bluuebunny/crossref_metadata_2025 huggingface dataset:
Are there latitudinal gradients in species turnover?
Authors: Koleff Patricia , Lennon Jack J. , Gaston Kevin J.
Published: October 2003

Aim  To examine the effect on the observed relationship between spatial turnover and latitude of both the measure of beta diversity used and the method of analysis.

Location  The empirical analyses presented herein are for the New World.

Methods  We take the spatial distributions of the owls of the New World as an exemplar data set to investigate the patterns of beta diversity across latitudes revealed by different analytical methods. To illustrate the strengths and weaknesses of alternative measures of beta diversity and different analytical approaches, we also use a simple random distribution model, focusing in particular on the influence of richness gradients and landmass geometry.

Results  Our simple spatial model of turnover demonstrates that different combinations of analytical approach and measure of beta diversity can give rise to strikingly different relationships between turnover and latitude. The analyses of the bird data for the owls of the New World demonstrate that this observation extends to real data.

Conclusions  For the particular assemblage considered, we present strong evidence that species richness declines at higher latitudes, and there is also some evidence that species turnover is greater nearer the equator, despite conceptual and practical difficulties involved in analysing spatial patterns of species turnover. We suggest some ways of overcoming these difficulties.
Modelling differential extinctions to understand big cat distribution on Indonesian islands
Authors: Wilkinson David M. , O'Regan Hannah J.
Published: October 2003

Aims To model differential extinction rates for island populations of tigersPanthera tigrisand leopardsP. pardus.

Location Indonesia.

Methods We built VORTEX population models of tiger and leopard populations on an island the size of Bali (3632 km2), using data from the literature.

Results The tiger populations were less extinction prone than the leopard populations. This was unexpected as tigers had the smaller population sizes and, as such, might be assumed to be more extinction prone. We identified several aspects of tiger breeding biology that explain the result.

Main conclusions Sea level reconstructions suggest that both tiger and leopard would have been present in Java, Sumatra and Bali at the end of the last glacial. Our model provides a plausible mechanism based on population ecology to explain why these leopard populations were more extinction prone than the tiger populations. In addition it illustrates the potential utility of population ecology models in understanding historical patterns in biogeography.
Geomicrobiology of deep‐sea deposits: estimating community diversity from low‐temperature seafloor rocks and minerals
Authors: Rogers Daniel R. , Santelli Cara M. , Edwards Katrina J.
Published: October 2003

The role of deep‐sea microbial communities in the weathering of hydrothermal vent deposits is assessed using mineralogical and molecular biological techniques. The phylogenetic diversity of varied deep‐sea bare rock habitats associated with the oceanic spreading centre at the Juan de Fuca Ridge was accessed using restriction fragment length polymorphism (RFLP) and rDNA sequencing. The mineralogical composition of the deposits used for phylogenetic analysis was determined by X‐ray diffraction in order to determine the proportion and composition of sulphide minerals, and to determine degree of alteration associated with each sample. RFLP analyses resulted in 15 unique patterns, or Operational Taxonomic Units (OTUs). Most environments examined were dominated by only one or two OTUs, which often comprised approximately 60% of the rDNA clones generated from that environment. Only one environment, the Mound, had a representative rDNA clone from every OTU identified in this study. For one other environment, ODP sediments, rDNA clones were all contained in a single OTU. The diversity of the microbial community is found to decrease with decreasing reactivity of the sulphide component in the samples and with increasing presence of alteration products. Phylogenetic analyses reveal that OTUs contain representatives of the epsilon‐, beta‐ and gamma‐subdivisions of the Proteobacteria. OTU1, which dominates clone libraries from every environment and is increasingly dominant with increasing rock alteration, is closely related to a group of chemolithoautotrophic iron‐oxidizing bacteria that have been recently isolated from the deep sea. The apparent abundance and widespread distribution within the samples examined of the putative iron‐oxidizing bacteria that may be represented by OTU1 suggests that this physiological group could play an important role in rock‐weathering and carbon fixation at the seafloor.
Biological and hydrogeological interactions affect the persistence of 17β‐estradiol in an agricultural watershed
Authors: Herman J. S. , Mills A. L.
Published: October 2003

17β‐estradiol (E2), one of the natural estrogen compounds, is an endocrine disruptor, and low levels in natural waters can impair the reproductive health of aquatic organisms. Its presence has been reported in animal faecal wastes and some aquatic habitats, including surface waters impacted by intense animal agriculture or sewage contamination. Little is known about its transport in hydrological systems or its persistence in water supplies. We routinely sampled stream and soil water over the growing season in an instrumented 1.2‐km2 agricultural watershed in central Virginia. E2 concentrations in stream water ranged from 0.01 to 0.12 ng mL−1; soil‐water values ranged from 0.03 to 0.18 ng mL−1. The highest concentrations were observed early in the growing season shortly after application of composted poultry litter to the cropped fields, and values decreased both with hydrological transport distance from the cropped field and over the course of the summer. Given the known application rate, E2 must be lost from the soil solution, and we explored biodegradation as a mechanism for this loss. A bacterial consortium cultured from the poultry compost biodegraded E2 in laboratory flasks amended with solutions of 1 : 1 acetate : glucose at concentrations ranging from 0.1 to 10 g L−1 dissolved organic carbon (DOC), spiked with 1.8 ng mL−1 E2, and incubated at different temperatures. A loss of 97–98% of the initial E2 occurred within 180 h in experiments at 22 °C and 28 °C with 1.0 or 0.1 g L−1 DOC amendments. Higher DOC concentrations and lower temperatures slowed the rates of reaction, suggesting that more readily available carbon inhibits use of the E2 by degrading micro‐organisms. The rapid rates of biodegradation in the laboratory incubations are inconsistent with the persistence of E2 in the watershed. This suggests that either the rates of biodegradation are reduced compared with the laboratory experiments or that E2 probably interacts with the components of the natural environment through complexation, sorption or abiotic transformation in the ageing process that leads to diminished bioavailability.
In situ growth of Gallionella biofilms and partitioning of lanthanides and actinides between biological material and ferric oxyhydroxides
Authors: Anderson C. R. , Pedersen K.
Published: October 2003

Gallionella ferruginea is an iron‐oxidizing chemolithotrophic micro‐organism that lives in low‐oxygen conditions (0.1–1.5 mg L−1 saturation). It produces a stalk structure from the concave side of the cell depending on population development, pH and redox conditions. After Gallionella oxidizes ferrous iron, bacteriogenic iron oxides (BIOS) precipitate on the stalk material and over time the stalks and/or the precipitated BIOS attenuate trace metals from surrounding groundwater. Gallionella ferruginea biofilms were cultured in situ in an artificial channel (2000 × 300 × 250 mm) using groundwater sourced from a borehole 297 m below sea level in the Äspö Hard Rock Laboratory in southern Sweden. The pH of the groundwater in the channels was always between 7.4 and 7.7 with oxygen saturation below 1.5 mg L−1 and Eh between 100 and 200 mV. Oxygen eventually declined to <0.3 mg L−1, terminating prolific biofilm growth. Biofilms formed within 2 weeks and were sampled every 2 weeks over 3 months. Cell number, stalk length and ferric iron concentration were measured for each sample and trace metal concentration was measured by inductively coupled plasma mass spectrometry. Results from well‐developed in situ biofilms suggest that Gallionella could concentrate metals at levels up to 1 × 103‐fold higher than found within the host rock and more than 1 × 106 times the levels found in the groundwater. These new experiments were used to support the results from the well‐developed biofilms and to relate biofilm development and population characteristics to metal attenuation. After 3 months, rare earth element (REE) plots indicated that BIOS can accumulate metals at levels up to 1 × 104‐fold higher than found in the groundwater and fractionate heavy rare earth elements over light rare earth elements. Generally the presence of the organic phase promotes the adsorption of all lanthanides and actinides that are not adsorbed by the inorganic phase. The iron oxides are directly correlated with stalk length (R = 0.96), indicating that rapid REE and actinide adsorption requires both iron oxides and a nucleating biological structure for the iron oxides.
Microbial diversity of a sulphide spire located in the Edmond deep‐sea hydrothermal vent field on the Central Indian Ridge
Authors: Hoek Joost , Banta Amy , Hubler Forrest , Reysenbach Anna‐Louise
Published: October 2003

A culture‐independent molecular phylogenetic survey was carried out for a bacterial and archaeal community of a mineralized crust coating a sulphide spire, which was collected from the Edmond vent field (23° S, 69° E, 3300 m depth) on the Central Indian Ridge. Small‐subunit rRNA genes (16S rDNA) were amplified from environmental DNA by PCR utilizing Bacteria‐specific, and Archaea‐specific 16S rDNA primers. PCR products were cloned and 26 bacterial and nine archaeal unique sequence types (phylotypes) were identified from 150 clones analysed by restriction fragment length polymorphism, representing eight and four distinct lineages, respectively. The majority (>90%) of the bacterial phylotypes group with the ɛ‐Proteobacteria and confirms the global prevalence of ɛ‐Proteobacteria in deep‐sea hydrothermal environments. Among the ɛ‐Proteobacteria, >40% of the phylotypes were closely related to the recently isolated deep‐sea vent thermophilic chemolithoautotrophic sulphur‐reducer, Nautilia lithotrophica. A single bacterial sequence was nearly identical (99% similarity) to the thermophilic hydrogen‐oxidizing Hydrogenobacter thermolithotrophum, and is the first report of Hydrogenobacter at deep‐sea hydrothermal vents. A majority (97%) of the archaeal phylotypes grouped with the ‘Deep‐sea Hydrothermal Vent Euryarchaeotal Group’, a phylogenetic lineage of uncultured Archaea that have only been reported from other deep‐sea hydrothermal vents on the Mid‐Atlantic Ridge, East Pacific Rise, Juan de Fuca Ridge, Isu–Ogasawara Arc, Okinawa Trough and the Manus Basin. A single sequence was closely related to the hyperthermophilic sulphur‐reducing Thermococcales frequently found in diverse deep‐sea vent environments. Scanning electron micrographs of the mineralized crust reveal abundant filamentous, rod and coccoidal forms encased in sulphur and sulphide mineral precipitate, suggesting that the thermophilic chemolithoautorophs and sulphide‐producing heterotrophs may influence the architecture and sulphur cycling of the sulphide spire.
Life tables and predation activity of Orius laevigatus and O. albidipennis at three constant temperatures
Authors: Cocuzza G. E. , De Clercq P. , Lizzio S. , Van de Veire M. , Tirry L. , Degheele D. , Vacante V.
Published: October 2003

Effects of three constant temperatures (15, 25, and 35 °C) on development and reproduction of Orius laevigatus (Fieber) and O. albidipennis (Reuter) (Heteroptera: Anthocoridae) and on their predation activity against the western flower thrips Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) were investigated in the laboratory. Small rooted plants of Spanish pepper (Capsicum annuum L. cv. ‘Creta’, long red) served as oviposition substrate and moisture source. Survival of eggs and nymphs of both species was high at 25 and 35 °C. At 15 °C, none of the eggs of O. albidipennis hatched and the number of nymphs completing the immature stage was extremely low. Developmental time of nymphs was not significantly different between species at 15 °C, but at 25 and 35 °C nymphs of O. laevigatus took significantly longer to develop than those of O. albidipennis. Females of O. albidipennis lived longer than those of O. laevigatus at 15 and 35 °C, but no differences were observed at 25 °C. Fecundity of O. albidipennis was greatly reduced at 15 °C, whereas a temperature of 35 °C was close to the upper reproduction threshold of O. laevigatus. Fecundity was highest at 25 °C for both species. At 15 °C, the intrinsic rate of increase (rm) reached a minimum for both species. For O. albidipennis, the rm‐value increased with temperature (0.121 at 25 °C and 0.202 at 35 °C), whereas for O. laevigatus it peaked at 25 °C (0.105) but decreased at 35 °C (0.051). At 15 and 25 °C, adults of O. laevigatus consumed more F. occidentalis adults during their total lifespan than those of O. albidipennis, but the latter showed a better predation activity at 35 °C; in all treatments, however, adults of O. laevigatus consumed more prey per day than did those of O. albidipennis. The performance of both anthocorids at the different temperatures is discussed in relation to their practical use in integrated pest control programmes.
Host selection by winged summer females of the aphid Sitobion avenae
Authors: Lushai G. , Sherratt T.N. , David O. , De Barro P.J. , Maclean N.
Published: October 2003

A total of 55 parthenogenetic lineages of the grain aphid, Sitobion avenae F. were established from single clones collected from winter wheat (agricultural host) and cocksfoot (natural host) at various locations in southern Britain. RAPD‐PCR profiles indicated that these lineages consisted of at least 15 genetically distinct clones. Twenty winged individuals (alatae) of known weight were taken from each lineage and presented with a choice of wheat and cocksfoot hosts (with a total leaf area each of 2 cm2) held in petri dishes (laboratory experiments) and flowerpots (field experiments). In both experimental designs host preferences were determined by a ranking of a proportion of counts (limited to −1 →+1) of the progeny produced on each host after 5 days. Overall, alatae tended to prefer the agricultural host. However, alatae from individual clones found exclusively on wheat generally had a higher preference for wheat than alatae from individual clones found exclusively on cocksfoot. Wheat‐derived lineages (aphid genotypes that were collected on wheat but also present on cocksfoot) showed a significantly greater preference for the agricultural host than the cocksfoot‐derived lineages. Individuals from a wheat‐derived lineage had significantly higher observed and potential progeny production on wheat than they did on cocksfoot, while individuals from a cocksfoot‐derived lineage had significantly higher potential progeny but lower mean progeny weights on wheat. In a second stage, reciprocal host transfer experiments were carried out in the laboratory, i.e. lineages collected from the agricultural host were reared for several generations on the natural host and vice versa prior to being tested for host preference. The preference of the lineages for their host of origin significantly decreased in this second trial, reversing the overall preference trends, while there was little evidence for between‐lineage variation in this change in preference. In summary these results indicate weak genotypic but strong environmental influences on alate host preference in S. avenae. This host plant conditioning effect may serve to promote host‐based genetic structuring observed in southern British populations of S. avenae.
Costs and benefits of acclimation to elevated temperature in Trichogramma carverae
Authors: Scott Megan , Berrigan David , Hoffmann Ary A.
Published: October 2003

The consequences of acclimation for survival and other fitness components in the parasitoid wasp, Trichogramma carverae (Oatman and Pinto), were examined. Heat hardening adult wasps at 33 °C or 35 °C for one to two h increased survivorship at 40 °C. This benefit was apparent for several hours after heat‐hardening and occurred in both males and females. Heat hardening at 33 °C during development also resulted in significant increases in survivorship of adults after exposure to 40 °C. However, this developmental hardening reduced longevity of adult male and female wasps and also reduced parastism rate. This suggests costs and benefits of exposure to non‐lethal temperature increases. Acclimating wasps by rearing them under constant temperatures (14, 25 or 30 °C) influenced parasitism rates at these temperatures at the adult stage; only females reared at 14 °C parasitised eggs at 14 °C, while parasitism at 25 °C and 30 °C was not significantly influenced by rearing temperature. Acclimation may be useful for increasing the survival or fecundity of mass‐reared Trichogramma in inundative releases, but any benefits could be offset by fitness costs of the acclimation process.
Spatial and temporal distribution of endemic and released entomopathogenic nematode populations in turfgrass
Authors: Campbell J. F. , Orza G. , Yoder F. , Lewis E. , Gaugler R.
Published: October 2003

Entomopathogenic nematodes (Rhabdita: Heterorhabditidae and Steinernematidae) have been effective as inundative biological control agents of scarab larvae (Coleoptera: Scarabaeidae) in turfgrass. Entomopathogenic nematodes also occur naturally in turfgrass and endemic or inoculated populations may be able to provide effective long‐term control. Variation in Heterorhabditis bacteriophora and Steinernema carpocapsae spatial and temporal distribution along transects placed at different turfgrass sites in central New Jersey, USA, was investigated. H. bacteriophora tended to be recovered from fewer sections in a transect than S. carpocapsae, but the two species, overall, did not differ in patchiness of distribution. In one transect with a H. bacteriophora population S. feltiae was also recovered, but the two populations seldom overlapped spatially. In transects with adequate scarab larvae density for analysis, H. bacteriophora density and Popillia japonica larvae density were inversely correlated. This suggests that endemic H. bacteriophora populations may suppress P. japonica populations. In one transect, an epizootic of H. bacteriophora in an undetermined host may have occurred. Edaphic factors were relatively uniform along transects and were, at most, weakly correlated with nematode recovery. Uniform inoculative releases of H. bacteriophora tended to return to patterns of distribution typical of endemic populations.
Different responses to temperature in three closely‐related sympatric cereal aphids
Authors: Turak E. , Talent R. , Sunnucks P. , Hales D. F.
Published: October 2003

Chromosomal races of the aphid Sitobion miscanthi (Takahashi), and a closely‐related species S. near fragariae (Aphididae: Macrosiphini) show seasonal differences in abundance in eastern Australia. We tested whether this was related to differences in temperature response, using controlled laboratory conditions. Intrinsic rate of increase, rm, mean relative growth rate (MRGR), and longevity were compared at different temperatures, and rates of increase were compared outdoors under ambient conditions. Using laboratory data, we simulated population growth, for comparison with outdoor populations. There were significant differences in responses to temperature regimes both in the laboratory and outdoors. Outdoor populations fell well short of predicted sizes. S. miscanthi (2n=18) showed evidence of adaptation to warmer conditions. In contrast, S. nr fragariae showed consistent evidence for adaptation to cooler conditions, and S. miscanthi2n=17 was approximately intermediate. These data indicate that temperature responses are important in the ecology, evolution and pest status of S. miscanthi clones and S. nr fragariae in Australia.
Selection of fruits for oviposition by the chestnut weevil, Curculio elephas
Authors: Desouhant E.
Published: October 2003

Under field conditions, females of the chestnut weevil Curculio elephas select their oviposition sites. In sleeve experiments, when the number of fruits is limited, females avoid 17% of available chestnuts and concentrate their eggs in the others. In the field, on average, 56.3 and 27.8% of the infested fruits contain one or two immatures (eggs and larvae). The oviposition site selection is neither influenced by host size nor by the presence of immature conspecifics. Choice experiments in the laboratory suggest that female weevils do not deposit repellent chemical markers on the fruits. Moreover, sleeve experiments indicate that selection is not influenced by the noise made by larvae while feeding inside a fruit. In general, the most probable hypothesis is that Curculio elephas exploits only hosts of highest feeding quality.
Plant feeding site selection on soybean by the facultatively phytophagous predator Orius insidiosus
Authors: Armer Christine A. , Wiedenmann Robert N. , Bush Daniel R.
Published: October 2003

Experiments were conducted to test whether the facultatively phytophagous predator Orius insidiosus (Say) (Heteroptera: Anthocoridae) ingested phloem, xylem or mesophyll contents from soybean plants (Glycine max L.). Potential uptake of phloem sap was examined by radiolabeling photosynthate with 14CO2 and then measuring the accumulation of radiolabeled metabolites in feeding animals. Most O. insidiosus feeding on radiolabeled plants ingested no or very low levels of label; only 3% ingested small amounts of label, indicating the experimental insects fed very little, if at all, on the phloem. In contrast, well known phloem feeding insects used as positive controls accumulated substantial levels of labeled metabolites after feeding on known host plants. O. insidiosus did feed on xylem contents, as shown by ingestion of safranin‐labeled xylem fluid. A few of the insects showed signs of feeding on the mesophyll, as indicated by the presence of chloroplasts in the gut. However, the small diameter of the food canal may cause limited passage of chloroplasts, which would contribute to an underestimation of the frequency of mesophyll feeding. Some radiolabeled metabolites remain in the mesophyll so those insects that ingested low levels of radiolabel probably ingested label from the mesophyll, which supports the notion that some level of mesophyll feeding occurred. Feeding site determines the nutrients ingested during phytophagy. These insects obtain water from the xylem, and may ingest small amounts of starches, sugars, and amino acids from the mesophyll. The results suggest that facultative phytophagy by this heteropteran predator primarily provides the insect with water, but also may provide some nutrients that supplement a prey diet and help the predator survive periods when prey are scarce.
The determination of larval phase coloration in the African armyworm, Spodoptera exempta and its consequences for thermoregulation and protection from UV light
Authors: Gunn A.
Published: October 2003

Spodoptera exempta exhibits a density‐dependent phase polyphenism in which caterpillars reared in isolation (phase solitaria) tend to be green/brown and cryptic while those reared in groups (phase gregaria) are black and highly visible. Differences in coloration between solitaria and gregaria phase larvae become apparent in the third instar and are pronounced by the final instar. Larval rearing densities as low as two larvae per 250 ml container are sufficient to induce gregaria coloration in 61% of the insects and at higher densities this is the only coloration expressed. Larvae transferred from isolated to crowded conditions or vice versa tend to retain or adopt gregaria phase coloration which suggests that this is highly advantageous. Black coloration is also induced in single larvae reared with other species of caterpillar (S. littoralis). Isolated larvae reared at low temperature tend to become melanic while crowded larvae reared at high temperature tend to be less melanised although they do not adopt the solitaria phase coloration. These results suggest that phase coloration is determined by non species‐specific inter‐larval contact, although it can be modulated by temperature. Under laboratory conditions, gregaria phase larvae heat up faster than solitaria; this is partially a consequence of their black coloration but their smaller size is a more important factor. The cuticles of the gregaria larvae absorb significantly more ultraviolet radiation than those of solitaria but this does not confer any protection when larvae are irradiated at 254 nm.
Methods of assessing population increase in aphids and the effect of growth stage of the host plant on population growth rates
Authors: Guldemond J. Adriaan , van, den Brink Wim J. , den Belder Eefje
Published: October 2003

Realistic values of population growth rates are needed when used in forecasting programmes, e.g., in a programme of integrated control. Therefore, comparisons were made in a chrysanthemum – aphid system between different methods of assessing population growth rates. The reproductive performances of the aphid species Aphis gossypii and Myzus persicae were measured on two chrysanthemum cultivars using three plant growth stages (young vegetative, budding and flowering). In the first set of experiments, development time and reproduction were used to estimate the population growth rate rm. The mean relative growth rates (MRGR) were also assessed. It was shown for the first time that the relationship between rm and MRGR was influenced by aphid species. In a second experiment, the aphid population increase on a whole plant was measured and rm was estimated by calculating the slope of the (ln transformed) population increase. It is shown that population growth rate is affected by the growth stage of the plant, and that cultivar and aphid species interact with plant growth stage in influencing population growth rate. Thus, no single growth stage of chrysanthemum for maximal aphid population growth can be assigned, but the budding and flowering stage are the most suitable in three out of four aphid × cultivar combinations. Comparison between the results from both experiments demonstrates clearly that more realistic values for rm are obtained when measured on whole plants.
The impact of nitrogen fertilization of tomato on feeding site selection and oviposition by Trialeurodes vaporariorum
Authors: Jauset A. M. , Sarasúa M. J. , Avilla J. , Albajes R.
Published: October 2003

Tomato plants, Lycopersicon esculentum Miller cv ‘Tres Cantos’, were supplied with high (308 ppm), medium (140 ppm) and low (84 ppm) nitrogen doses in order to determine the influence of nitrogen fertilization on feeding and oviposition site selection by greenhouse whitefly adults, T. vaporariorum (Westwood). The nitrogen and water content was higher in plants supplied with 308 N ppm than in plants with medium or low nitrogen doses and no differences were found in soluble sugar content. The leaves of the upper plant stratum (leaves 1–5) had the greatest nitrogen and water content, independent of the nitrogen dose applied. The plants were exposed to T. vaporariorum adults into a greenhouse under two current (late autumn‐winter and spring‐early summer) situations of the tomato crop in the Mediterranean area. The distribution of whitefly adults on the plants was affected by the nitrogen dose in both experimental conditions, the number of adults was higher on the plants supplied with high nitrogen dose. Within plants, adult distribution was affected by leaf position, the upper plant stratum being preferred for feeding. Whitefly females selected for oviposition and laid more eggs on plants and leaves of plants with higher nitrogen and water contents. We conclude that whitefly host selection for feeding and ovipositing are related to differences in nitrogen and water content of the host plant.
Phenol oxidising enzymes in the grain aphid's saliva
Authors: Urbanska Anna , Tjallingii W. Freddy , Dixon Anthony F. G. , Leszczynski Bogumil
Published: October 2003

Sucrose‐agarose gels and sucrose liquid diets were used to study the phenol oxidising enzymes in the salivary secretions of the grain aphid, Sitobion avenae (Fabricius). Activity indicating the presence of two oxidoreductases, polyphenol oxidase (PPO) and peroxidase (Px), was found. Both enzymes were present in the aphid's stylet sheath (gelling saliva) but only polyphenol oxidase activity was found in the halos around sheaths and thus in watery saliva. Electrical penetration graphs (EPG) revealed that the secretion of these enzymes into the gels, by an individual aphid, was associated with its probing activity observed during penetration of the epidermal and mesophyll tissues. The grain aphid's PPO, secreted in its saliva reacted with a range of phenolic compounds. As most of these phenolics occur naturally in cereals, the grain aphid could modify its host‐plant's phenolic composition. The importance of the grain aphid's polyphenol oxidase and peroxidase in detoxifying cereal phenolics is discussed.
Learning to discriminate between infochemicals from different plant‐host complexes by the parasitoids Cotesia glomerata and C. rubecula
Authors: Geervliet Jacqueline B. F. , Vreugdenhil Annemarie I. , Dicke Marcel , Vet Louise E. M.
Published: October 2003

Comparison of closely related species can elucidate adaptive differences in species characteristics. The present study compares the effect of experience on the host‐finding behaviour of two Cotesia (Hymenoptera: Braconidae) parasitoid species that differ in their degree of specialization. After multiple experiences with host larvae, females of the generalist parasitoid Cotesia glomerata showed a clear preference for volatiles from Pieris brassicae‐infested Brussels sprouts leaves over P. rapae‐infested Brussels sprouts leaves in two‐choice tests (‘preference learning at herbivore level’). A single experience with a host did not lead to such preferences.

Experience of adult C. glomerata with different P. brassicae‐infested cabbage varieties or nasturtium (Tropaeolum majus L.) led to preferences for the experienced plant‐host complex in most cases (‘preference learning at plant level’). No effect of rearing plant (early adult learning) on plant preference was found.

In contrast to the generalist C. glomerata, females of the specialist C. rubecula did not show preference learning at the herbivore level. At the plant level, experience with different P. rapae‐infested cabbage varieties in no case resulted in a difference in preference between treatments. The results support the hypothesis that learning plays a more important role in searching in generalists than in specialist parasitoids. The behaviour of the generalist C. glomerata was more easily changed by experience than that of the specialist C. rubecula.
Azadirachta indica metabolites interfere with the host‐endosymbiont relationship and inhibit the transmission of potato leafroll virus by Myzus persicae
Authors: van den Heuvel J. F. J. M. , Hogenhout S. A. , Verbeek M. , van der Wilk F.
Published: October 2003

The effects of neem (Azadirachta indica A. Juss) seed kernel extracts (NSKE) and azadirachtin on the ability of Myzus persicae (Sulz.) to transmit potato leafroll luteovirus (PLRV) was studied. Moreover, it was investigated whether treatments with these compounds would exert an effect on larval growth and mortality, and on the aphid intracellular symbionts. Endosymbiotic bacteria play an essential role in the performance of aphids, and in luteovirus transmission by aphids. NSKE and azadirachtin were offered to one‐day‐old M. persicae nymphs via a membrane feeding system. The neem metabolites displayed a 100% mortality at doses higher than 2560 ppm. At intermediate doses, ranging between 320 and 2560 ppm, larval growth and mortality were affected in a dose‐dependent manner. The transmission of PLRV by M. persicae was inhibited by 55–90%. The endosymbiont population of the aphid was clearly affected by a treatment with neem metabolites as the release of their most abundant protein, Buchnera GroEL, into the haemocoel of the aphid was inhibited. Moreover, morphological aberrations on the bacterial endosymbionts were observed in aphids which fed on 2560 ppm of azadirachtin. At doses lower than 160 ppm of NSKE or azadirachtin, the endosymbiont population of M. persicae, and mortality, growth and feeding behaviour were similar to that of the untreated groups of aphids. However, PLRV transmission was still inhibited by 40–70%. The possible targets of the neem metabolites in the aphid are discussed.
Effect of constituents of the foliar wax of Didymopanax vinosum on the foraging activity of the leaf‐cutting ant Atta sexdens rubropilosa
Authors: Salatino Antonio , Sugayama Regina L. , Negri Giuseppina , Vilegas Wagner
Published: October 2003

Leaf epicuticular waxes may affect substrate selection by leaf‐cutting ants, and host recognition by several phytophagous insects. The influence of the crude epicuticular wax of Didymopanax vinosum E. March. (Araliaceae), and its major constituents lupeol and free primary alcohols, on substrate selection by the leaf‐cutting ant Atta sexdens rubropilosa Forel, was investigated. Two ant colonies were used in laboratory bioassays. Corn flakes (zea) were impregnated with chloroform solutions of the substances being tested and fed to the adults. One of the colonies gave results, in most of the tests, not significantly different from the controls. The other colony, however, discriminated against the crude wax, a strong deterrent effect being observed from the first of a series of eight trials. The same colony was able to discriminate against lupeol after the second trial. The fraction of primary n‐alcohols (22% C28, 66% C30 and 12% C32) deterred feeding only after the fifth trial. The results demonstrate that some constituents of epicuticular waxes may deter the foraging activity of A. sexdens rubropilosa, depending, however, on the colony under observation. It is suggested that lupeol, of the foliar wax of D. vinosum, is an important deterrent to leaf‐cutting ants, although with less pronounced effects than those observed in tests with the crude wax.
Ovipositional enhancement through socially facilitated behavior in Rhagoletis pomonella flies
Authors: Prokopy Ronald J. , Reynolds Alan H.
Published: October 2003

Apple maggot females, Rhagoletis pomonella (Walsh), were maintained (with males) singly or in groups of 5 in laboratory cages without fruit from eclosion until 15 days of age (when males were removed). When hawthorn, apple or artificial fruit were introduced on Day 16, females caged in groups laid significantly more eggs per female, irrespective of fruit type, than females caged singly. A follow‐up laboratory experiment revealed that the oviposition‐enhancing effect of grouping was due largely or exclusively to caging regime on day of access to fruit and not to prior caging regime. Subsequent laboratory‐cage tests indicated that none of the following factors contributed significantly to the oviposition‐enhancing effect of grouping under laboratory cage conditions: odor of fruit punctures, odor of eggs, odor of marking pheromone, or presence of other females on fruit, all as potential stimuli eliciting female attraction to fruit; or presence of fruit punctures, eggs, or marking pheromone, all as potential oviposition‐enhancing stimuli following alighting on a fruit. The only contributing factor of significance uncovered here was the enhanced propensity of an arriving female to bore into a fruit shortly after encounter with an occupying female engaged in ovipositional behavior. We consider such enhancement as suggestive of socially facilitated egglaying behavior, which we discuss.
Fecundity and egg distribution of the herbivore Spodoptera pectinicornis as influenced by quality of the floating aquatic plant Pistia stratiotes
Authors: Wheeler G. S. , Van T. K. , Center T. D.
Published: October 2003

We determined the influence of larval host quality of the floating aquatic weed Pistia stratiotes L. (Araceae) on the fecundity and egg distribution of the biological control agent Spodoptera pectinicornis (Hampson) (Lepidoptera: Noctuidae). Different nutritional levels were produced by growing plants with relatively low and high levels of nitrogen, phosphorus and potassium fertilizer. Female and male pupal biomass were significantly greater when the larvae were fed leaves from the high fertilizer plants. Although the fertilizer treatments did not significantly influence total fecundity, there was an indirect effect as adults from larger pupae were more fecund. Regardless of treatment, ovipositing females formed a depression in the leaf surface by removing trichomes into which they deposited the egg masses. Most of the egg masses were laid on the lower leaf surface, on leaf positions 5–8 (counting from the young inner to the outer leaves) and during days 1–2 post‐eclosion. Most of the eggs were laid in masses but about 12% were solitary. Females fed the low fertilizer treatment laid a greater proportion (mean ± s.e.) of their eggs as solitary eggs (17.3 ± 3.4% of total eggs) than did females fed the high fertilizer treatment (8.3 ± 2.3% of total eggs). The increased percentage of solitary eggs laid by the females from the low quality larval diet may be an adaptive response to decrease competition among the progeny.
Discovery and utilization of Bemisia argentifolii patches by Eretmocerus eremicus and Encarsia formosa (Beltsville strain) in greenhouses
Authors: Hoddle Mark S. , van Driesche Roy G. , Elkinton Joseph S. , Sanderson John P.
Published: October 2003

The ability of two species of aphelinid parasitoids to find and attack Bemisia argentifolii was determined. Experiments were conducted with whitefly patches on single leaf poinsettia plants randomly distributed in canopies of four commercially grown poinsettia crops at an early and late stage of plant growth. Eretmocerus eremicus found experimental patches in canopies of small and large plants more quickly and frequently, and killed more nymphs following patch discovery than Encarsia formosa (Beltsville strain). E. eremicus exhibited a Type I functional response in small and large canopies while E. formosa (Beltsville strain) showed a Type II functional response in small canopies and a weak linear response in large canopies. In greenhouses treated with E. eremicus, canopy size increased 4.6× and nymphs per plant increased 14.2× between small and large canopy experiments. Consequently, area of search for this parasitoid increased 83%, number of wasps counted on patches decreased 74%, and proportion of nymphs killed in artificial patches decreased 47% between small and large canopies. In greenhouses treated with E. formosa Beltsville strain, canopy size increased 7.3× and nymphs per plant increased 25.4× between small and large canopy experiments. Consequently for E. formosa Beltsville strain, area of search increased 11%, number of wasps counted on patches decreased 86%, and proportion of nymphs killed in artificial patches decreased 47% between small and large canopies.
Population dynamics and dispersal of Lepthyphantes tenuis in an ephemeral habitat
Authors: Topping C.J. , Sunderland K.D.
Published: October 2003

The population dynamics of Lepthyphantes tenuis (Blackwall) were investigated in two fields of winter wheat in Sussex, England, with the aim of attributing the major factors controlling population fluctuations. Continuous measures of changes in density, reproductive rate and dispersal were obtained using a range of methodologies, including laboratory analysis, suction trapping, rotary sampling of the aerial fauna, caging, and detailed density estimations. The resulting data were then used to determine the major causes of the observed population fluctuations and to describe the processes of dispersal and reproduction in this population.

Population densities were initially very low following ploughing operations, but increased throughout the season as a result of high reproductive rates. Investigation of the reproductive potential of the spiders showed that the number of eggs per egg‐sac did not vary with season, and that egg development was temperature related. There was no evidence that the number of viable eggs per egg‐sac varied during the season. There were three peaks of hatchling production per year suggesting two to three generations of spiders. Dispersal was not responsible for the major changes in field density throughout the season although dispersal activity was high for this species. Dispersal activity increased with age and was highest in females. Dispersal activity as a ratio of activity/field density for females, males, sub‐adults, immatures and hatchlings was 4:2:3:1:1.

Aerial dispersal is only possible under suitable weather conditions. It was found that female dispersal was correlated with weather conditions far more strongly than other population groups. Calculations showed that under suitable weather conditions (e.g., 25% of the time being suitable for dispersal), almost 4% of the adult females could be expected to leave the population daily. The overall effect is therefore to displace individuals from the population but to have little effect on densities. Dispersal in other stages was controlled by the suitability of weather conditions but also by other, undetermined factors. It is postulated that L. tenuis has a life history strategy whereby suitable habitats act as sources of spiders, mainly females, which are continually involved in dispersal. Dispersal in other population groups may be triggered by factors such as the avoidance of adverse conditions. This type of life‐history strategy is typical of organisms, such as weeds, that are successful in ephemeral habitats and may indicate that this species originally evolved in unpredictable habitats such as dry river beds or coastal areas.
Detecting differences in arthropod aggregation by comparing the proportion of occupied sample units
Authors: Slone D. H. , Croft B. A.
Published: October 2003

Using data sets of phytophagous and predaceous mites, we introduce a method for estimating standard error bands for the proportion of habitat occupied by a species as a function of mean density, by transforming error bands from the variance‐mean power law. Error bands produced by this method were more conservative than bands produced by bootstrapping and repeated subsampling methods applied to the same data. Though conservative, the binomial model showed potential to be an easily interpreted, powerful method for detecting differences in the proportion of habitat occupied among data sets (interpreted as differences in species aggregation) on one spatial scale. This was demonstrated in three specific cases: between years for the predaceous mite Typhlodromus pyri Scheuten (Acari: Phytoseiidae) on ‘Red Delicious’ apple trees (Malus pumila Miller), for the phytophagous mite Tetranychus urticae (Koch) (Acari: Tetranychidae), whether or not it was preyed upon by the predaceous mite Neoseiulus fallacis (Garman) (Acari: Phytoseiidae) on hops (Humulus lupulus L.), and among individual life stages of the predaceous mite Metaseiulus occidentalis (Nesbitt) (Acari: Phytoseiidae) on apple.
Indiscrimination of Manduca sexta larvae to overexpressed and underexpressed levels of phenylalanine ammonia‐lyase in tobacco leaves
Authors: Eichenseer H. , Bi J.L. , Felton G.W.
Published: October 2003

Manduca sexta (L.) larvae were unable to discriminate between transgenic tobacco leaves expressing high or low levels of phenylalanine ammonia‐lyase (PAL) in dual choice arenas. Tobacco leaves overexpressing PAL had up to ten times more chlorogenic acid and up to twice as much rutin in their leaves than leaves containing the same sense‐suppressed gene. Caterpillars reared previously on artificial diet or tobacco leaves had no preference for either leaves over‐ or underexpressing PAL. Application of exogenous chlorogenic acid to PAL‐suppressed leaves at levels similar to the overexpressed leaves did not affect M. sexta's choice. When applied at higher rates, treated leaves were preferred by caterpillars reared on tobacco leaves but not by diet‐reared larvae. Our results with leaves confirm earlier studies with M. sexta using simpler substrates and mixtures of test compounds and provides further evidence that leaf phenolics, such as chlorogenic acid, do not act as feeding deterrents for larval M. sexta.
Oviposition and offspring survival within eggs of European corn borer: discrimination of the host embryo by female Trichogramma nubilale
Authors: Olson D.M.
Published: October 2003

Oviposition preference and offspring survival relative to the location of the host embryo was tested in the egg parasitoid Trichogramma nubilale on European corn borer host eggs. Females preferentially oviposited near to the embryo on hosts about 24 h old. Survival of Trichogramma was lower when females oviposited far from the embryo, and a higher proportion of host embryos hatched. Females did not show preferences for drilling or oviposition within very young hosts relative to where the embryo would develop, and these eggs did not produce wasps or host larvae. Female behavior was apparently adaptive in day‐old hosts, not to very young hosts.
Effects of targets impregnated with the chitin synthesis inhibitor triflumuron on the blowfly Lucilia sericata
Authors: Smith K. E. , Wall R.
Published: October 2003

The effects of exposure of adults of the blowfly Lucilia sericata (Meigen) for 24 h to cloth targets impregnated with the chitin synthesis inhibitor triflumuron plus sucrose or sucrose only, were considered. When both male and female L. sericata were exposed to targets treated with sucrose only, the percentage egg hatch varied between 60–75%. When both sexes were exposed to targets treated with 10% triflumuron plus sucrose the percentage egg hatch varied between 3–7%. When females alone were exposed to triflumuron, prior to the introduction of unexposed males, egg hatch varied between 4–14%. The exposure of males alone to 10% triflumuron treated targets, prior to the introduction of unexposed virgin females, did not give any consistent significant decrease in the mean percentage egg hatch. However, repetition of this trial with males exposed to targets treated with 15 or 20% triflumuron, resulted in a percentage egg hatch of 3.1% and 10.3%, respectively. These results suggest that at relatively high target concentrations, males can transfer effective doses of triflumuron to unexposed virgin females.

The exposure of adults to triflumuron treated targets did not significantly increase the mortality of either male or female L. sericata. Furthermore, bioassays showed that there was no significant decline in the ovicidal effectiveness of targets treated with 10% triflumuron and sucrose solution following exposure to sun and rain for up to 8 weeks in 1995 and 1996.

The results suggest that targets treated with triflumuron suspension concentrate and sucrose may form the basis of an effective system for the control of L. sericata in the field. However, the relatively high concentrations of triflumuron required and the low efficiency with which males are able to transfer effective doses to unexposed females may diminish one of the main theoretical advantages of using a chitin synthesis inhibitor, such as triflumuron, over a conventional insecticide.