India is one of the world’s largest agricultural countries, with more than 60% of the population employed in agriculture and related activities. Agriculture in India contributes an 18.6% share of the national GDP. India produces almost all crops, including cereals, vegetables and cash crops
(Vanitha et al., 2013; APEDA, 2020). Numerous horticultural products are exported to other countries, generating significant amounts of foreign exchange. These products include fruits, vegetables and flowers. Vegetables play a significant role in horticulture and are grown throughout the country, with key crops such as brinjal, tomato, chili, okra and cucurbits (
National Horticulture Board, 2018). Vegetables are critical sources of protein, vitamins, minerals, dietary fiber, micronutrients and antioxidants in our daily diets. They provide nutrition and also contain a variety of phytochemicals, such as flavonoids, glucosinolates and isothiocyanates, that aid in the prevention and treatment of various diseases. While vegetable output and productivity have increased, cultivation of these crops is constrained by a variety of factors, including insect pests, diseases and other biotic and abiotic factors. Among them, insect pests attack vegetables at various stages of growth, resulting in significant reductions in production and quality
(Sharma et al., 2017). They can cause variable damage to plants in protected structures such as net houses, polyhouses and glasshouses, as well as in open fields
(Rai et al., 2014). The majority of insects and mites attack tropical crops such as brinjal, tomatoes, chilies, okra and cucurbits. Aphids, red spider mites, jassids and whiteflies are major pests that can cause damage at various stages of growth. aphids, jassids, whiteflies, fruit and shoot borers, Hadda beetles and mealy bugs are all examples of these pests. While a variety of pest management techniques are available, chemical pesticides are the most frequently used, particularly during the post-green revolution years. Nonetheless, the widespread and unregulated use of chemical pesticides has resulted in a slew of issues, including chemical residues in finished goods, adverse effects on human and animal health and negative environmental consequences. On the other hand, several research findings indicate that the majority of insect pests have evolved resistance to commonly used pesticides. Pests are also making a comeback in several regions of the country. Researchers and farmers have been examining alternative or corrective pest management techniques in order to achieve sustainable crop protection, production and environmental safety.
Finally, biological control has gained widespread acceptance as an environmentally responsible alternative to synthetic pesticides for managing insect pests in crops. Living organisms and their products are used to keep pests below the economic threshold level (ETL), while also protecting natural enemies
(Altieri et al., 2005; Mahr et al., 2008).
Significant advances in biological control of insect pests have occurred in recent decades and over the last 50 years, biological control has remained a critical component of integrated pest management, demonstrating slow but hopeful progress in Integrated Pest Management (IPM) (
Orr, 2009). The following paragraphs discuss the pests that attack the major tropical vegetable crops and their biological control measures.
Pests of major tropical vegetable crops in india and the extent of their damage
Vegetable crops are subjected to a wide range of insect pests and these are the primary impediments to vegetable production, both on and off the field. Insects cause a variety of injuries depending on their feeding patterns (Table 1). Apart from direct injury, they serve as a vector for a variety of viral infections in persistent (Tomato Yellow Leaf Curl Virus transmitted by the whitefly), semi-persistent (Cucumber Mosaic Virus by aphids) and non-persistent modes (Potato Virus Y by aphids)
(Rai et al., 2014). Numerous studies conducted at various stages of crop development predicted crop losses of 30%-40%.
(Rai et al., 2014). The primary factors that contribute to pest outbreaks and epidemics are changes in production strategies such as intensive monoculture, the introduction of high-yielding but vulnerable varieties and hybrids and the increased inputs required under varying climatic conditions. Due to seasonal changes and favourable environmental conditions, minor pests have become a significant problem in some instances
(Vanitha et al., 2013; Rai et al., 2014). This has a direct economic impact, as India exports fresh fruits and vegetables to a large number of trading nations. Vegetable exports account for approximately 16.27 per cent of foreign earnings
(Shivalingaswamy et al., 2006). Shoot and fruit borers are the primary pests to vegetable crops. They cause undesirable symptoms such as wilted terminal shoots, boreholes in the stem and excreta-filled fruits.
The brinjal fruit and shoot borer, scientifically known as
Leucinodes arbonalis, is recognised as a significant pest in agriculture. This species is classified under the family Crambidae and is notable for its highly destructive behaviour in brinjal cultivation regions. Consequently, it is recognized as a significant pest of brinjal crops. The larvae exhibit a behaviour of penetrating the stem shortly after the seedlings are transplanted. As they progress in their development, they proceed to penetrate the fruits and consume them, resulting in detrimental effects on the plant. This not only diminishes the market worth of the fruits but can also render them unsuitable for harvesting, particularly in severe instances (
Raina and Yadav, 2018;
Nishad et al., 2019). The number 17 is a positive integer that falls between 16 and 18 on the number line. The infestation of pests has posed a significant challenge to the cultivation of brinjal across India, leading to substantial crop losses. Various studies have reported crop losses ranging from 20% to 80%
(Raju et al., 2007), 85% to 90% (
Misra, 2008) and 70% to 92% (
Chakraborti and Sarkar, 2011) during different seasons of the year. Farmers rely heavily on consistent and planned applications of chemical-based insecticides to effectively control pests.
Additionally, they result in the shedding of floral buds and the drying of leaves. Sap sucking insects such as leaf hoppers and aphids suck the plant sap, causing the foliage to wilt, crinkle, curl downward and die. Nymphs and adults are the most destructive stages
(Shivalingaswamy et al., 2002). Additionally, ants can cause damage to plants. They are indirect pests that cause damage to plants by cutting leaves to cultivate fungus gardens and also transport honeydew-producing homopteran insects between plants. This is a mutualistic relationship in which the homopterans benefit from increased opportunities to feed on a variety of plants and the ants benefit from the honeydew. Eco-friendly pest management strategies have gained prominence and significance in India following the World Trade Organization’s (WTO) signing of the general agreement on trade and tariffs (GATT). Biological control measures are being integrated with other control methods to maximize effectiveness over a range of time periods and environmental conditions.
India’s need for biological pest management
Vegetable production is expected to reach 188.91 million tonnes in final estimates, up from 183.17 million tonnes in 2018-19 (
Agriculture Post, 2021). This is critical in order to meet the country’s growing food demand. Apart from superior farming and crop output, farmers frequently confront a number of challenges, including an excessive reliance on inputs, particularly chemical fertilizers and nutrients, in order to obtain desired outcomes and management of numerous insect pests and illnesses. This has resulted in high cultivation and investment costs, which are reflected in the returns. On the other hand, chemical pesticides and fertilizers have contaminated the environment and harmed human and animal life. This has resulted in significant improvements in farmers’ attitudes toward and use of pesticides. Biological control is one such strategy, in which a variety of biocontrol agents are utilized to successfully manage pests in IPM. There is no deliberate introduction or manipulation of beneficial bacteria or insects for the goal of biological control. The most promising control chemicals are repeatedly evaluated against a target pest, followed by mass manufacture and commercial release under a controlled scenario
(Hodek et al., 2012).
Management of insect and mite pests using biological control agents
In India, the majority of plant protection measures are entirely reliant on chemical pesticides. Farmers apply pesticides on a calendar-based schedule. Given the high value of vegetable crops, even a little infestation can result in a loss of quality and reduced yields. As a result, farmers are regularly spraying pesticides, even if the chemical is below the ETL. This has become into a routine activity for vegetable growers throughout the years. Without being observed, natural flora and animals are being harmed, as well as economically valuable insects such as predators, parasitoids and bees. Farmers must therefore utilize organic management measures to save these beneficial insects while also protecting the environment
(Altieri et al., 2005; Mahr et al., 2008; Halder et al., 2011). In recent decades, continuous progress has been made in India’s biological management of insect pests. However, it must be supplemented with an increasing number of natural enemies and microbial biocontrol agents in order to manage insect pests successfully, starting with laboratory research, mass production and release in vegetable crops for a specific pest.
Predators
Predators are beneficial insects and other vertebrate animals that hunt and consume pests directly. Ladybugs (ladybird beetles) (Fig 1 A, B), preying mantids, green lacewings (Fig 1 C, D), carabid beetles, rover beetles, hoverflies, minute pirate bugs, mirid bugs, big-eyed bugs, arachnids such as spiders and predatory mites are all examples of general predatory insects. Most ladybird species are considered beneficial because they are predators of Homoptera or Acarina, many of which are pests. These predatory ladybirds help to regulate the populations of their prey and, in some cases, provide a high amount of control. People may benefit when ladybirds naturally offer a high degree of pest management, or when combined with other predators, parasitoids and diseases to provide a significant amount of pest population management. That is, gardeners, growers and farmers may benefit for free as they have no or little pest concerns. The adults and larvae of ladybug beetles consume a variety of tiny, soft-bodied insects, as well as their eggs and larvae. The majority of these predators are generalists who prey on a variety of pests, including phytophagous insects and mites. Predators typically have either chewing or sucking mouth parts and some predators have both
(Sampaio et al., 2009). Only select insect orders have predatory insects. For example, dragonflies belong to the order Odonata; aquatic nymphs are predatory and breathe through their gills, whereas adults are powerful flyers. They can capture prey while flying over gardens and agricultural fields. Another order is Mantodea, which contains carnivorous mantids. They are exceptional hunters, concealing themselves on leaves and plant surfaces to deceive their prey. They have strong front legs that are well-adapted for catching prey. Similarly, Neuroptera contains green lacewings and antlions, whose larvae feed on insects and adults on pollen and nectar
(Sampaio et al., 2009). Order rover flies are a suborder of Diptera that employ the same tactics as dragonflies to grasp their victim. Coleoptera includes ladybugs, which are exceptional predators belonging to the Coccinellidae family. Numerous mites belonging to the family Phytoseidae have also been observed to exhibit predatory behaviour towards other phytophagous mites.
Several natural predators can be introduced to control mealybug infestations, including the green lacewing, parasitoid wasps and the beetle known as the “mealybug destroyer”. These natural predators are more commonly used for outdoor infestations or in greenhouses (
The Spruce, 2021).
Several studies have highlighted the effectiveness of various biological agents in controlling aphid infestations. One study conducted by
Hodek et al., (2012) emphasized the role of ladybugs (Coccinellidae) as efficient predators of aphids. Ladybugs are known for their voracious appetite for aphids and their introduction into aphid-infested crops has been shown to significantly reduce aphid populations
(Hodek et al., 2012). Thrips are a major pest for many crops worldwide and their control is often hindered by their thigmotactic habits, which make it difficult to apply chemical control methods. Biological control agents, such as predatory insects and mites, have been suggested as an eco-friendly approach to manage thrips pests. One such predator is the banded thrips
Aeolothrips intermedius, whose larvae are considered the primary native predator of the onion thrips
Thrips tabaci (Abenaim et al., 2022). Another potential predator is the minute pirate bug
Orius insidiosus, which has been shown to be an effective control agent for thrips
(Silva et al., 2023). In addition, the predatory mite
Amblyseius swirskii and the pirate bug
Orius laevigatus have been used against the western flower thrips
Frankliniella occidentalis in greenhouse conditions
(Botond et al., 2020).
Parasitoids
Parasitoids are living organisms that live on or inside their hosts and feed on them. These parasites can thrive both within and outside the body of an insect. The parasites feed only on the immature stage of the insect host. Adult females of several parasites (for example, many hymenopteran wasps that prey on scale insects and whiteflies) feed on and provide a simple biological control supply for their hosts (
Sanda and Sunusi, 2014). They are classified according to their prey stage, which is attacked by a parasite, into egg parasitoids, which develop fully inside the egg of another insect. Egg-larval parasitoids are those that oviposit inside their host’s egg but complete their metamorphosis in the host larvae. Additionally, parasitoids are classified as larval, pupal and larvae-pupae. In some instances, the parasitoid uses the insect’s adult stage as a host (ectoparasitoid)
(Sampaio et al., 2009). When a parasitoid develops on the host, it is called an ectoparasitoid (Fig 2 A); when it develops within the host, it is called an endoparasitoid (Fig 2 B).
Diptera (flies) and Hymenoptera (wasps) account for the vast majority of parasitic insects. More than a dozen Hymenoptera families contain wasps that are parasitic on other wasps. Aphidiinae (a subfamily of Braconidae) are aphid predators that feed on aphids, which are a pest in many crops. Trichogrammatidae is another family that parasitizes eggs. Aphilinidae, Encyrtidae, Eulophidae and Ichneumonidae are some of the other parasitoid families (
Flint and Dreistadt, 1998). In India, 37 parasitoid species have been discovered on
Helicoverpa armigera, although only eight are deemed significant.
Trichogramma spp
. (Fig 2 C) was observed with an egg parasitism rate of 80% on tomato plants infested with
Neoleucinodes elegantalis (Fragoso
et al., 2019). The adult female wasp lays eggs in each aphid host; the eggs hatch into larvae that feed on and kill aphids. Aphids that have been parasitized will die and become mummies. Among the caterpillar parasites is the
Hyposoter exiguae wasp (Fig 2 D), which lays eggs on armyworms and consumes the insect host. Tachinid flies are parasitic flies that feed on a number of different insects. They lay their eggs on caterpillars, which hatch and burrow into the flesh of the host, feeding on its internal contents
(Hein et al., 2004).
Trichogramma chilonis Ishii stands out as the most efficacious biocontrol agent among the available options. This particular agent is classified as an egg parasitoid, specifically targeting the egg stage of the pest in question (
Krishnamoorthy, 2012).
According to
Alam et al., (2006), the regular introduction of the egg parasitoid
Trichogramma chilonis Ishii at a rate of 1 g of parasitized eggs per hectare per week, along with the larval parasitoid
Bracon hebetor. The population density of 800-1000 adults per hectare per week, has proven to be an effective method for lowering the population of the Brinjal Shoot and Fruit Borer. According to
Cork et al., (2003), the installation of Brinjal Shoot and Fruit Borer sex pheromone lures in traps has been found to effectively mitigate fruit damage and enhance yield, with a recommended density of 100 traps per hectare. According to
Alam et al., (2003), for optimal attraction, it is recommended to position traps either at the level of the canopy or slightly above it.
One approach involves the use of parasitic wasps, such as
Aphidius spp. on aphids. These tiny wasps lay their eggs inside aphids and as the wasp larvae develop, they consume the aphids from the inside, ultimately leading to aphid mortality (
Van Lenteren, 2012).
Insect pathogens
Similar to plant microorganisms, microscopic organisms such as protozoa, viruses, actinomycetes and nematodes attack and destroy insect and mite pests.
Bacteria
Bacterial pathogens are spore-forming, rod-shaped bacteria from the
Bacillus genus. Insectpathogenic bacteria with the potential to be employed in biological pesticides are limited to three types of spore-forming bacteria:
Bacillus thuringiensis, Bacillus sphaericus and
Bacillus papillae.
S. Ishitawa, a Japanese scientist, discovered
Bacillus thuringiensis in 1901.
Bacillus thuringiensis is a facultative anaerobic gram-positive bacterium that produces protein inclusions near the endospore. These proteins are naturally crystalline and dissolve only at an alkaline pH. By transcription and translation of the
cry 1 ac gene,
B. thuringiensis produces the cry 1 ac protein. These proteins breakdown in the alkaline pH of lepidopteran caterpillars’ guts, causing harm to the gut epithelial cells. As a result of the injury, the caterpillar is unable to feed and eventually dies and turns to dark brown colour (Fig 3 A).
Another bacterium,
Pseudomonas fluorescens, has shown potential in combating root and stem-feeding insects that often plague vegetable crops (
Péchy-Tarr et al., 2008). The utilization of these bacteria provides an environmentally friendly alternative to chemical pesticides, promoting sustainable agricultural practices and ensuring the safety of the produce
(Glare et al., 2012).
The symbiotic relationship between
Xenorhabdus bacteria and entomopathogenic nematodes has been harnessed to combat soil-borne pests that threaten the roots of vegetable plants, providing a two-pronged approach to pest management
(Elbrense et al., 2021). As the global demand for organic vegetables rises, the role of these bacteria in safeguarding crops without compromising environmental health becomes even more paramount.
Virus
Around 1600 strange viruses have been found to infect roughly 1100 insect and mite species. A category of baculoviruses infects around 100 species of insects. This baculovirus classification accounts for more than 10% of all entomopathogenic viruses. Baculoviridae is one of those viral families that infect solely invertebrates, which makes them ideal insect pathogens due to the low risk of cross-infection with mammals. Baculoviruses are circular double-stranded DNA genomes contained in rod-shaped particles. Baculoviruses are widely considered to be safe, posing little threat to non-target animals. Baculoviruses do not produce metabolites or poisons and, unlike bacteria and fungi, are incapable of replication outside of their host. This differentiation between bacteria and fungi is critical.
The larvae consume occlusion bodies (polyhedra for nuclear polyhedrosis viruses and granules for granular viruses). In a highly alkaline midgut pH, the occlusion body protein dissolves and is destroyed by host alkaline proteases. Polyhedral virus particles released into the environment bind to the midgut’s peritrophic membrane. The lipoprotein of the virus forms a covalent link with the plasma membrane of gut wall cells, releasing nucleocapsids into the cytoplasm. The nucleotide transports virus DNA into the cell’s nucleus, where virus gene activation is initiated. The virus rapidly replicates and eventually infects the host. Infected insects quit feeding and the larvae develop a pinkish-white colour on the ventral side due to polyhedral structure aggregation. If the infection is not treated at the larvae’s advanced stage, the larva becomes flaccid, the skin becomes flimsy and the larva eventually ruptures. Sick larvae crawl to the apex of the plant and dangle upside down from there in the field. Treetop disease is the term used to describe the ailment (Fig 3B).
Spodoptera litura and
Helicoverpa armigera are both very susceptible to NPV.
NPVs have long been recognized as an integral aspect of integrated pest management techniques against a number of insect pests
(Tanga et al., 2011), particularly lepidopteran pests such as moths and butterflies
(Rao et al., 2015). Another study was conducted to determine the toxicity of NPV against the 2
nd and 4
th instar larvae of
S. litura from diverse areas. Three concentrations of NPV were prepared: NPV-34 × 10
9, NPV-23 × 10
9 and NPV-12 × 10
9 POB ml/litre. The study discovered that high concentrations resulted in the highest larval mortality rate of 83.28 per cent.
NPVs were discovered to have a direct influence on eggs, larvae, pupae and adults in this study. The application of NPV shortened the duration of each developmental stage
(Yasin et al., 2020). Another study examined the combined effect of NPV, chlorantraniliprole and
Azadirachta indica on
Helicoverpa armigera and
S. litura larvae at various instar stages. The study discovered that whereas combined treatments had a high death rate, individual applications had a low mortality rate
(Qayyum et al., 2015).
Fungus
Louis Pasteur pioneered the use of fungus in vineyards to control microscopic insect pests. In contrast to entomopathogenic bacteria and viruses, which enter the host insect
via the mouth, entomopathogenic fungi (Fig 3 C) can enter
via the outer integument
(Patil et al., 2021). After adhering to the host, the fungus penetrates the insect’s body wall
via spore-derived hyphae. Invasion of the cuticle by hyphae occurs
via wounds, segmental junctions, or sensory organs. The insect dies as a result of significant fungal growth in the haemolymph and toxin poisoning caused by the fungal toxin.
Paecilomyces is a widespread fungus best known for its nematophagous ability, but it has also been found as an insect parasite and biological control agent of numerous fungi and phytopathogenic bacteria
via unique mechanisms of action. Numerous species of the genus
Paecilomyces produce a diverse array of secondary metabolites with a variety of chemical structures and biological activities, including insecticidal
(Asaff et al., 2005), nematicidal
(Saha et al., 2016). Paecilomyces have been found to parasitize fungi and nematodes
(Munawar et al., 2015). When the pathogen and the antagonist come into contact, enzyme complexes are formed and/or released, resulting in antagonist development at the expense of the host
(Talibi et al., 2014). Lipases, proteases and chitinases are the most effective entomopathogenic enzymes
(Khan et al., 2004). Thus, it has been demonstrated that the synthesis of these enzymes by
P. fumosoroseus is effective against
Tenebrio molitor (
Gómez et al., 2017),
Trialeurodes vaporariorum (Castellanos-Moguel et al., 2007) and other infections. Numerous studies on
Paecilomyces’ nematicidal effect have been conducted. Through spore germination and subsequent hyphal branching and appressoria development, species of this genus, notably
P. lilacinus, are capable of penetrating both the eggshells and structural components of several nematode species’ juvenile and adult stages
(Dong et al., 2007). It has been discovered that the creation of enzymes like as amylases, lipases, proteases and chitinases associated with this species has a nematicidal effect
(Khan et al., 2004). Overexpression of these enzymes boosts
P. lilacinus’s virulence and parasitic capacity against
Meloidogyne incognita, Panagrellus redivivus and
Caenorhabditis elegans (Yang et al., 2011).
Metarhizium anisopliae has the potential to be an extremely beneficial pathogen for insect pests and is currently being studied for myco-biocontrol of a number of well-known insect pests (Fig 3 D).
Hasan et al., (2002) explored how
M. anisopliae generates spores via solid-state fermentation. In a variety of horticultural growing media (Peat, coir, bark and peat blends with 10% and 20% composted green waste), the entomogenous fungus
Metarhizium anisopliae V275 was more effective at killing western flower thrips pupae than chemical insecticides (imidacloprid, fipronil) (70-90% versus 20-50%). By including
M. anisopliae in the growing media, drench treatments in coir and peat mixtures containing 20% composted green waste, insect pests were controlled more effectively.
M. anisopliae in combination with sublethal doses of insecticides gives slightly better control than the individual control agents, but no evident additive or synergistic effects are observed.
M. anisopliae is effective in all growth circumstances and is compatible with conventional insecticides, which makes it an appealing candidate for thrips control in an integrated pest management program
(Ansari et al., 2007).
Studies have evaluated the efficacy of novel insecticide molecules and entomopathogens to control Hadda beetle in brinjal. Among the biopesticides,
Metarhizium anisopliae and neem oil have been found to be effective against Hadda beetle. In laboratory and field experiments conducted at the Indian Institute of Vegetable Research, Varanasi,
Metarhizium anisopliae and neem oil provided the highest protection over control and indicated compatibility and synergistic activity at a 1:1 combination
(Kodandaram et al., 2014). Another study found that
M. anisopliae IIVR strain was most promising against Hadda beetle, followed by
M. anisopliae commercial formulation, whereas neem oil was the most effective biopesticide against the pest
(Halder et al., 2017). These studies suggest that entomopathogens and neem oil have the potential as eco-friendly and sustainable approaches to managing Hadda beetle in brinjal.
The microbial control agents
Bacillus thuringiensis, Beauveria bassiana and
Metarhizium anisopliae have been tested by
Sabbour, (2015) against the tomato pinworm
Tuta absoluta under laboratory and greenhouse conditions. The results showed that these agents were effective in reducing infestation and mortality rates of
T. absoluta, with
M. anisopliae showing the highest percentage of parasitism after treatments. A combination of mass release of
Trichogramma pertiosum and
B. thuringiensis resulted in only 2% fruit damage in South America.
Aphids, thrips, grasshoppers and certain beetles are all susceptible to white muscadine disease, which is caused by the entomopathogenic bacteria
Beauveria bassiana. Unlike
Nosema locustae, it does not require the host to consume the spores; instead,
B. bassiana spores simply contact a host (ARBICO Organics, n.d.). Physical forces attach conidia to the host cuticle, followed by germination and penetration of cuticular layers, which are accelerated by hydrolytic enzymes (
e.g., proteases, lipases, chitinases), mechanical pressure and other variables (
Ortiz-Urquiza and Keyhani, 2013). When the expanding hyphae reach the nutrient-rich haemolymph, the fungus can form single-celled, yeast-like blastospores (or hyphal bodies), which are specialized structures that enable the fungus to rapidly reproduce and exploit resources, invade interior tissues and evade detection by the host immune system (
Humber, 2008). Various pathogenic metabolites (antimicrobial peptides) are produced during colonization. They contribute to host immunological suppression, culminating in the destruction of host internal tissues and nutrient depletion, which eventually culminate in host death
(Gibson et al., 2014). B. bassiana surrounds the body with a white mold that develops an increasing number of infectious spores (ARBICO Organics, n.d.).
The bhendi fruit and shoot borer,
Earias vitella is a major pest of many crops, including okra and cotton, in India. While there is limited research on biological control methods specifically for
Earias vitella, some studies have evaluated the efficacy of biological control agents on other pests that may be effective against
Earias vitella. Spinosad and
Bacillus thuringiensis have been found to be effective against shoot and fruit borer pests in okra
(Choudhury et al., 2021).
A self-sustaining granular fungal treatment has been developed to control
Frankliniella occidentalis, also known as the western flower thrips. The treatment combines cooked, oven-dried millet with
Beauveria bassiana strain GHA to potting soil, which increases spore production and persistence of the fungus in the soil
(Davari et al., 2021). The method is relatively inexpensive and easy for growers to use in greenhouses because granular formulations of
B. bassiana are not commercially available.
Nematodes
Neoplectana carpocapsae is the most often employed entomopathogenic nematode for insect management and one of its strains, DD-136, is widely used to control insect pests infesting agricultural crops, vegetables and orchards
(Patil et al., 2021). Fig 4 A depicts the life cycle of an entomopathogenic nematode.
The nematode
Steinernema feltiae is used to manage
Helicoverpa armigera and a few soil pests and termites, while
Steinernema soodi is used to control
Galleria melonella (Fig 4 B).
Rhabditis sp. (Fig 4 C) is used to combat white grubs (
Holotrichia serrata) and
Tetradonema plicansis is used to fight sciarid flies and cultivable mushroom pests.
Protozoans
Microsporidia and their protozoan spores are ingested by the insect. Once within the stomach, they multiply vegetatively in the cytoplasm, gradually spreading throughout the body and causing chronic sickness. A protozoan-infested bug can be easily recognized by its soft body and easily breakable body. Several protozoans are still being exploited for pest management, including
Farinocystis tribolii, which infects the red flour beetle,
Tribolia castaneum, with no commercial product available to date. In other countries, one protozoan species,
Nosema locustae (Fig 4 D), which infects grasshoppers, is being exploited under the trade names “Noloc”, “Nolo Bait” and “Semaspore Bait”.
The species
Mettaisa frogodermae was examined and employed within a pest control initiative targeting the khapra beetle. The infective spores exhibit a complete absence of contents. The sporozoites that are in the process of developing become motile within the gastrointestinal tract and subsequently enter the gut to reach the haemocoel, where they proceed to infect cells in vulnerable tissues within a span of two days (
Agriinfo.in, 2023).
Vairimorpha necatrix, formerly known as
Nosema necatrix and
Thelohania diazoma, is a microsporidium that has been isolated from at least 14 species of field-collected lepidopteran larvae.
V. necatrix has been found to infect various species of Lepidoptera, including economically significant agricultural pests such as
Pseudaletia unipuncta, Heliothis zea and
Heliothis virescens (
Sarwar, 2017a). Additionally, it has been observed to infect
Autographa californica, Trichoplusia ni,
Spodoptera frugiperda, Spodoptera exigua, Spodoptera ornithogalli (
Sarwar, 2017b), as well as
Plathypena scabra, Pseudoplusia includens and
Hyphantria cunea, which have shown potential in controlling the black cutworm
Agrotis ipsilon (
Sarwar, 2019). Moreover, the utilization of
V. necatrix in the context of cabbage plants infested with
Trichoplusia ni and
Pieris rapae, as well as soybeans or sorghum plants affected by the green cloverworm
Plathypena scabra, yields substantial benefits in terms of safeguarding crop health and productivity.
The list of pests and their biocontrol agents including predators, parasitoids, entomopathogenic microorganisms and entomophagous nematodes are mentioned in the Table 2 and are as follows.
Biocontrol agents as commercial biopesticides
Chemical pesticide use in agriculture must be drastically decreased and sustainable biocontrol methods must be pushed. Interest in biological control agents or biopesticides has increased as a result of their ecological benefits (
Roger, 2012). On the other hand, their commercialization lags far behind since an acceptable regulatory framework is required for their authorization, commercialization and use. India’s growth has been gradual due to insufficient regulation, a lack of capability and the ineffective execution of policies relating to biopesticides and biological control agents (
Arjjumend and Koutouki, 2018). This results in a situation where manufacturers and importers of biopesticides and biocontrol agents face different regulatory frameworks and administrative barriers (
Arjjumend and Koutouki, 2018). Switching from chemical pesticides to biological agents would also improve the country’s environmental and ecological goals. A number of entities, including Indian Council of Agricultural Research (ICAR) institutions and state agricultural universities, are collaborating on biological pest management through an outreach program. These institutes have created a variety of beneficial biocontrol methods for farmers. Additionally, the National Institute of Plant Health Management (NIPHM) has developed low-cost technologies for producing these biocontrol agents (Fig 5 A, B).
The absence of toxic effects, the absence of development of resistance in pests, the absence of poison residues in the soil and rivers, the absence of toxic buildup in the food chain and the absence of the killing of pollinators and predators are all advantages of biological pest control. In addition, it has its own drawbacks, such as being slow to control pests and diseases, being unpredictable, some biocontrol agents being difficult and expensive to create and administer and requiring expert supervision during the handling and application of biocontrol agents.
