Pesticites and Bees

Pesticides have become synonymous with modern agriculture. Besides increasing agricultural production, these chemicals are also of immense value for the control of insect borne diseases of human beings. However the use of pesticides is accompanied by a variety of undesirable environmental effects including the effect on non target species. Bees and flowering plants are interdependent forming a mutually compatible system. Bees are the best pollen carriers and play a vital role in ensuring the productivity of crops. Hence, use of poisonous agro chemicals has become inevitable in scientific farming. While taking managerial decisions for sustaining crop productivity by employing pesticides, bee safety must be ensured. Farmers apply large quantities of pesticides and they are unware of their hazards to insect pollinators and other beneficial insects. Killing of bees by pesticides is the most discouraging facet of apiculture in India as also in other countries.

Symptoms of Bee Poisoning

Bees come in contact with pesticidal deposits while foraging on sprayed crops or weeds where pesticides reach by drifting. The nectar and pollen can also be contaminated with pesticides and there can be stromach poisoning to bees and also to brood when fed on contaminated pollen. Some pesticides may even cause hazards by fumigant action. After gaining entry into body, different pesticides have different modes of action. Followings are some common symptoms of pesticidal poisoning in bees.

• A very common symptom of bee poisoning is the appearance of large number of dead bees in front of the hive. Some bees die in the field.
• Bees become paralytic, loose the power of orientation, legs, wings and digestive tract stop functioning and poisoning bees show uncoordinated movements.
• Bees often die with their lapping tongue protruded out.
• Abdomen become distended.
• Bees exhibit abnormal and jerky movements.
• Bees may spin on their back.
• Bees may exhibit hopping flight and crawling.
• Bees stop hive cleaning duty.
• Bees becomes more aggressive.
• Regurgitation of contents of gut is noticed, particularly in case of phosphatic pesticidal poisoning.
• Guard bees are confused.
• Brood chilling can occur due to reduction in the population of adult bees.
• Dead brood can be seen inside the colonies, if poisoned pollen is stored and fed to brood.
• Pollen contamination and lack of warmth (brood chilling) may result in the brood death.
• Nurse bees feeding an contaminated pollen stop secreting royal jelly.
• Affected queen may lay eggs irregularly.
• Sometimes the queen may stop egg laying totally leading to a break in brood cycle.
• Queen cells may be raised and queens may be superseded in colonies which survive.
• Sometimes queenlessness may develop.

 

 

Factors influencing bee poisoning:

Stage of the crop

Crops are highly attractive to bees during the flowering phase. Hence, most severe bee poisoning problems involve blooming plants. Application of insecticides on flowers is highly hazardous to bees.

Type of formulation

The formulation of an insecticide has a lot to do with its hazards to bees. Liquid formulations are safer than wettable powders applied as sprays and wettable powders are safer than dusts. Granules and seed dressing chemicals are the safest formulations.

Time of application

Honey beef are diurnal insects. Hence, application of pesticides in late evening or night spare the bees.

Method of application

Aerial application of pesticides can result in more bee kill than ground application. Likewise coarse sprays are more harmful than fine sprays. Application of granules in the soil or central whorl does not affect bees. Systemic insecticides applied during flowering stage may contaminate pollen and nectar.

Nature of the pesticide

The toxicity of pesticides vary greatly according to their nature. Persistence and residual action greatly influence their toxicity.

Protecting bees from Pesticidal Poisoning

• Read the pesticide label. Pesticides and formulations which pose a special hazard to bees are required to include a notification on the label.
• Choose an insecticide of low toxicity to bees that will provide the needed pest control.
• Do not apply any pesticide unless the crop is so heavily infested that treatment is worthwhile. If the application of pesticide is necessary then use those insecticides which are non-toxic or less harmful to bees.
• Whenever possible, do not treat crops in bloom. If treatments are needed during bloom, choose a short-residual material. Make applications during the evening, when fresh pollen is enclosed within anthers and protected from insecticide contamination.
• Dust and wettable powder formulations tend to be more hazardous to bees than granules and emulsifiable concentrates. It is necessary to choose less hazardous formulations whenever available. Emulsions have a shorter residual toxicity to bees and granular formulations are less hazardous. Oily formulations are more dangerous and should be avoided.
• Apply pesticides when bees are not actively foraging. Honey bees are active primarily during the morning and early afternoon. Many pesticides can be effectively applied in the late afternoon or evening with relative safety to bees. Evening treatments may also help control the moths (adult stage) of many sweet corn pests that are active and laying their eggs at night.
• Ground applications are safer than aerial applications, the danger of drifting beingreduced in the former.
• Minimize spray drift onto adjacent crops or other plants in bloom.
• Pesticidal dusts and small granules should not be left open or carelessly thrown anywhere because bees are likely to collect such dusts during acute pollen dearth period.
• Use of repellents for reducing the hazard of insecticides has been investigated for morethan 90 years. An effective bee repellent must be strong enough to overcome the natural plant attractiveness and prevent honey bees from foraging on plants treated with a toxic insecticides.. The possibility utilizing neem oil mixed with insecticides could be considered to repel the bees till the residual effect of pesticides is reduced to sub lethal level.
• Honey bee hives should not be placed next to fields or orchards that are likely to be treated with pesticides toxic to bees.
• Beekeepers should inform farmers of the location of hives.
• Farmers should inform the beekeepers before applying pesticides and the beekeeper should either remove the colonies or should keep the bees confined inside the hive during the application. While confining bees due attention should be paid to the following points.
  
  a. Providing sufficient space in hive; while confinding the bees in the hive proper space for all the bees including foragers should be available.
  
  b. Providing proper ventilation : Ventilation must by provided at the top and / sides of the hive, not only through the entrance, because this may get blocked by dead bees. ventilating screen should have as large a mesh as possible.
  
  c. Shading hives : Shade is usually provided by the use of local materials. It must not hinder the flow of air past the hives.
  
  d. Covering hives with wet absorbed matting : Covering the hives with wet clothes / gunny bags can be of great benefit, because evaporation of the water helps to reduce the rise in colony temperature. If pesticides are applied from the air, it is important to cover whole of the hive; otherwise it may be sufficient to drape a very wet cloth over the flight entrance. This greatly reduces flight activity of bees that fly out but it does not prevent flight entirely.
  
  e. Providing water inside the hives : This water is taken by the bees and spread out in the hive, where it evaporates and thus reduces the temperature.
  
  f. Minimizing the period of confinement : The confinement must of course continue as long as the pesticide near the hive retains unacceptable toxicity and its duration can satisfactorily be reduced only if the pesticide applied does not have long residual action. If there is no store in the hive then pollen supplement and sugar syrup may also be provided.
  
  When the damage to bees (and also to brood) is due to pesticide contaminated pollen being carried back to the hive, two actions viz. prevention of pollen being stored in the hive and provision of a safe pollen supply inside the hive by the beekeepers may be helpful. Provision of pollen cakes in the hive during this period greatly reduces the collection of toxic pollen. Cakes of pure pollen were more effective than pollen supplement make with soybean flour.

 

Care of the Poisoned Colonies :

• Shift the bee colonies away from foreging range, from the source of poisoning.
• Provide sugar syrup and pollen substitute because most field force must have been killed.
• Contaminated pollen stored in combs can be removed by dipping the combs in water and washing by slight shaking.