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Plants have evolved several adaptive strategies through physiological changes in response to herbivore attacks. Plant secondary metabolites (PSMs) are synthesized to provide defensive functions and regulate defense signaling pathways to safeguard plants against herbivores. Herbivore injury initiates complex reactions which ultimately lead to synthesis and accumulation of PSMs. The biosynthesis of these metabolites is regulated by the interplay of signaling molecules comprising phytohormones. Plant volatile metabolites are released upon herbivore attack and are capable of directly inducing or priming hormonal defense signaling pathways. Secondary metabolites enable plants to quickly detect herbivore attacks and respond in a timely way in a rapidly changing scenario of pest and environment. Several studies have suggested that the potential for adaptation and/or resistance by insect herbivores to secondary metabolites is limited. These metabolites cause direct toxicity to insect pests, stimulate antixenosis mechanisms in plants to insect herbivores, and, by recruiting herbivore natural enemies, indirectly protect the plants. Herbivores adapt to secondary metabolites by the up/down regulation of sensory genes, and sequestration or detoxification of toxic metabolites. PSMs modulate multi-trophic interactions involving host plants, herbivores, natural enemies and pollinators. Although the role of secondary metabolites in plant-pollinator interplay has been little explored, several reports suggest that both plants and pollinators are mutually benefited. Molecular insights into the regulatory proteins and genes involved in the biosynthesis of secondary metabolites will pave the way for the metabolic engineering of biosynthetic pathway intermediates for improving plant tolerance to herbivores. This review throws light on the role of PSMs in modulating multi-trophic interactions, contributing to the knowledge of plant-herbivore interactions to enable their management in an eco-friendly and sustainable manner.

Extreme and irrational use of synthetic chemicals for improved plant protection and plant productivity causes several adverse impacts on ecosystem. Considerable amount of economic losses has been caused to crop especially fungal as well as nematode pathogens. Thus, eco-safer methods of plant disease control are requisite for maintaining sustained crop productivity with eco-stability. Disease suppression using antagonistic microbes has been proposed as a feasible substitute for managing fungal diseases of crop plants. Microbe-mediated biological control reduces the severity of crop disease/ damage, inflicted by numerous phytopathogens (fungi, nematode pests, etc.) via production of different antifungal compounds in natural conditions. In this approach, fungal pathogens are antagonized by microbial biocontrol agents through production secretion of mucolytic enzymes, antibiotics, volatile biocidal compounds, and/or competition for nutrients and space between biocontrol agents and pathogen. All these mechanisms are a powerful tool for lowering the harmful damages of pathogen through preventing their deleterious effects on crop growth. Microbes belonging to different taxonomic group of bacteria, viruses, and fungi are employed in the biological suppression of phytopathogens. Such bioagents can more efficiently grow, survive, and proliferate in several agro-horticultural ecosystems. In last few decades, such disease protection approach is considered a potential pest management strategy owing to accumulation of harmful chemical residues in biosphere. With this background, this chapter covers the aspects of crop disease control using biocontrol microbes, types of bioagents deployed in the biocontrol process, their modes of action, and commercialization aspect.

Bitter gourd, Momordica charantia Linn., is one of the most important traditional vegetable in India. Infestations of sucking pests especially jassid, and whitefly occurred thorough out the crop growth period in the region. For ecofriendly management, different pest management modules viz., bio-intensive, chemical, and integrated modules were evaluated against these sucking pests and compared under field conditions during 2019–2021. Among the three tested modules, the integrated pest management (IPM) comprised seed treatment with imidacloprid @ 5–10 g kg-1 of seed, installation of yellow sticky traps @ 25–30 ha-1, border crop with maize, spraying of azadirachtin 1500 ppm @ 10 ml L-1, thiamethoxam @ 1 g 3-1 L, imidacloprid @ 1 g 12-1 L, cyantraniliprole @ 1.8 ml L-1, neem oil (0.5%) + Lecanicillium lecanii @ 2.5 g L-1, and neem oil (0.5%) + Beauveria bassiana @ 2.5 g L-1 from 20 to 70 days after sowing at 10 days intervals each harboured lowest whiteflies population (0.63 per leaf) with maximum per cent reduction over control of 70.14. The number of predatory lady bird beetles and polyphagous spiders were also higher. The highest healthy fruit yields (171, 179, and 153 q ha-1) were recorded from the IPM module for three consecutive years (2019, 2020, and 2021, respectively). In terms of return, maximum net profit of ₹71,211 was obtained from the IPM module with the highest incremental cost-benefit ratio of 1:5.18. Therefore, the IPM module could be a viable ecofriendly option in the management of the sucking pests of bitter gourd, along with the conservation of natural enemies.

The atmospheric methane concentration is increasing rapidly at the rate of around 10 ppb/year. A concerted effort is required to reduce methane emission. Methanotrophs possess methane monooxygenase enzyme system and can consume a major portion of the methane produced in the environment. These microbes play a major role in the single-carbon-driven microbial food web. Microbial interaction is an important component of microbial ecology studies, and its role in community functioning and various biogeochemical cycles still remains unclear. A synergistic interaction occurs between the methanotrophs and non-methane-utilizing methylotrophs (NUM) in the natural ecosystem. The intermediates produced by the methanotrophs can be used as a carbon source by the NUM and support its existence. On the other hand, NUM consumes toxic intermediates like methanol and formaldehyde of the methanotrophs and prolongs their growth. The consumption of the intermediates (methanol, formaldehyde and formate) of the methane utilization pathway by methylotrophs as a result of cross-feeding enhances the methane utilization rate of that ecosystem. Co-inoculation of methanotrophs and NUM in the natural habitat particularly paddy ecosystem can aid in the reduction of net methane emission. This chapter highlights the role of microbial interactions, particularly between methanotrophs and methylotrophs, that can be harnessed to mitigate methane emission from the methane-rich environment.

Microbes are constituting elements of the soil environment and their abundance, enzymatic activity, degradation process, and biodiversity indicate the balance in the agro-ecological system. It is necessary to keep strengthening the scientific basis of modern agriculture because pesticides may be purposefully used only if their persistence, bioaccumulation, and toxicity in agro-ecosystems are strictly controlled. The use of agrochemicals, such as chemical fertilisers and pesticides, is important in modern crop management strategies (mainly insecticides and herbicides). Pesticide poisoning affects three million people worldwide, according to the WHO. Long-term and indiscriminate pesticide use has serious negative consequences for soil microbes, the nutrient cycle, the decomposition process, and the atmosphere, resulting in long-term negative consequences for food stability, human health, and the environment. Pesticide application can alter microbial diversity, which can be detrimental to plant growth and development by decreasing nutrient availability or disrupting the nutrient cycle. Therefore, the qualitative, innovative, and demand-driven pest management is the need of the hour. Hence, this chapter covers the positive and negative consequences of pesticides on microbes and their environment and current issues about the extensive use of pesticides.

Chitin is an important structural component of many plant pathogenic fungi. Similarly, it is also an important part of the insect cuticle and peritrophic matrices, which function as a permeability barrier, enhance digestive processes and protecting the brush border from mechanical disruption as well as from attacks by toxins and pathogens. Chitin degrading lytic enzymes (such as chitinases, and glucanase) produced by bacteria and other microorganisms can impede the growth of many insect pests and fungal phytopathogens that pose a severe risk to global crop production. Pathogenic microorganisms produce a variety of lytic enzymes such as proteases, chitinases, lipases etc. which play an important role in the virulence of entomopathogens. Many chitinolytic bacteria have the potential to control pests and fungal pathogens of crops owing to their ability to disintegrate chitin containing cellular structures. Currently, efforts are being made to discover producers of chitinolytic enzymes in nature. Production of lytic enzymes has been reported in a number of virulent pathogens such as Serratia, Pseudomonas or Bacillus spp. Bioprospecting and exploitation of chitinolytic bacteria will help in developing biocontrol agents, which have the potential to control fungal plant pathogens and insect pests. Thus, these bacteria-based biofungicides and biopesticides may replace or supplement the chemical fungicides and insecticides, reducing the negative impact of chemicals on the environment and supporting the sustainable development of agriculture-based ecosystem. This chapter focuses on the scope and potential of chitinolytic bacterial and fungal organisms in the management of insect pests and fungal pathogens of agricultural crops.

Twenty maize genotypes were screened for resistance against shoot fly during spring 2013 and 2014. Observations were recorded on the parameters viz., i) % plants oviposited, (ii) no of eggs laid, (iii) % deadheart formed, (iv) plant height, (v) days of oviposition, (vi) no of maggots/10 plants, and (vii) weight of maggots. Maximum % oviposition was observed in DC-2 (both years), whereas minimum was in WP-21 in spring 2013 and HKI-323 in spring 2014. The infestation level was too heavy and all the evaluated genotypes were oviposited with. Maximum eggs were laid on DC-2 and the least with HKI-1011. During 2013 and 2014, maximum % of deadheart was observed with DC-2, while the least one was with WP-21 (2013) and in HKI-1011 (2014). The maximum weight of maggot was observed with DC-2 and the least with WP-21 (2013); in 2014, it was observed with JCY-2-7 and WP-21, respectively. Thus the % plants oviposited, number of eggs laid, % deadheart formed, number recovered and weight of maggots indicates the genotype susceptibility level. These levels could be used as marker traits for resistance to shoot fly in maize.