Joanne Rebbeck

Leluthia astigma (Ashmead) (Hymenoptera: Braconidae: Doryctinae) as a Parasitoid of Agrilus planipennis Fairmaire (Coleoptera: Buprestidae: Agrilinae), with an Assessment of Host Associations for Nearctic Species of Leluthia Cameron

Abstract Published host associations are assessed for Leluthia astigma (Ashmead), Leluthia floridensis Marsh, and Leluthia mexicana Cameron, the three known species of Leluthia Cameron in the Nearctic Region. Leluthia astigma is reported as a parasitoid of Agrilus planipennis Fairmaire, emerald ash borer (EAB), infesting Fraxinus americana L., white ash, in Delaware County, Ohio. It is the first species of Leluthia for which a determined species of Agrilus Curtis has been confirmed as a host and the association vouchered. All other hosts reported in the literature for L. astigma require confirmation through rearing from an isolated host or documentation of an unequivocal host-parasitoid association. Leluthia astigma adults reared from parasitoid cocoons collected in Delaware County, Ohio parasitized and produced F1 adults in the laboratory on last-instar EAB larvae collected in Ingham County, Michigan. Parasitism of EAB and other natural history data are reported for L. astigma, including the first records of L. astigma from Kansas and New York.

Do chestnut, northern red, and white oak germinant seedlings respond similarly to light treatments? Growth and biomass

Northern red oak (Quercus rubra L.) seedling growth has been extensively studied. White oak (Quercus alba L.) and chestnut oak (Quercus prinus L.), however, are far less investigated despite their importance among upland oak species in eastern North American forests. We characterized white and chestnut oak seedling response to light and available soil nutrients while using northern red oak as a benchmark. Germinants were grown within one of three shade treatments (25%, 18%, and 6% of full sun) in one of two native forest soil mixes over two growing seasons. Leaf area, shoot mass, and root mass of all three species showed positive growth responses to increasing light. Growth and biomass were higher for all species grown in the more nutrient-rich forest soil, but chestnut oak displayed the greatest positive responses to the higher nutrient levels. White oak seedlings were the slowest growers and demonstrated the most root-centered growth, with root to shoot ratios almost twice that of either chestnut or nor...

Mycorrhizal associations in Ailanthus altissima (Simaroubaceae) from forested and non-forested sites

Abstract Ailanthus altissima tree seedlings were excavated from each of two habitats: (1) a forest adjacent to a trail and stream and (2) a non-forested steep, barren slope adjacent to a major highway. Each seedling root system was examined for colonization by mycorrhizal structures using light microscopy and transmission electron microscopy. The roots were colonized by one or more endomycorrhizal fungi with Arum-type colonization. Endomycorrhizal colonization of the seedlings from the non-forested site (65.2%) was significantly greater than that of the seedlings from the forested site (37.9%). Colonization by intercellular hyphae and vesicles was significantly greater in the non-forested habitat than the forested habitat. This exotic invasive species may benefit from the rapid colonization of endomycorrhizae in more extreme open environments.

Effect of Ozone and Elevated Carbon Dioxide on Cuticular Membrane Ultrastructure of Yellow Poplar (Liriodendron tulipifera)

Ozone causes damage to leaves of many tree species and has been shown to increase cuticular membrane thickness in a conifer (red spruce). It has been suggested that elevated carbon dioxide can protect plants against air pollutants by reducing pollutant flux into the leaves, but it is not known whether ozone-induced changes in the leaf cuticle will be altered by elevated carbon dioxide. In 1991, white pine (Pinus strobus) and yellow poplar (Liriodendron tulipifera) seedlings were planted in a previously forested area. In May 1992, seedlings were enclosed in open-top chambers and the following treatments were initiated: 1) charcoal-filtered (CF) air, 2) ambient air (1X ozone), 3) two times ambient ozone (2X ozone), and 4) 2X ozone plus 350 ppm carbon dioxide (2X plus CO2). First-year leaf samples were collected in August 1992. Midregions of white pine needles and yellow poplar leaves were prepared for electron microscopy by conventional methods and examined in a transmission electron microscope. The cuticular membrane of white pine grown in CF air was approximately 500 nm thick and consisted of an amorphous outer region and an inner reticulate region. Cuticular membrane thickness and wax tubule diameter were slightly greater in white pine needles grown in 2X plus CO2. The cuticular membrane of yellow poplar leaves grown in CF air was approximately 200 nm thick and consisted of an outer polylamellate region and a reticulate inner region. Cuticular membranes of leaves grown in 2X plus CO2 were also approximately 200 nm thick, but the outer membrane region had an amorphous structure. The cuticular membrane of yellow poplar leaves grown in 2X ozone were approximately 150 nm thick due to a thinner reticulate region. Second-year white pine and yellow poplar leaves will be collected in late August 1993, and cuticular membrane structure will be compared with the 1992 results.