Production of semiochemical and allelobiotic agents as a consequence of aphid feeding

Aphids have an extremely intimate relationship with their plant hosts. Although this might suggest that aphid infestation would be largely cryptic, there are a wide range of changes that can be detected behaviourally, chemically and also at the molecular genetic level. Colonisation by aphids can cause release of semiochemicals characteristic of the aphid species and besides reducing acceptability to incoming aphids; these can enable recruitment of specific parasitoids. Some semiochemicals involved in these processes can also influence the defence status of neighbouring intact plants through air or the rhizosphere. Electrophysiological and behavioural studies on the aphids, their parasitoids and other organisms facilitate the identification of compounds having direct effects on plant defence. New developments from work on semiochemicals such as (Z)-jasmone and 6-methyl-5-hepten-2-one, and allelobiotic agents such as 6-hydroxy-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid and 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one, as well as new work on these compounds and others as potential phytopheromones are discussed.     

Global climate change and the politics of disaster

The paper explores the potential political impact of global climate change and, more generally, of natural disaster. Because the affluent West has largely tamed the natural and the social domains, popular clamor for government to anticipate, prevent, and redress disaster increases. I delineate several consequences of the new politics of disaster.     

Female mimicry and resource defense polygyny by males of a tropical rove beetle,Leistotrophus versicolor (Coleoptera : Staphylinidae)

Summary Adults of the staphylinid beetle Leistotrophus versicolor Grav. aggregate at vertebrate dung and carrion where males and females forage for adult Diptera. Some males aggressively exclude others from dung and carrion. Winners in male combat gain access to many females, which are often receptive at these foraging sites. The mating system can be categorized as resource defense polygyny. Males vary greatly in size, are larger than females on average, and have allometrically enlarged mandibles that they use in fighting. Large males consistently defeat smaller ones. Some males employ female mimicry in order to avoid aggression, remaining at dung where they forage and even obtain copulations while being courted by rival males. Female mimicry is most often practiced by males that are smaller than their rivals or by males that are unable to use their jaws aggressively because they are feeding or courting females when encountered by an opponent. Female mimicry is a conditional tactic of mature males; some individuals behave like females toward larger males but attack smaller rivals. Offprint requests to: J. Alcock     

Evaluating Causes of Population Change in North American Insectivorous Songbirds

Although the North American Breeding Bird Survey (BBS) is a principal source of information regarding populations of most North American bird species, many features of the survey complicate analysis of population change. Correlation studies based on BBS data cannot be used to define cause and effect relationships unambiguously. Recently, Böhning-Gaese et al. (1993) presented an analysis of population trends in insectivorous songbirds using data from the BBS. They concluded that predation has played an important role in influencing population trends. We review aspects of the analysis methods for estimating population trends (e.g., observer effects, data subset) and for associating mean trends with species attributes (e.g., confounding of attributes). Using alternative analyses of the same BBS data, we demonstrate that the evidence that predation is associated with population declines is weaker than they suggested. Based on our analyses the only factor among those tested that was consistently associated with population trends was migration status (short-distance migrant/resident versus long-distance migrant) during the period 1978–1987. Also, we present evidence that the harsh winters of the mid-1970s severely depressed populations of short-distance migrant species and may have been responsible for the observed associations between migration status and population trends.     

Miscanthus for Renewable Energy Generation: European Union Experience and Projections for Illinois

Mitigation and Adaptation Strategies for Global Change -     

Genetic evidence of promiscuity in Peromyscus leucopus

Summary We collected pregnant female Peromyscus leucopus from natural populations during the summer of 1987 and 1988 and allowed these females to give birth to their field-conceived young in the laboratory. Blood samples were taken by suborbital puncture and phenotypes of five genetic loci (Esterase-1, trasferrin, hemoglobin, albumin and 6-phosphogluconate dehydrogenase) were studied using horizontal starch-gel electrophoresis to detect multiple paternity in single litters. Only esterase-1 was found to be highly polymorphic, with four alleles in samples of both years. One litter out of 29 in 1987 and 6 litters out of 32 in 1988 contained three different paternal alleles and served as direct evidence of multiple paternity in the field. The proportion of females engaging in multiple matings in natural populations of P. leucopus, assuming that all males were involved in every multiple mating, is 25%–100% (mean 68%). Because it is unlikely that all males are involved in every multiple mating, the actual proportion of females engaging in multiple matings should be greater. Offprint requests to: X. Xia at his Canadian address