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New insecticide molecules in IPM

S. Satpathy*, B.S. Gotyal, V. Ramesh Babu and P. N. Meena

ICAR-Central Research Institute for Jute and Allied Fibres

Barrackpore, Kolkata – 700 120

*satp1@rediffmail.com

 

 

Abstract

The new insecticides introduced in crop protection are quite different in chemical structure over the existing groups and target alternate physiological and biochemical effect and diverse mode of action.In India, 272 pesticides have been registered for use against different pests, diseases and weeds, among which more than 100 are insecticides alone. In recent years, several new insecticide groups having new chemistries viz., neonicotinoids, oxadiazines, diamides, ketoenols, phenylpyrazoles, pyridines, flonicamid, METI (Mitochondrial Electron Transport Inhibitor) acaricides, diafentiuron, tetrazines, thiazolidinones, oxazolines, and insecticides from soil microorganisms such as avermectins, milbemycins, spinosyns, pyrrole insecticides and IGRs have been discovered and commercialized for uses in modern crop protection. The ability of these new groups of insecticides to be effective at low rates or doses, high level of selectivity, greaterspecificity to target pests along with low toxicity tonon-target organisms and the environment, replacedmany conventional compounds. Most of the new insecticide groupsregistered in India during the recent past are safer, highly suitable and fit well intointegrated pest management (IPM). Insecticide-centric approaches mostly dominated which is characterised by continued evolution of chemicals against key insects of important crops. As the nature of pest pressures evolves, there will be continuing needs for new research-based tactics to pest control. Insecticide chemistry will play a major, if not dominant, role in these developments. However, it is important to maintain the diversity in chemistry of insecticides for maximizing flexibility, precision and stability in pest management.

 

Introduction

National agricultural productivity enhancement during the post-sixtieswas not solely contributed by the high yielding crop varieties rather many other farm technologies including the use of fertilizers and pesticides played important role. The problem of insect infestation in newly introduced high yielding and fertilizer–responsive crop varieties gradually built up because of theirsusceptibility to biotic stresses. This necessitated greater use of pesticidesto prevent 10-30%losses to the potential productivity of different crops. Despite the use of recommended crop protection chemicals, the spectrum of biotic stresses on different crops and the pest status of existing pests have shownincreasing trends. This may be due to climatic changes, misuse of chemical insecticides particularly with respect to dose and frequency of application. Pesticides continue to be the major component of crop production technologies consequently, the area under crop protectionhas consolidated a lot. In the developing countries more than 55% of the crop area consumes 26% of the pesticides produced globally. The pesticides have become essential in modern crop protection programmes which protects 45% of total food produced worldwide(Oerke, 2006).

Indiscriminate use of pesticides has many fallouts including the broad spectrum and persistent toxic effect on natural enemies causing resurgence, insect resistance for prolong use of chemicals having similar chemistry and mode of action, toxic residues on foodand the cases of human poisoning. Pest resurgence in many important insect pestslike leaf hopper and plant hoppers of rice, whitefly of cottonand red spider mite in vegetables are well evidenced.  Since the period of adoption of insecticides there are many reports on insect resistance to insecticides. Till date, globally 586 species of insect pests have become resistant against 325 insecticides. Majority of the cases of insect resistance involve the older groups of insecticides i.e., organochlorine andorgano-phosphates (Sparks and Nauen, 2015).

The development of new active ingredients and with softer chemistry and better cross-spectrum activity is a continuous process to phase out the older group of insecticides for better efficacy, environmental safety and sustainability.Besides, due to requirements for improved environmentaland toxicological profiles, changing regulatory requirements,and a shifting spectrum of insect pests, there has been acontinuous need to discover and develop new insecticides. Evolving agriculturalpractices as exemplified by the development and implementationof Integrated Pest Management (IPM) and Good Agricultural Practices (GAP)are also the drivers for alternate new insecticidal chemistries(Sparks, 2013). The new insecticides introduced in crop protection are quite different in chemical structure over the existing groups and targets alternate physiological and biochemical effect and diverse mode of action.With the adoption ofintensive agriculture by the farmers, there has been significant increase in thepest, disease and weed problems, necessitating use of agro-chemicals. InIndia, 272 pesticides have been registered for use against different pests,diseases and weeds, among which more than 100 are insecticides alone (http://cibrc.nic.in).The registration of novel pesticides during last two decades has initiated a new era of bio rational pesticides.

Rationalization in development and use of new insecticides

With an attempt to make the use of insecticides sustainable,the focus on insecticide research shifted to search for and development of new green chemistries having novel biochemical targets in the context of pest control and resistance management. In recent years, several new insecticide groups having new chemistries viz., neonicotinoids, oxadiazines, diamides, ketoenols, phenylpyrazoles, pyridines, flonicamid, METI (Mitochondrial Electron Transport Inhibitor) acaricides, diafentiuron, tetrazines, thiazolidinones, oxazolines, and insecticides from soil microorganisms such as avermectins, milbemycins, spinosyns, pyrrole insecticides and insect growth regulators like benzoylureas, triazines, diacylhydrazines, juvenile hormone analogues/mimics have been discovered and commercialized for uses in modern crop protection. The ability of these new groups of insecticides to be effective at low rates or doses, high level of selectivity, greaterspecificity to target pests along with low toxicity tonon-target organisms and the environment, replacedmany old/conventional compounds (Hara, 2000).

Most of the new insecticide groupswith unique mode of action registered in India during the recent pastare safer, highly suitable and fit well intointegrated pest management (IPM) or insect resistancemanagement (IRM) programs. The risk of secondary pest out break and resistance development in key pests like whiteflies and aphids is greatly reduced through introduction of these novel groups.Spinosadderived from soilactinomycete, Saccharopolysporaspinosais relatively harmless to a range ofnatural enemies(Williams et al., 2003). The anthranilicdiamidesare another novel class of recently released insecticides. Similarly, imidacloprid a neonicotinoid, which is a very effective systemicinsecticide, was reported non-toxic to a predatory mite, Agistemusfleschneri,used in apple orchard IPM.Indoxacarb, a reduced-risk pesticide was ranked very highly overall for safety to beneficial insects, largely because of its low dermal toxicity.  Laboratory evaluations have shown that avermectin has amyriad of non-target impacts. With greater health and ecological concern due to toxic residues, today a great demand forsafer and more selective insecticides.

These new insecticide classes play an important role in IPMwith proven bio-efficacy, high selectivity and low mammalian toxicity thatrender them attractive replacement for conventional insecticides.

 

Neonicotinoids:The neonicotinoid group of insecticides (imidacloprid, acetamiprid,thiamethoxam, thiachloprid, clothianidin and dinotefuran) are highly activeinsecticides for foliar application, soil and seed treatment which represents a novel and distinct class with remarkable chemical and biological properties. This group has been the fastest growing class of insecticides in modern crop protection (Simon-Delsoet al., 2015). The discovery of neonicotinoidsis a milestone in the history of insecticide research, development and use because of their broad insecticidal spectrum, exhibiting systemic and translaminar properties and high residual activity with unique mode of action (Elbert et al., 1998). Neonicotinoids are widely used for controlling whiteflies, aphids and leafhoppers, thrips and small lepidopteran and coleopteran pests. It acts at the synaptic nicotinic acetylcholine receptors in the central nervoussystem of insects. Specificity for novel type of receptor found moreoften in insect nervous systems than that of non-arthropods makes it very selective.

 

Phenyl pyrazoles: Among phenyl pyrazoles, Fipronil is broad spectrum neurotoxin thatworks as a GABA agonist. It has contact activity on both chewing and suckinginsects and controls insects belonging to Coleoptera, Lepidoptera, Diptera, Homoptera, Isopteraand Thysanoptera. It has systemic activity, with long residual and showexcellent potential for control of most sucking and chewing insects, thrips, beetles, termites and grasshoppers. It is effective at low fieldapplication rates against insects that are resistant to other conventional insecticides. Though fipronil is more toxic to various natural enemies than other new insecticides, it has little or no risk to beneficials when applied as a granule or seed treatment.

 

Phenoxypyrazole:Fenpyroximate is an acaricide also causes rapid knockdown effect against larvae, nymphs and adults, mainly by contact and ingestion. Beside this, it also has some moulting inhibitory activity on nymphs and also serves as an inhibitor of mitochondrial electron transport at complex I.

 

Oxadiazines:Indoxacarb is the first commercialized insecticide of the oxadiazinegroup. It is a pro-pesticide with unique mode of action. It inhibits the flow ofsodium ions into nerve cell in insects that cause paralysis and death. It entersinto insect body in two ways like through ingestion of treated foliage and alsopenetrates through insect cuticle. Once indoxacarb is absorbed or ingested, feeding cessation occurs almost immediately within 0-4 hrs. The major use is against chewing insectssuch as lepidopterous larvae, beetles on pigeonpea, soybean, cotton and otherlegume crops (pod borer complex) and DBM of cabbage (Satpathyet al., 2007). Because of very low dermal toxicity it is safe to beneficial insects.

 

Thiourea Derivatives:These are pro-insecticide activated by oxidative desulfurization to the insecticidal carbodiamide. Diafenthiuron is the insecticide which belong to this group whichinhibits the oxidative phosphorylation i.e., specially ATPsynthase. Besides sucking pest complex like whitefly, aphid, leafhoppers it is also effective againsttetranychid and tarsonemid mites and young larvae of lepidopteran pests. It has no cross resistance with any other existing insecticides or acaricides. Because of its unique chemical class, novel mode of action, biological spectrum, translaminar activity, high selectivity towards beneficial insects and lack of cross resistance with other conventional and new insecticide, make it important for any IPM program.

 

Pyrroles: Pyrrole insecticides are derived froma natural product, dioxapyrrolomycin, isolated from astrain of Streptomyces fumanus. Chlorfenapyr is a commerciallydeveloped pyrrole insecticide. It has broad spectrum activityagainst many species of Lepidoptera, Acarina,Thysanoptera and Coleoptera. It is extremely effective against DBM of cabbage (Satpathyet al., 2005).Chlorfenapyr actsat the mitochondrial level by uncoupling oxidativephosphorylation.They have translaminar activity and are toxic both by contact and ingestion to chewing and sucking arthropods.

 

Pyridine Azomethines: Pymetrozine, a novel pyridine azomethine insecticide, is very specificagainst sucking insect pests.It effects onneuro-regulation or nerve-muscle interactioncontrolling the salivary pump and causes immediate and irreversible cessation of feeding due to an obstruction of stylet penetration, followed by starvation and insect death. It has rapid knockdown effect on aphids,whiteflies and planthoppers. Pymetrozine has systemicand translaminar activities and can be used as drench or foliar applicationand is highly specific against sucking insectpests.

 

Pyridine carboxamide:Flonicamid is a novel pyridine carboxamidecompound with a unique modeof action.It has contact and upwardly systemic activity. It effectivelymanages population of aphids, thrips, leaf hoppers and other sucking insects by inhibiting feeding immediatelyafter treatment. The main insecticidal mechanism of this compound is starvation based onthe inhibition of stylet penetration to plant tissues(Morita et al., 2000). It isconsidered to be safe to natural enemies andpollinators.

 

Tetramicand Tetronic Acid Derivative or Ketoenol Group: This group includes spirodiclofen, spiromesifen andspirotetramatwhich are suitable for foliar and soil application. Themode of action of ketoenolsis characterizedby the inhibition of the enzyme in lipid biosynthesis or metabolism(Nauenet al., 2005)). Unique mode ofaction and lack of cross resistance make ketoenolsideal for sucking pest management.

Spirotetramat, a novel insecticide belonging to Ketoenoisgroup is a tetramic acid derivative. It is systemic in action, xylem and phloem mobile up tothe growing shoots and down to roots. It shows excellent activity against aphids, mealybugs, psyllids, scales, thrips, whiteflies andjuvenile stages of sucking pests even the cryptic stages and protects new shoots appearing after foliar application. Spiromesifen is a novelinsecticide/acaricide introduced recently belonging to the new chemical class of spirocyclic phenyl-substituted tetronic acids(Nauenet al., 2005). It is especially effective against whiteflies,tetranychid spider mite and alsoagainst all juvenile andnymphalstages.Because of its high selectivity, good residual activity,minimal risk to pollinators and predatory mite species (Nicolaus et al., 2005) combined with a novel mode of action makespiromesifen an excellent substitute forIPM programs.Spirodiclofen isa selective, non-systemic acaricidehaving excellent efficacyagainst mites. Due to its high lipophilicity,spirodiclofenhas got good residual acaricidal effect upto 14 days. Positive temperaturecoefficient enables it to be effective at higher temperatures.

 

Diamides:Flubendiamide and chlorantraniliprolearethe recent introductions, particularly significantbecause of its action at new biochemical targets sites selectively bind to the ryanodine receptors(RyRs) in insect muscle cells, leading to muscle paralysis, cessation of larval feeding andmortality after 1–3 days.

Chlorantraniliprole is the recently introducedanthranilicdiamidehas proven to be effective against lepidopteran pests as well as against selectedspecies in the order Coleoptera, Diptera and Hemiptera (Lahm et al., 2009).Thecessation of larval feeding soon after consumption causes rapid control. Italso has ovicidal and ovo-larvicidal action. Because of translaminar and systemic action,it can be applied as foliar spray and as soilapplication. It is safe to parasitods,predators and pollinators. Flubendiamide belongs to phthalic acid diamide group. It is well suitedfor the control of a broad range of lepidopteran pests. The compound is well suited for insect resistance management programmes (pigeonpea pod borers). It is considered as good alternative to indoxacarb and methoxyfenozide. Cyantraniliproleis the secondgeneration ryanodine receptor insecticide with crossspectrum activity against lepidopteran and homopteranpests (Lahm et al., 2009). It controls whiteflies,dipteran leaf miners, fruit flies, foliage feeding beetles, lepidopteran larvae, aphids, leafhoppers, thrips, psyllids and weevils. The translaminaractivity makes it suitable for soil application.

 

Dichloropropenyl ethers: Pyridalyl is the only member of this class whichis highly effectiveagainst lepidopterous and thysanopterous pests. It controls population ofH.armigera and S.litura

as well as against Thysanopteran insects. It also produces unique insecticidalsymptoms, so it may have different mode of action from existing insecticides.Its safety to beneficialarthropods, makes it an ideal candidate for IPM.

Spinosyns: Spinosyns are class of fermentation derived macro cyclic lactone bioinsecticides, produced from Sccharopolysporaspinosa. This class is represented by spinosad and spinetoram. Spinosad is derived from mixture of spinosyn A and B and spinetoram is from the mixtureof spinosyn J and L.Spinosyns primarilytarget the binding sites on nicotinic acetylcholinereceptors and also has effects on GABAgated ion channels. (Sparks et al., 2001).These insecticides are highly effective against lepidopterous larvae, dipterous leaf miners and thrips while maintaining the exceptional environmental and toxicological profile.Spinosadacts primarily as stomach poison, but also have somecontact action with translaminar activity targeting cryptic stages.Spinetoram, the second insecticide of this group providesprolong controlof a broad spectrum insect pests and exhibits excellent translaminar activity.

Mectins: The mectin family are complex macrocyclic lactones with (Abamectin and Emamectin benzoate) or without (Milbemectin) conjugation with sugarresidues. Abamectin is a mixture of two naturallyoccurring avermectins that arederived by fermentation from the soil micro-organism Streptomyces avermitishas primary activity against mites and limited range of insects.Emamectin benzoate is a “Semisynthetic” derivative ofabamectin. Emamectin affects the nervous system of lepidopterous pests by increasing chlorideion flux at the neuromuscular junction, resulting in cessation of feeding andirreversible paralysis. It has translaminar activity, providing a relativelyprolonged residual activity. Surface residues of the insecticidedecompose rapidly in sunlight, hence this compound is considered as important component in IPMprogrammes.Milbemectin is primarily a miticidewhich causes rapid and prolongedparalysis and death.

 

Benzoyl Phenyl Urea(BPU): BPUs are chitin synthesis inhibitors, disrupt moulting, act by ingestionand contact, causes abnormal endocuticular deposition and abortive moulting. Among theBPU group, Novaluron, Diflubenzuron,Teflubenzuron and Lufenuron are most important incontrolling lepidopteran and coleopteran larvae.Mostly larval stage of insect are vulnerable, theadult of beneficial species, predators andparasitoids are seldom affected. These compounds are highlyselective and affect the larval stage and acts mainly byingestion, but in some species they suppress fecundityand exhibit ovicidal and contact toxicity. Diflubenzuron is the first commercialcompoundin this group highly effective against key lepidopteran insects. Teflubenzuron isnon-systemic insect growthregulator with stomach action. It affects fertility offemale insects after contact or ingestion. It is used incontrol of Lepidoptera, Coleoptera, Diptera,Aleyrodidae, Hymenoptera, Psyllidae, and Hemiptera. Novaluron is the new BPU insecticide having more contact and translaminar activity as compared with other CSI.It has potent insecticidal activityagainst lepidopteran larvae (by ingestion) and whitefly nymphs (by contact).Novaluron is more active in suppressing developing stages of leaf miners.

METI acaricides or insecticides:Pyridaben belongs to pyridazionone groupof insecticide having non-systemic acaricidal and insecticidal properties with rapid knockdown and longresidual effect. It shows excellent activity against alldeveloping stages of wide range of phytophagus mitesand other sucking pests.Biochemically, it inhibits mitocondrial electrontransport of complex I(Wood et al., 1996). Fenazaquin is one of several acaricidesand insecticides and has an unique chemicalconfiguration consisting of quinazoline moiety. It is widely used as an acaricide formanagement of mites.

 

Conclusions

There has been a gradual change in theapproaches to pest management over the past 50 years and no doubt will continue to change. Insecticide-centric approach mostly dominated which is characterised by continued evolution of chemicals against key insects of important crops. Pest management now requires more knowledgeable users for production of agricultural products in an economically successful manner. A component of these more sophisticated approaches is the prescription use of pesticides for the control of specific pests in geographically defined areas. As the nature of pest pressures evolves, accompanied by societal concerns over pest control and the economic realities of agriculture and pest management change over time, there will be continuing needs for new research-based tactics to pest control. Insecticide chemistry will play a major, if not dominant, role in these developments. However, it is important to maintain the diversity in chemistry of insecticides for maximizing flexibility, precision and stability in pest management. The fundamental pest biochemistry, physiology, ecology, genomics, and genetics are to be elucidated to develop insecticides of diverse nature.

Table 1. Recommended dosages of insecticides of new groups in important crops against key pests

Crop

Name of insect

Dosages

( g a.i)/ha

Crop

Name of insect

Dosages

( g a.i)/ha

Neonicotinoids

Phenoxypyrazoles

Clothianidin 50 WDG

Fenpyroximate 5EC

Rice

BPH

10-12

Tea, Chilli

Mite

15-30

Cotton

Jassid, whitefly

15-20, 20-25

Tomato

Leaf miner, aphid, fruit borer

90

Imidacloprid 17.8 SL

CSI

Chilli

Jassid, aphid, thrips

25-50

Novaluron 10 EC

Rice

BPH, WBPH, GLH

20-25

Cotton

Bollworm

100

Cotton

Jassid, whitefly, thrips

20-25

Tomato

Fruit borer

75

Okra

Jassid, aphid, thrips

20

Tetranic acid derivative

Tomato

Whitefly

30-35

Spiromesifen 22.9 SC

Imidacloprid 48FS

Vegetables,tea

Yellow mite and red spider mite

96

Cotton, okra , sunflower

Jassid, aphid, thrips, whitefly

300-500/kg seed

Thiourea compounds

Millets

Shoot fly, termites

720/kg seed

Diafenthiuron 50 WP

Thiamethoxam 25 WG

Cotton

Jassid, aphid, thrips, whitefly

300

Rice

Stem borer, leaf folder, BPH, WBPH, GLH

25

Cabbage

DBM

300

Cotton

Jassid, whitefly, thrips

25-50

Chilli

Mites

300

Mango

Hoppers

25

Pyrroles

Tea

Mosquito bug

25

Chlorfenapyr 10SC

Potato

Aphid

25

Cabbage

DBM

75-100

Phenyl pyrazole

Chilli

Mite

75-100

Fipronil 50 SC

Mectins

Rice

Stem borer, gall midge, BPH, WBPH,

50-75

Emamectin benzoate 5SG

Cabbage

DBM

40-50

Cotton

Bollworm

10

Cotton

Jassid, aphid, thrips, whitefly

75-100

Brinjal

Shoot& fruit borer

10

Diamide group

Legume

Pod borer

11

Chlorantraniliprole 18.5 SC

Spinocyns

Rice

Stem borer, leaf folder

30

Spinosad 45SC

Cotton

Bollworm

30

Cotton

Bollworm

75-100

Soybean

Stem fly

30

Legume

Pod borer

70

Okra

Fruit borer

25

Chilli

Fruit borer, thrips

75

Pigeon pea

Pod borer

30

Oxadiazines

Sugarcane

Early & top shoot borer

75

Indoxacarb 14.5 SC

Flubendiamide 20 WG

Cabbage

DBM

30-40

Rice

Stem borer, leaf folder

25

Cotton

Bollworm

75

Cotton

Bollworm

50

Legume

Pod borer

50-60

Cyantraniliprole 10OD

Pyridine carboxamide

Grapes

Thrips

70

Flonicamid 50WG

Cabbage

Aphid, DBM

60

Cotton

Jassid, whitefly

150

(Reddy and PushpaLatha, 2015)

References

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Hara, A.H. (2000). Finding alternative ways to control alien pests – part 2: New insecticides introduced to fight old pests. Hawaii Landscape, 4 (1) :5

Lahm, George P., Cordova, D., Barry and James D. (2009). New and selective ryanodine receptor activators for insect control. Bioorganic and Medicinal Chemistry,17:4127–4133

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Satpathy, S., Kumar Akhilesh, Singh, A.K. and Pandey, P.K. (2005).Chlorfenapyr: A new molecule for diamondback moth(PlutellaxylostellaL.) management in cabbage. Annals of Plant Protection Sciences, 13(1): 88-90.

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Sparks, T.C. and Nauen, R. (2015). IRAC: Mode of action classification and insecticide resistance management. Pesticide Biochemistry and Physiology, 121:122–128

Sparks, T.C., Course, G.D. and Durst, G. (2001). Natural products as insecticides: the biology, biochemistry and quantitativestructure-activity relationship of spinosyns and spinosoids.Pest Management Science, 57: 896-905.

Williams, T., J. Valle and E. Vinuela(2003). Is the naturallyderived insecticide spinosad compatible with insect natural enemies? Biocontrol Science and Technology, 13: 459-475

Wood, E., Latli, B. and Casida, J.E. (1996).FenazaquinAcaricide Specific Binding Sites in NADH: UbiquinoneOxidoreductase and Apparently the ATP Synthase Stalk. Pesticide Biochemistry and Physiology, 54(2): 135-145

 

 

 


Source: OUAT Souvenir