Reconstruction of Yellow Perch (Perca flavescens) Cohorts from Examination of Walleye (Stizostedion vitreum vitreum) Stomachs

Number of young perch (Perca flavescens) consumed by walleye (Stizostedion vitreum vitreum) in Oneida Lake was determined from analysis of feeding chronology and digestion rates. Young perch were ingested between sunset and sunrise and digestion rates were estimated from the decrease in weight of perch in stomachs during the day. Walleye prédation began in late June and by October the number of young consumed ranged from 17,940 to 242,900 ∙ha−1 in 1971–73. Concurrent studies indicated an additional 590 to 56,130 young were eaten by adult perch.Minimum population of young perch in June was calculated by adding to the number of young that survived to fall, the number consumed by walleye and adult perch. Populations reconstructed in this manner approximated independent estimates of the pelagic population in June. Mortality of young perch was apparently attributable to predation by percids and reconstructed populations accurately portrayed seasonal trends in abundance of young perch. Key words: predation, walleye, yellow perch, digestion, mortality

Predatory Efficacy of Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae) on the Two Spotted Spider Mite Tetranychus urticae Koch (Acari: Tetranychidae)

The relative abundance Tetranychus urticae and Phytoseiulus persimilis as well as voracity of the predator were conducted on potted eggplants. After six weeks of release of ten female T. urticae in control plants, the highest mite population reached at 184.21 / leaf, against 67.92 and 107.48 / leaf in plants which received two predators after 1st and 3rd week respectively. After nine weeks the number of mite / leaf reduced to 13.21 and 23.97 / leaf after 1st and 3rd week of introduction of the predator, the control population was 81.32. Adult P. persimilis as single predator fed 8.2, 15.4 and 20.6 T. urticae eggs after 24, 48 and 72 h respectively. Again a single predator when tested separately fed 5.4, 10.8 and 14.6 T. urticae larvae after 24, 48 and 72 h respectively. A single adult predator fed on 3.6, 7.0 and 12.0 adult T. urticae after the same durations. When varying number (10, 20, 30, 40 and 50) of prey (larvae or adults) were provided to a single predator it fed 5.0, 6.6, 6.8, 9.0 and 9.4 larvae against 3.2, 3.2, 3.4, 3.6 and 3.6 adults respectively. Key words: Predation, spider mite, eggplant, voracity, release. Â doi: 10.3329/jbs.v15i0.2152 J. bio-sci. 15: 127-132, 2007