Seasonal dynamics of arthropods in Lucerne (Medicago sativa L.) and nutritional link to rodent foraging

Lucerne (Medicago sativa L.) is a highly nutritive crop with more vitamins and minerals used as a fodder legume since it is available throughout the year. In the Coimbatore district farmers prefer lucerne as a fodder crop because of its quality, year-round production, and seed yield fetches a high price. The monitoring study on lucerne crop pests, natural enemies and pollinators was conducted at Tamil Nadu Agricultural University, Coimbatore for three seasons from October 2021 to June 2024. The major sucking pests observed in Lucerne were aphids (Aphis craccivora Koch) and stink bugs (Nezara virudula, (L.)) and the natural enemy observed was coccinellid predators (Cheilomenes sexmaculata (Fabricius)). Natural enemies such as the Ladybird beetle (Coccinella repanda Thunberg) and Paper wasp (Polistes exclamans Vierick) were also documented as crucial in regulating these pest populations. The study also observed a diverse range of pollinators including the Alfalfa Leafcutter bee (Megachile rotundata (Fabricius)), various butterflies, and several species of bees that are vital for effective pollination and enhanced crop quality. The population of aphids and stink bugs ranged from 0.00 to 1.47 and from 0.00 to 1.35, respectively, from April to May. In contrast, from November to February, the aphid population varied from 0.07 to 0.45, while the stink bug population ranged from 0.02 to 0.38. The maximum population of coccinellids was recorded at 3.16 in October 2023. The correlation of pest and predator population with weather parameters showed maximum and minimum temperatures favoured the population development while it was negatively correlated with relative humidity and rainfall. Profiling of root nutrients showed lucerne roots contain a significant amount of essential nutrients that meet the dietary requirements of mice.