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 media. 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]

Dust and wettable powder pesticides tend to be more hazardous to bees than solutions or emulsifiable concentrates for contact pesticides.

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.[2][3]


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[4][5]

  • 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.

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 CCD have been proposed, but no one primary cause has been found. The US Department of Agriculture (USDA) has indicated in a report to Congress that a combination of factors may be causing CCD, including pesticides, pathogens, and parasites, all of which have been found at high levels in affected bee hives.[6]

For the majority of pesticides that are registered in the United States, EPA only requires a short-term contact toxicity test on adult honeybees. In some cases, the agency also receives short-term oral toxicity tests, which are required in Europe. 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.[7]

A March 2012 study[8] 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.

April 2013 the EU decided to restrict thiamethoxam, clothianidin, and imidacloprid.[9]

Bee kill rate per hive[edit]

The kill rate of bees in a single bee hive can be classified as:[10]

< 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


Common name (ISO) Examples of Brand names Pesticide Class length of residual toxicity Comments Bee toxicity
Sulfoxaflor Sulfoximine [11][12]
Aldicarb Temik Carbamate apply 4 weeks before bloom Relatively nontoxic
Carbaryl[13][citation needed] 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. It allows them time to take contaminated nectar and pollen back to the colony. Some crops treated with Sevin under the wrong conditions (in bloom, using a dust formulation, with large numbers of bees in the field) have been responsible for disastrous kills. Sevin is one of the United States' most widely used insecticides for a wide variety of insect pests. It is also one of the most toxic to honey bees, in certain formulations. These should never be sprayed on flowering crops especially if bees are active and the crop requires pollination. There are formulations, however, which are determined to be less toxic (see tables). Usually, applicator-beekeeper communication can effectively be used to adequately protect bees from Sevin poisoning. highly toxic
Carbofuran[14] 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)[14] highly toxic
Methomyl[15] 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[16] Zectran Carbamate highly toxic
Pirimicarb Pirimor, Aphox Carbamate Relatively nontoxic
Propoxur[17] Baygon Carbamate highly toxic
Acephate[18] Orthene Organophosphate 3 days Moderately toxic
Azinphos-methyl[19] Guthion, Methyl-Guthion Organophosphate 2.5 days banned in the European Union since 2006.[20] highly toxic
Chlorpyrifos[21] 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[22] 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[23] Systox Organophosphate <2 hours highly toxic
Demeton-S-methyl Meta-systox Organophosphate Moderately toxic
Diazinon[24] 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[25] Bidrin Organophosphate highly toxic
Dichlorvos[26] DDVP, Vapona Organophosphate highly toxic
Dimethoate[27] 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[28] 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[29] Sumithion Organophosphate highly toxic
Fensulfothion Dasanit Organophosphate highly toxic
Fonofos[30] 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 highly toxic
Methamidophos[31] Monitor, Tameron Organophosphate Should never be sprayed on flowering crops especially if bees are active and the crop requires pollination. highly toxic
Methidathion[32] Supracide Organophosphate Should never be sprayed on flowering crops especially if bees are active and the crop requires pollination. highly toxic
Methyl parathion Parathion,[33] Penncap-M Organophosphate 5–8 days By far the most potentially damaging pesticides for honey bees are those packaged in tiny capsules (microencapsulated). Microencapsulated methyl parathion (PennCap M), for example, is a liquid formulation containing capsules approximately the size of pollen grains, which contain the active ingredient. When bees are out in the field, these capsules can become attached electrostatically to the pollen-collecting hairs of the insects, and at times are collected by design. When stored in pollen, the slow-release feature of the capsules allows the methyl parathion to be a potential killer for several months. At the present time, there is no way to detect whether bees are indeed poisoned by micro-encapsulated methyl parathion, so a beekeeper potentially could lose replacement bees for those already poisoned by the pesticide. It is, therefore, strongly recommended by experts that this formulation be used only when honey bee exposure is not a possibility.

It is classified as a UNEP Persistent Organic Pollutant and WHO Toxicity Class, "Ia, Extremely Hazardous".

highly toxic
Mevinphos[34] Phosdrin Organophosphate highly toxic
Monocrotophos[35] Azodrin Organophosphate Should never be sprayed on flowering crops especially if bees are active and the crop requires pollination. highly toxic
Naled[36] 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[37] Metasystox-R Organophosphate <2 hours highly toxic
Phorate[38] Thimet EC Organophosphate 5 hours highly toxic
Phosmet[39] Imidan Organophosphate 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
Permethrin[40] 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[41] Ammo, Raid Synthetic pyrethroid Less than 2 hours Cypermethrin is found in many household ant and cockroach killers, including Raid and ant chalk. highly toxic
Fenvalerate[42] Asana, Pydrin Synthetic pyrethroid 1 day safened by repellency under arid conditions highly toxic
Resmethrin[43][44][45][46][47] Chrysron, Crossfire, Pynosect, Raid Flying Insect Killer, Scourge, Sun-Bugger #4, SPB-1382, Synthrin, Syntox, Vectrin, Whitmire PT-110 Synthetic pyrethroid highly toxic
Methoxychlor[48] DMDT, Marlate Chlorinated cyclodiene 2 hours available as a General Use Pesticide highly toxic
Endosulfan[49] Thiodan Chlorinated cyclodiene 8 hours banned in European Union (2007?), New Zealand (2009) moderately toxic
Clothianidin[50] 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.[51]

Highly Toxic[52]
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.[53] Highly Toxic
Imidacloprid Confidor, Gaucho, Kohinor, Admire, Advantage, 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
Dicofol Acaricide Relatively nontoxic
Petroleum oils Relatively nontoxic
2,4-D[54] ingredient in over 1,500 products Synthetic auxin herbicide Relatively nontoxic


Common insecticides toxic to bees and used on soybeans[edit]

Many insecticides used against soybean aphids are highly toxic to bees.[56]

  • Orthene 75S (acephate)
  • Address 75 WSP (acephate)
  • Sevin (Carbaryl)
  • Lorsban 4E (Chlorpyrifos)
  • Dimate (Dimethoate)
  • Steward 1.25 SC (Indoxacarb)
  • Lannate (Methomyl)
  • Cheminova Methyl 4EC (Methyl Parathion)
  • Penncap M (microencapsulated Methyl Parathion)
  • Tracer (Spinosad)

Highly toxic and banned in the US[edit]

See also[edit]


  1. ^ Ministry of Agriculture
  2. ^ Ecological Risk Assessment
  3. ^ University of Georgia Cooperative Extension
  4. ^ [1] Pollinator protection requirements for Section 18 Emergency Exemptions and Section 24(c) special local need registration in Washington State; Registration Services Program Pesticide Management Division Washington State Dept of Agriculture, Dec 2006
  5. ^ Hunt, G.J.; Using honey bees in pollination Purdue University, May 2000
  6. ^ USDA CCD Report
  7. ^ Non-target insect testing
  8. ^ Henry, M.; Beguin, M.; Requier, F.; Rollin, O.; Odoux, J. -F.; Aupinel, P.; Aptel, J.; Tchamitchian, S.; Decourtye, A. (2012). "A Common Pesticide Decreases Foraging Success and Survival in Honey Bees". Science 336 (6079): 348–350. doi:10.1126/science.1215039. PMID 22461498. 
  9. ^ EU to Restrict 'Bee-Harming' Pesticides April 29, 2013 Wall Street Journal
  10. ^ Radunz, L. and Smith, E. S. C. Pesticides Hazard to Honey Bees Entomology, Darwin, Australia
  11. ^ The National Beekeepers’ Association of New Zealand - Submission on Application ERMA200886
  12. ^ Effects of mutations in Drosophila nicotinic acetylcholine receptor subunits on sensitivity to insecticides targeting nicotinic acetylcholine receptors
  13. ^ carbaryl
  14. ^ a b carbofuran
  15. ^ methomyl
  16. ^ [2]
  17. ^ propoxur
  18. ^ acephate
  19. ^ azinphos-methyl
  20. ^ Scott, Alex (August 4, 2008). "Europe Rejects Appeal for Use of Azinphos-methyl Pesticide". Chemical Week. Retrieved 2008-08-11. 
  21. ^ chlorpyrifos
  22. ^ coumaphos
  23. ^ demeton
  24. ^ diazinon
  25. ^ dicrotophos
  26. ^ dichlorvos
  27. ^ dimethoate
  28. ^ fenthion
  29. ^ fenitrothion
  30. ^ fonofos
  31. ^ methamidophos
  32. ^ methidathion
  33. ^ parathion
  34. ^ mevinphos
  35. ^ monocrotophos
  36. ^ naled
  37. ^ oxydemeton-methyl
  38. ^ phorate
  39. ^ phosmet
  40. ^ permethrin
  41. ^ cypermethrin
  42. ^ esfenvalerate
  43. ^ resmethrin
  44. ^ Resmethrin Technical Fact Sheet - National Pesticide Information Center
  45. ^ Pyrethrins and Pyrethroids Fact Sheet - National Pesticide Information Center
  46. ^ Resmethrin Pesticide Information Profile - Extension Toxicology Network
  47. ^ MSDS for Scourge' Formula II
  48. ^ methoxychlor
  49. ^ endosulfan
  50. ^ EFSA report of 16 january 2013 labelling clothianidin, imidacloprid and thiamethoxam asdetrimental to bees
  51. ^ "Emergency Pesticide Ban for Saving the Honeybee"
  52. ^ EPA Clothianidin Reviews
  53. ^
  54. ^ [3]
  55. ^ Protecting Bees When Using Insecticides University of Nebraska Lincoln, Extension, May 1998
  56. ^ Commonly Used Insecticides for Soybeans Kansas State University Extension, Aug 2004
  57. ^ Aldrin
  58. ^ dieldrin
  59. ^ heptachlor

External links[edit]