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, especially neonicotinoids, have been investigated in relation to risks for bees such as Colony Collapse Disorder. A 2018 review by the European Food Safety Authority (EFSA) concluded that most uses of neonicotinoid pesticides such as clothianidin represent a risk to wild bees and honeybees. Neonicotinoids have been banned for all outdoor use in the entire European Union since 2018, but has a conditional approval in the U.S. and other parts of the world, where it is widely used.
Classification Insecticide toxicity is generally measured using acute contact toxicity values – the exposure level that causes 50% of the population exposed to die. Toxicity thresholds are generally set athttp://www.agr.wa.gov/pestfert/Pesticides/docs/PollinatorSLNSect18.pdf 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 highly toxic (acute LD50 < 2μg/bee) moderately toxic (acute LD50 2 – 10.99 μg/bee) slightly toxic (acute LD50 11 – 100 μg/bee) nontoxic (acute LD50 > 100 μg/bee) to adult bees.
Pesticide toxicity Acute toxicity The acute toxicity of pesticides on bees, which could be by contact or ingestion, is usually quantified by . 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. 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 can include disruptions to behavioral and motor functions, compromised immunity, and delayed development.
Colony collapse disorder
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.
Bee kill rate per hive The kill rate of bees in a single bee hive can be classified as:Radunz, L. and Smith, E. S. C. Pesticides Hazard to Honey Bees Entomology, Darwin, Australia < 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 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 namesPesticide Classlength of residual toxicityCommentsBee toxicityAldicarbTemik Carbamateapply 4 weeks before bloomRelatively nontoxicCarbarylSevin, (b) Sevin XLRCarbamateHigh 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 toxicCarbofuranFuradanCarbamate7 – 14 daysU.S. Environmental Protection Agency ban on use on crops grown for human consumption (2009) carbofuran (banned in granular form)Highly toxicMethomylLannate, NudrinCarbamate2 hoursShould never be sprayed on flowering crops especially if bees are active and the crop requires pollination.Highly toxicMethiocarbMesurolCarbamateHighly toxicMexacarbateZectranCarbamateHighly toxicPirimicarbPirimor, AphoxCarbamateRelatively nontoxicPropoxurBaygon CarbamatePropoxur is highly toxic to honey bees. The LD50 for bees is greater than one ug/honey bee.Highly toxicAcephateOrtheneOrganophosphate3 daysAcephate is a broad-spectrum insecticide and is highly toxic to bees and other beneficial insects.Moderately toxicAzinphos-methylGuthion, Methyl-Guthion Organophosphate2.5 daysBanned in EU since 2006.Highly toxicChlorpyrifosDursban, LorsbanOrganophosphateBanned 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 toxicCoumaphoscoumaphos Checkmite OrganophosphateThis 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 nontoxicDemetonSystoxOrganophosphate<2 hoursHighly toxicDemeton-S-methylMeta-systoxOrganophosphateBanned worldwide for toxicity to humansModerately toxicDiazinonSpectracideOrganophosphateSale 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 toxicDicrotophosBidrinOrganophosphateDicrotophos toxicity duration is about one week.highly toxicDichlorvosDDVP, VaponaOrganophosphateHighly toxicDimethoateCygon, De-FendOrganophosphate3 daysShould never be sprayed on flowering crops especially if bees are active and the crop requires pollination.Highly toxicFenthionEntex, Baytex, Baycid, Dalf, DMPT, Mercaptophos, Prentox, Fenthion 4E, Queletox, LebaycidOrganophosphateShould never be sprayed on flowering crops especially if bees are active and the crop requires pollination.Highly toxicFenitrothionSumithionOrganophosphateHighly toxicFensulfothionDasanitOrganophosphateHighly toxicFonofosDyfonate EC Organophosphate3 hoursList of Schedule 2 substances (CWC)Highly toxicMalathion Malathion USB, ~ EC, Cythion, maldison, mercaptothionOrganophosphate>8 fl oz/acre (58 L/km2) ⇒ 5.5 daysMalathion 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 toxicMethamidophosMonitor, TameronOrganophosphateShould never be sprayed on flowering crops especially if bees are active and the crop requires pollination.Highly toxicMethidathionSupracideOrganophosphateShould never be sprayed on flowering crops especially if bees are active and the crop requires pollination.Highly toxicMethyl parathionParathion, Penncap-MOrganophosphate5–8 daysIt is classified as a UNEP persistent organic pollutant and WHO Toxicity Class, "Ia, Extremely Hazardous".Highly toxicMevinphosPhosdrinOrganophosphatehighly toxicMonocrotophosAzodrin OrganophosphateShould never be sprayed on flowering crops especially if bees are active and the crop requires pollination.Highly toxicNaledDibromOrganophosphate16 hoursHighly toxicOmethoateOrganophosphateShould never be sprayed on flowering crops especially if bees are active and the crop requires pollination.Highly toxicOxydemeton-methylMetasystox-ROrganophosphate<2 hoursHighly toxicPhorateThimet ECOrganophosphate5 hoursHighly toxicPhosmetImidan OrganophosphatePhosmet is very toxic to honeybees.Highly toxicPhosphamidon DimecronOrganophosphateHighly toxicPyrazophosAfuganOrganophosphateFungicideHighly toxicTetrachlorvinphosRabon, Stirofos, Gardona, GardcideOrganophosphateHighly toxicTrichlorfon, MetrifonateDylox, DipterexOrganophosphate3 – 6 hoursRelatively nontoxicBifenthrinAgri-Medk, Abamectin, Talstar, Bifenthrine, Brigade, Capture, FMC 54800, OMS3024, Torant (with Clofentezine), and Zipak (with Amitraz)Pyrethroid< 1 day RT > 1 day ERTHighly toxicPermethrinAmbush, PouncePyrethroid1 – 2 daysSafened 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 toxicCypermethrinAmmo, Demon, Raid, ViperPyrethroidLess than 2 hoursCypermethrin is found in many household ant and cockroach killers, including Raid and ant chalk.Highly toxicFenvalerateAsana, PydrinPyrethroid1 daySafened by repellency under arid conditionsHighly toxicResmethrinMSDS for Scourge Formula IIBlack Flag Mosquito Fog Solution, Chrysron, Crossfire, Pynosect, Raid Flying Insect Killer, Scourge, Sun-Bugger #4, SPB-1382, Synthrin, Syntox, Vectrin, Whitmire PT-110PyrethroidResmethrin is highly toxic to bees, with an LD50 of 0.063 ug/bee.Highly toxicMethoxychlorDMDT, Marlate Chlorinated cyclodiene2 hoursavailable as a General Use Pesticide Highly toxicEndosulfanThiodanChlorinated cyclodiene8 hoursBanned in EU (2007?), Banned in NZ (2009)Moderately toxicClothianidinPonchoNeonicotinoidBanned in EU for outdoor use since 2018.Highly ToxicThiamethoxamActaraNeonicotinoidBanned in EU for outdoor use since 2018.Highly ToxicImidacloprid Confidor, Gaucho, Kohinor, Admire, Advantage, K9 Advantix, Merit, Confidor, Hachikusan, Amigo, SeedPlus (Chemtura Corp.), Monceren GT, Premise, Prothor, WinnerNeonicotinoidBanned in France since 1999. Banned in EU for outdoor use since 2018.Highly toxicFipronil Regent, Goliath, Nexa, Adonis, Termidor, Ultrathor, Fipforce, Taurus, Combat Ant-Rid, Anthem, Clearout, RadiatePhenylpyrazoleBanned in EU for use on maize and sunflowers since 2014.Highly toxicSulfoxaflorSulfoximineDicofolAcaricideRelatively nontoxicPetroleum oilsRelatively nontoxic2,4-DWeed B Gon (also contains dicamba), ingredient in over 1,500 productsSynthetic auxin herbicideRelatively nontoxic
Highly toxic and banned in the US Aldrin Banned by US EPA in 1974. Dieldrin Banned by US EPA in 1974. Heptachlor Lindane, BHC Banned in California. Banned for agricultural use in the US by the EPA in 2006.
Regulatory policy
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. Fipronil was also banned for use on maize and sunflowers.
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.