Orange peel soil amendments affect Brassica rapa growth and aphid development without disrupting parasitoid foraging behaviour

Abstract This study tested the effects of soil amendment with orange peel powder ( Citrus sinensis L.) on Brassica rapa growth, the performance of the aphid Myzus persicae Sulzer, and the foraging behaviour of its parasitoid Aphidius gifuensis Ashmead. Three peel: soil ratios (1:10, 1:15, 1:20 w/w) were compared with an unamended control. The 1:10 amendment significantly reduced seed germination, plant height, leaf size, and fresh weight, while the 1:20 amendment also decreased fresh weight. Aphid nymphal development was significantly delayed in the 1:10 and 1:15 treatments, and adult weight gain was reduced in the 1:15 treatment. Aphid population growth and parasitoid foraging time were unaffected across treatments. The results indicate that orange peel amendments can delay aphid development but also suppress plant growth at higher concentrations, highlighting the need for optimized application rates. This study supports further exploration of orange peel as a sustainable soil amendment in integrated pest management.