Simpson’s index of diversity of insect pests and natural enemies inhabiting the rapeseed mustard (Brassica juncea) agroecosystem in the Kanpur region of Uttar Pradesh (India)

Abstract

This study investigated the diversity and succession of insect pests and their natural enemies in the rapeseed mustard (Brassica juncea) agroecosystem in the Kanpur region of Uttar Pradesh, India, during the Rabi seasons of 2023-24 and 2024-25. Key pests identified were the mustard sawfly (Athalia lugens proxima), mustard aphid (Lipaphis erysimi), and painted bug (Bagrada cruciferum). Natural enemies observed included ladybird beetles (Coccinella spp.) and syrphid flies (Spilomyia longicornis). Seasonal incidence patterns were recorded for each species, with pest activity and predator populations showing correlation with meteorological parameters. For instance, the mustard sawfly appeared during the vegetative stage, while aphids peaked later in the season. Ladybird beetles and syrphid flies generally increased in numbers as aphid populations grew, indicating their role as biocontrol agents. A relative abundance analysis for the 2023-24 season revealed that aphids (Lipaphis erysimi) were overwhelmingly dominant, constituting 92.22% of the total observed insects. This dominance, along with lower numbers of other species, resulted in a low Simpson's Index of Diversity (SID) of 0.14, indicating a less diverse ecosystem. Similar trends were observed in the 2024-25 season, where aphids represented 88.54% of the population, leading to an SID of 0.21. The study highlights the significant impact of specific pests, particularly aphids, on the ecosystem's diversity.