Lecture 6: Effect of agricultural inputs on bee activity – Pesticide poisoning
The use of pesticides has become inevitable in modern agriculture. Most of
crops are attacked by some or the other pests. The control of insect pests, diseases and
weeds, in most cases is done by applying some pesticide. Pesticides used on field
crops for the control op pests have their own side effects, one of which is their
toxicity to honey bees. Honeybees are susceptible to many pesticides, especially
insecticides. Each year honeybee colonies are damaged or destroyed by pesticides,
primarily insecticides. Such losses have devastating impact on the beekeepers, who
may have to relocate damaged hives or perhaps even be forced out of business. It is
very difficult to assess the extent of losses of bees from pesticides. Three types of
harmful effects evident in agriculture are:
1. Loss in production of honey.
2. Contamination of bee products.
3. Reduction in the yield of cross-pollinated crops.
These effects may happen as a result of the direct exposure of bee fauna to
pesticides or through indirect contact with their residues. Direct exposure occurs from
treatment of bee hives with pesticides for disinfestation purpose or honey bees visiting
the fields at the time of spray. While the indirect exposure occurs from spray drift
from nearby fields or bee foraging in sprayed crops. Honeybees may also come in
contact with spray fluid spilled inadvertently or thrown in the watercourses.
Symptom’s of bee poisoning
Dead or dying bees near the entrance of hives /colonies.
Dead bees on the top of frames or bottom board.
Lack of recognition of guard bees.
General aggressiveness.
Fighting among bees at the entrance or inside of colonies.
, Paralysed or stupefied bees crawling on nearby objects of the colony and also on
blades of the grass.
Sudden cessation of food storage and brood rearing.
Dead and deserted brood in the hive.
Poor recognition of pollen and nectar.
And finally a depleted population of the colony.
Causes of poisoning
Bee poisoning mainly occurs when pesticides are applied to crop during bloom. It
may also be caused by drift of toxic chemicals onto non-target areas or bees
contacting residues of pesticides on plants for pollen and nectar and also bees
drinking or contacting contaminated water in watercourses or spillage. If the chemical
is highly poisonous the bees may get killed in or near the field. However, if the
chemical has delayed action the bees may reach their hives but die near the entrance.
Some of workers may even enter the hive and store nectar and pollen inside and thus,
result in exposure of the nurse bees to the contaminated pollen, carried by the foragers
and stored in the comb. The resultant cumulative effect of the contaminated pollen
may lead to depletion of brood, death of young ones, nurse bees and other workers.
Hence, not only the population of colony decreases substantially but also results in
contamination of bee products.
Factors of bee poisoning
Many factors involving pesticides affect the potential for honey bee poisoning.
The important factors are described below.
Plant growth stage: Severe bee poisoning most often results from spraying
insecticides directly on flowering plants, either the crop itself or flowering
weeds within its margins.
Relative toxicity of chemical: Pesticides vary in their toxicity to honeybees.
Among the pesticides, most fungicides and herbicides are relatively less toxic to
honeybees. Insecticides are most toxic. Honeybees are most vulnerable to broad-
spectrum insecticides. Insecticides that are highly toxic can not be applied to
blooming crop when bees are present without causing serious to colonies.
Insecticide like dimethoate, malathion, methyl parathion etc. carbaryl come
The use of pesticides has become inevitable in modern agriculture. Most of
crops are attacked by some or the other pests. The control of insect pests, diseases and
weeds, in most cases is done by applying some pesticide. Pesticides used on field
crops for the control op pests have their own side effects, one of which is their
toxicity to honey bees. Honeybees are susceptible to many pesticides, especially
insecticides. Each year honeybee colonies are damaged or destroyed by pesticides,
primarily insecticides. Such losses have devastating impact on the beekeepers, who
may have to relocate damaged hives or perhaps even be forced out of business. It is
very difficult to assess the extent of losses of bees from pesticides. Three types of
harmful effects evident in agriculture are:
1. Loss in production of honey.
2. Contamination of bee products.
3. Reduction in the yield of cross-pollinated crops.
These effects may happen as a result of the direct exposure of bee fauna to
pesticides or through indirect contact with their residues. Direct exposure occurs from
treatment of bee hives with pesticides for disinfestation purpose or honey bees visiting
the fields at the time of spray. While the indirect exposure occurs from spray drift
from nearby fields or bee foraging in sprayed crops. Honeybees may also come in
contact with spray fluid spilled inadvertently or thrown in the watercourses.
Symptom’s of bee poisoning
Dead or dying bees near the entrance of hives /colonies.
Dead bees on the top of frames or bottom board.
Lack of recognition of guard bees.
General aggressiveness.
Fighting among bees at the entrance or inside of colonies.
, Paralysed or stupefied bees crawling on nearby objects of the colony and also on
blades of the grass.
Sudden cessation of food storage and brood rearing.
Dead and deserted brood in the hive.
Poor recognition of pollen and nectar.
And finally a depleted population of the colony.
Causes of poisoning
Bee poisoning mainly occurs when pesticides are applied to crop during bloom. It
may also be caused by drift of toxic chemicals onto non-target areas or bees
contacting residues of pesticides on plants for pollen and nectar and also bees
drinking or contacting contaminated water in watercourses or spillage. If the chemical
is highly poisonous the bees may get killed in or near the field. However, if the
chemical has delayed action the bees may reach their hives but die near the entrance.
Some of workers may even enter the hive and store nectar and pollen inside and thus,
result in exposure of the nurse bees to the contaminated pollen, carried by the foragers
and stored in the comb. The resultant cumulative effect of the contaminated pollen
may lead to depletion of brood, death of young ones, nurse bees and other workers.
Hence, not only the population of colony decreases substantially but also results in
contamination of bee products.
Factors of bee poisoning
Many factors involving pesticides affect the potential for honey bee poisoning.
The important factors are described below.
Plant growth stage: Severe bee poisoning most often results from spraying
insecticides directly on flowering plants, either the crop itself or flowering
weeds within its margins.
Relative toxicity of chemical: Pesticides vary in their toxicity to honeybees.
Among the pesticides, most fungicides and herbicides are relatively less toxic to
honeybees. Insecticides are most toxic. Honeybees are most vulnerable to broad-
spectrum insecticides. Insecticides that are highly toxic can not be applied to
blooming crop when bees are present without causing serious to colonies.
Insecticide like dimethoate, malathion, methyl parathion etc. carbaryl come
