By Inge Lotter 15 October 2020
The Effect of Pesticide and Fungicide Application on Apis mellifera (honey bees)
In the previous article we looked at one of the challenges that face beekeepers in South Africa which is theft and vandalism of their bee hives.
The second and very serious challenge that beekeepers face is directly related to the farming practices of the sites where the bees are situated. It is fully understood that in order to protect crops from weeds, fungi and pests farmers have to use chemicals and pesticides. As the target of many of these chemicals are insects, it has to be taken into serious consideration that most beneficial pollinators are also insects, including the African honey bee Apis mellifera scuttelata that occur in the summer rainfall areas of South Africa.
There is now widespread consensus that pesticides are having a devastating effect on the sustainability of pollinator populations which is much more than just the effect it has on honey bee colonies. Numerous scientific studies have been done across the globe to ascertain why pollinator and honey bee populations are decreasing at such an alarming rate. Many of the pesticides and chemicals implicated in these effects on pollinators are regarded as “safe” to use even when honey bee colonies are present.
As a beekeeper I am in no way an expert on chemicals or pesticides, but the devastation and economic losses incurred by colonies being poisoned are sadly felt all too frequently. Seeking to understand how chemicals and pesticides are affecting our colonies are an ongoing and difficult task for beekeepers. Constant development of new chemical and pesticide formulations make it very challenging for all parties seeking to minimise risk to pollinators to keep up with new releases and their effects. In addition, any discussion of findings and/or interpretations of the effects of pesticides/chemicals can be potentially contentious. I believe however that it is necessary to consider as much information as possible in order to guide our actions to have as little impact on the ecology of our area as possible. This is a compilation of my own desktop research in order to understand the effects of pesticide and chemicals on my colonies. The losses caused are very real.
Pesticides that have sub-lethal or chronic effects on the colony’s health are even more devastating to the sustainability of our colonies as they slowly deteriorate over a period of weeks or even months. In this way acute toxicity is almost preferred as the forager bee will die before making it back home which means that the queen bee, brood and nurse bees are not affected and the colony survives. Alternatively, when the bee takes an insecticide back to the colony through contaminated pollen or nectar or even on its body, it can potentially contribute to widespread colony death.
Many farmers regard some pesticides as “nontoxic or bee friendly”. How the toxicity of these chemicals are generally measured is to determine what the acute exposure dose would be to cause 50% of the exposed population to die (LD= lethal dose). Nontoxic therefore does not mean that no bees die, just that a much higher dose is required to kill 50% of the test population.
Use of Organophosphates (OPs), Methylcarbamates (MCs) & Pyrethroids (pyr)
According to Dr Hannelie Human Neonicotinoids are neurotoxic insecticides and even field-realistic sublethal doses result in impaired navigation, homing, and olfactory learning in honeybees. It disrupts neural pathways and thermoregulation processes, and in addition decrease foraging and flight ability. This class of insecticide is highly toxic to honeybees in very small quantities via synergistic interactions between multiple stressors. Exposure to these chemicals can affect the entire colony and future generations since they are highly water soluble and therefore have the potential to contaminate non target flowering plants and weeds in addition to the target crop (Human H 2020, Personal communication, 12 October).
It has been shown in recent studies that honey bees experience a learning and memory impairment after ingesting even small doses of the often used insecticide chlorpyrifos, potentially threatening their survival. Chlorpyrifos is a highly neurotoxic organophosphate pesticide used worldwide on crops including macadamia. Exposure to this chemical may be reducing bees effectiveness as nectar foragers and pollinators. Both the lethal was well as sub-lethal effects on bees need to be taken into account.
In other studies it has been found that exposure to sub lethal doses of insecticides known as pyrethroids including permethrin, which is often used on macadamia orchards, may reduce honey bee movement and social interaction. The functioning of a healthy honey bee colony relies on all its members being able to perform all of the necessary duties, such as foraging for food and communicating with other bees. If sub lethal exposure to pesticides affect or reduce the ability for movement, social interaction and feeding of bees, it could potentially impact the whole colony performance and/or survival.
Fipronil is one of the main chemicals blamed internationally for the spread of colony collapse disorder among bees. It has been found by the Minutes-Association for Technical Coordination Fund in France that even at very low nonlethal doses for bees, the pesticide still impairs their ability to locate their hive, resulting in large numbers of bees getting lost with every foraging expedition which may negatively affect the development and maintenance of colonies. Fipronil has also been found to be highly toxic to fish and aquatic invertebrates.
In some other studies it has been found that the fungicides may be having a more profound effect on bees than previously thought. It is especially true when a cocktail of chemicals is used. Fungicides especially affect brood development by reducing the micro-organisms that ferment bee bread and therefore make it palatable to the young developing brood. This makes our modern farmland a very inhospitable place for bees. Insecticides are meant to kill insects, so people have been really interested in how insecticides kill beneficial insects. But fungicides are not meant to kill insects, so they’ve often been passed over.
What can farmers do to minimise the effect of their pest control programmes on pollinators?
- Pesticide application to any blooming flowers should be avoided as honeybees are attracted to all types of blooming flowers including weeds and cover.
- If blooming flowers absolutely must be sprayed with pesticides, they should be sprayed in the evening or night hours as bees are not in the field at that time.
- If aerial spraying is required, spray planes should not turn over fields containing blooming crops or weeds. Ground application is generally less hazardous than aerial application because there is less drift and smaller areas are treated each time.
- Limit the contamination of water sources. Bees drinking water which contains pesticides can be very hazardous to them, even water on foliage or flowers.
The following are some classic signs of Bee Poisoning:
- Large numbers of dead and dying honey bees in front of the hives
- Increased defensiveness (caused by most insecticides)
- Lack of foraging bees on a normally attractive blooming crop (most insecticides)
- Abnormal jerky, wobbly, or rapid movements; spinning on the back (organophosphates, organochlorines, and neonicotinoids)
- Forager disorientation and reduced foraging efficiency (neonicotinoids)
- Immobile, lethargic bees unable to leave flowers (many insecticides)
- Regurgitation of honey stomach contents and tongue extension (organophosphates and pyrethroids)
- Performance of abnormal communication dances, fighting, or confusion at the hive entrance (organophosphates)
- Bees seeming unable to fly. Bees move slowly as though they have been chilled (carbaryl).
- Dead brood; dead, newly emerged workers; or abnormal queen behaviour, such as egg laying in a poor pattern (carbaryl)
- Queenless hives (acephate, carbaryl, malathion, methamidophos)
To minimise the effect on pollinators and especially honey bee colonies, the following are recommended:
- Consider alternatives to pesticides. Well-planned, integrated pest-management programs often are less dangerous to pollinators and other beneficial insects than last-minute efforts to suppress pest outbreaks.
- Treat only when necessary by doing scouting – look before you shoot! Scouting and economic thresholds ensure that pesticides are used only when their benefits (the rand value of crop loss prevented by pesticide use) are greater than the cost of the pesticide and its application. In this equation, also weigh the value of pollination to your crop and the value of hives to beekeepers.
- Treat only the areas where necessary – NO COVER SPRAYS
- Always use minimum risk pesticides – Use insecticides that are least toxic to bees. Choose the least hazardous insecticide formulation.
- Do not apply pesticides unless absolutely necessary whilst there are still flowers in the orchard. This is difficult where several cultivars are present as flowering periods differ.
- ALWAYS follow the instructions on the label
- Mixing pesticides with sugar will attract bees
- Do not spray in conditions where spray can drift onto hives or fields supporting bees
- Avoid tank mixing insecticides and fungicides
- Remember fungicides also affects bees as it limits the fermentation of pollen making it useless to the bees and can even lead to starvation of brood dependent on pollen protein
- Apply insecticides in late evening or night when bees are not foraging (generally between 8 p.m. and 3 a.m.) Evening applications are less hazardous to bees than early morning applications. Warm days and nights and full moon conditions can extend the foraging period; therefore applications may be necessary later in the evening under unusually warm conditions.
- Do not apply insecticides when cool temperatures or damp conditions are expected after treatment. Residues will remain toxic to bees for a much longer time under these conditions.
- Contact the beekeeper at least 48 hours in advance to inform him or her of your pesticide application plans so he/she can confine or move the colonies before pesticides are applied and losses incurred.
- Always notify neighbouring farmers in order that their bees and beekeepers can also be protected
Remember: A WET BEE IS A DEAD BEE
Honey bee recovery from pesticide poisoning
- If a honey bee colony has lost many of its foragers, but has sufficient brood and adequate stores of uncontaminated pollen and honey, it may recover without any intervention. Move bees to a pesticide-free foraging area if available. If sufficient forage is unavailable, feed them with sugar syrup and pollen substitute, and provide clean water to aid their recovery. Adding probiotics and trace minerals to your artificial feed may assist the colony to recover. Protect them from extreme heat and cold, and, if needed, combine weak colonies.
- If the pesticide has accumulated within pollen or nectar stores, brood and workers may continue to die until the colony is lost. Many pesticides freely transfer into beeswax, and you may consider replacing the comb with new foundation, drawn comb from unaffected colonies, or shaking the bees into a new hive and destroying the old comb. Artificial feeding with added probiotics and trace minerals in the sugar syrup and pollen substitute may assist the colony to recover. Replacing brood comb on a regular schedule (typically 3 to 5 years) may prevent accumulation of pesticides to lethal levels in brood comb wax.
In 1962 Rachel Carson wrote the book Silent Spring. She introduced the world to the dangers of pesticides that started the Global Environmental Movement, but now more than 50 years later, we still seem to be ignoring the dangers of pesticide use. Can we still claim ignorance? We need to see the bigger picture that everything is connected – when there are no longer what we consider “pests” there might be nothing left at all.
The health of our environment is in our hands…. We can all make a difference
Casida JE, Durkin KA (2013) Neuroactive insecticides: targets, selectivity, resistance, and secondary effects. Annu Rev Entomol 58