Abstract: World-wide scientists are providing clean and safe food to all human beings and live-hoods by adapting many green technologies. Considering overall merits of nanomaterials investigators recommend theist application in variously spheres of sustainable agriculture. Because nanotechnology will be helpful to meet the food security challenges; targeted delivery of pesticides, promote the seed germination and plant growth, increase crop yield, improve food quality, control of pestiferous insects that destroy crops and their products in the field as well as in storage. This review provided various research findings of usage of both chemical and bio-nanomaterials for pest management.
Friedrich1 concludes that in 2050, the expected population is 9.2 billion and the global food production will be about 70%. This could be achieved by adapting safe, abundant, sustainable and nutritious food supply innovative techniques. Some of them are traditional, mobile and vertical farming, cultivation of insect-protected and virus-resistant biotech crop varieties, engineered crops which grows in a places where they would not survive before, herbicide/pesticides-tolerant varieties, nutritionally (high protein, antioxidants and vitamins and lower amounts of fats) enhanced traits; following plant specific protection measures and adapt bio-intensive integrated pest and disease management.
Nanotechnology has revolutionized the world with tremendous advancements in many fields of science like engineering, biotechnology, analytical chemistry and agriculture. Their use in crop protection is just in its infancy2. Nanomaterials measure between approximately 1 and 100 nm. Over many decades, nanotechnology and nanomaterials have been employed successful and safely in various fields like medicine, environmental science and food processing. However, the use of nanomaterials in agriculture, especially for plant protection and production, it is an under-explored research area3. It has been used as conductors and semi-conductors, medical devices, sensors, coatings, catalytic agents and also as pesticides4.
Many countries are now being switching over from chemical-based agriculture to green agriculture, where the utilization of biopesticides and also biological nanomaterials have a lots of role to play in pest control5-11. Meliaceae (Azadirachta indica A. Juss), Annonaceae (Asimina triloba, Annona muricata and Annona squamosa), Compositae [Tanacetum cinerariifolium (Trev.) Schultz Bip., Pyrethrum cinerariifolium Trev. and Chrysanthemum cinerariifolium (Trev.) Vis.], Leguminaceae (Pongamia pinnata (L.) Pierre.) have been utilized world-wide for various pestiferous insects management.
Since, the biogensis of nanomaterials and their characterization was simple and reliable, biogenic silver nanoparticles (AgNPs) for Pongamia pinnata12,13, Azadirachta indica14,15, Annona squamosa16, Chrysanthemum17 were prepared and utilized for various biological purposes. However, their utility value was not evaluated against crop pests. Furthermore, a variety of metal nanoparticles silver (Ag), gold (Au), aluminum (Al), silica (Si) and zinc (Zn) and metal oxide-based polymers Zinc oxide (ZnO) and titanium dioxide (TiO2) are being developed for crop pest management. However, very few studies have been made in the field of nano-material and pest management and a lot more are expected in the near future. Hence, this review planned to provide about the use of nanomaterials and bio-nanomaterials against pestiferous insects and also post-harvest pests.
CROP LOSS AND ITS ASSOCIATES
Crop production loss was mainly caused by weeds (monocots and dicots and parasitic weeds), animals pests (pestiferous insects, mites, mollusks, rodents, birds, mammals) and phytopathogens (bacteria, fungi, viruses). All these organisms are classified as stand reducers (damping-off pathogens), photosynthetic rate reducers (fungi, bacteria, viruses), leaf senescence accelerators (pathogens), light stealers (weeds, some pathogens), assimilate sappers (nematodes, pathogens, sucking arthropods) and tissue consumers (chewing animals, necrotrophic pathogens) (http://www.agrivi.com/yield-losses-due-to-pests/). They have been managed by practicing different cultivation (cultivar choice, crop rotation) and mechanical weeding methods or utilizing various biological control agents (antagonists, predators, parasitoids etc.) and also using chemicals (pesticides/ insecticides/acaricides/rodenticides/pheromones etc.). Traditional pesticides have many limitations as well as fewer efficacies to control highly devastating pests. Increased use of nanomaterials in agriculture has led to the need to study the impact of nanomaterials on the environment in general and on insect before recommending the same for pest management.
WHY NANOTECHNOLOGY-BASED AGRICULTURE
Biotechnology has considered a safe agricultural tool to enhance crop protection, subsequently to produce more agricultural produce and products, improve food process, nutritional value and better flavor etc. At the same it has harmful ecological consequences like spreading genetically engineered genes to indigenous plants, increasing toxicity, which may move through the food chain, disrupting natures system of pest control, creating new weeds or virus strains, loss of biodiversity and insecticidal resistance etc18. Hence, it is necessary to bring forth new innovative technology/methods to overcome the above mentioned problems.
One such novel technology is nonotechnology, which has been revolutionized in health care, textile, materials, information and communication technology and energy sectors too.
|Table 1:||List of chemical and biological nanoparticles for pestiferous insect management with citations|
With the global population explosion, the demand for increased supply of food has motivated scientists and engineers to design engineered nanoparticles (ENPs) to reduce pestiferous insect infestation subsequently to increase agricultural production. Available literature reveals that both chemical and biological nano materials have also place substantial role in the crop protection as irrigation water filtration, remediation of harmful pesticides/insecticides, preparation of new pesticidal formulations19; efficient delivery of pesticides, fertilizers and other agrochemicals, development of organic farming and plant disease control20 etc. Since this field is in infancy stage, by trial and error method, this innovative technology can be utilized in crop protection and production purposes considering their consequences.
PESTIFEROUS INSECTS MANAGEMENT
Chemical nanomaterials: Initially, Christenson and Foote21 compared the effectiveness of colloidal Ca and nano-Ca on infestations of the oriental fruit fly [Bactrocera dorsalis (Diptera: Tephritidae: Dacinae)] in fruits and on red scale insects (Aonidiella aurantii). Chakravarthy et al.22 used inorganic nanoparticles CdS, nano-Ag and nano-TiO2 against Spodoptera litura Fab. (Lepidoptera: Noctuidae) control under laboratory conditions. During the same period, Rouhani et al.23 proved the bioefficacy of silver and zinc nanoparticles against Aphis nerii Boyer De Fonscolombe (Hemiptera: Aphididae). Vinutha et al.24 suggested to utilize nanotechnology for the management of an economically important polyphagous pest Helicoverpa armigera (Hubner). Recently, Hua et al.25 reported that calcium carbonate nanoparticles can enhance plant nutrition and insect pest tolerance.
Yasur and Rani26 studied the impact of silver nanoparticles (AgNPs) on growth and feeding responses of two lepidopteran pests namely Asian armyworm, S. litura and castor semilooper, Achaea janata L. (Lepidoptera: Noctuidae). The larvae were fed with PVP coated-AgNPs treated castor leaf at different concentrations and their activity was compared to that of silver nitrate (AgNO3) treated leaf diets. Larval and pupal body weights decreased along with the decrease in the concentrations of AgNPs and AgNO3 in both the test insects. Low amounts of silver were accumulated in the larval guts, but major portion of it was eliminated through the feces26. Previously, silica nanoparticle (SNPs) could effectively kill second stadium larvae of S. litura27 (Table 1).
Spodoptera spp.: A chitin derivative (N-(2-chloro-6- fluorobenzyl-chitosan), chitosan has been found to showstrong insecticidal activity in some plant pests37,38. Chitosan nanoparticle coated fungal metabolite (CNPCFM), Uncoated Fungal Metabolite (UFM) and Fungal Spores (FS) of entomopathogenic fungi Nomuraea rileyi (F.) Samson were evaluated against S. litura29. Results showed that among the tested materials, CNPCFM was found to be more effective than UFM and FS. The LC50 value for I, II, III and IV instars were 1.67, 1.85, 1.98 and 2.45 μg respectively for CNPCFM, while LC50 value for I, II, III and IV instars were1.87, 2.01, 2.38 and 3.97 μg, respectively for UFM. For FS, the LC50 values were 2.28×108, 2.92×106, 4.75×1010 and 5.55×1010 spores mL1 for I, II, III and IV instars, respectively. The UFM showed better toxicity compared to the FS and less effective than the CNPCFM. When the instars grew older, a decrease in mortality and an increase in LT50 were recorded with respect to the concentration of CNPCFM, UFM and FS. Adult longevity (LT50) for CNPCFM, UFM and FS were 2.17±0.2, 4.21±0.2 and 32.7±0.2 h, respectively.
Chandrashekharaiah et al.30 developed DNA-tagged nanogold, DNA-tagged CdS, nano-TiO2 and nano-Ag and were tested against S. litura third, fourth and fifth stadium larvae. Results revealed that DNA-tagged nanogold caused 30.50, 57.50 and 75.00% mortality respectively on third, fourth and fifth instar S. litura larvae, CdS nanoparticle caused highest S. litura larval mortality of 21.41-93.79% at 150 and 2400 ppm, respectively. The nano-TiO2 showed maximum of 73.79% S. litura larval mortality at 2400 ppm and the least was 18.50% at150 ppm. Nano-Ag caused maximum 56.89% S. litura mortality at 2400 ppm followed by 46.89 and 33.44% mortality at 1200 and 600 ppm, respectively. Previously, Chakravarthy et al.31 was also utilized DNA-tagged nano gold for S. litura management. They further developed nanoparticles coated with ecdysteroid analogues like tebufenozide and halofenozide and tested against Corcyra cephalonica (Stainton) (Lepidoptera:Pyralidae). Previously, an in vivo experiment was conducted for the Egyptian cotton leaf worm Spodoptera littoralis Boisd. (Lepidoptera: Noctuidae) using nanoparticles of novaluron. Results reveal that the toxicity of nanoparticles of novaluron resembled that of the commercial formulation32.
Other pests: Bionanomaterials were synthesized using plant extracts39 or microbes culture or their bioactive principles and protein to enzymes. Antifeedant, larvicidal and cytotoxic activities of synthesized silver nanoparticles (AgNPs) using aqueous leaf extract of Aristolochia indica against third instar larvae of H. armigera and HeLa cell lines showed that maximum antifeedant and larvicidal efficacy was observed in crude aqueous and synthesized AgNPs against H. armigera larvae (LC50 = 127.49, 84.56 mg L1, 766.54 and 309.98 mg mL1, respectively). The extract of A. indica and AgNPs elicited low cytotoxic effect with TC50 values of >100 and 89 μg mL1, respectively33. Combining a pyrethroid insecticide bifenthrin with AgNPs was more toxic to Lygus hesperus, however, bifenthrin-only mixture was more toxic than the bifenthrin+n-Ag mixture against Acheta domesticus under cotton filed condition28. The treated eggs did not hatch due to arrest of embryonic development. Essential oils from Zanthoxylum rhoifolium leaves-containing nanoparticles for control of Bemisia tabaci were developed by Christofoli et al.34 and reported that the a anospheres containing this essential oil exhibited encapsulation efficiency higher than 96%.
Chandra et al.29 confirmed that chitosan nanoparticle coated fungal metabolite (CNPCFM) showed higher pesticidal activity when compared with Uncoated Fungal Metabolite (UFM) and Fungal Spores (FS). Very recently, chitosan (CS)-g-poly (acrylic acid) PAA nanoparticles reduced egg laying of Aphis gossypii (20.9±9.1 and 28.9±9.2 eggs/female for laboratory and under semi-field conditions, respectively) than control (97.3±4.9 and 90.3±4.9 eggs/female for laboratory and under semi-field conditions, respectively35 (Table 1).
POST-HARVEST PESTS MANAGEMENT
Major post-harvest pests and their consequences: Two major groups of insects such as Coleoptera (beetles) and Lepidoptera (moths and butterflies) comprises the most economically important post-harvest insect pests. Several species of Coleoptera and Lepidoptera attack crops both in the field and in store. They cause physical damage, grain spilling or deterioration, loss of weight and quality, vigor loss, germination reduction, lose value for marketing and consumption or planting (http://www.fao.org/3/a-av013e.pdf). Fumigants and residual insecticides are commonly used to combat stored grain pests. In recent years, consumer awareness of the health hazard from residual toxicity and the growing problem of insect resistance to these conventional insecticides have led the researchers to look for alternative strategies for stored grains protection.
Sitophilus spp.: Stadler et al.6 for the first time studied the insecticidal activity of nanostructured alumina against two insect pests viz., Sitophilus oryzae (L.) (Coleoptera: Curculionidae) and Rhyzopertha dominica (F.) and reported significant mortality after 3 days of continuous exposure to nanostructured alumina-treated wheat. Nanostructured alumina was tested against S. oryzae L. and R. dominica and significant mortality after 3 days of continuous exposure to treated wheat was observed, whereas, nine days after treatment, the median Lethal Doses (LD50) ranged from 127-235 mg kg1 6. Furthermore, the nanoparticles of SiO2 show nearly 100% mortality against S. oryzae40. Entomotoxicity of Surface-functionalized silica nanoparticles (SNP) was tested against rice weevil S. oryzae and its efficacy was compared with bulk-sized silica (individual particles larger than 1 μm). Amorphous SNP was found to be highly effective against this insect pest causing more than 90% mortality, indicating the effectiveness of SNP to control insect pests41.
|Table 2:||Chemical and biological nanoparticles utilize for the management of post-harvest pests with citations|
Nanoparticles (Al2O3 and TiO2) proved their insecticidal activity against S. oryzae under laboratory conditions42.
Callosobruchus spp.: Magnetite octadecylsilane nanoparticles were synthesized and used for pest control43; the bioefficacy of β-cyfluthrin formulations synthesized poly (ethylene glycols) based amphiphilic copolymers were evaluated against Callosobruchus maculatus44. Results reveal that the formulations showed greater efficacy after 14 days as evident from EC50 value (1.58 mg L1) as compared to the control (EC50 value on the first day (0.51 mg L1). Silica nanoparticles (SNPs) with the pulse seeds of Cajanus cajan, Macrotyloma uniflorum, Vigna mungo, Vigna radiata, Cicer arietinum and Vigna unguiculata against the infestation of stored pulse beetle, Callosobruchus maculatus revealed a significant reduction in oviposition, adult emergence and seed damage potential45 (Table 2).
Tribolium spp.: Polyethylene glycol-coated nanoparticles loaded with garlic essential oil, against adult Tribolium castaneum (Herbst) demonstrated the insecticidal activity of the bionano polyethylene glycol-coated nanoparticles46. Similarly, Nano-Diatomaceous Earth (Nano-DE) in comparison with natural Diatomaceous Earth (DE) against Tribolium confusum (Jacquelin) and T. castaneum under laboratory and stored conditions caused increased larval mortality with increase of Nano-DE and DE. Larvae of T. confusum was more susceptible to the treatments than T. castaneum larvae. Nano-DE was more effective than natural-DE. The fecundity of tested insects was highly affected with both DE and nano-DE. Further, nano-DE strongly suppressed the number of deposited eggs by T. confusum more than T. castaneum (3.8±1.5, 17.8±7.5 and 26.6±3.5 eggs/female and (13.8±1.5, 37.8±7.5 and 46.6±3.5 eggs/female) after 20, 90 and 120 storage interval days, respectively. The persistent effect of nanoparticles displayed several different modes of action by reducing oviposition, adult emergence and infestation. The results showed that DE-nanoparticles can be used as a valuable tool in pest management programs of T. confusum and T. castaneum47. Yang et al.46 nanoparticles coated with garlic oil then combined with polyethylene glycol (PEG) using melt-dispersion method. This nanomaterial caused 100% mortality to T. castaneum after five months. It was mainly due to the slow and continuous release of the active components from nanoparticles. Dueing the same period control test materials caused only 11% mortality.
Sitophilus spp.: Green synthesis of AgNPs have been reported using Euphorbia prostrata and used to control the adult of S. oryzae48. Silver and lead nanoparticles synthesized utilizing mangrove plants extract of Avivennia marina showed pesticidal activity against S. oryzae and the results revealed that treatment caused 100% mortality within 4 days of treatment49. Nanomaterials can be beneficial in agricultural research and applications due to their size which is similar to that of most biological molecules so that, they can diffuse through cell membranes to act on the target. Silver nanoparticles (Ag NPs) were synthesized by using aqueous leaves extracts of Euphorbia prostrate showed insecticidal activity against adult of S. oryzae48. The LD50 values of aqueous extract, AgNO3 solution and synthesized Ag NPs were 213.32, 247.90 and 44.69 mg kg1; LD90 = 1648.08, 2675.13 and 168.28 mg kg1, respectively.
Callosobruchus spp.: Chitosan nanoparticles reduced egg laying of C. maculatus (10.9±9.9 and 19.9±9.9 eggs/female laboratory and under semi-storage conditions, respectively) than control (95.3±4.9 and 94.3±4.9 eggs/female laboratory and under semi-storage conditions, respectively)35. Similar kind of results was also recorded in C. chinensis (Table 2).
MERITS AND CONSEQUENCES OF CHEMCIAL AND BIONANOMATERIALS
Before introducing the ENPs in agriculture application particularly insect pest and phytopathogens management, there impacts on biological organisms dwelled water, or soil and also their possible harmful effects on living beings including human beings. Literature survey mainly emphasized the potential benefits of ENPs, although meager is known about the safety of nanomaterials or nanoparticles in agriculture sector. Considering the soil pollution, very recently it was reported50 that nanoparticles pollution in soil is still in the process of development.
Nanoparticles (multi-walled carbon nanotube, aluminum, alumina, zinc and zinc oxide) showed anti-germicidal activity except by nanoscale zinc (nano-Zn) on ryegrass and zinc oxide (nano-ZnO) on corn at 2000 mg L1 (Lin and Xing, 2007). They further reported that the suspensions of 2000 mg L1 51 nano-Zn or nano-ZnO practically terminated root elongation of the radish, rape, ryegrass, lettuce, corn and cucumber. Fifty percent Inhibitory Concentrations (IC50) of nano-Zn and nano-ZnO were estimated to be near 50 mg L1 for radish and about 20 mg L1 for rape and ryegrass.
The CuO nanoparticles significantly inhibited the growth and development, reduced the uptake of nutrients, such as B, Mo, Mn, Mg, Zn and Fe of both transgenic and conventional cottons. However, at low concentration of CuO NPs enhanced the expression of the Bt toxin protein of Bt-transgenic cotton52 is a desirable character of this chemical nanoparticles. Similarly, ZnO NPs particles adhere onto the root surface indicates the absorption, however, not transported from root to shoot53. Another study reveals that plants are being developing one or other mechanisms to resist or neutralize the accumulation of nanomaterials. For instance, the radial penetration of the metals such as Zn2+, Cu2+ or Ce4+ into the taproot and subsequent translocation to shoots of carrot (Daucus carota) were also generally greater for plants receiving the ionic treatment than those receiving the ENP like ZnO, CuO, or CeO2 NPs treatment resulted accumulation of Zn, Cu, or Ce in the taproot was restricted to the taproot periderm54 reveals no marked impact against the root crops. Armstrong et al.55 reported that silver nanoparticles (AgNPs), like almost all nanoparticles, are potentially toxic beyond a certain concentration because the survival of the organism is compromised due to scores of pathophysiological abnormalities past that concentration.
Considering the nominal impact as well as little benefits of chemical nanomaterials, it is essential to utilize biogenic nanomaterials for pest management. It was reported by Joy56 that in green synthesis we are using safer solvents and biomareial, hence it is safer than chemical synthesis. In addition, selection of more biocompatible metal is more important rather than synthesis or utilization. Freitas57 suggested utilizing very biocompatible gold, platinum and palladium than moderately biocompatible silver and not biocompatible single crystal silicon. Furthermore, many soil doweled microbes were utilized for the biomimitics of nanoparticles. For instance, 37 different bacterial soil isolates of Bacillus cereus and Escherichia fergusonii were used for biosynthesis of AgNPs58. Hence it is expected that biogenic nanoparticles does not harm against many soil-microorganism. Biogeneic nanoparticles were also safer to vertebrates. However, AgNPs synthesized using Malva crispa Linn. leaves extract showed oxidative stress and immunotoxicity in adult zebrafish (Danio rerio)59.
Functionality and charge (nature of the surface), size and portal of entry (lungs, intestinal or skin) of NPs place crucial role for entry of nanoparticles into the human body accordingly we select the particles. However, the mechanism of AgNPs toxicity remains undetermined. It is suggested to study the physical, chemical and biological properties, bio-encapuslation process, suitability of carriers and behaviors and also mechanism of single or multiple NPs or NPs with chemical or biological or natural materials with its surrounding environment like soil, water and organism inhabiting on them before recommending for agriculture purposes. Furthermore, formulation methods, handling and application technologies can also be devised for the better utilization of ENPs in agriculture sector. Moreover, compared to commercially available insecticides, chemical and biogenic nano-structured selected metals can provide a cheap and reliable alternative for control of insect pests and such studies may expand the frontiers for nanoparticle-based technologies in pest management.
I gratefully acknowledge the financial assistance of Ministry of Earth Sciences, New Delhi (ref. no. F.No. 14/23/2008-ERS/RE). I also thank the members of St. Xaviers College management for the laboratory facilities.