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Plant Sciences


The hemlock woolly adelgid, Adelges tsugae Annand, is a major threat to hemlocks in the eastern United States. As part of efforts to control this pest, Scymnus (Neopullus) sinuanodulus Yu et Yao, a potential predator, was collected from hemlocks in Yunnan, China. Three shipments were imported during 1996 and 1997 to a quarantine laboratory to study the beetle’s biology. Beetles began oviposition immediately after transferal from 5°C in the spring, ceased oviposition by June, and laid the same number of eggs, whether egg laying began in February or in April. Two-year-old beetles laid as many eggs per year as 1-yr-old beetles. We observed only one generation per year. Yearly fecundity averaged 130 eggs with a maximum of 200 per female. Newly emerged beetles remained preovipositional until the following spring, but could be induced to oviposit in the fall by prior exposure to 5 or 10°C for 1.5 mo. The egg, larval (four instars), and pupal stages lasted 10, 20, and 10 d, respectively, at 20°C. From egg to adult took 73, 40, and 35 d at 15, 20, and 25°C, respectively. Larval survival was only 5% at 25°C. Both larvae and adults fed on all stages of A. tsugae, but larvae grew faster with much higher survival on adelgid eggs, and could not complete development on adelgid nymphs alone. When given adelgid eggs, the beetles laid more eggs initially; however, adelgid nymphs seem to satisfy nutritional requirements for oviposition. Laboratory-reared beetles were similar to field-collected beetles in oviposition, fecundity, feeding, survival, and development.

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