The established circadian rhythm regulator known as melatonin demonstrates growing importance in ecosystem-wide effects which extend past its biological functions. The importance of melatonin for controlling insect behavior and parasitology and plant–insect interactions continues to grow according to recent scientific investigations. Insect organisms use melatonin to control their circadian cycles and stress reactions and feeding patterns which impacts how different species connect with each other in food chains and ecosystem functions. Research in parasitology reveals that melatonin exhibits potential effects on host–parasite relationships and disease parasite life cycles as well as immunological responses, thus providing new possibilities for disease control. The growing interest in plant defense biology focuses on melatonin because this molecule demonstrates the ability to reduce insect feeding and strengthen plant resistance against insect attacks. This chapter examines how melatonin functions in various ecological roles to reveal its potential applications in sustainable farming and pest control and biodiversity preservation. This research study combines botanical, entomological, and parasitic findings about melatonin to demonstrate its ecological significance in boosting ecosystem resilience against environmental threats.