ABSTRACT
Interactions among seed-feeding insects are well noted in the literature, with many of these interactions being asymmetrical and causing a disadvantage for one of the species involved. While often effective, the use of the cumulative stress approach to biological control (where multiple natural enemy species are released) may increase the risk of interaction, which may lead to less effective biological control programs. Spotted knapweed (Centaurea stoebe ssp. micranthos (Gugler) Hayek) is an invasive plant that causes damage in rangelands and pastures. In Arkansas, two biological control agents for spotted knapweed, Larinus minutus Gyllenhal and Urophora quadrifasciata Meigen, are established. Both species attack the capitula of spotted and diffuse knapweeds. There is potential for interactions between these species, and this could affect the efficacy of the biological control program. To evaluate these potential interactions, we collected spotted knapweed capitula weekly from three sites in Arkansas from 2010 to 2012. Capitula were monitored for emergence of L. minutus and U. quadrifasciata, and the effect on seed reduction was analyzed. Over all three years, L. minutus and U. quadrifasciata were present in 35.8% (492) and 22.8% (313) of the capitula, respectively. We determined that the occurrences of L. minutus and U. quadrifasciata were not independent of each other, and that L. minutus is more effective at reducing spotted knapweed seed production than U. quadrifasciata within individual capitula. Seed production in capitula with both natural enemies present was no different from capitula with L. minutus.
ABSTRACT
Japanese beetles, Popillia japonica Newman (Coleoptera: Scarabaeidae), were evaluated for ovipositional preferences among four turfgrasses common in northwestern Arkansas. Choice assays revealed females preferred to oviposit in tall fescue (Festuca arundinacea Schreb.) and zoysiagrass (Zoysia japonica Steud.), and that they avoided oviposition in common bermudagrass (Cynodon dactylon [L.] Pers.) and hybrid bermudagrass (C. dactylon x C. transvaalensis Pers.). Significantly fewer eggs were oviposited in hybrid bermudagrass in a no-choice assay, suggesting that chemical and/or physical plant characteristics deter oviposition in that grass. The percentage of turfgrass cores with evidence of female activity (presence of female or eggs, or signs of female digging) in choice assays revealed no differences among treatments, yet significantly fewer hybrid bermudagrass cores had eggs. These results suggest that many females did not initially reject hybrid bermudagrass based on aboveground plant characteristics, but rather they left without ovipositing. Therefore, resistance in hybrid bermudagrass is likely expressed below ground. Our results suggest that the use of hybrid bermudagrass as a means of cultural control in an integrated pest management program may discourage Japanese beetle oviposition and subsequent grub infestations in lawns, golf courses, or sports fields.
