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Nano technology Perspective

February 3, 2019 0 Comment

Nano technology Perspective: Application of Nanotechnology in Insect Pest Management – A review
Abstract
Sustainable agriculture is the key to balance surplus food production to feed the growing population and being environmental friendly. Pest management plays a critical role in sustainable agriculture where the present day management practices are becoming futile thereby creating huge requirement of new innovations/methods. Nanotechnology and its application in pest management would be relevant in this trend and would be a better alternative. Its advanced techniques are effective in providing better spread, deeper penetration, and efficient control over conventional methods. Since it is novel and with fewer research data some part of it still remains enigmatic, particularly the toxicity of Nanopesticides to the environment and human health and further this has limited its use in agriculture. Improved strategies/techniques with proper trials and testing would certainly open up Nanotechnology for broader utilization.

Key words: Nano pest management; Nano cantilevers; Entomology; Nanoparticles
Introduction
Today’s agriculture should exploit present day technology and grow along with it. It is a high time to create conducive environment in agriculture to better utilize technology and bring revolution in production of crops/foodgrains with higher quality while preserving the environment for our future generations. Nanotechnology, an interdisciplinary science stands out among various available new technologies and is more relevant to present day agriculture.

Richard Philips Feynman’s talk in 1959 (“There’s Plenty of Room at the Bottom”) (Feynman, 1960) inspired the field of nano science and technology, he envisioned an enormous number of its practical applications in computation, information science, biology and engineering. Almost fifty years after Feynman’s talk, there has been explosion in academic and industrial interest in nanomaterials, which arises from the novel properties that emerge from materials at nano range, such as changes in electrical conductivity, surface chemistry and reactivity. New products are being developed with the help of nanotechnology in medicine, communications, electronic devises, material research, defense research, textiles, agriculture, food industry and many more and are simultaneously reported by many researchers across the globe. Its application in entomology has been on rise and will definitely become an integral part in crop protection within coming years. Nanotechnology deals with the materials of sizes ranging from 0.1 to 100nmand their applications. In other words, and by definition provided by National Nanotechnology Initiative (NNI), USA Nanotechnology is research and technology development at the atomic, molecular and macromolecular level at the scale of approximately 0.1-100 nanometer range.
Engineering the materials or products at nano scale can be performed by two approaches, i.e., top-down and bottom-up. These two approaches are essential to understand the basic principles of nanotechnology and how it works.

Manipulation of living organisms and merging of biological and non-biological materials with the help of nanotechnology refers to nano-biotechnology (Scrinis and Lyons, 2007). Further it can be used to develop new organisms. This can be used in medicine and in agriculture to create GM crops.
Insect pests are major threat to food production, to manage these pests we are using enormous amounts of pesticides which are dangerous to both human health and environment. In 1962 Rachael Carson, a marine biologist explained the effects of pesticides on environment in her book “Silent Spring”, which created great awareness regarding the side effects of pesticides (Fig.1). Due to the lack of effective alternatives for managing pests, till today we are still heavily dependent on pesticides in agriculture. This creates an urgent need to look for alternatives to save our health and environment. Nanotechnology could be a new hope for us.

Most intriguing questions which is being discussed within various entomologists is; do we really need nanotechnology in entomology? In this review we approach this question focusing on use of nanotechnology/nanomaterials related to insect pests and their management. Further, this will provide new dimensions for research in entomology and zoology.

Tools of Nanotechnology
There are many tools available in nanotechnology to enable its easy application in different fields. Some of the tools are being described below for the benefit of the readers.

Carbon nanotubes (CNT)
Nanotubes can be either single walled (SWCNTs) or multi-walled (MWCNTs). Some of the greatest advantages of CNTs are their ability to functionalize and to encapsulate biological and chemical materials. This function can be utilized in agricultural, environmental and medical fields for site specific delivery of materials.

Fullerenes
These are also molecules made up of carbon and were discovered in 1985 and this discovery was awarded with Nobel Prize in 1996. They appear in various forms including spherical, elliptical and in tube forms. They are widely used in Solar cells, to store hydrogen gas and developing Inter digitated capacitors (IDCs). Further they can be used in food packaging and other fields of agriculture.

Quantum dots
These are semi-conductors that are in nanometer scale. It is mainly used in biomedical applications like imaging and disease detection in human beings, Fluorescence resonance energy transfer (FRET) technology, cell tracking, pathogen and toxin detection and in gene technology (Jamieson, 2007). It can also be used in developing genetically engineered plants. In entomology it can be used for marking insects in behavioral and diversity studies, detecting and tracking of biological molecules, detection of mode of action of chemicals and also useful in constructing transgenic insects.

Nano sensors
A sensor is an instrument that responses to a physical stimulus such as heat, light, sound, pressure, magnetism, or motion. Nano sensors communicate information about nanoparticles to the macroscopic world (Jain and Siddiqui, 2014). It is an extremely small device capable of detecting and responding to physical stimuli with dimensions of one millionth of a meter. Nanosensors are already being used in medicine (detection of cancer cells, drug delivery), pesticide residue detection in vegetables, can also be used for early detection of insect pests and diseases.

Dendrimers
Dendrimers are spherical polymeric molecules, made from monomer of acrylic acid and diamine. These are widely used in biomedicine, imaging (MRI) (as a contrast agent – particularly anatomical images) and drug delivery (Klajnert and Bryszewska, 2001).

Nanoparticles: Synthesis and application in insect pest management
A wide variety of materials like metal oxides, ceramics, silicates, magnetic materials, semiconductor quantum dots (QDs), lipids, polymers, dendrimers, emulsions and polymers are used to build nanoparticles (NPs) which are beneficial in controlled release of pesticides. Metal NPs display size dependent properties, such as magnetism (magnetic NPs), fluorescence (QDs) and degradation by photo catalysis (e.g., metal oxide NPs) and these have corresponding biotechnological applications in sensor development for pest detection.
Nanoparticles are synthesized by various methods, namely, Physical, chemical and biological methods (Ghormade et al., 2011; Mittal et al., 2013). Chemical method is widely used for synthesis of NPs in large numbers using organic solvents and reducing agents for instance: elemental hydrogen, sodium ascorbate, sodium citrate, and sodium borohydride for synthesis of silver nanoparticles (Khatoon et al., 2011). The size of the NPs depends on the strength of reducing agent, higher the reduction rate smaller the particle size and vice-versa. Recently biological synthesis, a non-toxic method is getting popular and is widely practiced (Reisner, 2012). The use of this biological method is having more advantages than other methods, viz., free from toxic chemicals, less expensive chemicals, faster and easier to synthesize and easily alter the particle size. The chemical constituents of plants and microbes (proteins, amino acids, enzymes, polysaccharides, aldehydes, ketones etc.) acts as reducing as well as chelating agents and influence the size, activity and morphology of the nanoparticles. Further these synthesized nano particles having more activity (antimicrobial, insecticidal/pesticidal) (Naveena et al., 2018; Pavunraj et al. 2017), longer shelf life, less residue and environmentally safer when compared to chemically synthesized ones.

Greener synthesis of nanoparticles for insect pest management:
Synthesis of nanoparticles using plant materials, microbes and other natural products is considered as greener synthesis. The greener techniques like, microwave synthesis, ultrasound, hydrothermal, magnetic and other biological methods without contacting the reaction media, air and at lower temperature (Kharissova et al., 2013) are being widely practiced. Among the materials used, plant materials have much scope and advantages over others in changing the synthesized particle morphology and its bioavailability which is mainly attributed to the presence of more number of secondary metabolites (phenolics, alkaloids) in larger quantities. Secondary metabolites act as reducing and capping agents, thereby arresting the growth and agglomeration of particles. This action prevents any further reactions in the synthesized nanoparticles and leads to increased shelf life/longevity and stability of the particles.

Major advantages of Greener synthesis of nanoparticles over other methods are, it is simple (one pot reaction), cost-effective (no additional chemicals and surfactants), relatively reproducible, and often results in more stable materials.
At present many researchers synthesizing different metal nanoparticles (Kharissova et al., 2013) using various types of plants and their parts including leaves, roots, bark, stem, and fruits (Mittal et al., 2013; Rajan et al., 2015). They were successful in studying the effect of such nanoparticles on insects (most of the studies were on stored grain insects (Stadler et al., 2010) and very few on other insects) but yet to confirm the exact mode of action of these nanoparticles when used as pesticides.

Synthesis of nanoparticles using the active ingredient with insecticidal activity will be more effective than the use of the complete extract of the plant parts. However, this process is time consuming but precise nanoparticles with less contamination/impurity and more bioavailability can be synthesized as a result minute quantity is sufficient to kill the large number of insects. Karanjin, an insecticidal compound present in Pongamia pinnata was extracted and used for the synthesis of silver nanoparticles (Fig.2), which are more stable with enhanced properties (Naveena et al., 2018).

Nano-Pesticides
Insect pests are the major biotic factors affecting crop production. Thus for the control of insect pests several strong insecticides have been used. Major problem with synthetic insecticides are resistance, resurgence and residues. Addressing these issues several new formulations like eco-friendly pesticides, allele chemicals, insect growth regulators etc. have been introduced. The main strategy in pest management is to suppress insect pests as early as possible. In this context, the most exciting new development in insecticides is the nano-pesticides. Nanotechnology is reliable with new or improved activity or more targeted application of pesticides.

Pesticides – a broad term comprising insecticide, herbicide, fungicide, nematicide, etc. and are general biocides. Compounds which may be a chemical or of biological origin and kills or destroys the unwanted things or pests are called pesticides and if the compounds are in nanoscale and variations in morphology and activity are called nano pesticides. There is no universal definition for Nanopesticides. However, Bergeson (2010) mentioned that ‘Nanopesticides are particles of pesticidal active ingredients or other small engineered structures in nanoscale with useful pesticidal properties’.

India is leading in research and development on nano pesticides particularly nano insecticides followed by China and USA according to number of publications in the past few years (2009 onwards). However due to lack of research on their effect on environment these nanoinsecticides are not being released to general public. This void should be addressed by researchers in India and there by device better pest management strategies to increase the food production with limited resources.

Why there is much research/scope in Nanopesticides
Majority of the conventional pesticidal active ingredients (ai’s) are soluble in organic solvents. Hence there is a huge need to develop water soluble compounds which are in fact target specific, safer to non-target organisms, environmental friendly, should provide resistance for longer period, naturally stable for the environmental variations and premature degradation. Following qualities of nano-pesticides (Fig.3) could meet the criteria of ideal pesticides.

Nano pesticide delivery Techniques
Nano-emulsions
The emulsions with the droplet size of 20-200 nm are called nano-emulsions. These are also called by various names, like miniemulsions, ultrafine emulsions and submicron emulsions. There are two basic types of nano emulsions i.e., oil-in-water or water-in-oil nano emulsions. Most of these were prepared by dispersion or high-energy emulsification methods (high shear stirring, high-pressure homogenizers and ultrasound generators/ultrasound emulsification), low – energy emulsification methods and phase inversion temperature (PIT) technique. These are mainly used for preparation of nanoparticles.

Nanocapsules
Nanocapsules are made of an oily or an aqueous core surrounded by thin polymer membrane. These are in a range of 10 – 100nm. The cavity formed in the core is filled with active ingredients (a.i) and this protective coat is usually pyrophoric and gets oxidized easily and delays the release of a.i. These are having wider applications viz., agrochemicals, genetic engineering, cosmetics, cleansing products, wastewater treatments, adhesive component applications, strategic delivery of the drug in tumors, radiotherapy and as liposomal nanocapsules in food science and agriculture (Kothamasu et al., 2012).

Nanocontainers
These are the containers with their inner cavities having at least one dimension and are in nanoscale size. These have great potentials in targeted drug delivery, holding nanogram quantities of materials and nanospace-confined bio-chemical reactions. There are different types of nanocontainers available for application namely, polymersomes and micelles, carbon nanohorns, protein capsids, gold nanospheres, and mesoporous silica matrices (Zhao et al., 2013). These nanocontainers are mainly used in controlled release of pesticides.
Nanocages
It comprises a novel class of nanostructures possessing hollow interiors and porous walls. These are having various biomedical applications and at present mainly used for early detection of cancer, contrast enhancement agents for photo acoustic tomography (PAT). PAT combines optical and ultrasonic imaging, measuring the ultrasonic waves that arise from the thermo elastic expansion of tissue due to the absorption of light. It provides greater resolution than purely optical imaging in deep tissues while overcoming the disadvantages of ultrasonic imaging like biochemical contrast and speckle artifact (Skrabalak et al., 2008). This can also be used in imaging the insects during taxonomic identification.
Nanogels
These are the formulations with the size range of 100 nm, varying solvent quality and branching. The volume fraction can be altered variably to maintain a three dimensional structures. By definition, these are nano-sized hydrogel systems which are highly cross linked systems in nature involving polymer systems which are either co-polymerized or monomers. Mechanism of action is dependent on the sensitive characteristics of polymer systems such as temperature (Thermo-sensitive), pH, volume transition and light responsive behavior which further affect the loading or release capacity of nanogels (Dorwal, 2012). Recently a study was successful in managing fruitflies with this technique, where they prepared nanogels with pheromone of fruitfly and they observed very good control over pheromone alone. These pheromone nanogels are having longer shelf life, adaptability to varied climatic conditions and eco-friendly (Bhagat et al., 2013). These could be more effective and modernize pest management practices and may replace the present pheromone traps in coming days.

The below mentioned table (Table 1) represents the research studies on various methods of nano pesticide delivery technique for the management of insect pests damaging to crops and stored grains. However, there is still scope for further development in effective application of these techniques.
Table 1. Application of nanomaterials for the control of insect pests in Agriculture
Sl. No Different Nanoformulations Test Insect pest References
01 Poly-ethylene glycol-coated nanoparticles loaded with garlic essential oil Tribolium castaneum Yang et al. (2009)
02 Chitosan (CS)-g-poly (acrylic acid) (PAA) nanoparticles Callosobruchus maculatus 
Aphis gossypii Sahab et al. (2015)
03 Nanoformulations of ?-cyfluthrin C. maculates Loha et al. (2012)
04 Pyridalylnanocapsule suspension Helicoverpa armigera Saini et al. (2014)
05 Nano-imidacloprid Glyphodes pyloalis Memarizadeh et al. (2014)
06 Nano-Imidacloprid, Martianus dermestoides, Tenebrionidae Guan et al. (2008)
07 Nanoparticles of novaluron Spodoptera littoralis Eleka et al. (2010)
08 CdS, Nano-Ag and Nano-TiO2 Spodoptera litura Chakravarthy et al. (2012)
09 Aluminium oxide Al2O3 and Titanium dioxide (TiO2) nanoparticles Sitophilus oryzae L. Sabbour, 2012
10 Trichoderma viride mediated synthesis of titanium dioxide nanoparticles (TDNPs) H. armigera Chinnaperumal et al. (2018)
11 CuO nanoparticles S. littorals Shaker et al. (2016)
12 Nanostructured alumina S. oryzae L.
Rhyzopertha dominica (F.) Stadler et al. (2010); Stadler et al. (2012)
13 S. oryzae L. López-García et al. (2018)
14 Nanoalumina dust S. oryzae L.
Rhyzopertha dominica (F.), Buteler et al. (2015)
15 Nano-micro scale sized alumina powders Acanthoscelides obtectus Lazarevi? et al. (2018)
16 Nanogel- pheromone Bactrocera dorsalis Bhagat et al. (2013)
17 silica gel with essential plant oils S. oryzae (L.)
Tribolium confusum Athanassiou et al. (2013)
18 MA-chitosan nanogel loaded with Cuminum cyminum essential oil Sitophilus granarius L.
Tribolium confusum Ziaee et al. (2014)
19 Nanoemulsions of Achillea essential oils Tribolium castaneum Nenaah, 2014
20 Nanoemulsions of Asteraceae essential oils C. maculatus Nenaah et al. (2015)
21 Alginate Imidacloprid nanoemulsion Sucking pest (leafhoppers) Kumar et al. (2014)
22 Nanospheres containing
essential oils from Zanthoxylum rhoifolium leaves Bemisia tabaci Christofoli et al. (2015)
23 MEMS sensors using microcantilevers and fixed-fixed beams as resonant mass sensors for the selective detection of pest Female sex pheromone of H. armigera (Hubner). Moitra et al. (2016)
24 Silica-nano particles (SNPs) S. oryzae Debnath et al. (2011)
25 Corcyra cephalonica Vani and Brindhaa, 2013
26 S.littoralis in Squash El-Helaly et al. (2016)
27 Nanostructured silica C. maculatus Arumugam et al (2016)
28 SNPs formulated with ?-pinene and linalool Achaea janata L
Spodoptera litura F Usharani et al. (2014)
29 Surface functionalized SNPs Sitophilus Debnath et al. (2010)
30 Fipronil-encapsulated SNPs Termites (field trial) Wibowo., 2015
31 Mesoporous silica nanoparticles (MSNs) are employed as DNA nanocarriers Tuta absoluta Hajiahmadi et al. (2019)
32 Silver nanoparticles (AgNPs) prepared by ?-carboline and quinazoline alkaloids of Peganum harmala L. seeds. Trogoderma granarium Almadiy et al. (2018)
33 Silver nanoparticles Musca domestica Kamaraj et al. (2012)
34 Ergolis merione Moorthi et al. (2015)
35 Plutella xylostella Roni et al (2015)
36 S. litura F. ; A. janata Yasur and Rani, (2015)
37 Heliothis virescens
Trichoplusia ni
Podisus maculiventris (spined soldier bug) Afrasiabi et al. (2016)
38 Bombyx mori Meng et al. (2017)
39 Silver nanoparticles,
Alumino silicate nanoparticles S. oryzae
Grasserie disease of silk worm Goswami et al. (2010)
40 Ag and Zn nanoparticles Aphis nerii Rouhani et al. (2012)
41 AgNPs using leaf extract of Euphorbia prostate S. oryzae Zahir et al. (2012)
42 AgNPs using leaf extract of Euphorbia hirta H. armigera. Devi et al. (2014)
43 AgNPs and PbNPs using Avicennia marina S. oryzae Sankar and Abideen, (2015)
44 Ag NPs from Stearic Acid, Leaf Extract of Catharanthus roseus Earias vittella Pavunraj et al. (2017)
45 Biosynthesized nickel NPs C. maculatus Elango et al. (2016)
46 Ni-Pd bi metallic nanoparticles C. maculatus Elango et al. (2016)
47 Sargassum wightii-synthesized ZnO NPs H. armigera. Murugan et al. (2018)
48 ZnO NPs Trialeurodes vaporariorum Khooshe-Bast et al. (2016)
49 Bt-ZnO NPs. C. maculatus Malaikozhundan et al. (2017)
50 ZnO-TiO2-Ag nanoparticles Western flower thrips, Frankliniella occidentalis Rouhani et al. (2011)
51 Pongamia pinnata leaf extract coated zinc oxide nanoparticles (Pp-ZnO NPs) C. maculatus Malaikozhundana and Vinodhinib, (2018)
52 Hematite (?-Fe2O3) nanoparticles Myzus persicae Asoufia et al. (2018)
53 Novaluron nanoparticles S. littoralis  Eleka et al. (2010)
Methods of preparation nanoparticles for development of nano insecticides
There are different methods available for the preparation of nano particles for further development of nano insecticides. Here we enlist some of the methods of preparation as reported in Goshen and Magdassi (2012) (Table 2). Preparation of these nanoparticles depends on type of insecticidal material used, their physical, chemical and biological parameters, mode of action, expected size, formulation required and financial status.

Nanopesticides encompass a great variety of products. Every new innovation creates harmful and beneficial effects on human health and environment. The application rates of nanopesticides are low hence reduction in run off/washed away chemicals and through various other means and further reduces the environmental contamination. However, due to the enhanced transport, longer persistence and higher toxicity of nanopesticides leads to surface and ground water contamination and also pollute the soil (Kah et al., 2013).

Table 2. Different methods of development of nanopesticides
Methods Advantages Disadvantages
High Pressure homoginization
Sonication
Wet/dry milling Easy, Higher yield, Suitable for materials poorly soluble in water and organic solvents High energy
Shear force
Excess heat production so cooling is required
Particle size >100nm
Controlled precipitation
anti-solvent precipitation
solvent displacement To prepare NPs with insecticides which are insoluble in water but soluble in organic solvents
Simple and Cost effective Organic solvent required to solubilize compound and time consuming
reactive precipitation Suitable for insecticides having acidic moieties (ex: carboxylic acid) Not suitable with others
Flash Nano precipitation 60-200nm (ex: bifenthrin) Higher/fast mixing rate
Supercritical fluids based methods
Rapid expansion of Supercritical solutions (RESS)
Gas antisolvent (GAS)
Particles from gas-saturated solutions Dissolve hydrophobic materials without using organic solvent.

Environmental friendly High energy
Expensive
Spray drying (Ex: Lambda cyhalothrin) Rapid, simple, easily measurable Require High temperature
Suitable for solvents with high evaporation rate
Sol-gel process Useful for inorganic nanoparticles Inorganic nano pesticides only
Greener synthesis Organic nanoparticles, plant based, less or non toxic chemicals in the preparation, higher biological activity Less yield
Difficult to control the size of nanoparticles
In sustainable agriculture, nanoparticles are used to control harmful insects. However, it is necessary to know the effects on beneficial insects in the same environment (Agroecosystem). In this direction, Afrasiabi et al. 2016 reported that Ag NPs affects the beneficial insect (Predatory bug, Podisus maculiventris) which, alerted the researchers to look in depth on effect of NPs on non-target organisms in the agroecosystem.
Mode of action of Nanoparticles as pesticides
Nanoparticles can be used as insecticides. Research activities (see Table 1) towards developing nano-insecticides gave promising results. These nano-insecticides are more effective in controlling insects when compared to conventional pesticides. However, the information on exact mode of action on insects is inadequate. Benelli, 2018 reviewed and reported complete available information on mode of action of nanoparticles on insects. The figure 4 reveals the mechanism of action of various types of nanomaterials on insects. Figure 5 shows the effect of nanosilica on insects in grain storage.
Nanotechnology and pest management
Agricultural diagnostics and drug delivery with nanotubes
Progress in nanomaterials science and technology has resulted in the development of several devices which have potential applications in agricultural and related biological industries. For instance, nanotube devices can be integrated with other chemical, mechanical, or biological systems, and can be excellent candidates for electrical sensing of individual bio-molecules. Nanotube electronic devices have been shown to function very well under certain extreme biological conditions such as saline (salty) water and have dimensions comparable to typical bio-molecules such as DNA, width of approximately 2 nm (McEuen et al., 2002). Despite the practical difficulties in achieving reliable, rapid and reproducible nanofabrication of complex arrays of nanotubes, such devices have the potential to revolutionize site-specific and process exact diagnosis, drug delivery and in livestock disease and health management as well as in the identification and site-specific control of plant pests and diseases.

Nano sensors in crop protection
Nanotechnology based sensor systems for pest management is still at the primitive level. Development of sensors and diagnostic devices for on-site monitoring of pathogens will allow farmers to closely monitor the variations in crop field and identify the possible reasons and take appropriate measures. These will also add more value to the present day precision farming system. Hence we can reduce the input cost and save the environment from pesticide pollution and improve the soil health.

Nano biosensors for pesticide detection
Several studies were conducted for development of analytical tools for pesticide residue determination. In parallel with typical chromatography (GC/LC-MS), immunochemical assays based on bio-molecules were employed as an alternative for pesticide measurement by virtue of its high selectivity, sensitivity, reliability, low detection limits, small sizes and quick response (Gabaldon et al., 1999). Nanoparticles added more value for various biosensors making them more sensitive and stable. Some of such sensors include nanoparticle-based Optical Biosensors, Electrochemical Biosensors and Nanotube-based Electrochemical Biosensor. Biosensors were used to detect pesticide in water (Sassolas et al., 2012). Further, nanosensors were developed for detection, degradation and removal of insecticidal pollutants from ground water using metallic nanoparticles, iron and titania nanoparticles as reviewed in (Goshen and Magdassi, 2012). However, there are some issues needs to be addressed in this application of sensors for pesticide detection. According to Khot et al., 2012 the issues are,
Availability of the nanomaterials sensitive to common pesticide residues,
Manufacturing techniques,
Accuracy in minute level detection,
Cost, and
Environmental effects of nanomaterials.

Nano cantilevers: will they be an alternative to pheromone traps?
Nano cantilevers are very small in size, made of silicon are effective in sensing the materials compare to bigger sensing devices. These were used to detect viruses, bacteria and other contaminants in air and liquids (Gupta et al., 2006).

The basic working principle of cantilever sensors is that any physical, chemical or biological stimuli can affect the mechanical characteristics of the micromechanical transducers in such a way that a resulting change can be measured. Nano cantilever based biosensors operate in a closely related principle, where interaction with biological molecules changes the bending (static mode) or resonance frequency (resonant mode) of the cantilever (Larvik et al., 2004), thereby the compounds/entities can be detected. This principle is being used by various research groups in detecting viruses, bacteria and other contaminants in air. Entomologists, chemists and engineers working together to use these cantilevers with appropriate modification and fabrication for insect detection in field or in grain storage conditions (Fig.6). Moitra et al. 2016 reported the list of insect pheromones tested by this technology under controlled conditions. He pointed out that out of the 12 experiments conducted by different workers on different insects, two experiments done on H. armigera and Scirpophaga incertulas showed positive results. This resulting nano cantilever could be an alternative for pheromone traps used for monitoring pest population. It could be believed that these technologies will soon be available for farmers to use in their crop fields.

Nano Toxicology
A novel area of research in nanotechnology is study of the poisonous effects of nano materials on health (living organisms) and environment. Once Nanotechnology has started being used in various fields, nanoparticles are found to be present in air, soil and water suggesting us for a need of nanotoxicology. There has been a very few detailed study on long term detrimental effects of nano particles on health and environment. There have been many researchers working at a small scale showing us the adverse effect of these particles. Nano particles could enter the body through various routes, viz., inhalation, ingestion, dermal exposure and injection, and then accumulate in tissues. This accumulation may further lead to serious inflammation, neurological and other severe disorders (Demirbag et.al 2012). It would be ideal if the nanoparticles after accomplishing their function were to be removed from the body. Some particles can be removed without any degradation process (excretion), while others are immobilized in the body and further may produce secondary products or byproducts and these may lead to newer complications. There is a much scope in studying the effect of nano pesticides on health and environment.

Future perspectives and Conclusion
The development of nanomaterials with good dispersion and wettability, biodegradable, less toxic and more photo-generative, with well understood toxicokinetics and toxicodynamics, smart and stable, and ease of fabrication and application in crop field, would be ideal for their effective use in crop protection.
WHO/FAO guidelines (2010) (Fig. 7) should be followed by every researcher involved in nanotechnology to protect our health and environment.

Scientific assessment and unbiased reporting on the environmental impacts of nanotechnology in agriculture would assist in dispelling such perceived extreme fears. We have learnt from public reactions towards agricultural biotechnology, particularly in Europe, that a lot of damage can occur when public trust in technology and the developers is eroded. In India also we are facing the same problem with public in implementing the GM food crops. So, we need to work with the harmony of nature and value the faith and believes of people and resolve them scientifically with enough evidence of nano particles being safer to the environment.
In a recent article on the societal issues facing nanotechnology, Roco (2003) argued that the success of nanotechnology could not be determined only by doing good research and development in academic and industry laboratories. The author noted that key questions asked by technology users and public are about economic development and commercialization, education, infrastructure, and societal implications, environmental and health effects. Thus, research and development at the nanoscale, nanotechnology applications and societal implications form a coherent and interactive system, which may be visualized as a closed loop. Summarizingly we require nanotechnology and its applications in the crop protection as a holistic approach for better crop growth and sustainable production and some need-based research should be prioritized.
Acknowledgement
Author, NLN thanks to UGC, New Delhi for providing Post Doctoral Fellowship. Thanks are also due to CeNSE, IISc for providing facilities.
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