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Summary 1.Although it is well established that different plant species vary considerably in the quality of pollinator rewards they offer, it is unclear how plant reproductive systems, in particular an obligate dependence on insects for pollination, might influence the evolution of pollinator rewards. Moreover, unlike the interaction between nectar reward and pollinator visitation, we have a limited understanding of the way in which pollen quality influences pollinator foraging behaviour. 2. We quantified the pollen protein and amino acid content for 23 NW European plant species. Pollen quality was compared with breeding system (facultative-vs. obligate insect-pollinated). A subset of 18 plants was sampled from a single habitat. For these we compared the proportion of pollen collection visits made by bumblebees with the quality of pollen offered. 3. We found a significant association between pollen quality and reproductive system; pollen of obligate insect-pollinated species contained higher protein content. We also found a significant relationship with pollinator use; plants most frequently visited by pollen-collecting bumblebees produced the highest-quality pollen. 4. We discuss how the close relationship between pollen quality and bumblebee attraction may have important benefits for plant reproductive success. However, we also show how the disruption of this mutualism can have detrimental consequences for plant and pollinator alike.

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Summary 1.The relative palatabilities of the seedlings and adults of a range of British herbaceous plant species (14 annuals and 15 perennials) were compared using a generalist native herbivore (the slug Deroceras reticulatum) in a food-choice experiment. A palatability index (0 to 1) was devised. 2. A general linear model analysis showed that, overall, there was a highly significant difference between seedling and adult palatability. 3. In the majority of cases, seedlings were more palatable than adults. However, in species with highly palatable adults the opposite tended to be the case. 4.No consistent difference between annual and perennial species was seen with respect to the relative palatabilies of adults vs seedlings. 5.No evidence of a trade-off between seedling palatability and relative growth rate was found. 6. In view of the role that selective seedling predation may play in determining species composition in the field, the results of this experiment indicate the need for caution in making ecological inferences from the exclusive use of adult material in palatability tests.

Exposure to decreasing oxygen tensions progressively increased xanthine dehydrogenase (XD) and xanthIne oxidase (XO) activities over 48 hr in cultured pulmonary artery endothelial cells (EC) without altering XD/XO ratios. Increases in XD and XO activity in EC induced by hypoxia were associated upon reoxygenation with increased (P < 0.05) extraceflular superoxide anion (O2 ) levels that were inhibited by treatment with XO inhibitors (tungsten, allopurinol) or an anion-channel blocker (4,4'-diisothiocyanatoslbene-2,2'-disulfonic acid). EC monolayers subjected to hypoxia/reoxygenation also leaked more preioaded 51Cr, were more adherent to neutrophils, and permitted greater albumin transit than control monolayers.Treatment with tungsten, aflopurinol, and/or superoxide dismutase decreased (P < 0.05) 5'Cr release, neutrophil adherence, and albumin transit in EC monolayers exposed to hypoxia/reoxygenation. We conclude that prolonged hypoxia increases both XO and XD activity in EC and may predispose the endothelium to oxidative and inflammatory damage. Recently, we found a marked suppression of XD and XO activity in EC exposed to high oxygen tensions (6). Accordingly, we examined the effects of prolonged hypoxia on EC XD and XO activities. We found that prolonged hypoxia increased both XD and XO activities in cultured EC and, further, that increases in XD and XO activities contributed to 0j -mediated injury and neutrophil adherence to EC. Measurement of XD and XO Activity. EC were grown in 75-cm2 flasks (Falcon, Becton Dickinson). Medium was removed from confluent EC monolayers and replaced with Hanks' balanced salt solution/5% fetal calf serum; then flasks were placed in sealed chambers, flushed with 5% C02/0-95% 02 and 95-0o N2, and incubated at 370C. 02 tensions of parallel saline samples measured with a Clark electrode were 15, 33, 66, 120, and 660 torr (1 torr = 133.3 Pa) after 48-hr incubations in 0, 3, 10, 21, and 95% 02, respectively, at Denver altitude. In some experiments, EC were grown for three-passages in sodium tungstate (10 ppm final) before use; or allopurinol (100 AM), 4,4'-diisocyanatostilbene-2,2'-disulfonic acid (DIDS, 100 ,AM), or SOD (10 jug/ml) was added to EC before incubation. Monolayers of EC were triply washed with phosphate-buffered saline (20 mM, pH 7.4), mechanically harvested with a plastic policeman in 50 mM phosphate buffer, pH 7.8/1 mM EDTA/1 mM phenylmethylsulfonyl fluoride/1 mM dithioerythritol/SOD at 20 ,ug/ml/catalase at 20 ,ug/ml and sonicated on ice. Nuclei were removed by centrifugation, and supernatants were desalted by using a Centricon filter system. Aliquots (0.25 ml) were incubated aerobically at 370C for 3 hr with xanthine (200 AuM) to measure XO activity or xanthine plus NAD' (300 AM) to measure XO plus XD activity in a final volume of 0.5 ml. Lactic dehydrogenase (70 units per ml) and pyruvate (1.75 mM) were added to tubes containing NAD' to prevent inhibition of XD by NADH (9). Baseline values were obAbbreviations: XO, xanthine oxidase; O-., superoxide anion; XD,...

Much of the ecology of rare bumblebee species remains poorly understood and in need of further study. It has recently been suggested that differences in the range and rate of decline among bumblebee species may relate to differences in their degree of habitat specialization. We examine biotope use by 17 bumblebee species in the Hebrides, southern UK and South Island, New Zealand. We identify a cluster of widespread and abundant species that occur in almost all biotopes and exploit man-made environments such as gardens and arable margins; this group corresponding to the "mainland ubiquitous" species of previous studies. A second grouping of species includes those associated to varying degrees with heathland. It is notable that some species occupy markedly different biotopes in different parts of their range; for example B. soroeensis is found largely on upland heaths in the Hebrides, but on calcareous grassland in the south. Some species, such as B. subterraneus and B. distinguendus, now survive only in specific rare biotopes and could be mistaken for habitat specialists, but it is clear from their historic distributions that they formerly occupied a broader range of biotopes. Surviving populations of several of the species that have declined most (B. distinguendus, B. sylvarum, B. muscorum sladeni, B. humilis) exhibit a markedly coastal distribution, when once they were widespread inland. We suggest that this is probably simply because some coastal biotopes are less amenable to agricultural improvement, and so more have escaped the detrimental effects of intensive farming. Our results concur with previous suggestions that bumblebees are generally not habitat specialists, so that the conservation of most bumblebee species could be achieved by restoration of flower-rich unimproved meadows.

Summary 1.Calyptrate flies include numerous species that are disease vectors and have a high nuisance value, notably Musca domestica . Populations are often associated with livestock farms and domestic waste disposal facilities such as landfill, where the accumulating organic matter provides suitable breeding conditions for a range of species. 2. We examined the relationship between fly numbers and weather conditions using a 4-year data set of weekly fly catches from six sites in southern UK, together with meteorological data. The first 3 years were used to develop predictive models, and these were then used to forecast fly populations in the fourth year. The accuracy of these predictions was assessed by comparison with the actual fly catches for that year. Separate models were developed for M. domestica , Calliphora spp. and all calyptrate flies combined. 3. Predictions based only on humidity, temperature and rainfall were strongly correlated with observed data ( r 2 values ranged from 0·52 to 0·84), suggesting that fly population changes are largely driven by the weather rather than by biotic factors. We can forecast fly populations so that control measures need only be deployed when weather conditions are suitable for a fly outbreak, reducing the need for prophylactic insecticide use. 4. Climate change was simulated using the most recent predictions of future temperature increases. Our models predicted substantial increases in fly populations up to 244% by 2080 compared with current levels, with the greatest increases occurring in the summer months. 5. Synthesis and applications. Models developed use weather data to predict populations of pestiferous flies such as M. domestica , which may prove valuable in integrated control programmes. These models predict substantial increases in fly populations in the future under likely scenarios of climate change. If this occurs we may expect considerable increases in the incidence of fly-borne disease.