Razi University

Understanding pest population structure, spatial distribution, and the biodiversity of natural enemies is a fundamental component in designing sustainable integrated pest management programs. This study investigated the aphid fauna associated with alfalfa, population fluctuations, spatial distribution patterns, and biodiversity of natural enemies in forage alfalfa fields of Kermanshah County during the cropping years of 2024 and 2025. Aphid and natural enemy samples were collected using a 20 × 20 m grid with the diagonal sampling method, and aphid species were identified by preparing microscopic slides. Taylor’s power law and Iwao’s patchiness regression were used to analyze spatial distribution, and biodiversity indices (Shannon–Wiener, Simpson, Brillouin, Smith–Wilson, and Jackknife) were applied to evaluate the natural enemy community. Three aphid species were identified—Acyrthosiphon pisum, Therioaphis trifolii, and Aphis craccivora—with A. pisum dominant in both years. The peak density of A. pisum occurred mainly in June, whereas T. trifolii peaked in August. Aphid distribution was largely random, tending toward aggregation at higher population densities. The natural enemy community comprised seven ladybird species, two parasitoid wa  , two predatory bugs, one syrphid fly, and the green lacewing. The dominant enemies—Coccinella septempunctata, Hippodamia variegata, Aphidius ervi, and Praon exsoletum—showed temporal overlap with aphid population dynamics. Correlations between enemy abundance and aphid density were positive but mostly non-significant, and climatic variables had no significant effect on aphid fluctuations. Biodiversity indices revealed varying diversity and evenness across fields, with high Smith–Wilson evenness values (up to 0.999) indicating a balanced species distribution, while Jackknife estimates highlighted the role of habitat heterogeneity in species richness. The Bray–Curtis matrix showed relatively high faunal similarity among fields. Overall, the alfalfa ecosystem in the study region supports a relatively balanced predator–prey structure and a suitable capacity for natural control of aphids, providing a scientific basis for integrated pest management, conservation of native natural enemies, and reduced insecticide use in alfalfa fields of Kermanshah Province.