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Pesticides are deadly for bees and people
Pollution of the environment by pesticides is an increasing problem in the tropics and subtropics. It arises from the development of large-scale cultivation of single crops - monocultures. Increased use of exotic cultivars of crops is often accompanied by increased use of pesticides. When these plants growing under new environmental conditions are attacked by pests to which they are not adapted, the problem is often approached by using more and more pesticides.
We often find heavy use of pesticides in small vegetable gardens producing food for the family and local markets. The use of pesticides should be banned in these places. Pesticides used on crops often contaminate farmers, and the food and drinking water of local people.
From my own experience in Africa and the Caribbean, it seems that the basic problem is lack of information about the harmful effects of pesticides. Most farmers and many extension officers are not aware of the risks to people, nor of the risks to useful honeybees and other bees.
Knowledge is lacking also about the need for bees to pollinate most tropical fruits, nuts, berries and some of the seeds. We cannot expect farmers to protect bees unless they understand the bees' importance for pollination. Better knowledge is necessary both for the farmers, and for the beekeepers, so that they can co-operate to protect bees against destruction from sprays.
Use of pesticides without care for pollinating bees has brought disaster for many beekeepers. Wherever this has occurred it has also caused a poorer harvest of bee-pollinated crops.
The problem is still growing.
Many pesticides have been forbidden in Europe and the USA because they are too dangerous. Some producers and dealers have then tried to intensify the sale of these products in developing countries where they are delivered to farmers without any warnings.
Lack of knowledge about the need for bees to pollinate many crops has resulted in careless use of pesticides on flowering plants, and this causes the death of all the bees in a neighbourhood. The result is that harvests are never as big as they could be if the pesticides were used in a way safe for bees.
Some pesticide producers are more interested in selling their products than in giving information concerning the dangers of pesticides. In developing countries, it is easy to get hold of cheap pesticides, but often impossible to get sufficient protective equipment for use by the person spraying.
The use of pesticides in countries where people are not told, or are not able to read warnings written in foreign languages, has caused plenty of accidents.
In many countries pesticides are sold in second-hand food containers like cola bottles or sugar bags. This results in people accidentally drinking or eating the poison. In some places pesticide containers are subsequently used for rainwater containers, and people are poisoned in that way.
In 1981 OXFAM declared that 750,000 people were poisoned in one year from pesticides (especially insecticides). Half of these incidents and 75% of the people killed were in developing countries. Other statistics from the World Health Organisation tell that one person dies from pesticide poisoning every minute in this part of the world.
The situation is even worse now.
In my own country, Denmark, we have a law to prevent the use of insecticides in daytime on crops with open flowers, when the bees are flying. If a farmer applies pesticide at an inappropriate time and causes the death of bees of surrounding beekeepers, he or she has to pay compensation to them. There have even been cases where the farmer who sprayed the pesticide in a careless way was forced by the court to pay compensation both to the beekeepers and to other farmers who obtained smaller harvests because of the lack of bees.
Types of pesticides
Pesticides kill by direct contact, stomach poisoning or fumigation.
There are eight types of pesticides:
1. Rodenticides - kill rats, mice;
2. Fungicides - kill fungi;
3. Miticides/acaricides - kill mites;
4. Herbicides - kill plants;
5. Insecticides - kill insects;
6. Nematicides - kill nematodes;
7. Molluscides - kill molluscs, slugs and snails;
8. Bactericides - kill bacteria in humans and other animals.
It is mainly the insecticides which harm bees, but some of the other pesticides harm them too. Insecticides are dangerous for people as well as bees. In the following we will concentrate on insecticides.
There are 4 major groups of synthetic insecticides:
Pesticides with high toxicity to bees
(After Verma & Partap, 1993; Johansen & Mayer, 1990; Adey, Walker & Walker, 1986)
For least hazard to bees these should be applied only during late evening and night. They should NOT be applied on blooming crops or weeds. Many of these chemicals have a high residual toxicity, even 10 hours after they have been sprayed.
D = dust
EC = emulsifiable concentrate
F = flowable
G = granular
WP = wettable powder
Carbaryl 50% WP, D
Carbophenothion 20 EC, D
Cypermethrin 10 EC
Decamethrin 20 EC
Dichlorvos 100 EC
Dimethoate 30 EC
DDVP 100 EC
Naled D, WP
Oxydementon-methyl 25 EC
Phosphamidon 100 EC
Permethrin 25 EC
Quinalphos 25 EC
Sumithion 50 EC
Thiometon 25 EC
Do not use insecticides (fly killer) to kill bees
Some honey hunters in the tropics are now using insecticides made for spraying mosquitoes, to kill bees. They do not know that the poison enters the honey. People who eat this honey can become very ill - some people die from eating the poisoned honey.
Poisoning of bees by insecticides
Too many farmers are using insecticides without thinking of the honeybees they need for pollination of the same crop they are spraying. If they spray a flowering crop in daytime with dangerous types of insecticides many bees will be killed. Depending on the type of chemical used, the bees will either die quickly or after some days.
If the bees are poisoned the symptoms can be:
1. Dead honeybee workers accumulated at the hive entrance. They usually represent 10-20% of the total number being killed, but ants often remove them very fast. The rest of the poisoned foragers will have died in the field.
2. Many types of poisoning cause bees to be more agitated and aggressive - especially evident with lindane and organophosphorus compounds.
3. The bee colonies can produce loud angry sounds, and behave in a stressed and nervous way, running around with fast movements.
4. Inside the hive some bees will make a special "alarm dance". The returning bees and some hive bees are running around on the combs in spirals or irregular zigzags. This can stop flight activity completely for some time. Outside the hive, bees are performing abnormal communication dances. This can be observed if you use frame hives with horizontal landing boards.
5. Bees will crawl around on the ground in front of the hive, unable to fly. Sometimes this continues for three days before they die. Some are spinning on their backs.
6. Many bees killed by poison have their tongues extended.
7. Regurgitation of the stomach contents is especially associated with exposure to organophosphorus insecticides.
Sometimes all bees in a colony die quickly, but often the bees will survive for some time before they die. A poisoned bee colony has lost its forager bees, and most of the young bees will die after some time, because they eat contaminated pollen. If dead and dying light-coloured, newly emerged workers are seen, it is a sure sign of pollen contamination. It means that no bees are cleaning the empty cells or feeding the brood, and the queen will not be able to find empty cells for egg laying.
When stored in the combs, pollen can remain toxic to bees for up to eight months or a year. Usually the queen will be superseded within the first 30 days following the poisoning, or the colony becomes queenless. When there is a lack of pollen the hive bees will begin feeding on the eggs. Once there are no eggs or young larvae present, the workers can no longer rear a new queen. Another symptom can be that the queen produces drone eggs only. After a while this will lead also to extinction of the colony, because drones do not collect food for the colony.
Fortunately there are some repellent insecticides, with a smell that makes bees abandon the flower instantly. Unfortunately farmers do not know to select such products to protect the pollinating bees.
Alternatives to pesticides
The use of pesticides is not without problems. A detailed knowledge of the life cycle of the pest is necessary. A pesticide used at the wrong time, in the wrong place, and in the wrong way can be more harmful than not using it.
The wrong use of an insecticide can kill the pest for a time, but it will kill also the natural predators of the pest. After some time the pest will recover, but now there will be few natural enemies left to eat the pest. This is because the predators are present in smaller numbers than the pest and will not recover their population as fast. So the pest will have time to grow to even larger populations. Then even more insecticides are needed!
After some time pests show resistance to the chemicals being used, and then new and more expensive ones must be bought.
This can continue until so much poison is being used that the environment is spoiled, or the farmers ruined. This happened in Central America in cotton areas where the fields eventually had to be sprayed 44 times during their growing time. The cotton growing had to stop, and the environment was so polluted that the export of meat to the USA was also stopped.
These examples show that if pesticides must be used, it must be in combination with other ways of fighting pests.
How to control crop pests without using imported pesticides
Often the farmer has a traditional knowledge of how to live with, or fight pests and these methods seem to work. In reality most pesticides used in the tropics are for export crops.
1. Make sure that cultivated plants are properly nourished. Too much or too little fertiliser, water, or sun can for example cause aphid attack.
2. Plants should be grown in mixtures, so that the pest or disease cannot spread as easily as in a monocrop. For example, maize intercropped with cassava reduces the spread of cassava bacteria wilt.
3. The right plant density can help prevent some pests. For example, groundnut plants should be placed close together. This helps prevent aphid attack to the lower part of the plants, because of shadow and high humidity.
4. Remove and destroy all infested fruits or tubers so that pests from them cannot make new generations.
5. Do not let fruits and leaves touch the ground. Straw could help here.
6. Prevent water flow, runoff or splash from infected plant parts to healthy ones.
7. Rotate the cultivation of different plants. Crop rotation is very unfavourable to nematodes.
8. Always use healthy seeds.
9. If possible use resistant plant varieties. For example, some of the old types of millet are better protected against birds and beetles because of sticky hairs.
10.Self-made natural products can be used to fight pests without making them become resistant. For example, fine ashes can be used to discourage chewing insects, the juice of tobacco stems is poisonous to aphids, and vegetable oil or fatty soaps mixed with water can be used against aphids.
11.Proper weeding and destruction of infested plants. If possible use the weeds in compost making, where the high temperature will destroy diseases, before the material is returned to the fields.
12.Indirect biological control. This is done by organising the environment and fields so that they provide habitat for a great variety of the farmer's natural allies such as insect-eating birds, spiders, wasps, etc.
13.Biological control. This means the importation or cultivation of the natural enemies of a pest. It could be with parasitic wasps, or by spraying bacteria on to the field. The point is to attack only the pest and not to poison other creatures.
14.Different types of traps can be used against bigger pests. For example, a fly trap made of a bottle with a sugar solution, a slug trap made of a plastic bottle with beer.
How to protect bees against pesticides
The beekeeper can help reduce bee poisoning in different ways:
1. Bees can be kept at a distance safe from areas where pesticides are being applied. This must be at least 7 km, although this will also mean the farmer will get no crops pollinated.
2. The beekeeper and the farmer can co-operate. If beekeepers learn about different pesticides, they can discuss with farmers, warn them against the most dangerous pesticides, and develop beneficial agreements concerning pollination services and the prudent use of pesticides.
3. Bees can be moved away before the spraying, and kept away as long as the poisons are still in the flowers.
4. If pesticides are used on flowering plants near the hives, and it is too difficult to move the hives away, the bees can be confined inside the hives. The hives can be covered by large burlap sacks. It is necessary to put water on the sacks to cool the bees. The bees should also be provided with water inside the hive, so that they are able to cool the brood. If the hives are placed in shade, and the sacking is kept wet, the bees can be covered for up to two days. It may be necessary to apply water to the sacking every one to three hours to keep the colony sufficiently cool. Overheating of a colony of bees can lead to their rapid death. Larger colonies are more sensitive to overheating than small, and it is important that there is plenty of space and good ventilation in the hive.
5. If the bees are near a water pipe it can be possible to keep them inside their hive by constantly sprinkling them, so that they believe it is a rainy day.
Adey,M; Walker,P; Walker,T (1986) Pest control safe for bees. London, UK.
Crane,E (1990) Bees and beekeeping: science, practice and world resources. Oxford, UK.
Crane,E; Walker,P (1983) The impact of pest management on bees and pollination. London, UK.
Dupriez,H; De Leener,P (1989) African gardens and orchards. London, UK.
Johansen,C A; Mayer,D F (1990) Pollinator protection: a bee and pesticide handbook. Connecticut, Cheshire, USA.
Verma,L R; Partap,U (1993) The Asian hive bee, Apis cerana, as a pollinator in vegetable seed production. Kathmandu, Nepal.
Weir,D; Schapiro,M (1981) Circle of poison, pesticides and people in a hungry world. San Francisco, USA.
This supplement has been published with support from the Danish Beekeepers' Association and DANIDA.
[Bees for Development Journal #34]