Cuticular hydrocarbons of the flea beetles,Aphthona lacertosa and Aphthona nigriscutis,biocontrol agents for leafy spurge (Euphorbia esula)

The adult beetles Aphthona lacertosa and Aphthona nigriscutis, used as biocontrol agents for leafy spurge, had a complex mixture of hydrocarbons on their cuticular surface consisting of alkanes, methylalkanes, alkenes and alkadienes as determined by gas chromatography-mass spectrometry. A trace amount of wax esters were present. In both species, the hydrocarbons were the major cuticular lipid class and the gas chromatographic profiles of the total hydrocarbons were similar. However, the profiles for the saturated hydrocarbon fraction were distinct for each species. Alkanes (n-alkanes and methyl-branched alkanes), alkenes and alkadienes comprised 26, 44 and 30%, respectively, for A. lacertosa, and 48, 26 and 26%, respectively, for A. nigriscutis, of the total hydrocarbons. The major methyl-branched hydrocarbons were 2-methylalkanes: 2-methyloctacosane and 2-methyltriacontane. The major monoene was hentriacontene and the major diene was tritriacontadiene. The species were unique in that a number of di- and trimethyl-branched alkanes were present in minor quantities in which the first methyl branch was on carbon 2 or 3. Examples of structures were 2,10-, 2,12-, 2,6-, 2,4- and 3,7-dimethylalkanes. 2,10,12-Trimethylalkanes and a 2,10,12,24-tetramethylalkane with one methylene between adjacent methyl branch points also were identified. The adjacent methyl branch points of the 2,4- and 2,10,12- and 2,10,12,24-methyl-branched alkanes appeared to cause additional fragmentations in the mass spectra. Dimethylalkanes with an odd number of carbons in the backbone of the molecule were identified as 2,23-dimethylnonacosane and 2,25-dimethylhentriacontane; their mass spectra also corresponded to mass spectra expected for a 2,6 branching sequence. However, a 2,6 branching sequence is not biosynthetically feasible because such a structure has a straight-chain tail with an odd number of carbon atoms beyond the last methyl branch point. The 2,23 and 2,25 branching sequences could be synthesized starting with a primer derived from the amino acid leucine which would account for both the even number of carbons between the branch points and an even number of carbons beyond the last methyl branch point.     

Post hoc assessment of an operational biocontrol program: efficacy of the flea beetle Aphthona lacertosa Rosenhauer (Chrysomelidae: Coleoptera), an introduced biocontrol agent for leafy spurge

Mixed populations of Aphthona lacertosa and Aphthona czwalinae were released at more than 50 locations in Alberta in 1997. Two and 3 years post-release, beetle populations were primarily A. lacertosa, with A. czwalinae forming less than 0.5% of the sampled populations. Beetle densities were moderate (10–70 beetles per m²) or high (>70 beetles per m²) at 14% and more than 60% of the sampled sites in 1999 and 2000, respectively. Larger beetles had greater instantaneous egg loads (r²=0.424,P=0.003). In 2000, the largest beetles were found at moderate density sites and there was a significant negative relationship between beetle size and the time taken to accumulate a degree day threshold of 1230 (for females: r²=0.678,P=0.001). Sites with the most rapid accumulation of degree days have the greatest potential for beetle population growth based on potential fecundity. Changes in leafy spurge percent cover, stem density, and canopy height from 1997 to 2000 were assessed across sites with low (<10 beetles per m²), moderate, and high beetle densities in 2000. Sites with high beetle densities had significantly greater reductions of leafy spurge within 5 m of the release point than sites with low beetle densities (P<0.017). Damage caused by the beetles at high-density sites was often visible as a halo-shaped patch of dead leafy spurge stems. The significant overall reduction of leafy spurge within release patches makes A. lacertosa a promising biocontrol agent for leafy spurge in Alberta.     

Individual and population level determinants of immigration success on local habitat patches: an experimental approach

The effect of population density on immigration success of young root voles was studied in a factorial experiment where immigrants of three different types were translocated from donor populations to recipient habitat patches with experimentally manipulated population sizes. The different types of immigrants were: (1) residents, animals that had remained in their natal patch; (2) colonists, animals that already had successfully dispersed and settled in a new patch; and (3) transients, animals roaming around in a non-habitable matrix area of the donor population. Generally, we found evidence for a negative density-dependent immigration success in terms of survival, rate of sexual maturation and body growth rate. With respect to the survival rate, the degree of density dependence differed among the three immigrant types. Our findings are discussed with respect to the degree of rescue effect immigrants may have on a recipient population depending on population density, and also its relevance concerning translocation of individuals for conserving endangered populations.     

The influence of glucosinolates and sugars on feeding by the cabbage stem flea beetle,Psylliodes chrysocephala

Agar was used as an artificial substrate to investigate the feeding behaviour of the cabbage stem flea beetle,Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae), an important pest of winter oilseed rape (Brassica napus) in Europe. Both glucosinolates and sugars stimulated feeding when added to agar. The amount of feeding that occurred was affected by the type and concentration of glucosinolate and surgar and also by combinations of components. Although glucosinolates were potent feeding stimulants forP. chrysocephala, they were not a prerequisite for feeding, nor does it seem likely that glucosinolate profiles are used by this species to discriminate amongst cruciferous plants at the gustatory level.     

Characterization, expression and function of DORMANCY ASSOCIATED MADS-BOX genes from leafy spurge

DORMANCY ASSOCIATED MADS-BOX (DAM) genes are related to AGAMOUS-LIKE 24 and SHORT VEGETATIVE PHASE genes of arabidopsis and are differentially regulated coordinately with endodormancy induction and release in buds of several perennial plant species. DAM genes were first shown to directly impact endodormancy in peach where a deletion of a series of DAM resulted in loss of endodormancy induction. We have cloned and characterized several MADS box genes from the model perennial weed leafy spurge. Leafy spurge DAM genes are preferentially expressed in shoot tips and buds in response to cold temperatures and day length in a manner that is relative to the level of endodormancy induced by various environmental conditions. Over-expression of one DAM gene in arabidopsis delays flowering. Additionally, we show that at least one DAM gene is differentially regulated by chromatin remodeling. Comparisons of the DAM gene promoters between poplar and leafy spurge have identified several conserved sequences that may be important for their expression patterns in response to dormancy-inducing stimuli.     

Carbon and nitrogen reserves of leafy spurge (Euphorbia esula) roots as related to overwintering strategy

Leafy spurge ( Euphorbia esula L.), a serious perennial weed of temperature range and pasture lands, has continued to colonize despite various control strategies. The persistence of this species can be attributed in part to the presence of an extensive root system containing abundant organic reserves. These components, established towards the end of the growing season, are remobilized to support early spring growth. Carbohydrates comprise the bulk of reserve material with late fall incrents in free sugars being associated with reductions in starch content. Nitrogenous components undergo significant seasonal fluxes, with free amino acids and soluble proteins reaching maxima during late fall. Asparagine, glutamic acid, serine, ornithine, proline, arginine and aspartic acid all contribute significantly to the storage of nitrogen. Changes in nitrate content are associated with the overwintering process. These observations are indicative of the role that nitrogen plays in the overwintering strategy and regenerative capacity of leafy spurge roots.     

Interaction of rhizobacteria with leafy spurge (Euphorbia esula L.) callus tissue cells

The interaction of two rhizobacterial isolates,Pseudomonas fluorescens isolate LS 102 andFlavobacterium balustinum isolate LS 105, with leafy spurge cells at the cellular level was studied using scanning and electron microscopy. Leafy spurge callus tissue inoculated with either isolate showed considerable changes compared to non-inoculated tissue. The attachment of rhizobacteria to cell surfaces was associated with the elaboration of fibrillar material which may anchor bacteria to surfaces and contribute to mediation of the phytotoxic effect caused by rhizobacteria. At the ultracellular level, inoculated callus tissue showed numerous cell alterations including esiculation and convolution of the plasmalemma, cell wall degradation and disorganization of the cytoplasm, similar to those detected in the whole plant. It is concluded that callus tissue may provide an excellent working model to investigate the mode and/or mechanism of action of potential biocontrol agents on their host plants.     

The influence of immigration on demography of sympatric voles

We studied the influence of immigration on the dynamics ofMicrotus ochrogaster Wagner, 1842 andM. pennsylvanicus Ord, 1815 populations in alfalfa, bluegrass, and tallgrass prairie in east-central Illinois for 25 years. The numbers of immigrants in a site were positively correlated with overall population densities of the species in the vicinity of the study sites and within the study site. Population density of the other species was not correlated with immigration of either species. Immigrants did not differ significantly from residents with respect to sex-ratio and reproductive condition. Persistence of immigrantM. pennsylvanicus was lower than that of resident adults in all three habitats, while that of immigrantM. ochrogaster was lower than that of resident adults in alfalfa, where the species was most abundant. Neither the absolute number of immigrants nor the proportion of the population composed of immigrants indicated an effect of immigrants on among- and within-habitat differences in demography and population fluctuations of either species. Immigrants may have been an important factor in maintenance ofM. pennsylvanicus in alfalfa, a low-quality habitat, but the influence of immigration on the dynamics of populations inhabiting other habitats was insubstantial.     

Effect of drying on yield and calorific values of extractables from leafy spurge (Euphorbia esula)

The effect of dehydration on yield and calorific values has been investigated for oils, hydrocarbons, and polyphenols extracted from leaves of Euphorbia esula/ (leafy spurge). Methods of dehydration employed were with a warm oven (50 degrees C), a hot oven (105 degrees C), at room temperature (25 degrees C), and with freeze drying. Generally, dehydration resulted in a loss of yield for all extractives. Noteworthy exceptions were oil yields from the warm-oven- or air-dried biomass which did not differ significantly from fresh tissue. Significant differences in calorific values (range 4643-5192 cal/g) were observed for each category of whole leafy biomass dehydrated as indicated above. Dehydration reduced the calorific value of oils (range 9483-10,095 cal/g) but tended to increase the calorific values of polyphenols (range 4178-6033 cal/g). NMR spectroscopy of the oil fraction suggested that dehydration did not grossly alter the composition of oils, despite differences in yield and calorific values.     

Matrix habitat and plant damage influence colonization of purple loosestrife patches by specialist leaf-beetles

The characteristics of the matrix, that is, the unsuitable habitat connecting host-plant patches may facilitate or limit herbivore movement thus affecting their population dynamics. We evaluated the effect of matrix habitat, distance between patches, and plant damage on movement of two leaf-beetles (Galerucella calmariensis Linnaeus and G. pusilla Duft) introduced to North America as biocontrol agents of the invasive purple loosestrife (Lythrum salicaria Linnaeus). Mark-recapture/resight experiments indicated (1) that leaf-beetles are more likely to colonize purple loosestrife patches surrounded by meadow than forest; (2) that previously attacked purple loosestrife plants are more likely to be colonized by Galerucella spp. than unattacked plants, especially in the forest habitat; and (3) that leaf beetle colonization of purple loosestrife decreased with distance from release point. Low colonization rates of purple loosestrife patches embedded in forests suggest either insufficient detection or active avoidance of such habitats. Biological control programs intend to manage dispersal of specialized insect herbivores for the purpose of sufficient and sustained control of their host plants. Such management needs to be informed by knowledge of interactions of habitat structure, plant damage, and dispersal capabilities of herbivores to facilitate release programs and control at the local and regional level.     

The role of habitat patches on mammalian diversity in cork oak agroforestry systems

Habitat patches, depending on the degree of differentiation from the matrix, can add few or many elements to the species pool of a particular landscape. Their importance to biodiversity is particularly relevant in areas with complex landscapes, where natural, naturalized, or managed habitats are interspersed by small patches of habitat types with very different biophysical characteristics; e.g., fruit orchards and riparian areas. This is the case of the montado landscape, a cork oak agroforestry system that largely covers south-western Portugal. We evaluated whether the high mammalian biodiversity found in this system is, in part, the cumulative result of the species found in the non-matrix habitats. Our results indicate that in areas where there are inclusions of orchards/olive yards and riparian vegetation in the cork oak woodland, a significantly higher number of mammalian species are present. We further detected a positive effect of low human disturbance on mammal diversity. Ultimately, our results can be used by managers to augment their management options, since we show that the inclusion and maintenance of non-matrix habitat patches in cork oak agro-silvo-forestry systems can help to maximize mammal biodiversity without compromising services associated with agriculture and forestry.     

Organogenesis in cell cultures of leafy spurge (Euphorbiaceae) accessions from Europe and North America

Plants were regenerated from leafy spurge (Euphorbia esula L.) cell suspensions obtained from stem callus. A North Dakota accession was highly regenerable, but two accessions from Oregon and Austria formed only a few plantlets. Organogenesis occurred in media without growth regulators, under fluorescent lights (30 to 90 E m^–2 s^–1, 14 h photoperiod). Organogenesis was greatest in larger size clumps subcultured during maximum cell growth into media containing a reduced:oxidized nitrogen ratio of 33:67. Roots formed first and some clumps produced shoots. Organogenic suspension cultures also were initiated from hypocotyl and root segments of germinated seedlings, directly in liquid medium. Plantlets of the North Dakota accession formed in vitro adapted to greenhouse conditions. They were phenotypically similar to the parent plants.     

Combined effects of immigration potential and habitat quality on diadromous fishes

In river systems, considerable debate exists as to why small-scale conservation with a primary focus on habitat quality brings little improvement to biological communities. To reveal potential causes of the enigmatic consequences, further explorations should focus on how species’ response to local environments is determined within a watershed. Here, we examined how immigration potential influences habitat associations of four diadromous fishes in the Shubuto River system in Hokkaido, Japan: sculpins (Cottus sp. ME and C. hangiongensis), gobies (Gymnogobius opperiens) and sea lamprey larvae (Lethenteron japonicum). We used closeness to the sea (i.e., distance from the sea) as a proxy for immigration potential, since the source of immigrants of the diadromous fishes is the river mouth. A multilevel modeling approach revealed that immigration potential had a “bottom-up effect” on local habitat–abundance relationships (current velocity and substrate coarseness), but habitat preferences did not vary along the gradient of immigration potential. This likely reflects the limited dispersal capabilities of the study species, whereby shorter travel distances may greatly enhance colonization success. Our study raises the possibility that the effectiveness of small-scale riverine conservation can be improved by selecting areas where successful colonization would be expected. Explicitly incorporating this consideration into conservation decision-making would help achieve greater success in environmental restoration and preservation actions.     

Local species immigration,extinction, and turnover of butterflies in relation to habitat area and habitat isolation

Temporal dynamics of insect communities in terrestrial habitat fragments have been rarely studied. Here it was tested whether immigration, extinction, and turnover of butterfly species change with area and isolation of 31 calcareous grasslands. The area ranged from 0.03 to 5.14 ha, the isolation index from 2,100 to 86,000 (edge-to-edge distance 55–1,894 m). In both study years (1996, 2000), the total number of individuals (16,466, 15,101) and species (60, 54) sampled across all sites were similar and number of species increased with area in both years indicating an equilibrium. Rates of extinction (38% for habitat specialists vs. 20% for generalists) and turnover (51% vs. 35%) were higher, and rates of immigration (11% vs. 30%) were lower for habitat specialists than for generalists. Extinction and turnover rates decreased with increasing fragment size for both specialist (n =25 species) and generalist (n =36) butterflies, but specialists showed a significantly steeper decrease with increasing fragment size than generalists. Immigration rates increased with area. As a result, species number of habitat specialists declined in small habitats but not in large habitats between 1996 and 2000. No significant impact of habitat isolation on the butterfly community was found. The data suggest that large habitat fragments are of special importance for the conservation of the specialized, most endangered butterfly species. Habitat isolation appears to be less important, as butterflies can cope with the habitat mosaic in our study region.Due to an error in the citation line, this revised PDF (published in December 2003) deviates from the printed version, and is the correct and authoritative version of the paper.