Ecophysiology of Pesticides: Interface between Pesticide Chemistry and Plant Physiology

By Talat Parween and Sumira Jan

Ecophysiology of Pesticides: Interface between Pesticide Chemistry and Plant Physiology is the first comprehensive overview of the physical impact of this increasingly complex environmental challenge. Designed to offer state-of-the-art knowledge, the book covers pesticide usage and its consequences on the ecophysiology of plants. It includes the challenge of policymaking in pesticide consumption and a risk analysis of conventional and modern approaches on standard usage. In addition, it summarizes research reports pertaining to the physio-ecological effects of pesticides, discusses the environmental risks associated with the over-utilization of pesticides, and covers pesticide usage on the micro-flora and rhizosphere.

This book is a valuable reference for plant ecologists, plant biochemists and chemists who want to study pesticide consumption and its biochemical and physiological evaluation effects on plants. It will also be of immense help to university and college teachers and students of environmental biotechnology, environmental botany and plant ecophysiology.

• Contains comprehensive coverage of topics on pesticides, environmental ecology and strategies for pesticide control
• Presents all data available on the intensification of pesticide stress on non-target organisms
• Includes an appendix of products containing active ingredients

• Language: English
• Publisher: Academic Press
• Release date: Jul 31, 2019
• ISBN: 9780128176153

Talat Parween

PhD with 4 Years of post-doctoral research experience. Selected for UGC Junior and Senior Research fellowships. Currently working on Pest management by integrated approach and indigenous technologies.

Book preview

Ecophysiology of Pesticides

Interface between Pesticide Chemistry and Plant Physiology

Talat Parween

Sumira Jan

Table of Contents

Cover image

Title page

Copyright

Dedication

About the authors

Preface

Acknowledgments

Chapter 1. Pesticides and environmental ecology

1.1. Introduction

1.2. Historical perspective and current position of pesticides

1.3. Classification of pesticides

1.4. Worldwide consumption of pesticides

1.5. Ecological effect of pesticides

1.6. Conclusion

Chapter 2. Pesticide consumption and threats to biodiversity

2.1. Introduction

2.2. Effects of pesticides on species richness

2.3. Pesticide effect on invasive species

2.4. Pesticide effect on genetic variability

2.5. Pesticide production and species extinction

2.6. Policy and method for conservation of biodiversity

2.7. Conclusion

Chapter 3. Nutrient depletion and pesticide use

3.1. Introduction

3.2. Effects of pesticides on nutrient cycling and mineralization

3.3. Effect of pesticide on soil and rhizosphere microflora population

3.4. Degradation of soil enzymes due to pesticide use

3.5. Conclusion

Chapter 4. Physiological impacts of pesticides on crop

4.1. Introduction

4.2. Physiological effects of pesticides in different plants

4.3. Uptake, metabolism, and persistence of pesticides

4.4. Physiological reaction and defense mechanism due to pesticide

4.5. Conclusion

Chapter 5. Pesticide consumption and risk assessment

5.1. Introduction

5.2. Ecological consequences of overutilization of pesticides

5.3. Environmental impact assessment

5.4. Pesticide risk assessment and management

5.5. Simulation model for monitoring pesticide toxicity

5.6. Conclusion

Chapter 6. Perceptive exploitation of pesticides: connecting link between pesticide consumption and agricultural sustainability

6.1. Introduction

6.2. Pesticide regulations and registration

6.3. International scenario

6.4. Pesticide production scenario

6.5. Pesticide consumption and distribution pattern

6.6. Challenges

6.7. Pesticide management and control strategies

6.8. Conclusions

Chapter 7. Ecological effect of pesticide on microbial communities and human health

7.1. Introduction

7.2. Pesticide and ecophysiology of microbes—an over view

7.3. Role of microbes in degradation of pesticide

7.4. Effect of pesticide on human health

7.5. Conclusion

Chapter 8. Strategies for preventing and controlling pesticide toxicity

8.1. Introduction

8.2. Amelioration of pesticide toxicity by phytohormones

8.3. Amelioration of pesticide toxicity by nanoparticles

8.4. New generation synthetic pesticide formulation technology

8.5. Biopesticides

8.6. Plant growth–promoting rhizobacteria

8.7. Conclusion

Index

Copyright

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Notices

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Dedication

This book is dedicated to the most inspiring person of my life, my Father.

Late MD Daud Ansari

(16.05.1943–21.07.2018)

About the authors

Dr. Talat Parween has completed her PhD (Bioscience) from Jamia Millia Islamia and MSc (Environmental Botany) from Jamia Hamdard, New Delhi (India). She has served the Institute of Pesticide Formulation Technology (Ministry of chemical and fertilizer), Gurugram (India), as Research Associate in the Department of Bioscience. Earlier, she worked at agrochemical industry, New Delhi, in Regulatory affair and Product development. She has produced more than 17 research articles, 3 reviews, 13 book chapters, and 1 book on important aspects of plant physiology, abiotic and biotic stress tolerance on nontarget species, and crop production. She is the member of Plant Protection Society and Entomology Society of India. Parween received fellowship from India for her doctoral research. She is the reviewers of several high impact international journals.

Dr. Sumira Jan has completed her PhD (Botany) from Jamia Hamdard. Presently, she is working as Tenure Track Scientist in the SKUAST in the Department of Basic Sciences and Humanities. She has several national and international fellowships. She was selected for the prestigious Fast Track Young Scientist Award in 2015 and the BioCaRe Early Career Scientist Award in 2014. She has more than 35 research articles, 12 review articles, and 22 book chapters. She has three books as first author, and her first book as a lead author was released in 2016.

Preface

Ecophysiology of pesticides is the basic and fundamental subject which focuses on the interaction of the environmental factors with the physiology of the pesticides. The ecophysiology of the pesticides provides the base for the most intricate studies such as metabolomics, transcriptomics, and proteomics. This book draws a lucid frame depicting the exact relationship between the external surrounding and internal metabolome of the organism. Ecophysiology of pesticides will reveal how the physiology of the organism gets affected by the indiscriminate use of the pesticides. During recent years, there has been an upward surge toward more advanced research subjects, thereby shifting the focus from basic to advanced approaches. This led to the huge gap in the understanding of the underlying mechanistic pathways of any physiological damage resulting from excessive exposure to pesticides. In this book, we will summarize developments and outline progresses made in the fundamental physiological research over the last decade from varied angles. Furthermore, we will recapitulate eco-physiological topics such as (1) pesticides and environmental ecology, (2) pesticide consumption and threats to biodiversity, (3) nutrient depletion and pesticide use, (4) physiological impacts of pesticides, (5) pesticide consumption: risks and policy, (6) perceptive exploitation of pesticides: connecting link between pesticide consumption and agricultural sustainability, (7) ecological effect of pesticide on microbial communities, and (8) strategies for preventing and controlling pesticide toxicity. The summarized version offers concise tool for connecting physiology of pesticides with the ecology of the organism. We have tried our best to endow with glimpse into wide field of ecophysiology but there is always possibility for more perfection. We will be delighted if students or readers/naturalists could add to our volume by inculcating their findings.

Dr. Talat Parween

Dr. Sumira Jan

Acknowledgments

We are thankful to our Universities and Research Institute SKUAST-K, Jamia Hamdard, Jamia Millia Islamia, and Institute of Pesticide Formulation Technology (IPFT), wherein we have been working on ecophysiology of plants under pesticide stress. We had chance to work on metabolite analysis in legumes and evaluate their nutritional status. We are thankful to reviewers and all the members of production team of Elsevier.

Chapter 1

Pesticides and environmental ecology

Abstract

Pesticides are used to kill the pests and insects that attack on crops and harm them. Pesticides of various kinds have been used for crop protection for centuries. The crops get benefit from the pesticide; however, indiscriminate use of pesticides may lead to the destruction of ecosystem and biodiversity. This chapter intends to discuss about evolution of pesticides from use of sulfur to DNA insecticide that is paid to the perspective of creating preparations based on nucleic acids, in particular DNA insecticides. Also, classifications based on the mode of entry, pesticide function and the pest organism they kill, and the chemical composition of the pesticide is discussed here. Meanwhile, the global consumption of pesticide was also discussed. Moving toward the end, the chapter discusses acute and chronic effect of pesticide on the environment.

Keywords

Acute; Agriculture; Chemical insecticides; Chronic; Crop protection; Ecosystem; Environment

1.1. Introduction

A pesticide is a toxic chemical substance or a mixture of substances or biological agents that are released by an anthropogenic activity into the environment to control and/or kill populations of insects, weeds, rodents, fungi, or other harmful pests (Eldridge, 2008). Pesticides work by attracting, seducing, and then destroying or mitigating the pests. Pests can be broadly defined as "the plants or animals that jeopardize our food, health and/or comfort" (Mahmood et al., 2016).

Human has learnt to use agriculture to supply the food needed for his own sustenance since Neolithic times. About 11,000 years ago, cereal crops started as first agricultural practices in the Fertile Crescent, and subsequently developed in other regions of the world (Bayo, 2011). To maximize crop yields, most of the staple plant foods have been grown as monocultures, which is an unusual ecosystems in which no diversity of plants other than the crop is allowed to grow on the same land and where all means possible are used to ensure this is the case; the unwanted competing plants are called weeds. Because of this feature, monocultures are ideal targets for specialized consumer animals (usually insects, birds, and rodents) that feed on them. Once such animals find a crop that suits them, they multiply explosively and become pests. With the exception, perhaps, of locust plagues, all other agricultural pests are a product of monocultures, and from early times, humanity has struggled to keep at bay the pest species that decimated our crops.

After World War II, chemical pesticides have become the most important consciously applied form of pest management. People engaged in agricultural practices usually face a harvest management problem due to loss caused by a variety of insect pests. It may be impossible to say who decided to apply insecticides first, but apparently it happened a very long time ago. It could have been a farmer who thought about protecting his crops from pest insects. In any case, the very first control means, for controlling pest insects, were prompted by nature itself. People noticed the negative effects of natural compounds on various insects and used the natural compounds in everyday life.

Currently 835 chemical compounds used in all sorts of agricultural enterprises are reported (Tomlin CDS, 2002), comprising some 1300 registered products, of which 31% are herbicides, 21% insecticides, 17% fungicides, 9% acaricides, and 2% rodenticides; the remaining 20% of products include a plethora of biocides for control of snails (molluscicides), algae (algicides), and nematodes (nematicides) as well as plant growth regulators (6%) and natural or artificial pheromones (5%). Additionally, there are 610 products, including most of the less-utilized organochlorine (OC) insecticides, which were used in the past but not nowadays—they were banned for safety and environmental reasons or because they were no longer efficient (due to resistance) and have been replaced by newer products. Despite using so many chemicals, world crop losses are estimated at 37% of agricultural productivity: 13% due to insects, 12% to weeds, and 12% to diseases (Pimental et al, 1991).

The toxicity and specificity of pesticides depends on the mode of action of the active ingredients (a.i), whereas the effects on organisms depend on the dose they are exposed. Thus, organochlorine, cholinesterase inhibitors (organophosphates (OP) and carbamates), synthetic pyrethroid and neonicotinoid insecticides are neurotoxic substances that disrupt the nervous system of arthropods and other animals. Given the similarities in neuronal physiology among all kinds of animals, it is not surprising that insecticides are also toxic to aquatic and terrestrial arthropods and, to a lesser extent, vertebrates, whereas they are harmless to plants and the majority of microbial organisms. Other insecticides affect cellular or physiological mechanisms of animals (e.g., chlorfenapyr, arsenic salts). Weedicides are very toxic to plants and algae, as they target physiological pathways specific to plants such as the photosynthesis; however, some herbicides can also interfere with metabolic and reproductive processes in animals, often in ways that are unrelated to their specific mode of action in plants. Fungicides are considered in some countries to be the medicine for the crops as they control fungal infections of the roots or other parts of the plant; many of them are antibiotics or metabolic inhibitors of certain fungi, while organomercurial compounds are neurotoxic and poisonous to many animals. Rodenticide poisons are usually anticoagulants, and therefore are very dangerous to humans and all vertebrates alike. Thus, the specificity of action of pesticides is not restricted to the target pest or weed species, but it is rather general, affecting large taxonomic groups often at the order or class level, even though within the same class of organisms some species are more susceptible than others due to differences in body size and/or physiological traits (Baird and Brink, 2007).

The pesticide application reduces the risk of the environmental damages via eradication of invasive weeds in parks and wilderness and prevented the high algal growth in the ponds and the lakes. Despite the above benefits, there is some concern about the adverse ecological effects of pesticides ranging from fish and wildlife kills to forest decline; ecological effects can be long-term or short-lived changes in the normal functioning of an ecosystem, resulting in economic, social, and aesthetic losses. A number of pesticides can persist in the environment for a long period and are bioaccumulative and toxic (persistent, bioaccumulative, and toxic substances or PBT). DDT, endosulfan, and chlordane have a high potential to bioaccumulate in biota (log Kow >4). All pesticides are toxic to some forms of life. Organophosphorous and carbamate pesticides are usually more toxic to invertebrates than fish, but their toxicity varies from one species to another. Synthetic pyrethroids are generally low toxic to mammals and birds, but they are highly toxic to fish and invertebrates. Many herbicides have low toxicity to fish and invertebrates. A number of pesticides are also known as endocrine disruptors such as 2, 4-D, atrazine, chlorpyrifos, DDT and its metabolites, diuron, endosulfan, simazine, etc, for example, DDT caused sex reversal in Japanese medaka fish, Oryzias latipes (Kibria, 2016). These potential effects are an important reason for regulation of pesticides, toxic substances, and other sources of pollution.

This chapter intends to discuss about evolution of pesticides from use of sulfur to DNA insecticide. Also, classifications based on the mode of entry, pesticide function and the pest organism they kill, and the chemical composition of the pesticide are discussed here. Varieties and consumption of pesticides worldwide have been increasing dramatically as a result of increased human population and crop production. In this process, pesticide misuses become more and more serious, which has resulted in heavy environmental pollution and health risk of humans. So, the global consumption of pesticide was also discussed. This chapter also focuses on the ecological effect of pesticides with special emphasis on acute and chronic effect of pesticide on environment.

1.2. Historical perspective and current position of pesticides

People engaged in agricultural practices usually face a harvest management problem due to loss caused by a variety of insect pests. It may be impossible to say who decided to apply insecticides first, but apparently it happened a very long time ago. It could have been a farmer who thought about protecting his crops from pest insects. In any case, the very first control means, for controlling pest insects, were prompted by nature itself. People noticed the negative effects of natural compounds on various insects and used the natural compounds in everyday life.

1.2.1. Evolution of plant protection from ancient sulfur to synthetic and DNA insecticides

Ancient people used natural chemicals against pest insects since 1000 BC. One of these natural chemicals used were inorganic sulfur (via fumigation). "The Iliad and The Odyssey was written by Homer about the divine cleansing" ritual using sulfur that helped to get rid of lice. Arsenics began to be used in 900s AD, later lead arsenate (PbHASO4) and cryolite (Na3AlF6) as cellular poisons, and borax (Na2B4O7) as a dehydrator, were used in insect baits (Oberemok et al., 2015a,b; Popov et al., 2003).

Earlier botanical preparations were used as insecticides, for example, up to 1.5% of pyrethrin extracted from Dalmatian pyrethrum flowers that were used as active insecticidal substance. This ingredient was used as an insecticide in ancient China and Middle Ages in Persia (Davies et al., 2007). Other form of dried and grounded Dalmatian pyrethrum were used in Europe against cockroaches, bedbugs, flies, and mosquitoes, which were sold as Persian powder (Persian dust, insect powder) by an Armenian merchants (Davies et al., 2007). In the middle of the 19th century, plant protection chemicals started to be used in a wider range. Paris green (mixed copper acetoarsenite) was successfully applied in 1871 against the pest Colorado potato beetle (Alyokhin, 2009). Paris green was widely used in many countries around the world until the middle of the 20th century, in particular for the control of the malaria vectors, mosquitoes of the genus Anopheles (Majori, 2012).

Othmar Zeidler, a chemist, synthesized DDT in 1874, while working in J. R. Geigy Ltd. Swiss chemist Paul Muller discovered its insecticidal properties in 1939. In 1948, he won the Nobel Prize in Medicine for the discovery of the high efficiency of DDT as a contact poison.

Until the second half of 20th century, the era of DDT was replaced by widespread use of organophosphates (dichlorvos, cyanophos, fonofos, etc.) and carbamates (carbaryl, carbofuran, aldicarb, etc.). Despite harming the environment with carbamates and organophosphates, these insecticides are still among the most widely used classes of preparations (19% of the world market) and play a major role in the control of pest insects (Casida and Durkin, 2013). It should be noted that production of carbaryl is connected to the biggest man-made disaster that has ever happened in the world. The disaster took place in Bhopal (India), in 1984. An explosion at the Union Carbide Corporation plant released toxic methyl isocyanate that killed about 3800 people the first day (Broughton, 2005).

Pyrethrins were restored as insecticides after allethrin was synthesized in 1949 because of having low toxicity to those who were warm-blooded. Synthetic insecticides such as permethrin, cypermethrin, and deltamethrin had a serious drawback in the early 1970s that they quickly lost activity in contact with ultraviolet light. Currently, pyrethroids constitute 17% of the global insecticide market (Davies et al., 2007). Today the most popular insecticides are neonicotinoids (Goulson, 2013). They act by systematically moving in the plant tissues and protecting all parts of the plant. Acting as neurotoxins for most arthropods, they provide effective control of insect pests (Goulson, 2013). Neonicotinoids irreversibly bind the nicotinic acetylcholine receptors (nAChRs) to produce overstimulation of nerve cells, which paralyses the insect. The very first neonicotinoid that appeared on the insecticide market was imidacloprid. It was registered as Hachikusan in Japan in 1993. Imidacloprid is now the most frequently used insecticide in the world (Jeschke et al., 2011). It is now possible to find a large number of represented neonicotinoids, such as acetamiprid, thiamethoxam, dinotefuran, and thiacloprid. In 2008, the neonicotinoids comprised 24% of the global insecticide market (Jeschke et al., 2011).

In the recent years, search for new insecticides and the improvement of old ones still continues. Almost all species of insects develop resistance to applied insecticides. A lot of new chemical insecticides are now coming into the market. Examples of such insecticides are phenyl pyrazoles, pyrethroids of fourth generation, avermectins, diamides, and spinosyns, and there are also insect growth regulators (IGRs), pyrazole insecticides, macrocyclic lactone insecticides, formamidine insecticides (amitraz), botanical insecticides (e.g., azadirachtin), etc. The onset of the postgenomic period of plant protection led to the emergence of new opportunities to create new preparations. For example, baculoviruses are being genetically modified to accelerate their action on insect pests (Rosell et al., 2008). Recombinant (Federici et al., 2010) and more efficient serotypes of entomopathogenic bacteria are being created. Genetically modified plants synthesizing bacterial toxins (cry proteins) within the plant cell are being produced (Sanchis, 2011).

The newest insecticides can be grouped into the following classes:

1.2.1.1. Macrocyclic lactones (avermectins and milbemycins)

Natural and semisynthetic 16-membered macrocyclic lactones belong to this group (Khalil, 2013). They hinder the flow of chloride ions, thereby affecting the cellular activity. This process shuts down the electrical impulses in the nerve cells of their target organisms. The naturally occurring novel macrocyclic lactones are avermectins, emamectin benzoate, and milbemycin. The whole family of macrocyclic lactones displays an unprecedented potency against mites and insects as well as nematodes. Avermectin is used on various crops such as citrus, pome fruits (for example, apples and pears), vegetables, and cotton. The products are nonsystemic and are removed relatively rapidly from the environment after application. In human organism, avermectin has been reported to block LPS-induced secretion of the tumor necrosis factor, nitric oxide, prostaglandin E2, and also an increase of intracellular concentration of calcium ions (Viktorov and Yurkiv, 2003).

1.2.1.2. Phenylpyrazoles

A familiar member of this class of insecticides is fipronil. Fipronil can be applied to the foliage, soil, and seeds. Fipronil is a broad-spectrum insecticide that disrupts an insect's central nervous system by blocking GABA-gated (γ-aminobutyric acid) chloride channels and glutamate-gated chloride (GluCl) channels, resulting in central nervous system toxicity. However, it has a limited ability to translocate through the plant. Fipronil acts on insect pest species such as the Lepidoptera (moths), Coleoptera (beetles), and Diptera (flies, mosquitoes). Fipronil is used to control different species of subterranean termite. It might be proved very beneficial for the control of urban pests such as ants and cockroaches. It is effectively used in animal health care for controlling ticks and fleas of cats and dogs. On the other hand, the widely used fipronil is known to be highly toxic to marine fish, aquatic invertebrates, and bees (Oberemok et al., 2015b).

1.2.1.3. Nereistoxin analog

Research has been carried out in finding some potential chemicals, which will inhibit the nAChR from functioning correctly. Insecticides such as cartap, thiosultap, bensultap, and thiocyclam are the first example for this purpose. They are sensitive and break down either by action of water or light to produce the toxin that is called nereistoxin. It is a substance that was first isolated from the naturally occurring marine nereid worm Lumbrineris heteropoda. Nereistoxin acts efficiently by paralyzing the insect pest through contact route (Oberemok et al., 2015b).

1.2.1.4. Neonicotinoids

Another group of insecticides that affects the nAChR is neonicotinoids. They are now the fastest growing group of insecticides and one of the major classes of insecticides in insect pest management. They are active against a broad range of insect pests and exhibit activity through both oral (ingestion) and contact routes of application. They have a high level of efficacy and a favorable environmental and toxicological profile. This has led to their rapid adoption in numerous agricultural areas for quick control of a broad range of chewing and sucking pests. Neonicotinoids are said to have a minimum impact on beneficial insects. This group of insecticides acts on and overstimulate the insect's central nervous system (Gordana and Janko, 2013). Imidacloprid, thiamethoxam, clothianidin, thiacloprid, and acetamiprid are the best examples of neonicotinoids.

1.2.1.5. Diamides

Diamides are new class of insecticides. The best examples are phthalic acid diamides and the anthranilic diamides (chlorantraniliprole). They potently activate the ryanodine receptor, releasing stored calcium from the sarcoendoplasmic reticulum causing impaired regulation of muscle contraction (Qi et al., 2013). Flubendiamide is a very good example of a phthalic acid diamide where as chlorantraniliprole is an example of anthranilic diamide. It is marketed under several trade names, one of which is Rynaxypyr. Diamides are very effective for protecting fruit and vegetables from various insect pests: beetles, weevils, leaf miners, and caterpillars. They act on the ryanodine receptors of vertebrates very weakly, most probably explaining their excellent toxicological profile, being specific to the insect pests and relatively nontoxic to mammals, fish, and birds (Oberemok et al., 2015b).

1.2.1.6. Benzoylureas

Benzoylureas have been developed and used as commercial IGRs that acts by inhibiting the biosynthesis of chitin (Msangi et al., 2011). The first of this class to be used commercially was diflubenzuron. It is used for the control of chewing insects and coleopteran pests (beetles and weevils) in fruit, cotton, soybeans, and vegetable crops. Benzoylureas, such as lufenuron and triflumuron, due to their relative nontoxic nature to vertebrates, are used in veterinary medicine and in the home against animal and human health pests such as fleas, ticks, and cockroaches. It is important to note that benzoylureas possess a high potential for bioaccumulation in the food chain and are a high risk to aquatic organisms (Oberemok et al., 2015b).

1.2.1.7. Cyclic ketoenols

They are a new chemical class of insecticides that acts by inhibiting acetyl-CoA-carboxylase and subsequent lipid biosynthesis (Nojumian et al., 2015). An example of this class is spirodiclofen that has excellent long-lasting efficacy. Spirodiclofen is effective in early-to-late season applications for mite/insect control. Spirodiclofen is being developed for worldwide use in pome fruit (e.g., apples, pears), stone fruit, citrus fruit, grapes, almonds, and nuts, being very effective against mites.

Spiromesifen is a new foliar contact acaricide and has been used worldwide on vegetables, fruits, cotton, corn, beans, tea, and some ornamentals. Chemical insecticides were largely influenced by the development of chemistry. In addition to chemical insecticides, biological preparations have been in use as well. Louis Pasteur and Ilya Metchnikov were the first to use microbiological preparations in insect pest control in the 1870s (Sanchis, 2011). In practice, the most commonly used biological preparations are of bacterial, viral, and fungal origin.

1.2.1.8. Bacterial agents

Among the bacterial agents, an important role is played by the Gram-positive, ubiquitous, spore-forming soil bacterium Bacillus thuringiensis. It was first discovered in 1901 by Ishiwata in Japan. Later, it was officially described by Berliner in 1915, isolated from Mediterranean flour moth in province of Thuringia in 1911. The parabasal body (known as the crystal) is proteinaceous in nature and possesses insecticidal properties. The parasporal body comprises of crystals and is tightly packed with proteins called protoxins or endotoxins (cry proteins) that are being used against different groups of insect pests. Cry proteins have a high specificity in their action on the target insects (Lepidoptera, Diptera, Coleoptera, Hymenoptera), whereas they are harmless to vertebrates and other insects (De Maagd et al., 2001). In today's market, there are a lot of insecticide-like preparations based on B. thuringiensis var. kurstaki, namely Dipel, Javelin. Thuricide, Worm Attack, Halt, Caterpillar Killer, B. thuringiensis var. aizawai, Certan, B. thuringiensis var. israelensis, Vectobac, Teknar, Bactimos, Skeetal, Mosquito attack, B. thuringiensis var. san deigo M-one. These products, based on B. thuringiensis, constitute 75% of the market of biological preparations and 4% of all insecticides (Sanchis, 2011). It must be sprayed when caterpillars are still small and completely cover all leaf surfaces. The insects must ingest the bacteria when they are feeding. Spray should be done in the evening or during cloudy (but not rainy days). There may be a need to reapply if it rains soon after application. As far as bacterial preparations are concerned, the more complex the structure of the insecticidal agent, the more selective it is in action and the more expensive it is to produce. Viral preparations are not an exception to this rule.

1.2.1.9. Viral agents

They are insect-specific viruses that can be highly effective natural controls of several caterpillar pests. Almost all registered viral preparations that are used to protect plants are based on baculoviruses (Bahvalov, 2001; Szewczyk et al., 2006). Baculoviruses have rod-shaped DNA viruses. It is pathogenic for Lepidoptera (83%), Hymenoptera (10%), and Diptera (4%). Baculoviruses started to be used widely as insecticides after the application of the nuclear polyhedrosis virus against alfalfa caterpillars by the American microbiologist Edward Steinhaus, in 1945 (Tarasevich, 1985). Subsequently, viral preparations have proven to be expensive and selective, acting effectively but slowly (Rosell et al., 2008). The slow action of baculoviruses is associated with a latent period in the life cycle of the virus when it has to look around in the cell. Baculoviruses are represented by two phenotypes, namely the budded virus and the occlusion-derived virus. The budded virus transmits viral infection from cell to cell, whereas the occlusion-derived virus transmits infection from insect to insect (Jehle et al., 2006). The process of polyhedral formation continues until the cell nucleus is completely filled with them; as a consequence, one larva may contain around 1010 polyhedra, representing more than 30% of the dried biomass of the insect (Miller et al., 1983). Viral polyhedral are composed of virions embedded in a matrix of the polyhedrin protein, which is highly resistant to various environmental factors (Chiu et al., 2012). Baculoviral preparations are made based on viral polyhedra to cause oral infection of phytophagous insects. The use of baculoviral preparations lag significantly behind that of preparations based on B. thuringiensis (Moscardi et al., 2011).

Granulosis viruses are developing in the nucleus/cytoplasm/tracheal matrix/epithelial cells of host. The virions are occluded singly in small inclusion bodies called capsules. It has rod-shaped virion and disc-shaped DNA. The oval occlusion bodies measures about 200   ×   400   nm. They enter the host cell through the process of ingestion. The diseased larvae are less active, flaccid, fragile, wilted prone to rupture in later stages, and ultimately dead in 6–20 days.

1.2.1.10. Fungal agents

Nowadays, fungi are not often used as insecticides, compared with other chemical pesticides, due to the fact that fungal agents are slow in action and rather inconsistent in use. They have the advantage of being cheap and of having little adverse effect on the environment as compared with some chemical insecticides. In recent years, crop protection management has also looked into integrated pest management (IPM) through the use of fungi. Approximately 750 species of fungi are pathogenic to insects. Generally, those fungi used as an insecticide include Beauveria bassiana, Metarhizium anisopliae, Nomuraea rileyi, Verticillium lecanii, Lagenidium giganteum, and Hirsutella thompsonii (Chakoosari, 2013).

1.2.1.11. DNA insecticides

This type of insecticide is an entirely new approach, which is now used to control insect pests. One of them is the conception of insecticides based on nucleic acids. In particular, there are the DNA insecticides based on short single-stranded fragments of antiapoptotic (IAP) genes of nuclear polyhedrosis viruses (Oberemok, 2011; Oberemok et al., 2013a,b; Oberemok and Skorokhod, 2014; Oberemok and Nyadar, 2015; Oberemok et al., 2015a,b) and formulations based on long double-stranded RNA fragments (Wang et al., 2011; Gu and Knipple, 2013). The idea of the development and application of such preparations is similar to methods of blocking the expression of genes important for life using the mechanisms of RNA interference (RNAi) (Wang et al., 2011). The first practical results in this direction show the potential of the insecticidal preparations based on nucleic acids. It was Oberemok and Skorokhod (2014) who showed that the insecticidal potential of the viral DNA fragments can be used to create safe, relatively inexpensive, and fast-acting DNA insecticides to control the quantity of gypsy moth populations. The gypsy moth is a serious pest of agriculture and forestry. Gypsy moth populations are controlled by Lymantria dispar multicapsid nuclear polyhedrosis virus (LdMNPV), in nature (Oberemok, 2008). Their results show that DNA insecticides based on DNA fragments of the antiapoptosis gene of LdMNPV can be selective in action and are not harmful to the tobacco hornworm (Manduca sexta [Linnaeus]) and black cutworm (Agrotis ipsilon [Hufnagel]). The perspective of such an approach in practice is clearly seen because it provides the same effect with less effort. For example, instead of the expensive baculovirus preparation based on LdMNPV, it is possible to use small parts of the viral genome and get the same effect. Also, it was recently found by Oberemok et al. (2015a,b) that treating baculovirus-infected gypsy moth caterpillars with sense and antisense DNA oligonucleotides of vIAP gene significantly increased insect mortality. Such treatments eventually lead to a more effective use of baculoviral preparations. The data of this work indicate that specific DNA oligonucleotides may interfere with expression of vIAP gene(s) to induce apoptosis in infected insects.

It is very essential to show that DNA insecticides will be safe for the ecosystem and environment. The scientific literature discusses how the potential hazards posed by RNAi-based pesticides and genetically modified