Pesticide toxicity to bees

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. When the bee comes in contact with pesticides while foraging, the bee immediately dies and does not return to the hive. In this case, the queen bee, brood, and nurse bees are not contaminated and the colony survives. The more deadly way is when the bee comes in contact with an insecticide and transports it back to the colony, either as contaminated pollen or nectar or on its body.[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][4]

Pesticides are linked to Colony Collapse Disorder and considered a now a main cause, and the toxic effects of Neonicotinoids on bees are confirmed.[5] Currently, many researches are being conducted to further understand pesticides toxic effects on bees and many agencies like the EPA[6] and EFSA[7] are making action plans to protect bees health in response to calls from scientists and the public to ban or limit the use of the pesticides with confirmed toxicity.

Classification

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[8][9]

Pesticide Toxicity

Acute toxicity

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, like agitation, vomiting, wing paralysis, arching of the abdomen similar to sting reflex, and uncoordinated movement. Some pesticides like Neonicotinoids are more toxic to bees and cause acute symptoms with lower doses compared to older classes of insecticides. 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, though more lethal, is less common than the other two types.[10][11]

Sub-lethal toxicity

Most commonly field exposure of bees to pesticides is sub-lethal and especially to Neonicotinoids, that is why it is a major concern. Some of the sub-lethal effects of pesticides on honey bees include behavioral disruptions to honey bees such as disorientation, reduced foraging, impaired memory and learning, and a shift in the communication behaviors. There are other important sub-lethal effects including compromised immunity of the bees and delayed development.[10]

Cumulative and Chronic effects

Neonicotinoids especially can cause cumulative effects on bees, as this pesticide group function by binding to nicotinic acetylcholine receptors in the brains of the insects, and such receptors are particularly abundant in bees. Over-accumulation of acetylcholine results in paralysis and death.[10]

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 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.[12]

Colony Collapse Disorder has more implication than the extinction of some bee species; disappearing of honeybees can cause catastrophic health and financial impacts. One mouthful in three of the food we eat may depend directly or indirectly on pollination by honeybee. Honeybee pollination has an estimated value of more than $14 billion annually to the United States agriculture. Honeybees are required for pollinating many crops which range nuts to vegetables and fruits, that are necessary for human and animal diet.[13]

The EPA updated their guidance for assessing pesticide risks to honeybees in 2014. For the EPA, when certain pesticide use patterns or triggers are met, current test requirements include the honey bee acute contact toxicity test, the honey bee toxicity of residues on foliage test, and field testing for pollinators. EPA guidelines have not been developed for chronic or acute oral toxicity to adult or larval honey bees. On the other hand, the PMRA (Pest Management Regulatory Agency) requires both acute oral and contact honey bee adult toxicity studies when there is potential for exposure for insect pollinators. Primary measurement endpoint derived from the acute oral and acute contact toxicity studies is the median lethal dose for 50% of the organisms tested (i.e., LD50), and if any biological effects and abnormal responses appear, including sub-lethal effects, other than the mortality, it should be reported.

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 because the interpretation of such whole-colony effects studies is very complex and relies on comprehensive considerations of whether adverse effects are likely to occur at the colony level.[14]

A March 2012 study[15] 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.[16]

Bee kill rate per hive

The kill rate of bees in a single bee hive can be classified as:[17]

< 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 Formulations

Pesticides come in different formulations:[18]

Pesticides

Common name (ISO) Examples of Brand names Pesticide Class length of residual toxicity Comments Bee toxicity
Sulfoxaflor Sulfoximine [19][20]
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. 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[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. Severe bee losses may be expected if propoxur is used when bees are present either at treatment time or within a day after treatment.[26] highly toxic
Acephate[27] Orthene Organophosphate 3 days Acephate is a broad-spectrum insecticide and is highly toxic to bees and other beneficial insects.[28] Moderately toxic
Azinphos-methyl[29] Guthion, Methyl-Guthion Organophosphate 2.5 days banned in the European Union since 2006.[30] highly toxic
Chlorpyrifos[31] 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[32] 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[33] Systox Organophosphate <2 hours highly toxic
Demeton-S-methyl Meta-systox Organophosphate Moderately toxic
Diazinon[34] 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[35] Bidrin Organophosphate Dicrotophos toxicity duration is about one week.[36] highly toxic
Dichlorvos[37] DDVP, Vapona Organophosphate highly toxic
Dimethoate[38] 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[39] 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[40] Sumithion Organophosphate highly toxic
Fensulfothion Dasanit Organophosphate highly toxic
Fonofos[41] 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.[42] highly toxic
Methamidophos[43] Monitor, Tameron Organophosphate Should never be sprayed on flowering crops especially if bees are active and the crop requires pollination. highly toxic
Methidathion[44] Supracide Organophosphate Should never be sprayed on flowering crops especially if bees are active and the crop requires pollination. highly toxic
Methyl parathion Parathion,[45] 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[46] Phosdrin Organophosphate highly toxic
Monocrotophos[47] Azodrin Organophosphate Should never be sprayed on flowering crops especially if bees are active and the crop requires pollination. highly toxic
Naled[48] 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[49] Metasystox-R Organophosphate <2 hours highly toxic
Phorate[50] Thimet EC Organophosphate 5 hours highly toxic
Phosmet[51] Imidan Organophosphate Phosmet is very toxic to honeybees.[52] 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[53] 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[54] 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[55] Asana, Pydrin Synthetic pyrethroid 1 day safened by repellency under arid conditions highly toxic
Resmethrin[56][57][58][59][60] Chrysron, Crossfire, Pynosect, Raid Flying Insect Killer, Scourge, Sun-Bugger #4, SPB-1382, Synthrin, Syntox, Vectrin, Whitmire PT-110 Synthetic pyrethroid Resmethrin is highly toxic to bees, with an LD50 of 0.063 ug/bee.[61] highly toxic
Methoxychlor[62] DMDT, Marlate Chlorinated cyclodiene 2 hours available as a General Use Pesticide highly toxic
Endosulfan[63] Thiodan Chlorinated cyclodiene 8 hours banned in European Union (2007?), New Zealand (2009) moderately toxic
Clothianidin[64] 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.[65]

 Highly Toxic[66]
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.[67] 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[68] ingredient in over 1,500 products Synthetic auxin herbicide Relatively nontoxic

[69]

Neonicotinoids

Neonicotinoids are one of the leading suspected causes of colony collapse disorder in honey bees. Ubiquitously used for management of harmful insects in the last decade, these systemic chemicals persist in the environment, thereby promoting their contact with non-target organisms such as pollinating bees. The specific causes are unclear, however, there has been some research to show that neonicotinoids have deleterious health effects on colony queens. Queen health is crucial to colony survival of social bees. Recently, queen failure has been proposed to be a major driver of managed honey bee colony losses. Managed honeybee colonies are colonies that are “man-made.” That is, they are not naturally occurring. Rather they are raised and rented out to farmers.

Exposure to field-realistic concentrations of neonicotinoid pesticides during development can severely affect queens of western honeybees (Apis mellifera). In neonicotinoid-exposed queens, reproductive anatomy (ovaries) and physiology (spermathecal-stored sperm quality and quantity), rather than flight behavior, were compromised and likely corresponded to reduced queen success (alive and producing worker offspring).[70]

Interestingly, there is some controversy surrounding the specific issue of whether or not neonicotinoids actually do negatively affect managed honeybee colonies. Perhaps one of the most popular studies showing a significant association between colony collapse disorder and neonicotinoids is Sub-lethal exposure to neonicotinoids impaired honeybees Winterization before proceeding to colony collapse disorder by Chensheng Lu.[71] Chengsheng became somewhat of a folk hero among environmental activists after his Harvard study was published, however, there has been some dissent from bee researchers in Australia,[72] Canada,[73] and even the USDA.[74] That is not to say that Mr. Lu’s findings are not accurate. The problem is that there simply is not a consensus yet on the real association between neonicotinoids and colony collapse disorder.

Common insecticides toxic to bees and used on soybeans

Many insecticides used against soybean aphids are highly toxic to bees.[75][76]

Highly toxic and banned in the US

EPA Proposal to Protect Bees from Acutely Toxic Pesticides in the US

EPA is proposing to prohibit the applications of certain pesticides when crops are in bloom and in pollination periods. These restrictions would prohibit application of most insecticides and some herbicides that are toxic to bees during bloom. Growers routinely contract with honeybee keepers to bring in bees to pollinate their crops that require insect pollination. Bees are typically present during the period the crops are in bloom. Application of pesticides during this period can significantly affect the health of bees. These restrictions are expected to reduce the likelihood of high levels of pesticide exposure and mortality for bees providing pollination services. Moreover, EPA believes these additional measures to protect bees providing pollination services will protect other pollinators as well.

The proposed restrictions would apply to all products that have liquid or dust formulations as applied, foliar use (applying pesticides directly to crop leaves) directions for use on crops, and active ingredients that have been determined via testing to have high toxicity for bees (less than 11 micrograms per bee). These restrictions would not replace already existing more restrictive, chemical-specific, and bee-protective provisions. Additionally, the proposed label restrictions would not apply to applications made in support of a government-declared public health response, such as use for wide area mosquito control. There would be no other exceptions to these proposed restrictions.[82]

Prevention of Pesticide Kills

[83][84]

Application of Pesticides at evening or night

Avoiding spraying the blooming flower directly with pesticides as much as possible can help limit the exposure of to the toxic materials, as honeybees are attracted to all types of blooming flowers. In case it is needed to spray the blooms for any reason, they can be sprayed in the evening or night hours as bees are not in the field at that time. Usual foraging hours of honeybees are when the temperature is above 55-60 °F during the daytime, and by the evening, the bees return to the hives. Spraying pesticides in the evening can greatly reduce honey bee mortality.

Choosing the appropriate pesticide formulation

The appropriate choice of pesticide formulation is another way to avoid honey bee pesticide kills. Solutions, emulsifiable concentrates, and granular forms are the best to use. Solutions and emulsifiable concentrates dry quickly and do not leave a powdery residue unlike the dust form and wettable powders. Although the granular form pesticide is similar to dusts, they are larger in particle size and they are applied to the soil or broadcast on the surface of the ground and they are seldom used on blooming plants and are essentially non-hazardous to bees. On the other hand, dusts and wettable powders are more hazardous as they adhere to the thousands of tiny hairs found on the body surface of the honey bee. These dust particles are then transferred back to the hive and stored along with the pollen. This can cause an entire colony to collapse if the pollen is fed to the queen or the brood.

Using less toxic and degradable pesticides

Using less toxic pesticides that degrade rapidly is also very important in reducing honey bee mortality. Newer pesticides have faster residual time which is the time required to reduce the activity of the chemical to safer levels for bee activity. When these pesticides are sprayed in the fields, it takes only a few hours for them to degrade as opposed to a few days or weeks.

Alteration of the application method

The method of application can also affect the risk of pesticide poisoning. Aerial applications have the highest potential risk for causing bee death. Most bee kills occur when the pesticide drifts or moves from the target area into the apiary or onto crops attractive to the bees. The outcome of drift can be catastrophic. Spraying during windy days greatly increases the risk of drift. Using granular formulations, soil treatments or equipment that confines the spray to the intended target can help reduce the risk of drift from pesticides.

Placement of apiaries in safe locations

The location of the apiary is one of the most important factors in eliminating the risk of pesticide poisoning. The farther colonies are away from fields or orchards that are treated with pesticides, the better chance the bees have against pesticide poisoning. Apiaries should be placed at least 4 miles from crops being treated with toxic materials and subjected to drift. If the apiaries are already located in an area where pesticide use is high, moving them may be the best insurance against future pesticide kills since preventing honey bees from foraging on pesticide-contaminated flowers is not applicable. If moving is impossible, covering colonies with a well-ventilated screen to restrict honeybee flight during peak foraging hours may be the only course of action. However, this method has dangerous side effects and could lead to higher mortality than would have occurred from pesticide exposure. Colonies may have difficulty controlling their hive temperature when confined and can easily overheat, so care must be taken. Providing water inside the screen will allow the bees to reduce temperatures. The colonies should not be kept covered for more than two days. Covering the colonies with large wet burlap sacks and providing them with shade is another method for preventing overheating.

Recovery from Pesticide Exposure

Recovery from pesticide is possible for the colonies that have been exposed if proper steps are taken. Even if a colony has lost a majority of its field force but has plenty of honey and pollen, it can usually recover even without any help from the beekeepers. If the pesticide is still present in the hive, which is probably in the pollen supplies, the colony may continue to die as long as the poison remains in the hive. In these cases, the combs must be cleaned or removed, the wax comb can be replaced with new foundation.

Some measures are to be taken to help bee colonies recover from bee poisoning, these colonies can be fed sugar syrup, pollen, and water, another package of bees can be added and weak colonies can be combined, bees should be protected from heat or cold. Another important method is to move the recovering and weak colonies to a pesticide-free area with natural nectar and pollen sources.[85]

See also

References

  1. ↑ Ministry of Agriculture
  2. ↑
  3. ↑
  4. ↑
  5. ↑
  6. ↑
  7. ↑
  8. ↑ 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
  9. ↑
  10. 1 2 3
  11. ↑
  12. ↑ USDA CCD Report
  13. ↑
  14. ↑
  15. ↑ 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.
  16. ↑ EU to Restrict 'Bee-Harming' Pesticides April 29, 2013 Wall Street Journal
  17. ↑ Radunz, L. and Smith, E. S. C. Pesticides Hazard to Honey Bees Entomology, Darwin, Australia
  18. ↑
  19. ↑ The National Beekeepers’ Association of New Zealand - Submission on Application ERMA200886
  20. ↑ Effects of mutations in Drosophila nicotinic acetylcholine receptor subunits on sensitivity to insecticides targeting nicotinic acetylcholine receptors
  21. ↑ carbaryl
  22. 1 2 carbofuran
  23. ↑ methomyl
  24. ↑
  25. ↑ propoxur
  26. ↑
  27. ↑ acephate
  28. ↑
  29. ↑ azinphos-methyl
  30. ↑ Scott, Alex (August 4, 2008). "Europe Rejects Appeal for Use of Azinphos-methyl Pesticide". Chemical Week. Retrieved 2008-08-11.
  31. ↑ chlorpyrifos
  32. ↑ coumaphos
  33. ↑ demeton
  34. ↑ diazinon
  35. ↑ dicrotophos
  36. ↑
  37. ↑ dichlorvos
  38. ↑ dimethoate
  39. ↑ fenthion
  40. ↑ fenitrothion
  41. ↑ fonofos
  42. ↑
  43. ↑ methamidophos
  44. ↑ methidathion
  45. ↑ parathion
  46. ↑ mevinphos
  47. ↑ monocrotophos
  48. ↑ naled
  49. ↑ oxydemeton-methyl
  50. ↑ phorate
  51. ↑ phosmet
  52. ↑
  53. ↑ permethrin
  54. ↑ cypermethrin
  55. ↑ esfenvalerate
  56. ↑ resmethrin
  57. ↑ Resmethrin Technical Fact Sheet - National Pesticide Information Center
  58. ↑ Pyrethrins and Pyrethroids Fact Sheet - National Pesticide Information Center
  59. ↑ Resmethrin Pesticide Information Profile - Extension Toxicology Network
  60. ↑ MSDS for Scourge' Formula II
  61. ↑
  62. ↑ methoxychlor
  63. ↑ endosulfan
  64. ↑ EFSA report of 16 january 2013 labelling clothianidin, imidacloprid and thiamethoxam asdetrimental to bees
  65. ↑ "Emergency Pesticide Ban for Saving the Honeybee"
  66. ↑ EPA Clothianidin Reviews
  67. ↑ http://www.purdue.edu/newsroom/research/2012/120111KrupkeBees.html
  68. ↑
  69. ↑ Protecting Bees When Using Insecticides University of Nebraska Lincoln, Extension, May 1998
  70. ↑
  71. ↑
  72. ↑
  73. ↑
  74. ↑
  75. ↑ Commonly Used Insecticides for Soybeans Kansas State University Extension, Aug 2004
  76. ↑
  77. ↑ Aldrin
  78. ↑ dieldrin
  79. ↑ heptachlor
  80. ↑
  81. ↑
  82. ↑
  83. ↑
  84. ↑
  85. ↑

External links

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