Pesticide toxicity to bees

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

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.

Banned in France

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