Pesticide toxicity to bees
Pesticides vary in their effects on bees. Contact pesticides are usually sprayed on plants and can kill bees when they crawl over sprayed surfaces of plants or other areas around it. Systemic pesticides, on the other hand, are usually incorporated into the soil or onto seeds and move up into the stem, leaves, nectar, and pollen of plants.
Of contact pesticides, dust and wettable powder pesticides tend to be more hazardous to bees than solutions or emulsifiable concentrates. When a bee comes in contact with pesticides while foraging, the bee may die immediately without returning to the hive. In this case, the queen bee, brood, and nurse bees are not contaminated and the colony survives. Alternatively, the bee may come into contact with an insecticide and transport it back to the colony in contaminated pollen or nectar or on its body, potentially causing widespread colony death.
Actual damage to bee populations is a function of toxicity and exposure of the compound, in combination with the mode of application. A systemic pesticide, which is incorporated into the soil or coated on seeds, may kill soil-dwelling insects, such as grubs or mole crickets as well as other insects, including bees, that are exposed to the leaves, fruits, pollen, and nectar of the treated plants.
Pesticides are linked to Colony Collapse Disorder and are now considered a main cause, and the toxic effects of Neonicotinoids on bees are confirmed. Currently, many studies are being conducted to further understand the toxic effects of pesticides on bees. Agencies such as the EPA and EFSA are making action plans to protect bee health in response to calls from scientists and the public to ban or limit the use of the pesticides with confirmed toxicity.
Insecticide toxicity is generally measured using acute contact toxicity values LD50 – the exposure level that causes 50% of the population exposed to die. Toxicity thresholds are generally set at
- highly toxic (acute LD50 < 2μg/bee)
- moderately toxic (acute LD50 2 - 10.99μg/bee)
- slightly toxic (acute LD50 11 - 100μg/bee)
- nontoxic (acute LD50 > 100μg/bee) to adult bees.
The acute toxicity of pesticides on bees, which could be by contact or ingestion, is usually quantified by LD50. Acute toxicity of pesticides causes a range of effects on bees, which can include agitation, vomiting, wing paralysis, arching of the abdomen similar to sting reflex, and uncoordinated movement. Some pesticides, including Neonicotinoids, are more toxic to bees and cause acute symptoms with lower doses compared to older classes of insecticides. Acute toxicity may depend on the mode of exposure, for instance, many pesticides cause toxic effects by contact while Neonicotinoids are more toxic when consumed orally. The acute toxicity, although more lethal, is less common than sub-lethal toxicity or cumulative effects.
Sublethal and chronic effects
Field exposure to pesticides, especially with relation to neonicotinoids, may lead to multiple physiological and/or behavioral sublethal effects in exposed bees. Sublethal effects to honey bees are of major concern and include behavioral disruptions such as disorientation, thermoregulation, reduced foraging, decreased flight and locomotion abilities, impaired memory and learning, phototaxis (response to light), and a shift in communication behaviors. Additional sub-lethal effects may include compromised immunity of bees and delayed development.
Neonicotinoids are especially likely to cause cumulative effects on bees due to their mechanism of function as this pesticide group works by binding to nicotinic acetylcholine receptors in the brains of the insects, and such receptors are particularly abundant in bees. Over-accumulation of acetylcholine results in paralysis and death.
Colony collapse disorder
Colony collapse disorder is a syndrome that is characterized by the sudden loss of adult bees from the hive. Many possible explanations for it have been proposed, but no one primary cause has been found. The US Department of Agriculture has indicated in a report to Congress that a combination of factors may be causing colony collapse disorder, including pesticides, pathogens, and parasites, all of which have been found at high levels in affected bee hives.
The development of a bee from egg to adult takes about three weeks. The queens daily laying rate will decline if contaminated materials are brought back to the hive such as pesticides.31.6% of exposed honey bees will fail to return to their colony every day while the rest will bring back contaminated pollen which in turn will not only affect the worker bees but also the queen. As a consequence there will be an upset in colony dynamics.
Colony Collapse Disorder has more implication than the extinction of one bee species; the disappearance of honeybees can cause catastrophic health and financial impacts. Honeybee pollination has an estimated value of more than $14 billion annually to the United States agriculture. Honeybees are required for pollinating many crops, which range from nuts to vegetables and fruits, that are necessary for human and animal diet.
The EPA updated their guidance for assessing pesticide risks to honeybees in 2014. For the EPA, when certain pesticide use patterns or triggers are met, current test requirements include the honey bee acute contact toxicity test, the honey bee toxicity of residues on foliage test, and field testing for pollinators. EPA guidelines have not been developed for chronic or acute oral toxicity to adult or larval honey bees. On the other hand, the PMRA (Pest Management Regulatory Agency) requires both acute oral and contact honey bee adult toxicity studies when there is potential for exposure for insect pollinators. Primary measurement endpoint derived from the acute oral and acute contact toxicity studies is the median lethal dose for 50% of the organisms tested (i.e., LD50), and if any biological effects and abnormal responses appear, including sub-lethal effects, other than the mortality, it should be reported.
The EPA's testing requirements do not account for sub-lethal effects to bees or effects on brood or larvae. Their testing requirements are also not designed to determine effects in bees from exposure to systemic pesticides. With colony collapse disorder, whole hive tests in the field are needed in order to determine the effects of a pesticide on bee colonies. To date, there are very few scientifically valid whole hive studies that can be used to determine the effects of pesticides on bee colonies because the interpretation of such whole-colony effects studies is very complex and relies on comprehensive considerations of whether adverse effects are likely to occur at the colony level.
A March 2012 study conducted in Europe, in which minuscule electronic localization devices were fixed on bees, has shown that, even with very low levels of pesticide in the bee's diet, a high proportion of bees (more than one third) suffers from orientation disorder and is unable to come back to the hive. The pesticide concentration was order of magnitudes smaller than the lethal dose used in the pesticide's current use. The pesticide under study, brand-named "Cruiser" in Europe (thiamethoxam, a neonicotinoid insecticide), although allowed in France by annually renewed exceptional authorization, could be banned in the coming years by the European Commission.
Based on a risks to bee health as identified by EFSA, in April 2013 the EU decided to restrict thiamethoxam, clothianidin, and imidacloprid. The UK voted against the ban saying it would harm food production. Agrochemical companies Syngenta and Bayer CropScience both began legal proceedings to object to the ban. It is their position that there is no science that implicates their pesticide products.
Bee kill rate per hive
The kill rate of bees in a single bee hive can be classified as:
- < 100 bees per day - normal die off rate
- 200-400 bees per day - low kill
- 500-900 bees per day - moderate kill
- 1000+ bees per day - High Kill
Pesticides come in different formulations:
- Dusts (D)
- Wettable powders (WP)
- Soluble powders (SP)
- Emulsifiable concentrates (EC)
- Solutions (LS)
- Granulars (G)
All substances listed are insecticides, except for 2,4-D, which is an herbicide. Some substances are arachnicides too.
|Common name (ISO)||Examples of Brand names||Pesticide Class||length of residual toxicity||Comments||Bee toxicity|
|Aldicarb||Temik||Carbamate||apply 4 weeks before bloom||Relatively nontoxic|
|Bifenthrin||Agri-Medk, Abamectin, Talstar, Bifenthrine, Brigade, Capture, FMC 54800, OMS3024, Torant (with Clofentezine), and Zipak (with Amitraz)||Pyrethoid||< 1 day RT
> 1 day ERT
|Highly toxic to bees||highly toxic|
(b) Sevin XLR
|Carbamate||High risk to bees
foraging even 10 hours after spraying; 3 – 7 days (b) 8 hours @ 1.5 lb/acre (1681 g/Ha) or less.
|Bees poisoned with carbaryl can take 2–3 days to die, appearing inactive as if cold. Sevin should never be sprayed on flowering crops, especially if bees are active and the crop requires pollination. Less toxic formulations exist.||highly toxic|
|Carbofuran||Furadan||Carbamate||7 – 14 days||U.S. Environmental Protection Agency ban on use on crops grown for human consumption (2009) carbofuran (banned in granular form)||highly toxic|
|Methomyl||Lannate, Nudrin||Carbamate||2 hours||Should never be sprayed on flowering crops especially if bees are active and the crop requires pollination.||highly toxic|
|Pirimicarb||Pirimor, Aphox||Carbamate||Relatively nontoxic|
|Propoxur||Baygon||Carbamate||Propoxur is highly toxic to honey bees. The LD50 for bees is greater than one ug/honey bee.||highly toxic|
|Acephate||Orthene||Organophosphate||3 days||Acephate is a broad-spectrum insecticide and is highly toxic to bees and other beneficial insects.||Moderately toxic|
|Azinphos-methyl||Guthion, Methyl-Guthion||Organophosphate||2.5 days||banned in the European Union since 2006.||highly toxic|
|Chlorpyrifos||Dursban, Lorsban||Organophosphate||banned in the US for home and garden use Should never be sprayed on flowering crops especially if bees are active and the crop requires pollination.||highly toxic|
|Coumaphos||Checkmite||Organophosphate||This is an insecticide that is used inside the beehive to combat varroa mites and small hive beetles, which are parasites of the honey bee. Overdoses can lead to bee poisoning.||Relatively nontoxic|
|Demeton||Systox||Organophosphate||<2 hours||highly toxic|
|Diazinon||Spectracide||Organophosphate||Sale of diazinon for residential use was discontinued in the U.S. in 2004. Should never be sprayed on flowering crops especially if bees are active and the crop requires pollination.||highly toxic|
|Dicrotophos||Bidrin||Organophosphate||Dicrotophos toxicity duration is about one week.||highly toxic|
|Dichlorvos||DDVP, Vapona||Organophosphate||highly toxic|
|Dimethoate||Cygon, De-Fend||Organophosphate||3 days||Should never be sprayed on flowering crops especially if bees are active and the crop requires pollination.||highly toxic|
|Fenthion||Entex, Baytex, Baycid, Dalf, DMPT, Mercaptophos, Prentox, Fenthion 4E, Queletox,Lebaycid||Organophosphate||Should never be sprayed on flowering crops especially if bees are active and the crop requires pollination.||highly toxic|
|Fonofos||Dyfonate EC||Organophosphate||3 hours||List of Schedule 2 substances (CWC)||highly toxic|
|Malathion||Malathion USB, ~ EC, Cythion, maldison, mercaptothion||Organophosphate||>8 fl oz/acre (58 L/km²) ⇒ 5.5 days||Malathion is highly toxic to bees and other beneficial insects, some fish, and other aquatic life. Malathion is moderately toxic to other fish and birds, and is considered low in toxicity to mammals.||highly toxic|
|Methamidophos||Monitor, Tameron||Organophosphate||highly toxic|
|Methyl parathion||Parathion, Penncap-M||Organophosphate||5–8 days||It is classified as a UNEP persistent organic pollutant and WHO Toxicity Class, "Ia, Extremely Hazardous".||highly toxic|
|Naled||Dibrom||Organophosphate||16 hours||highly toxic|
|Oxydemeton-methyl||Metasystox-R||Organophosphate||<2 hours||highly toxic|
|Phorate||Thimet EC||Organophosphate||5 hours||highly toxic|
|Phosmet||Imidan||Organophosphate||Phosmet is very toxic to honeybees.||highly toxic|
|Tetrachlorvinphos||Rabon, Stirofos, Gardona, Gardcide||Organophosphate||highly toxic|
|Trichlorfon, Metrifonate||Dylox, Dipterex||Organophosphate||3 – 6 hours||Relatively nontoxic|
|Permethrin||Ambush, Pounce||Synthetic pyrethroid||1 – 2 days||safened by repellency under arid conditions. Permethrin is also the active ingredient in insecticides used against the Small hive beetle, which is a parasite of the beehive in the temperate climate regions.||highly toxic|
|Cypermethrin||Ammo, Demon, Raid, Viper||Synthetic pyrethroid||Less than 2 hours||Cypermethrin is found in many household ant and cockroach killers, including Raid and ant chalk.||highly toxic|
|Fenvalerate||Asana, Pydrin||Synthetic pyrethroid||1 day||safened by repellency under arid conditions||highly toxic|
|Resmethrin||Black Flag Mosquito Fog Solution, Chrysron, Crossfire, Pynosect, Raid Flying Insect Killer, Scourge, Sun-Bugger #4, SPB-1382, Synthrin, Syntox, Vectrin, Whitmire PT-110||Synthetic pyrethroid||Resmethrin is highly toxic to bees, with an LD50 of 0.063 ug/bee.||highly toxic|
|Methoxychlor||DMDT, Marlate||Chlorinated cyclodiene||2 hours||available as a General Use Pesticide||highly toxic|
|Endosulfan||Thiodan||Chlorinated cyclodiene||8 hours||banned in European Union (2007?), New Zealand (2009)||moderately toxic|
|Clothianidin||Poncho||Neonicotinoid||Banned in Germany
In June 2008, the Federal Ministry of Food, Agriculture and Consumer Protection (Germany) suspended the registration of eight neonicotinoid pesticide seed treatment products used in oilseed rape and sweetcorn, a few weeks after honey bee keepers in the southern state of Baden Württemberg reported a wave of honey bee deaths linked to one of the pesticides, clothianidin.
|Thiamethoxam||Actara||Neonicotinoid||Clothianidin is a major metabolite of Thiamethoxam. A two-year study published in 2012 showed the presence of clothianidin and thiamethoxam in bees found dead in and around hives situated near agricultural fields. Other bees at the hives exhibited tremors and uncoordinated movement and convulsions, all signs of insecticide poisoning.||Highly Toxic|
|Imidacloprid||Confidor, Gaucho, Kohinor, Admire, Advantage, K9 Advantix, Merit, Confidor, Hachikusan, Amigo, SeedPlus (Chemtura Corp.), Monceren GT, Premise, Prothor, and Winner||Neonicotinoid||(see also Imidacloprid effects on bee population)Banned in France since 1999||highly toxic|
|Petroleum oils||Relatively nontoxic|
|2,4-D||Weed B Gon (also contains dicamba), ingredient in over 1,500 products||Synthetic auxin herbicide||Relatively nontoxic|
Highly toxic and banned in the US
- Aldrin banned by US EPA in 1974
- Dieldrin banned by US EPA in 1974
- Lindane, BHC (banned in California). Lindane was also denied re-registration for agricultural use in the US by the EPA in 2006
EPA Proposal to Protect Bees from Acutely Toxic Pesticides in the US
The EPA is proposing to prohibit the application of certain pesticides and herbicides known toxic to bees during pollination periods when crops are in bloom. Growers routinely contract with honeybee keepers to bring in bees to pollinate their crops that require insect pollination. Bees are typically present during the period the crops are in bloom. Application of pesticides during this period can significantly affect the health of bees. These restrictions are expected to reduce the likelihood of high levels of pesticide exposure and mortality for bees providing pollination services. Moreover, the EPA believes these additional measures to protect bees providing pollination services will protect other pollinators as well.
The proposed restrictions would apply to all products that have liquid or dust formulations as applied, foliar use (applying pesticides directly to crop leaves) directions for use on crops, and active ingredients that have been determined via testing to have high toxicity for bees (less than 11 micrograms per bee). These restrictions would not replace already existing more restrictive, chemical-specific, and bee-protective provisions. Additionally, the proposed label restrictions would not apply to applications made in support of a government-declared public health response, such as use for wide area mosquito control. There would be no other exceptions to these proposed restrictions.
General Measures to Prevent Pesticides Bee Kills
Application of Pesticides at evening or night
Avoiding pesticide application directly to blooming flowers as much as possible can help limit the exposure of honeybees to toxic materials as honeybees are attracted to all types of blooming flowers. If blooming flowers must be sprayed with pesticides for any reason, they should be sprayed in the evening or night hours as bees are not in the field at that time. Usual foraging hours of honeybees are when the temperature is above 55-60 °F during the daytime, and by the evening, the bees return to the hives.
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