Pesticide and Insecticide Poisoning

Pesticide poisoning usually shows itself, after spraying nearby, as a sudden appearance of large numbers of freshly dead bees in front of the hive, and it affects many hives in the apiary at once. There is no cure for poisoning: what needs to be done is to document it, take a sample of freshly dead bees and freeze it, report it immediately to the official veterinary service / local agriculture authority, and provide the colonies with clean water and food.

How do bees get poisoned?

Insecticides are the most dangerous group for bees. Most fungicides and herbicides are less toxic on their own; however, some fungicides can markedly increase toxicity when used together with certain insecticides. Bees come into contact with pesticides in the following ways:

• Direct spraying: Spray landing on foragers working the flowers; the most sudden mass deaths happen this way.
• Residues in flowers: The nectar and pollen of the sprayed crop or of flowering weeds beneath it.
• Wind drift: Spray carried from a neighbouring field to the apiary, water sources and flowering areas.
• Sowing treated seed: Treated dust raised into the air during sowing.
• Contaminated water: Water from containers in which pesticides were mixed, from puddles or from droplets on plant surfaces.
• Pollen carried into the hive: Pollen containing residues is stored in the combs; it can affect nurse bees and brood even weeks later.

How to recognise it

Sudden (acute) poisoning

• Suddenly large numbers of freshly dead bees in front of the hive and on the landing board; most of the dead are foragers
• Bees trembling, writhing, turning on their backs and spinning, crawling without being able to fly
• Bees that have died with their tongue extended; with some pesticides, wet-looking bees that have regurgitated
• Several hives affected on the same day, often the strongest colonies (those with the most foragers suffer most)
• The colony being nervous and aggressive
• Recent spraying in the area

Delayed or insidious poisoning

• Deaths in brood fed on pollen containing residues, scattered brood
• Impaired orientation and foraging ability in foragers; bees that fail to return to the hive
• The population dwindling over weeks, queen problems

Insidious effects cannot be told apart by eye; they are easily confused with other causes, and a link can only be established by residue analysis.

How it differs from similar conditions

What to do if you suspect poisoning

1. Document it immediately. Photograph or video the dead bees in front of the hive, the affected hives and, if possible, the sprayed field, so that the date is visible. Note which hives are affected, the time and the weather.
2. Take a sample of freshly dead bees. Collect only recently dead bees; take as many as possible (ask the laboratory how many it needs; usually a few hundred bees are required). Put them in a clean paper bag or a glass jar, write the date, place and hive details on it, and freeze it immediately.
3. Keep other samples too. Take a piece of comb containing fresh pollen or newly stored nectar and, if possible, a sample of the plant you think was sprayed, and freeze them separately.
4. Make an official report. Contact the official veterinary service / local agriculture authority and ask for an official report to be drawn up; also inform the local village or neighbourhood administration. Residue analysis shows which pesticide was used and is necessary for any claim for compensation.
5. Support the colonies. Provide clean water. If there is no nectar flow or the loss of foragers is large, feed syrup; unite weakened colonies.
6. Prevent renewed exposure. If spraying is continuing, move the hives elsewhere if possible. If short-term closure is necessary, always ensure ventilation and shade the hive; a colony shut in without air in hot weather can suffocate.

Prevention

What the beekeeper can do

• Register your apiary with the official registration system and inform the local village or neighbourhood administration; this is how you get to hear of spraying announcements.
• Get to know the farmers in the area and leave your phone number; ask to be notified before spraying.
• Do not place hives right next to intensively sprayed orchards and field crops, especially during the spraying season.
• In migratory beekeeping, ask in advance about the surroundings of the site and the sowing and spraying calendar.
• Provide a clean water source near the apiary; this reduces bees turning to contaminated puddles.
• Be careful with the chemicals you use yourself: do not apply insecticide, fly spray or ant powder around the hives; hive paint and wood preservatives must be harmless to bees; use varroa treatments only in the form of authorised products and according to their label.

What to ask of the farmer

• No insecticides applied during flowering; this rule must be strictly observed for products whose label carries the warning "harmful to bees"
• Mowing flowering weeds under the trees and at the field edges before spraying
• Application at times when bees are not flying, late in the evening
• No spraying in windy weather, and precautions against drift
• Preference for products and methods less harmful to bees; not leaving pesticide containers and rinse water in the open

Common mistakes

• Clearing away dead bees without taking a sample, or leaving the sample for days without freezing it
• Delaying the report; as time passes residue analysis becomes more difficult
• Shutting hives in hot weather without ventilation
• Attributing every mass death to poisoning; starvation, robbing and diseases must also be considered