Pesticide toxicity to bees

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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.[1]

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.[2]

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.[3]

Pesticides, especially neonicotinoids, have been investigated in relation to Colony Collapse Disorder. Potentially toxic effects studied in the laboratory have often been followed by field studies that fail to show effects on actual bee populations.[4] Despite gaps in the scientific evidence, regulators have restricted the use of neonicotinoids in Europe[5] and elsewhere[6] largely on the basis of concerns for bee health.


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[7][8]

  • 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.

Pesticide toxicity[edit]

Acute toxicity[edit]

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. 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.[citation needed] The acute toxicity, although more lethal, is less common than sub-lethal toxicity or cumulative effects.[9]

Sublethal and chronic effects[edit]

Field exposure to pesticides, especially with relation to neonicotinoids,[10] may lead to multiple physiological and/or behavioral sublethal effects in exposed bees.[11] Sublethal effects to honey bees can include behavioral disruptions such as disorientation,[12] thermoregulation,[13] reduced foraging,[14] decreased flight[15] and locomotion[16][17] abilities, impaired memory and learning, phototaxis (response to light),[16] and altered communication behaviors.[citation needed] Additional sub-lethal effects may include compromised immunity of bees and delayed development.[18]

Colony collapse disorder[edit]

Colony collapse disorder (CCD) 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 indicated in a 2010 report to Congress that a combination of factors could be causing colony collapse disorder, including pesticides, pathogens, and parasites. Although pesticides were suspected to be part of the problem, a survey of healthy and CCD-affected colonies revealed similar levels of pesticides in wax and pollen.[19]

Bee kill rate per hive[edit]

The kill rate of bees in a single bee hive can be classified as:[20]

< 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

Pesticide formulations[edit]

Pesticides come in different formulations:[2]

  • 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
Carbaryl[21] Sevin,

(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[22] 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)[22] Highly toxic
Methomyl[23] Lannate, Nudrin Carbamate 2 hours Should never be sprayed on flowering crops especially if bees are active and the crop requires pollination. Highly toxic
Methiocarb Mesurol Carbamate Highly toxic
Mexacarbate[24] Zectran Carbamate Highly toxic
Pirimicarb Pirimor, Aphox Carbamate Relatively nontoxic
Propoxur[25] Baygon Carbamate Propoxur is highly toxic to honey bees. The LD50 for bees is greater than one ug/honey bee.[citation needed] Highly toxic
Acephate[26] Orthene Organophosphate 3 days Acephate is a broad-spectrum insecticide and is highly toxic to bees and other beneficial insects.[27] Moderately toxic
Azinphos-methyl[28] Guthion, Methyl-Guthion Organophosphate 2.5 days Banned in EU since 2006.[29] Highly toxic
Chlorpyrifos[30] Dursban, Lorsban Organophosphate Banned in 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[31] 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
Demeton-S-methyl[32] Meta-systox Organophosphate Banned worldwide for toxicity to humans Moderately toxic
Diazinon[33] 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[34] Bidrin Organophosphate Dicrotophos toxicity duration is about one week.[35] highly toxic
Dichlorvos[36] DDVP, Vapona Organophosphate Highly toxic
Dimethoate[37] 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[38] 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
Fenitrothion[39] Sumithion Organophosphate Highly toxic
Fensulfothion Dasanit Organophosphate Highly toxic
Fonofos[40] 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.[41] Highly toxic
Methamidophos[42] Monitor, Tameron Organophosphate Should never be sprayed on flowering crops especially if bees are active and the crop requires pollination. Highly toxic
Methidathion[43] Supracide Organophosphate Should never be sprayed on flowering crops especially if bees are active and the crop requires pollination. Highly toxic
Methyl parathion Parathion,[44] Penncap-M Organophosphate 5–8 days It is classified as a UNEP persistent organic pollutant and WHO Toxicity Class, "Ia, Extremely Hazardous".[citation needed] Highly toxic
Mevinphos[45] Phosdrin Organophosphate highly toxic
Monocrotophos[46] Azodrin Organophosphate Should never be sprayed on flowering crops especially if bees are active and the crop requires pollination. Highly toxic
Naled[47] Dibrom Organophosphate 16 hours Highly toxic
Omethoate Organophosphate Should never be sprayed on flowering crops especially if bees are active and the crop requires pollination. Highly toxic
Oxydemeton-methyl[48] Metasystox-R Organophosphate <2 hours Highly toxic
Phorate[49] Thimet EC Organophosphate 5 hours Highly toxic
Phosmet[50] Imidan Organophosphate Phosmet is very toxic to honeybees.[51] Highly toxic
Phosphamidon Dimecron Organophosphate Highly toxic
Pyrazophos Afugan Organophosphate Fungicide Highly toxic
Tetrachlorvinphos Rabon, Stirofos, Gardona, Gardcide Organophosphate Highly toxic
Trichlorfon, Metrifonate Dylox, Dipterex Organophosphate 3 – 6 hours Relatively nontoxic
Bifenthrin[52][53] Agri-Medk, Abamectin, Talstar, Bifenthrine, Brigade, Capture, FMC 54800, OMS3024, Torant (with Clofentezine), and Zipak (with Amitraz)[54] Pyrethroid < 1 day RT

> 1 day ERT

Highly toxic
Permethrin[55] Ambush, Pounce 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[56] Ammo, Demon, Raid, Viper Pyrethroid Less than 2 hours Cypermethrin is found in many household ant and cockroach killers, including Raid and ant chalk. Highly toxic
Fenvalerate[57] Asana, Pydrin Pyrethroid 1 day Safened by repellency under arid conditions Highly toxic
Resmethrin[58][59][60] Black Flag Mosquito Fog Solution, Chrysron, Crossfire, Pynosect, Raid Flying Insect Killer, Scourge, Sun-Bugger #4, SPB-1382, Synthrin, Syntox, Vectrin, Whitmire PT-110 Pyrethroid Resmethrin is highly toxic to bees, with an LD50 of 0.063 ug/bee.[citation needed] Highly toxic
Methoxychlor[61] DMDT, Marlate Chlorinated cyclodiene 2 hours available as a General Use Pesticide Highly toxic
Endosulfan[62] Thiodan Chlorinated cyclodiene 8 hours Banned in EU (2007?), Banned in NZ (2009) Moderately toxic
Clothianidin Poncho Neonicotinoid Banned in EU for outdoor use since 2018. Highly Toxic[63]
Thiamethoxam Actara Neonicotinoid Banned in EU for outdoor use since 2018. Highly Toxic
Imidacloprid Confidor, Gaucho, Kohinor, Admire, Advantage, K9 Advantix, Merit, Confidor, Hachikusan, Amigo, SeedPlus (Chemtura Corp.), Monceren GT, Premise, Prothor, Winner Neonicotinoid Banned in France since 1999. Banned in EU for outdoor use since 2018. Highly toxic
Fipronil Regent, Goliath, Nexa, Adonis, Termidor, Ultrathor, Fipforce, Taurus, Combat Ant-Rid, Anthem, Clearout, Radiate Phenylpyrazole Banned in EU for use on maize and sunflowers since 2014. Highly toxic
Sulfoxaflor Sulfoximine [64][65]
Dicofol Acaricide Relatively nontoxic
Petroleum oils Relatively nontoxic
2,4-D[66] Weed B Gon (also contains dicamba), ingredient in over 1,500 products Synthetic auxin herbicide Relatively nontoxic

Highly toxic and banned in the US[edit]

Regulatory policy[edit]

Based on a risks to bee health as identified by the European Food Safety Authority (EFSA), in April 2013 the EU decided to restrict the use of the neonicotinoids thiamethoxam, clothianidin, and imidacloprid.[72] Fipronil was also banned for use on maize and sunflowers.[citation needed]

In 2015, the US Environmental Protection Agency (EPA) proposed to prohibit the application of certain pesticides and herbicides that are known to be toxic to bees during pollination periods when crops are in bloom. Seed treatments were not considered to present a risk to bee health. A modified form of these proposals was adopted as EPA policy in January 2017.[73]

In April 2018, member states of the European Union agreed upon a total ban on neonicotinoid insecticide use, except within closed greenhouses.[5] The vote on the proposed ban followed a February 2018 report from the EFSA which concluded that neonicotinoids posed a high risk to both domestic and wild bees.[74] The ban had strong public support, but faced criticism from the agrochemical industry, and from certain farmers' groups.[75]

In 2020, the EPA supplemented its policy with a proposal to restrict the use of neonicotinoids on residential lawns and turf, but otherwise confirmed that they would remain in use in the US.[76]

General measures to prevent pesticide bee kills[edit]

Application of pesticides at evening or night[edit]

Avoiding the application of pesticides directly to blooming flowers can help limit the exposure of honeybees to toxic materials. If blooming flowers must be sprayed with pesticides for any reason, they should be sprayed in the evening or night hours when bees are not in the field. The usual foraging hours of honeybees are during the daytime when the temperature is above 55–60 °F (13–16 °C).[2][53][77]

See also[edit]


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External links[edit]