The distribution, abundance and host plant relationships of Salix- feeding psyllids (Homoptera: Psylloidea) in arctic Alaska

Abstract. 1. Five species of psyllid occurred on seven species of Salix at Meade River, Alaska. Studies were made on the two common species Psylla pclmeni Löw and P.phlebophyllae Hodkinson. The former feeds on the phanerophy tes Salix pulchra, S.lanata, S.alaxensis and S.glauca , the latter on the chamaephytes S.phlebophylla and S.reticulata.
2. Both P.palmeni and P.phlebophyllae had a 1-year life cycle and nymphal development took place on the female Salix catkin. The life cycle was generally closely synchronized with the period of catkin development. However, only a few eggs were laid on S.glauca
3. Seasonal perturbation of the host plant by flooding, ice movement and blown sand prevented psyllids breeding in certain areas colonized by the host plant.
4. In P.palmeni densities and 'feeding pressure', measured as biomass of psyllids per gram of catkin, on the different host plants followed the sequence S.pulchra>S.lanata> S.alaxensis > S.glauca. In P.phlebophyllae densities and feeding intensities were similar on S.phlebophylla and S.reticulata and grazing intensity was comparable with P.palmeni on S.pulchra.
5. A highly significant negative correlation was found between psyllid density and catkin dry weight in S.pulchra, S.phlebophylla and S.reticulata , suggesting that psyllid feeding is affecting catkin growth.
6. Predation of psyllid nymphs by syrphid larvae was heavy but there was no evidence of parasitism.
7. The life history strategies of the five psyllid species are discussed within the context of the constraints imposed by the arctic environment.     

Corbicula (Bivalvia: Sphaeriacea) vs. Indigenous Mussels (Bivalvia: Unionacea) in U.S. Rivers: A Hard Case for Interspecific Competition?

At a time when populations of indigenous river mussels havebeen dwindling and/or disappearing, the introduced Asian clam,Corbicula, has spread through many U.S. rivers from Californiato Florida. In the Arkansas River Navigation System, a heavilymanaged waterway, Corbicula presently has a different "competitive"presence than it does in the relatively unmanaged Buffalo Riverin Arkansas. Comparative studies of both Corbicula and indigenousbivalved mollusks reveal biological bases for the contrastingkinds of benthic faunal change. There are ecologically relevant,distinctive differences between the two kinds of animals: inmantle/shell and mantle/gill apparatus, in the reproductivecomplex and neuroanatomy, and in spawning and locomotor behaviors.It is argued that the conservative molluscan characteristicsof Corbicula enable it to function in an exclusive, "contradictory"role with indigenous bivalves in a heavily managed waterway,and in a "contrary" competitive role elsewhere. Rationale ispresented for incorporating organismic evaluation into studiesof competition between distantly related taxa.     

Ultrastructure of the Invasion of Eimeria magna Sporozoites into Cultured Cells*†‡

SYNOPSIS. Monolayers of bovine kidney cells were overlaid with Eimeria magna sporozoites and observed with phase-contrast optics until penetration of the cells by the parasites had begun. Cells and penetrating parasites were fixed with glutaraldehyde and OsO₄-containing ruthenium red, dehydrated, and embedded in situ. Cells being penetrated were selected for study in the electron microscope. The lack of intracellular staining with ruthenium red and intact plasmalemmas of cells being penetrated, was accepted as evidence that the sporozoites did not disrupt the plasma membranes. The sporozoite caused invagination of the host cell plasmalemma until the parasite was entirely within the cell, after which the invagination was sealed off by short pseudopodia enclosing the sporozoite within a membrane-lined vacuole inside the cell. Often myelin-forms, apparently of host cell origin, were seen in the space between the sporozoite and the cell.     

Reproductive ecology of the endemic Lecocarpus pinnatifidus (Asteraceae) in an isolated population in the Galápagos Islands

Lecocarpus pinnatifidus is an endemic member of the Asteraceae occurring on only one island in the Galápagos archipelago. The capitula are large with female ray florets and male disc florets. They are self-compatible but this study suggests fruit set is pollen limited. Visits from Xylocopa darwini and other larger insect pollinators are rare, and small insects seem to be the main pollinators. Small insects carry few pollen grains and most likely mediate self-pollinations. Self-compatibility and seed set after selfing are the most common reproductive strategy in the Galápagos Islands and L. pinnatifidus seemingly fits well into this group.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 146 , 171–180.     

The endangered Tunbridge buttercup (Ranunculus prasinus): Ecology,conservation status and introduction to the Township Lagoon Nature Reserve,Tasmania

Abstract Ranunculus prasinus is a mat-forming species of the marginal herbfields and tussock grasslands of brackish wetlands. It is only known from four wetlands, all on private land, in the driest part of Tasmania. The species has been successfully introduced from divisions from three of the populations into a secure reserve with similar vegetation to that of the natural populations. This is considered to be desirable and morally sound in that it increases the chances of survival of native biological diversity as a whole. However, ex situ measures and a gaining of security for natural populations would also be prudent.