*5.3.1.1 Acetyl cholinesterase Inhibitors*

*Modern Beekeeping - Bases for Sustainable Production*

significant changes than the normal chronology [27].

**5.3 Agrochemicals**

scientific community [7, 44–50].

piled through ECOTOX database [54].

*5.3.1 Insecticides*

mite body, thus, its repeated application to a colony can be proved as lethal to the honey bees as well. A high queen mortality and reduced number of sealed brood have been reported in the colonies treated with OA [35]. The OA treatment has also been reported to be associated with an increased apoptosis in bee midgut [36]. Worker bees have been reported to be showing an abnormal age-related patterns problem while treated with oxalic acid during their early life stages. A dose of 3.5% oxalic acid dehydrates at after 24 h of emergence have been reported to have a disturbance in the normal age-related patterns of worker honey bees. All the agerelated patterns of the workers appear in the natural chronology: they shows first events of behavioral patterns for nursing, followed by, honey or pollen manipulation, wax manipulation and patrolling at the same time but in different intensity. The bees start showing all age-related patterns somewhat earlier than the normal. Treated bees show an increased self-grooming, a superior tendency to inactivity and decreased nursing behavior. For all other behavioral patterns, including trophallactic interactions, house-cleaning, honey manipulation and patrolling, bees show no

Chemical control for insect pest management contributes as the major part of insect pest management strategies used all over the world [37]. Insecticides have been used since early 1940s for the effective pest management and have been a successful tool for the pest management as saving serious crop losses through insect pest infestations [38]. But, at the same time, the negative effects of these synthetic chemicals have created havoc throughout the world by suppressing the overwhelming populations of several non-target insect species, mainly including the biological control agents and the pollinators. Honey bees are susceptible to many insecticides and different harmful effects of these insecticides are believed to be the prime most reason for the decline in global honey bee populations [9, 39, 40]. The different insecticides have been highly criticized for their possible role in widely discussed and seriously concerning worldwide losses of honey bee colonies [41, 42]. Since the first detailed report and description of the term 'colony collapse disorder' (CCD) in 2006 [43] in America and followed by Europe, had again initiated the long term agitation of banning the use of insecticides, posing a serious threat to the billion dollar industry. Since the CCD, possible role of insecticidal residues in weakening the honey bee colonies for an increased susceptibility towards different environmental and pathogenic pressure on different colony levels has widely been discussed in

Lethality of any pesticide to honey bee is measured during toxicological tests of lethality by observing the mortality of bees after the application of pesticides either by oral administration or by topical application. The bee is usually considered dead when it exhibits "no movements after prodding". Investigation on lethality of any insecticide includes the use of correlation metrics to link the lethality and dose of a toxic chemical or substance to the bees [51, 52]. List of lethality of different class of insecticides was compiled from supporting information from Hardstone and Scott [53], and for the same information regarding fungicides and herbicides was com-

The different class of chemical insecticides poses variable threat to the individual honey bee and a colony level health, thus, the toxic effects and toxicity symptoms of different insecticides can be discussed under one umbrella of major classes of insecticide causing toxicity to the honey bees which is described here.

**20**

The two widely used groups of insecticides, organophosphates and carbamates acts on insects in a similar way as acetyl cholinesterase (AChE) inhibitors which in normal conditions, inhibits the activity of neurotransmitter acetylcholine in the insect nervous system [53]. These two groups of insecticides have deeply investigated for their toxic effects on honeybees and have been reported to have high larval as well as chronic toxicity to the adult bees causing toxicity symptoms like memory loss and behavioral agitations [55–60]. These two classes of insecticides have a variable amount of topical toxicity to the bees with LD50 ranging between 0.018 and 31.2 μg/bee [61, 62], with some of the widely used insecticides enlisted in **Tables 2** and **3**.


#### **Table 2.**

*List of organophosphate insecticides with respective toxicity to the bees.*


#### **Table 3.**

*List of carbamates insecticides with respective toxicity to the bees.*

### *5.3.1.1.1 Toxic symptoms of organophosphates*


#### *5.3.1.1.2 Toxic symptoms of carbamates*


#### *5.3.1.2 Nicotinic acetylcholine receptor agonists*

Leaves of *Nicotiana tabacum*, the plant producing the nicotine which mimics the neurotransmitter acetylcholine, activates the nicotinic acetylcholine receptor (nAChR), and promotes the generation of action potentials in postsynaptic nerve cells, contain up to 90,000 ppm of the nicotine, its pollen may contain up to 23 ppm and nectar 0.1–5 ppm alkaloid content [21, 46]. Adult bees have been proven to be successfully detoxifying nicotine in nectar with a median lethal concentration of 2000 ppm for nicotine [21], whereas the larva are sensitive to nicotine and usually die at the third or fourth larval instar at 5 ppm [46].

The neonicotinoids which are synthetic analogs of nicotine insecticides have a greater affinity to nAChR in the insect nervous system, including bees as well. In recent years, several studies and workers have portrayed these insecticides as the most serious cause of well discussed CCD [63–66]. However, these studies have been criticized for using unrealistic doses and duration of exposure [67]. The nitro guanidine neonicotinoids, including imidacloprid, clothianidin and thiamethoxam have been reported to be highly toxic to bees [68], with toxicity levels ranging from 0.004 to 0.075 μg/bee [69, 70] (**Table 4**). The insecticides like, thiacloprid and acetamiprid which are the member chemicals of cyanoguanidine neonicotinoid group, were much less toxic to the bees with topical or contact LD50 in a range of

**23**

**Table 5.**

*Detailed Review on Pesticidal Toxicity to Honey Bees and Its Management*

probably due to rapid cytochrome P450 detoxification.

*List of neonicotinoid insecticides with respective toxicity to the bees.*

to the bees (LD50 = 0.05–0.21 μg/bee) [73] (**Table 5**).

show their action on the voltage-gated Na+

*Source: Data compiled in Hardstone and Scott [53].*

*List of pyrethroid insecticides with respective toxicity to the bees.*

delaying the closing of the Na+

*5.3.1.3 Voltage-gated Na<sup>+</sup>*

**Table 4.**

the ability of foraging honey bees to return to the hive [28, 71, 72].

 *channel agonists*

7.1–14.6 μg/bee [70]. This relatively lesser toxicity of cyanoguanidines to the bees is

**Insecticide (neonicotinoids) LD50 (μg/bee) Risk ranking**

Acetamiprid 8.1 — Moderate Imidacloprid 0.0039 — High Thiacloprid 17.32 Low Thiamethoxam 0.0005 — High Clothianidin 0.00368 — High Dinotefuran 0.0023 — High

**Mean Range**

The nitroguanidine insecticides also show their toxic effect through impairing

Pyrethrin insecticides, produced by pyrethrum flowers (*Chrysanthemum cinerariaefolium*) are again a widely used group of insecticidal compounds. Even though, the pyrethrin has a natural origin, still these chemicals are known to be highly toxic

channel in the axons of nerve cells, by

channel and prolonging the recovery period of the

**Mean Range**

Other than pyrethrins, the pyrethroids, and organochlorine insecticides,

nerve cells, following the transmission of an action potential [74]. Bees show more tolerance towards some of the pyrethroids because of their rapid detoxification by cytochrome P450s. Being a pyrethroid, tau-fluvalinate a widely used miticide also

**Insecticide (organophosphate) LD50 (μg/bee) Risk ranking**

Bifenthrin 0.0146 — High Cyfluthrin 0.037 — High Esfenvalerate 0.017 — High Fenpropathrin 0.05 — High Gamma-Cyhalothrin 0.0061 — High Lambda-cyhalothrin 0.038 — High Permethrin 0.024 — High Pyrethrin + PBO 0.002 — High Pyrethrum 0.022 — High Zeta-cypermethrin 0.181 — High

*DOI: http://dx.doi.org/10.5772/intechopen.91196*

*Source: Data compiled in Hardstone and Scott [53].*

*Detailed Review on Pesticidal Toxicity to Honey Bees and Its Management DOI: http://dx.doi.org/10.5772/intechopen.91196*


#### **Table 4.**

*Modern Beekeeping - Bases for Sustainable Production*

*5.3.1.1.1 Toxic symptoms of organophosphates*

• Regurgitation of ingested food

• Erratic movement of the bees

*5.3.1.1.2 Toxic symptoms of carbamates*

• Erratic movement of the bees

• Stupefaction (numb)

• Break in brood cycle

• Queen ceases egg laying

• Most bees die at colony

• Development of supersedure queen bees

*5.3.1.2 Nicotinic acetylcholine receptor agonists*

die at the third or fourth larval instar at 5 ppm [46].

Leaves of *Nicotiana tabacum*, the plant producing the nicotine which mimics the neurotransmitter acetylcholine, activates the nicotinic acetylcholine receptor (nAChR), and promotes the generation of action potentials in postsynaptic nerve cells, contain up to 90,000 ppm of the nicotine, its pollen may contain up to 23 ppm and nectar 0.1–5 ppm alkaloid content [21, 46]. Adult bees have been proven to be successfully detoxifying nicotine in nectar with a median lethal concentration of 2000 ppm for nicotine [21], whereas the larva are sensitive to nicotine and usually

The neonicotinoids which are synthetic analogs of nicotine insecticides have a greater affinity to nAChR in the insect nervous system, including bees as well. In recent years, several studies and workers have portrayed these insecticides as the most serious cause of well discussed CCD [63–66]. However, these studies have been criticized for using unrealistic doses and duration of exposure [67]. The nitro guanidine neonicotinoids, including imidacloprid, clothianidin and thiamethoxam have been reported to be highly toxic to bees [68], with toxicity levels ranging from 0.004 to 0.075 μg/bee [69, 70] (**Table 4**). The insecticides like, thiacloprid and acetamiprid which are the member chemicals of cyanoguanidine neonicotinoid group, were much less toxic to the bees with topical or contact LD50 in a range of

• Paralysis

• Wings hooked together, held away from body

• Disoriented movements

• Distended abdomens

• Extended tongues

• Death of the bee

**22**

*List of neonicotinoid insecticides with respective toxicity to the bees.*

7.1–14.6 μg/bee [70]. This relatively lesser toxicity of cyanoguanidines to the bees is probably due to rapid cytochrome P450 detoxification.

The nitroguanidine insecticides also show their toxic effect through impairing the ability of foraging honey bees to return to the hive [28, 71, 72].

#### *5.3.1.3 Voltage-gated Na<sup>+</sup> channel agonists*

Pyrethrin insecticides, produced by pyrethrum flowers (*Chrysanthemum cinerariaefolium*) are again a widely used group of insecticidal compounds. Even though, the pyrethrin has a natural origin, still these chemicals are known to be highly toxic to the bees (LD50 = 0.05–0.21 μg/bee) [73] (**Table 5**).

Other than pyrethrins, the pyrethroids, and organochlorine insecticides, show their action on the voltage-gated Na+ channel in the axons of nerve cells, by delaying the closing of the Na+ channel and prolonging the recovery period of the nerve cells, following the transmission of an action potential [74]. Bees show more tolerance towards some of the pyrethroids because of their rapid detoxification by cytochrome P450s. Being a pyrethroid, tau-fluvalinate a widely used miticide also


#### **Table 5.**

*List of pyrethroid insecticides with respective toxicity to the bees.*

appears to be less toxic or safer to the honey bees but in higher concentrations this chemical has been reported to affect the health of different castes of honey bee colony. Colonies exposed to high doses of tau-fluvalinate had smaller queen bees [75]. Drones exposed to tau-fluvalinate during development were also reported to be affected with lesser chances of attaining sexual maturity [14].
