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Changing scenario of insecticides and role of new molecules in IPM

Gururaj Katti

Principal Scientist (Entomology) & Head (Crop Protection)

ICAR-Indian Institute of Rice Research, Rajendranagar, Hyderabad

 

Food production anywhere in the world is increasingly becoming more challenging mainly due to burgeoning growth of world population leading to declining availability of cultivable land to population. Hence, there is an imperative need to overcome the challenges to achieve sustainable food production. Biotic stresses including insect pests, diseases, weeds as well as other pests pose a constant and formidable threat across the world thwarting the efforts for enhancement of crop yields.

The severity of pest problems has been changing with the developments in agricultural technology and modifications of farming practices. In India, evidences indicate that pests cause 25 percent loss in rice, 5-10 percent in wheat, 30 percent in pulses, 35 percent in oilseeds, 20 percent in sugarcane and 50 percent in cotton. The changing scenario of insect pest problems in agriculture as a consequence of green revolution technology has already been well documented. There has been further shift in the status of several insect pests after the introduction of transgenic crops and the current scenario of climate change (Dhaliwal et al., 2010).

Integrated Pest Management (IPM) – a long term solution for managing pest problems

Integrated Pest Management (IPM) is a system that, in the context of the associated environment and the population dynamics of the pest species, utilizes all suitable techniques and methods in as compatible a manner as possible and maintains the pest populations at levels below those causing economically unacceptable damage or loss (FAO).  It is an ecologically based strategy that focuses on long term solution of pests through a combination of techniques such as use of resistant varieties, biological control, chemical control, modification of agronomic practices and habitat manipulation.

Among the components of IPM, pesticide use is one of the most effective and quick methods of reducing pest populations particularly in emergency situations such as pest outbreaks where there is no suitable alternative. The widespread pesticide use is also largely due to convenience, simplicity, effectiveness, flexibility, and economy subject to their judicious use. Pesticides are not only vital in increasing food production but a reliable food supply on a large scale and at reasonable cost can be guaranteed only with the help of crop protection products. By making agriculture more productive, these tools help to keep food prices in check for the consumer and commodities that were available once seasonal are now in year-round abundance. Pesticides reduce and, in some cases, eliminate, pest damage allowing the consumer to purchase high quality produce. They enable farmers to produce more food to meet the current needs without expanding their land base. This indirectly benefits biodiversity by the prevention of bringing more wildlife habitats, forests, wetlands and grasslands under cultivation. Hence, the contribution of pesticides towards plant health management for food and nutritional security is obvious (Gururaj Katti et al., 2016). However, to  maximise the benefits of pesticide use at minimum human, environmental and economic cost, pesticides must be strictly regulated and used judiciously by properly trained and appropriately equipped personnel, ideally in harmonious integration with other  complementary technologies (Jerry Cooper and Hans Dobson, 2007).

 

Changing role of insecticides in IPM

 

Synthetic insecticides

 

During the last three decades of 20th century (1970-2000), insecticides belonging mainly to four groups viz., organo chlorines(OCs), organophosphates(OPs) carbamates and synthetic pyrethroids, played a significant role in IPM of various crops. Among the OCs, use of first generation insecticides such as DDT, BHC, lindane, endrin, dieldrin, chlordane, aldrin and endosulfan was advocated till 80’s. These products were very persistent and efficacious with good properties for agriculture and for public health, though their long persistence made them undesirable after control due to health and environmental concerns. Hence, the introduction of organophosphates brought a new class of insecticides with reduced persistence and lower risks to both users and the environment. The commonly recommended OPs initially included ethyl and methyl parathion, phosphamidon, sumithion, mephospholan, metasystox, dimethoate, phorate followed by monocrotophos, chlorpyriphos, quinalphos and diazinon, while popular carbamates included carbaryl, carbaryl plus lindane, BPMC and carbofuran.   During the late eighties and nineties, synthetic pyrethroids derived from the plant origin pyrethrum emerged as a new class of selective chemicals which were effective at very low doses. Some more newer chemicals belonging to phenyl pyrazoles such as fipronil and ethiprole, as well as nereistoxin derivatives such as cartap hydrochloride were also found effective. Since 2000, availability of newer insecticide molecules with novel modes of action, higher toxicity to target pests at very low doses, less toxicity to non target organisms and low persistence in nature, such as neonicotinoids (imidacloprid thiamethoxam and dinotefuran), ether derivatives (ethofenprox), fermentation products (spinosad), pyrazoles (Chlorantraniliprole), diamides (flubendiamide), oxadiazine group (indoxacarb) and sulfoximines (sulfoxaflor) has further strengthened the role of insecticides in IPM. They have played an important role in managing many arthropod pests with good bioefficacy, high selectivity, short re-entry and pre-harvest intervals as well as low mammalian toxicity, making them attractive replacement for conventional synthetic pesticides and best fit in Integrated Pest Management (IPM) system as an important and ultimate component (Gururaj Katti, 2014).

 

 Biorational pesticides

 

Pesticide development has been evolving and diversifying in response to public awareness of environmental and health impacts of synthetic chemical pesticides and resulting legislation.  In this process, biorational pesticides comprising mainly of biopesticides were developed as key components of integrated pest management (IPM) programs as a means to reduce the load of synthetic chemical products being used for control of pests. Biopesticides are certain types of pesticides derived from natural materials as animals, plants, bacteria, and certain minerals.  The biopesticides used so far fall into two major catgories viz., plant based or botanical pesticides and microbial pesticides (Ranga Rao, 2007).

Four major types of botanical products have been used for insect pest management (pyrethrum, rotenone, neem and essential oils), along with three others in limited use (ryania, nicotine and Sabadilla). Additional plant extracts and oils (eg. Garlic oil, Capsicum oleoresin etc.) have also been or being used in a limited way.  However, neem and its products have more potential and investigated both in crude form and as formulated products. Ready to use formulations based on plant products are available in market for use in insect pest management. These formulations are mixed with water and applied as high volume sprays for control of insect pests. However they are not comparable to the quick knock down and curative action of synthetic insecticides which has psychological impact on the farmers preferences. Some of the deterrents for their use include a wide variability in concentrations of registered formulations, price, field stability, lower efficacy and shelf life, phytotoxicity after repeated applications and non availability of suitable formulations.

Among the microbial pesticides most widely used  ones are derivatives of the bacterium Bacillus thuringiensis, or Bt, which produces a toxin protein that is harmful mainly to lepidopterans. Several Commercial formulations of Bt developed by Private companies have been evaluated for their effectiveness (Gururaj Katti, 2014a). In the last decade, Bt transgenics have been developed which are plant-pesticides where in the Bt toxin gene is introduced into the plants own genetic material so that the plant, itself manufactures the toxin that destroys the pest..

Recently evolved 4th generation biorational pesticides also offer the opportunity of new modes of action with less environmental disruption. Use of chitin synthesis inhibitors, juvenile hormone analogues, anti juvenile hormones, non steroidal ecdysteroids and non terpenoid juvenile hormone compounds in pest management can significantly reduce pesticide use, particularly when used in combination with other control tactics.

Overall, synthetic pesticides with single active principle are likely to induce the development of resistance in insects. Biorational pesticides on the other hand contain complex array of compounds with multiple effects and there is less likelihood of development of resistance. Therefore, wherever possible, these can be alternated with synthetic pesticides to hinder the development of insecticide resistance. There is a need to educate farmers about the special behavioural effects of biorational products and also create awareness among extension specialists and policy makers of the potential utilization of biopesticides. More focused research efforts in production, formulation and development of effective delivery systems are needed to effectively harness their potential and convince the farmers about their role as eco-friendly alternatives to conventional chemical pesticides.  However, for an effectiveness of any chemical including the new molecules, the correct choice of active ingredient, suitable formulation and application techniques need to be made on the basis of pest biology and crop phenology to ensure ecological, economical and social benefits for the farmers.

 

Selected Bibliography

 

·        Dhaliwal, G.S. Vikas Jindal and Dhawan, A.K.. 2010. Insect Pest Problems and Crop Losses: Changing Trends. Indian Journal of Ecology 37(1): 1-7

·         Gururaj Katti, Anitha Kodaru, Nethi Somasekhar, G.S. Laha, B. Sarath Babu and K.S. Varaprasad (Eds.). 2016. Plant health management for food security-Issues and approaches. Plant Protection Association of India, NBPGR Regional Station, Hyderabad. Published by Daya Publishing House, New Delhi. Pp. 230

·         Gururaj Katti. 2014. Pesticides for increasing crop productivity and food security. pp 32-43 in, “ Measurement and Management of resistance to chemical pesticides” (Eds. T.V.K. Singh, J. Satyanarayana and C. Narendra Reddy), Indian Council Of agricultural Research, Professor Jayashanker Telangana State Agricultural University and Acharya N.G. Ranga Agricultural University, Rajendranagar, Hyderabad. p 457

  • Gururaj Katti. 2014a. Current status and potential of biopesticides in pest management in rice. pp 22-47 in, “ Biopesticides in sustainable agriculture – Progress and potential” (Eds. Opender Koul, G.S. Dhaliwal, S. Khokhar and Ram Singh), Scientific Publishers (India) 5 A, New Pali Road, P.O. Box 91, Jodhpur , India, p474
  • Jerry Cooper and Hans Dobson. 2007. The benefits of pesticides to mankind and the environment. Crop Protection 26: 13371348

·        Ranga Rao, G.V., Rupela, O.P., Rameshwar Rao, V. and Reddy, Y.V.R. 2007.  Role of biopesticides in crop protection: Current status and future prospects. Indian Journal of Plant Protection, 35, 1-9


Source: OUAT Souvenir