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.

Climate change poses a major threat to global crop production and food security, with cucurbit crops particularly vulnerable to heat, drought, and other climatic stresses. In this study, seven Cucurbitaceae species—bottle gourd, sponge gourd, ridge gourd, pumpkin, ash gourd, Summerfit (an interspecific hybrid of snap melon), and cucumber—were evaluated for tolerance to moisture stress. Plants were subjected to two irrigation regimes (50% and 75% of field capacity) after 15 days of transplanting, and morphological, physiological, and biochemical traits were assessed after 65 days. Severe reductions in growth and physiological performance occurred at 50% field capacity, indicating intense water-deficit stress. Bottle gourd exhibited the lowest reduction in relative water content (7.72%), while ash gourd showed the lowest reduction in membrane stability index (22.88%). Hierarchical clustering grouped bottle gourd and ash gourd as highly drought-tolerant species. Principal component analysis confirmed their superior performance, with higher catalase activity, root length, root surface area, root volume, root density, shoot length, and shoot dry weight under moisture stress. These findings suggest that ash gourd and bottle gourd enhance water uptake through improved root architecture, making them promising rootstocks for cucumber cultivation in water-limited environments.