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Pesticide toxicity to bees

Pesticides vary in their effect on bees. Contact insecticides, those which kill by touching the organism, affect the worker bee that is directly sprayed. Systemic insecticides, those that are incorporated by treated plants, can contaminate nectar or pollen, and kill bees in the hive.

Dusts and wettable powders tend to be more hazardous to bees than solutions or emulsifiable concentrates.

Actual damage to bee populations is a function of the degree of toxicity of the compound, in combination with the mode of application; a highly potent insecticide applied only to the soil, for instance, would be expected to kill mainly soil-dwelling insects, such as grubs or mole crickets, and not bees.

Classification of pesticide toxicity

Insecticide toxicity is generally measured using LD50 - the exposure level that causes 50% of the population exposed to die. Toxicity thresholds are generally set at

highly toxic (acute LD50 less than 2μg/bee)
moderately toxic (acute LD50 2ug/bee to 10.99μg/bee)
slightly toxic (acute LD50 11ug/bee to 100μg/bee)
practically non-toxic (acute LD50 more than 100μg/bee) to adult bees.

LD50 is an incomplete measure of toxicity to honeybees (Apis mellifera) and other social insects because it is a measure of individual toxicity, not colony toxicity. It does not account for the ways in which bee behavior can mitigate or exacerbate the effects of the pesticide on the colony. For example, a moderate to low toxicity pesticide (by LD50 measurement) which is used in granular form and is collected and concentrated along with pollen can be highly lethal to the colony. On the other hand, a pesticide which is so toxic that the exposed bees die in the field can be less dangerous to the colony than a less toxic pesticide which allows the exposed bees to return to the hive and contaminate their fellows. Likewise, a highly toxic pesticide (according to LD50 measures) is "safe" for bees if it is applied on a grass lawn or other location without blooming flowers which would attract the bees. Furthermore, LD50 studies are conducted against adult bees and do not measure the effects on larvae, etc.

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

Toxicity of Pesticides to Bees

Common name (ISO)	Examples of Brand names	Pesticide Class	length of residual toxicity	Comments	Bee toxicity
propoxur	Baygon	Carbamate			highly toxic
carbofuran	Furadan	Carbamate	7 - 14 days		highly toxic
methomyl	Lannate, Nudrin	Carbamate	2 hours +		highly toxic
pirimicarb	Pirimor, Aphox	Carbamate			Relatively non-toxic
aldicarb	Temik	Carbamate		apply 4 weeks before bloom	Relatively non-toxic
methiocarb	Mesurol	Carbamate			highly toxic
carbaryl	Sevin, (b) Sevin XLR	Carbamate	3 - 7 days (b) 8 hours @ 1.5 lb/acre (168 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. 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
acephate	Orthene	Organophosphate	3 days		Moderately toxic
demeton-s-methyl	Meta-systox	Organophosphate			Moderately 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 non-toxic
trichlorfon	Dylox, Dipterex	Organophosphate		3 - 6 hours	Relatively non-toxic
pyrazophos	Afugan	Organophosphate			highly toxic
monocrotophos	Azodrin	Organophosphate			highly toxic
fenthion	Baytex	Organophosphate			highly toxic
dicrotophos	Bidrin	Organophosphate			highly toxic
dimethoate	Cygon, De-Fend	Organophosphate	3 days	banned in the US	highly toxic
fensulfothion	Dasanit	Organophosphate			highly toxic
dichlorvos	DDVP, Vapona	Organophosphate			highly toxic
naled	Dibrom	Organophosphate	16 hours		highly toxic
chlorpyrifos	Dursban, Lorsban	Organophosphate		banned in the US for home and garden use	highly toxic
fonofos	Dyfonate EC	Organophosphate	3 hours		highly toxic
tetrachlorvinphos	Gardona	Organophosphate			highly toxic
azinphos-methyl	Guthion, Methyl-Guthion	Organophosphate	2.5 days		highly toxic
phosmet	Imidan	Organophosphate			highly toxic
malathion	Malathion USB, ~ EC, Cythion	Organophosphate	>8 fl oz/acre (58 L/km²) ⇒ 5.5 days		highly toxic
oxydemetonmethyl	Metasystox-R	Organophosphate	<2 hours		highly toxic
methamidophos	Monitor, Tameron	Organophosphate			highly toxic
methyl parathion	parathion 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.	highly toxic
diazinon	Spectracide	Organophosphate			highly toxic
fenitrothion	Sumithion	Organophosphate			highly toxic
methidathion	Supracide	Organophosphate			highly toxic
phorate	Thimet EC	Organophosphate	5 hours		highly toxic
mevinphos	Phosdrin	Organophosphate			highly toxic
phosphamidon	Dimecron	Organophosphate			highly toxic
demeton	Systox	Organophosphate	<2 hours		highly toxic
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	Synthetic pyrethroid	Less than 2 hours		highly toxic
esfenvalerate	Asana, Pydrin	Synthetic pyrethroid	1 day	safened by repellency under arid conditions	highly toxic
resmethrin		Synthetic pyrethroid			highly toxic
methoxychlor	DMDT, Marlate	Chlorinated cyclodiene	2 hours		highly toxic
endosulfan	Thiodan	Chlorinated cyclodiene	8 hours		moderately toxic
imidacloprid	Confidor, Gaucho, acetamiprid, clothianidin, nitenpyram, thiacloprid, thiamethoxam, Kohinor, Admire, Advantage, Merit, Confidor, Hachikusan, Premise, Prothor, and Winner	Neonicotinoid		(see also Imidacloprid effects on bee population)	highly toxic
mexacarbate	Zectran			highly toxic
dicofol		Acaricide			Relatively non-toxic
petroleum oils					Relatively non-toxic
2,4-D		Synthetic auxin herbicide			Relatively non-toxic

Source: Protecting Bees When Using Insecticides University of Nebraska Lincoln, Extension, May 1998

Common insecticides toxic to bees and used on soybeans

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

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

Aldrin banned by US EPA in 1974
carbofuran (banned in granular form)
dieldrin banned by US EPA in 1974
heptachlor
lindane, BHC (banned in California)

Lawsuit against the EPA in the United States

In August 2008, the National Resources Defense Council, a New York environmental advocacy group, filed a lawsuit against the federal Environmental Protection Agency accusing the agency of withholding information about the risks pesticides pose to honeybees.

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.