Larval performance of the oriental fruit moth across fruits from primary and secondary hosts

A common characteristic of many invasive herbivorous insects is their ability to utilize a broad range of host plants. By using various hosts in phenological succession, multivoltine herbivores may increase the number of successful annual generations, at the same time as potentially increasing their overall fitness. To achieve such success, herbivores must be able to develop efficiently on the nutritional resources offered by their hosts. The oriental fruit moth Cydia (= Grapholita) molesta (Busck) (Lepidoptera: Tortricidae) is one of the most damaging invasive insect species. Peach (Prunus persica) is its primary host, whereas the pome fruits apple (Malus × domestica Borkh) and pear (Pyrus communis) are considered as secondary hosts. In many parts of its geographical range, including southern Europe, populations of the moth switch from peach to apple or pear orchards during the growing season. The present study tests whether this temporal switch is supported by the physiological capability of the larvae with respect to developing efficiently on fruits of these taxonomically‐related host plants. Larvae are reared on peach, apple or pear fruits; several life‐history traits are measured; and correlations between the traits are calculated. The results obtained show that larvae do not have the same physiological capability with respect to using apple or pear fruits as hosts compared with using peach fruit. Pear fruit in particular is a sub‐optimal diet. These findings suggest that, in the case of continuous geographical expansion, concomitantly with global warming, apple orchards might support oriental fruit moth populations better than pear orchards, and that the switch onto novel hosts might be accompanied by restricted population growth.     

Effects of Blue Light on the Vertical Colonization of Space by White Clover and their Consequences for Dry Matter Distribution

The morphology of white clover is very sensitive to the lightenvironment, especially to the ratio of red:far-red light andto photon irradiance. However, less is known about the effectsof blue light on clover morphogenesis. Cuttings of white cloverwere grown for 56 d in two controlled chambers receiving lightwith similar photosynthetic efficiency and phytochrome photoequilibriumstate but different levels of blue light: some plants were grownunder orange light (very low blue light, 0.02 µmol m^-2s^-1)or under white light containing blue light (83 µmol m^-2s^-1).Other plants were switched from white light to orange lightorvice versa,after 30 d. The absence of blue light modifiedthe growth habit of clover and raised the laminae in the upperlayer of the canopy by increasing petiole length, and petioleangle from the horizontal, and by raising stolons above theground surface. Moreover, the absence of blue light had no effecton total leaf area and total dry weight per plant, but increasedthe leaf area and biomass of petioles of the main axis. Largerpetioles and laminae were associated with the allocation ofmore dry weight to the petiole at the same petiole thicknessbut with thinner laminae. These results indicate that a decreasein blue light is involved in the perception of, and adaptationto, shading by the plant.Copyright 1997 Annals of Botany Company Biomass allocation; blue light; growth habit; leaf area; light quality; photomorphogenesis; Trifolium repensL.; white clover     

Development of a stable isotope index to assess decadal-scale vegetation change and application to woodlands of the Burdekin catchment, Australia

Forty-four study sites were established in remnant woodland in the Burdekin River catchment in tropical north-east Queensland, Australia, to assess recent (decadal) vegetation change. The aim of this study was further to evaluate whether wide-scale vegetation ‘thickening’ (proliferation of woody plants in formerly more open woodlands) had occurred during the last century, coinciding with significant changes in land management. Soil samples from several depth intervals were size separated into different soil organic carbon (SOC) fractions, which differed from one another by chemical composition and turnover times. Tropical (C₄) grasses dominate in the Burdekin catchment, and thus δ¹³C analyses of SOC fractions with different turnover times can be used to assess whether the relative proportion of trees (C₃) and grasses (C₄) had changed over time. However, a method was required to permit standardized assessment of the δ¹³C data for the individual sites within the 13 Mha catchment, which varied in soil and vegetation characteristics. Thus, an index was developed using data from three detailed study sites and global literature to standardize individual isotopic data from different soil depths and SOC fractions to reflect only the changed proportion of trees (C₃) to grasses (C₄) over decadal timescales. When applied to the 44 individual sites distributed throughout the Burdekin catchment, 64% of the sites were shown to have experienced decadal vegetation thickening, while 29% had remained stable and the remaining 7% had thinned. Thus, the development of this index enabled regional scale assessment and comparison of decadal vegetation patterns without having to rely on prior knowledge of vegetation changes or aerial photography.     

Stability of population structure and genetic diversity across generations assessed by microsatellites among sympatric populations of landlocked Atlantic salmon (Salmo salar L.)

It may often be necessary to perform genetic analyses of temporal replicates to estimate the significance of spatial variation independently from that of temporal variation in order to ensure the reliability of estimates of a defined population structure. Nevertheless, temporal studies of genetic diversity remain scarce in the literature relative to the plethora of empirical studies of population structure. In vertebrates, a limited number of studies have specifically assessed the temporal stability of population structure for more than one generation. In this study, we performed a microsatellite analysis of DNA obtained from archived scales to compare the population structure among four sympatric landlocked populations of Atlantic salmon ( Salmo salar ) over a time frame of three to five generations. The same patterns of allele frequency distribution, θ, R _ST and genetic distance estimates were observed among populations for two time periods, confirming the temporal stability of the population structure. Despite population declines and stocking during this period, no statistically significant changes in intrapopulation genetic diversity were apparent. This study illustrates the feasibility and usefulness of microsatellite analysis of temporal samples, not only to infer changes of intrapopulation genetic diversity, but also to assess the stability of population structure over a time frame of several generations.