Arthropod predator occurrence and performance of Geocoris uliginosus (Say) on pest-resistant and susceptible turfgrasses

Interactions between host plant resistance and biological control maybe advantageous or disadvantageous for pest management. Turfgrass cultivars have rarely been tested for extrinsic resistance characteristics such as occurrence and performance of beneficial arthropods on plants with resistance to known turf pests. Among six turfgrass cultivars tested, the bigeyed bug, Geocoris uliginosus (Say) nymphs varied in ability to reduce numbers of fall armyworm, Spodoptera frugiperda (J. E. Smith), larvae. The six grasses tested (Sea Isle I and 561-79 seashore paspalum, Paspalum vaginatum Swartz; TifSport and TifEagle bermudagrass, Cynodon dactylon [ L.] x C. transvaalensis [ Burtt-Davy]; and Cavalier and Palisades zoysiagrass Zoysia japonica von Steudel and Z. matrella [L.] Merrill) represented a range in resistance to S. frugiperda. In the laboratory, the greatest reduction in S. frugiperda larvae by a low density of G. uliginosus occurred on the resistant Cavalier zoysiagrass. A 7-fold difference in weight of 10-d-old larvae between those feeding on susceptible versus resistant grasses suggested that on the resistant grass larvae remained for a longer period in a size range susceptible to predation. Results of laboratory studies were not directly translated to the field, in which a diverse predatory arthropod community varied in composition depending on turfgras cultivar. In the field, the greatest reduction in S. frugiperda larvae by a low density of G. uliginosus occurred on Sea Isle I and 561-79 seashore paspalum grass. In the field, vacuum samples indicated that predaceous Heteroptera were most abundant in paspalum grasses and bermudagrasses, while Carabidae, Staphylinidae, and Araneae were more common in zoysiagrasses. In contrast, pitfall traps indicated that carabids were more common in bermudagrasses, Araneae and Staphylinids were similar among grass taxa, and Cicindellidae were most common in paspalum grasses and bermudagrasses. Predation was never significantly decreased on resistant turfgrass cultivars in any of the experiments described in this work, indicating no negative tritrophic interactions.