The Potential of Landscape Plants Photinia × fraseri and Pittosporum tobira as Refuge for Natural Enemies of Pest Insects in Rice–Wheat Rotation Systems

The rice–wheat rotation is a predominant cropping pattern in China, frequently challenged by pests such as aphids in wheat, and Chilo suppressalis and Cnaphalocrocis medinalis in rice. This study investigates the potential of two common landscape plants, Photinia × fraseri and Pittosporum tobira, as functional plants for conserving natural enemies across crop cycles. Arthropod communities were systematically monitored using Malaise traps during the wheat, wheat–rice transition, and rice seasons from 2023 to 2024. Results revealed that both species successfully conserved a diverse natural enemy community, though their structural differentiation was strongly driven by seasonal variation, as confirmed by Heatmap and principal component analysis (PCA) (P. × fraseri: PC1 = 46.3%, PC2 = 23%; P. tobira: PC1 = 40.2%, PC2 = 25%). During the wheat season, both plants synergistically supported rich functional guilds, including predatory guilds (e.g., Episyrphus balteatus, Gnathonarium dentatum, and Harmonia axyridis) and parasitic guilds (e.g., Microplitis tuberculifer and Cotesia spp.). Notably, during the critical wheat-to-rice transition, these shrubs functioned as “habitat anchors,” where P. × fraseri demonstrated superior retention capacity for functional groups like Aphidius gifuensis, mitigating post-harvest habitat fragmentation. During the rice season, distinct functional complementarity emerged: P. × fraseri appeared to function as a habitat-type plant, potentially providing stable shelter for predatory groups (e.g., spiders and lady beetles), while P. tobira appeared to act as a resource-type plant, potentially attracting a significant rebound of parasitoids (e.g., Xanthopimpla flavolineata) in August. This mid-summer rebound on P. tobira was primarily attributed to its dense evergreen foliage providing a microclimatic refuge, rather than an active flowering resource. Analysis of shared dominant taxa (H. axyridis, Cotesia spp., and E. balteatus) showed highly significant seasonal fluctuations, with peak conservation during the wheat season. This study confirms that P. × fraseri and P. tobira have cross-cycle potential as a “natural enemy bank” in rice–wheat rotation agricultural systems. Their synergistic effects—integrating stable structural shelter with seasonal nutritional subsidies—support the conservation of diverse natural enemy communities throughout the annual crop cycle and significantly enhance the sustained pest control capacity of farmland ecosystems, identifying them as exemplary functional plants for ecological engineering in rice–wheat landscapes and providing a foundation for future studies on biological control efficacy.