Life-history traits of Myzus persicae under co-occurrence with multiple Brassica pests from different feeding guilds

Understanding how co-occurring herbivores from different guilds alter host plant quality and influence each other's performance is essential for developing effective integrated pest management (IPM). This study investigated the plant-mediated effects of simultaneous co-infestation by chewing (Mamestra brassicae, Pieris brassicae, Plutella xylostella) and piercing-sucking (Eurydema ornata) pests on the peach-potato aphid (Myzus persicae) on Brassica rapa. We hypothesised that herbivores from different feeding guilds induce distinct plant responses, differentially influencing aphid performance during co-occurrence. Each pest was confined to a single leaf, with a one-day-old aphid nymph placed on an adjacent leaf on the same plant to avoid direct interaction. Life-history analysis revealed that aphid immature duration (nymphal development time) was significantly extended on plants co-infested with P. xylostella (6.60 d) and E. ornata (6.10 d) compared to the control (5.60 d). Female longevity and total lifespan were significantly reduced by E. ornata infestation (13.10 d and 19.20 d, respectively). Fecundity was lowest on E. ornata-infested plants (10.20 nymphs/female). The intrinsic rate of increase (r) was lowest on plants infested with E. ornata (0.2167 d−1) and P. xylostella (0.214 d−1), while the highest r values occurred in the M. brassicae and control treatments (0.2674 and 0.2669 d−1). Female longevity was also significantly reduced by E. ornata infestation. Aphid weight gain was also significantly reduced by E. ornata and M. brassicae. These results suggest that feeding guild determines the plant-mediated impact on co-occurring aphids, with piercing-sucking E. ornata exerting the strongest inhibitory effect. These cross-guild interactions are ecologically significant for shaping pest dynamics in Brassica crops.