receding target of world food needs could be brought down to a figure less stressing on farmers and the environment by reducing the population increase, but few people want to hear this.

Tropical Fruit News, December 1992

DATE: September 1993

* * * * * * * * * * * * *