Diversity, composition, and freedom to choose drive the effects of St. Augustinegrass cultivar blends on an herbivorous insect

Warm-season turfgrasses are conventionally produced and maintained as cultivar monocultures, which leaves them less resilient to pest attack than more diverse plantings. Recent evidence has indicated that mixing St. Augustinegrass [Stenotaphrum secundatum (Walter) Kuntze] cultivars can provide pest management benefits compared with cultivar monocultures. Research in other systems has shown that the effects of plant diversity on herbivores often depends on the number and identity of plant species present. Host plant diversity can affect herbivore fitness via postconsumptive physiological effects or before consumption by influencing herbivore behavior or plant defenses. To investigate the mechanisms by which St. Augustinegrass cultivar diversity and composition affect an insect herbivore, six cultivars were mixed to create two levels of cultivar diversity, and fall armyworm life history traits were tracked under no-choice diet mixing conditions and conditions where the larvae could forage among mixed cultivars. These experiments demonstrated that specific cultivar blends can reduce herbivore fitness and herbivory, and that the effects on fall armyworm fitness are likely driven by insect–plant interactions rather than postconsumptive physiological effects. The results will inform pest management strategies in warm-season turfgrass production and management, adding to the literature focused on the effects of intraspecific plant diversity.