Host plant growth characteristics as determinants of abundance and phenology in jumping plant-lice on downy willow

1. Salix lapponum host plants at an upper altitudinal site differed significantly in size, structural density, phenology, growth performance, and spatial isolation from those growing at a lower site. 2. Plant differences were paralleled by significant differences in psyllid population density and phenology parameters, with psyllid population density, percentage of catkins occupied, and phenological development relatively lower or retarded at the upper site. Population densities at the upper site, nevertheless, remained high. 3. Plant measurements were good predictors of insect density, often explaining up to 73% of the variance in abundance among plants at a given site. 4. Sets of four plant characters identified by best subsets regression were better predictors of psyllid density and development than single factors, although differences were often not great and the combinations of characters selected by multiple regression sometimes differed from the best single predictors. 5. Best single predictors of psyllid density on catkins were measurements of plant size, particularly height, length, and basal stem diameter. Shoot density and catkin phenology were occasionally important but plant isolation and prior growth performance were less important. 6. By contrast with density, age structure of the psyllid population was predicted best from plant phenological measurements, notably catkin phenology.     

Estimating woody and herbaceous vegetation cover from time series satellite observations

In this paper we test a method to estimate the tree and grass vegetation cover over Australia from satellite-derived normalized difference vegetation index (NDVI) time series (monthly 1981–91, ≈5 km pixels) observations. The evergreen cover is assumed to track along the base of the NDVI time series, which is assumed to be equivalent to the woody vegetation cover. The base of the NDVI time series is estimated using modifications to a classical econometric model (i.e. time series is the sum of trend, seasonal and random components). Estimates of the average evergreen component during 1982–85 and 1986–89 were generally consistent with known vegetation distributions. Changes in evergreen cover were largely restricted to the south-west and south-east of Australia. Those changes were largely the result of differences in rainfall between the two periods. The proposed method for estimating woody vegetation cover is found to be generally robust. However, there are some regions where the grass (or pasture) is mostly evergreen. Some possible refinements are proposed to handle such cases.     

Gene transfection of the HuLy-m2 (Leu-9) antigen into mouse L cells

Human DNA was transfected into mouse L cells and tk⁺ HuLy-m2⁺ (= CD7⁺) transfectants isolated after growth in hypoxanthine, aminopterin, thymidine medium and repeated cloning. After several cycles of transfection, > 90% of HuLy-m2⁺ L cells could be detected, by rosetting and by cytofluorography, which showed the transfectants to have a density of CD7 two to five times that found on peripheral blood lymphocytes. Despite this, the 37 kd CD7⁺ dimer could only be identified with difficulty using cell-surface radioiodination and sodium dodecyl sulfate-polyacrylamide gel electrophoresis techniques. An antiserum was produced (C3H anti-HuLy-m2⁺ L cells) which, after absorption, was shown to react with HuLy-m2 antigens present on human thymocytes and lymphocytes and on CD7⁺ transfected L cells.Abbreviations BSA bovine serum albumin - DME Dulbecco's modified Eagle's medium - EDTA ethylenediamine-tetraacetate - HAT hypoxanthine, aminopterin, thymidine - HSV herpes simplex virus - PBL peripheral blood lymphocyte - PBS phosphate-buffered saline - RFC rosette-forming cell - SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis - tk thymidine kinase     

Some factors affecting the composition of tropical ichneumonid faunas

An increasing accumulation of data shows that tropical ichneumonid faunas are no more species-rich than extra-tropical ones, despite the fact that most of their host groups show increased tropical species-richness. This lack of increase in ichneumonid species-richness can be attributed to the absence of groups whose hosts are not present (e.g. Ctenopelmatinae) and poor tropical representation by many groups of diurnal koinobionts (e.g. Campopleginae). Low host density has been postulated as a barrier to tropical koinobiont species-richness, but it is here suggested that this is not the only limiting factor as groups of nocturnal koinobionts, such as the Ophioninae, show increased tropical species-richness. It is postulated that koinobionts have the capability of being able to locate sparse hosts, but as they host-search in flight, a prolonged daytime host-searching period in the tropics would expose them to a high level of predation pressure. By being active at night koinobionts can avoid diurnally active predators. It is also postulated that sparse hosts may be located more easily at night and more habitats may be climatically suitable for ichneumonid activity when they are not subject to direct sunlight. Idiobionts, such as the Mesostenini and Pimplini, are more species-rich and morphologically diverse in the tropics than they are in extra-tropical regions. It is suggested that this results from the fact that tropical idiobionts can be active during the whole of the diapausing period, when their hosts are available, whereas activity by temperate idiobionts is prevented by inclement weather. Although many idiobionts are probably less exposed to predators than koinobionts, many have evolved obvious protective devices.     

Workshop on algal polysaccharides

Summary This workshop was an impromptu event, but the fact that a number of interesting problems were identified by the participants from the floor may indicate that it is worth repeating. If it is to be repeated, however, it is important that notice be given, and that the scope of the workshop be defined in advance, so that participants can be better informed and bring supporting data. The best approach would be to identify a convenor and define the scope of the workshop prior to the first circular for the next Seaweed Symposium; invitations could then be issued by the convenor for specific topics and data, and a very brief program could be issued with the third circular. Such a procedure may very well allow the identification of new areas for research.