Diversity, composition, and freedom to choose drive effects of cultivar blends on an herbivore insect

Authors: DOHERTY, ETHAN - Louisiana State University; Meagher, Robert - Rob; DALE, ADAM - University Of Florida

Submitted to: International Turfgrass Society Research Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/9/2022
Publication Date: 2/23/2022
Citation: Doherty, E.M., Meagher Jr, R.L., Dale, A.G. 2022. Diversity, composition, and freedom to choose drive effects of cultivar blends on an herbivore insect. International Turfgrass Society Research Journal. 1-5. https://doi.org/10.1002/its2.123.
DOI: https://doi.org/10.1002/its2.123

Interpretive Summary: Turfgrasses occupy over 3 times the surface area of any other irrigated crop in the continental United States. Warm season turfgrasses, such as those planted in the southeast, are maintained as variety monocultures. Therefore, lawns and golf courses that are composed only of one turfgrass variety makes them less resilient to pest attack than more diverse plantings. One of the important pests of turfgrasses is the fall armyworm (FAW), a moth pest that feeds and damages many crops. Previous research by scientists from Louisiana State University, the University of Florida, along with an USDA-ARS CMAVE, Gainesville, FL entomologist, have shown that mixing St. Augustinegrass varieties can provide pest management benefits compared to single varieties. To investigate how St. Augustinegrass diversity affects FAW, we mixed six varieties to measure FAW life history traits under no-choice diet mixing tests and tests where caterpillars could forage among mixed varieties. The results showed that specific varietal blends can reduce feeding and survival of FAW. These results will provide pest management strategies in warm season turfgrass production and management, and add to the growing body of literature that demonstrates the effects of increasing diversity within a plant species.

Technical Abstract: Warm season turfgrasses are conventionally produced, planted, and maintained as cultivar monocultures, which makes them less resilient to pest attack than more diverse plantings. Recent evidence indicates that mixing St. Augustinegrass cultivars can provide pest management benefits compared to cultivar monocultures. Research in other systems has shown that effects of plant diversity on herbivores often depends on plant species composition and richness. Host plant diversity can affect herbivore fitness via post-consumptive physiological effects or pre-consumption by influencing herbivore behavior or plant defenses. To investigate the mechanisms by which St. Augustinegrass cultivar diversity and composition affect an insect herbivore, we mixed six cultivars to create two levels of cultivar diversity and tracked fall armyworm life history traits under no-choice diet mixing conditions and conditions where larvae could forage among mixed cultivars. We found that the effects of increasing cultivar diversity depended on the delivery method and composition of cultivar blends. We demonstrate that specific cultivar blends can reduce herbivore fitness and herbivory, and that effects on fall armyworm fitness are likely driven by plant-plant or insect-plant interactions rather than post-consumptive physiological effects. These results will directly inform pest management strategies in warm season turfgrass production and management, and add to the growing body of literature that demonstrates the effects of increasing intraspecific plant diversity.