Development, Survival, and Reproduction of Scymnus frontalis (Coleoptera: Coccinellidae), an Imported Predator of Russian Wheat Aphid, at Four Fluctuating Temperatures

Development, survival, and reproduction of Scymnus frontalis (F.) were studied in the laboratory at four temperature regimes with means ranging from 15 to 30°C, with daily fluctuations of ±5°C. S. frontalis has four instars and a distinct prepupal stage. Developmental times from egg to adult averaged 79.7, 45.3, 21.4, and 17.2 d at mean temperatures of 15, 18.7, 26.2, and 30°C, respectively. Calculated stage-specific developmental thresholds ranged from 10.1°C for first instars to 13.0°C for fourth instars. Development from egg to adult required an average of 312.2 degree-days above a base of 11.7°C. Survival was highest at the two intermediate temperatures and lowest at a mean temperature of 15°C with mortality being highest in eggs and first instars. Preoviposition periods ranged from 20.5 d at a mean temperature of 15°C to 7.7 d at 30°C. Daily oviposition rates per female during the first several weeks of reproductive life were highest at a mean temperature of 26.2°C (7.25 eggs per female per day). The proportion of females ovipositing was highest at 26.2°C (0.97) and lowest at 15°C (0.42). Compared with its prey, Diuraphis noxia (Mordvilko), the Russian wheat aphid, S. frontalis requires higher temperatures to complete development and reproduce.