bluuebunny/crossref_metadata_2025_split huggingface dataset:
Larval population density affects female weight and fecundity in the dung beetle Aphodius ater
Authors: Hirschberger Petra 
Published: March 2003

Summary1. Competition for food at high densities during larval development leads to reduced adult weight in the northern temperate dung beetle Aphodius ater.2. Analysis of female beetles caught in the field showed that numbers of eggs and total egg load per female were correlated positively with beetle size.3. Female beetles reared at different population densities during larval development in the laboratory were analysed with regard to their lifetime fecundity and reproductive lifespan.4. High population densities during development had a negative influence on the number of eggs per female and on reproductive lifespan. Lifetime fecundity was correlated positively with female weight.5. It was concluded that competition during larval development in the first generation of offspring will result in a lower number of offspring in the second generation in Aphodius ater, and thereby reduce parental fitness.
Nest site preference and success in a gregarious, ground‐nesting bee Dieunomia triangulifera
Authors: Wuellner Clare T. 
Published: March 2003

Summary1. The characteristics of preferred nest sites of the solitary bee Dieunomia triangulifera, which nests gregariously in alluvial soil, were investigated. Nest presence was used as an indication of preference. In those cases where nests were more than a few days old, therefore, this study also investigated nest success.2. Independent variables tested were soil surface moisture, presence of nesting conspecifics, smooth vs. irregular soil surface, distance to visual landmarks, percentage of vegetation cover, soil compaction, vehicular traffic, soil surface temperature, and light intensity.3. Bees preferred to nest in moist, compact soil with an irregular surface. More bees nested near visual landmarks and in places with little or no vegetation. They preferred nesting in areas with warmer soil surface temperatures and brighter illumination. The presence of nesting conspecifics did not influence nesting decisions. Vehicular traffic also seemed to have no impact on nest initiation but did seem to have a negative impact on nest success.4. Although it might seem that ground‐nesting bees should not be limited by nesting sites, relatively little of the study area met all their apparent criteria. This might account, in part, for gregarious nesting in this species.
Preference–performance linkage in the neotropical spittlebug Deois flavopicta, and its relation to the Phylogenetic Constraints Hypothesis
Authors: Pires C. S. S. , Price P. W. , Fontes E. G. 
Published: March 2003

Summary1. Predictions from the Phylogenetic Constraints Hypothesis were tested for the first time in a tropical system using the pasture pest Deois flavopicta Stal, which oviposits into the ground and not into plant tissues. The prediction that there is no oviposition preference–larval performance linkage was supported. The absence of such a link provides an evolutionary basis for eruptive population dynamics.2. The effects of host species and host plant quality on the preference of ovipositing females of D. flavopicta and performance of their offspring on the selected host plants were tested at the population level.3. Female oviposition behaviour was affected by the presence of the host plant. Females of D. flavopicta showed a strong preference to oviposit close to host plants. The number of eggs was higher in pots containing Brachiaria ruziziensis (121.88 ± 13.70) than in pots containing only the wet oviposition substrate (5.2 ± 1.98) or dry oviposition substrate (0.067 ± 0.067). Ovipositing females did not, however, discriminate between plants of Brachiaria decumbens and Axonopus marginatus and did not show a strong oviposition preference in relation to differences in plant quality (protein and fibre content). They did show oviposition preference for plants under the high watering regime. The mean number of eggs collected from pots with non water‐stressed plants was 60% higher than the mean number of eggs collected on pots with water‐stressed plants.4. Although females did not show ovipositional preference, spittlebug larval performance, measured as percentage survival and duration of nymphal period, was better on plants of high protein and low fibre content. These results indicate that there is not a linkage between female oviposition preference and subsequent nymphal performance in relation to differences in protein and fibre content in the host plants. There was, however, a limited linkage between oviposition preference and nymphal performance in relation to plant water content. Females showed preference for moist sites that have high survival of newly hatched nymphs.5. Evidence indicates that for D. flavopicta, the influences of natality and female oviposition behaviour in response to plant quality are not the major factors driving population outbreaks, which is in accordance with the Phylogenetic Constraints Hypothesis.
The effect of egg load and host deprivation on oviposition behaviour in aphidophagous hoverflies
Authors: Sadeghi H. , Gilbert F. 
Published: March 2003

Summary1. Two species of aphidophagous hoverfly, Episyrphus balteatus and Syrphus ribesii, were tested for the effects of egg load and host deprivation on oviposition choices.2. Egg load affected the total number of eggs laid in E. balteatus but not in S. ribesii, however it did not affect the proportion laid on any one aphid in E. balteatus but did affect the proportion laid on any one aphid in S. ribesii. The rank order of preferences remained unchanged by age or host deprivation.3. The dominant effects on host choices were aphid species (in both syrphids) and presentation order (in E. balteatus).4. Being deprived of hosts increased egg load substantially in E. balteatus, and increasing time of deprivation also had an effect on discrimination; there was no effect of host deprivation in S. ribesii.5. Reasons for these patterns are discussed.
Can imperfect host discrimination explain partial patch exploitation in parasitoids?
Authors: Outreman Y. , Le Ralec A. , Wajnberg E. , Pierre J. S. 
Published: March 2003

Summary1. Host discrimination by Aphidius rhopalosiphi (De Stefani Perez) (Hymenoptera: Braconidae) was first studied on the grain aphid Sitobion avenae (Fabricius) (Homoptera: Aphididae). Females tended to avoid oviposition in hosts parasitised 3 h earlier. No evidence of host discrimination ability on freshly parasitised hosts was suggested, however, and ovipositional experience had no effect on host discrimination.2. The effects of host discrimination ability on the exploitation strategy of patches containing different proportions of unparasitised hosts and hosts parasitised for 3 h were studied. Females spent less time on patches with a higher proportion of parasitised hosts, reflecting the females' ability to perceive the potential profitability of the patch. This ability may be based on the nature of the hosts encountered (unparasitised or parasitised).3. Incomplete exploitation of unparasitised hosts was also observed. It seems that this partial exploitation is related to the inability of A. rhopalosiphi to recognise freshly parasitised hosts. As a female may experience a risk of self‐superparasitism during patch depletion, this could promote early departure from incompletely exploited patches.4. The effect of previous experience on the patch exploitation strategy was also assessed. Females were tested twice on two patches of the same quality. Results suggested that the experience acquired during a previous visit led the females to leave the patch sooner and to lay fewer eggs in parasitised hosts.5. Patch exploitation strategy may therefore be the result of different factors such as host discrimination and experience. The evolutionary consequences of the results are discussed.
Limiting the potential for intraspecific competition: regulation of Trioza eugeniae oviposition on unexpanded leaf tissue
Authors: Luft P. A. , Paine T. D. , Redak R. A. 
Published: March 2003

Summary1. Trioza eugeniae (Homoptera: Triozidae) females oviposit pre‐ ferentially on the margin of young, incompletely expanded Syzygium paniculatum leaves. As the density of eggs on the leaf increases, females will oviposit on the surface of the leaf blades.2. The survivorship of eggs laid on the abaxial leaf midrib and near the abaxial leaf margin was significantly greater than that of eggs laid on the leaf margin.3. Controlled environment studies demonstrated that maximum carrying capacity for T. eugeniae nymphs on a fully expanded leaf is approximated closely by the number of eggs that can be laid on the margin of a young, unexpanded leaf.4. In field populations, nymphal densities fell below the hypothetical carrying capacity calculated from laboratory studies on 71% of the leaves examined.5. The leaf margin appears to be a proximal cue used by ovipositing females for resources available to developing nymphs. Females that limit oviposition to available leaf margins appear to improve the probability of survival of their progeny through reduced intraspecific competition.
Effect of soil hardness on aggression in the solitary wasp Mellinus arvensis
Authors: Ghazoul Jaboury 
Published: March 2003

Summary1. Two alternative nesting strategies are exhibited by soil‐nesting Mellinus arvensis females, digging a new nest (diggers) and searching for an old unoccupied burrow (searchers). Wasps appear unable to distinguish between occupied and unoccupied nests, and aggressive interactions between searchers and nest owners at nest entrances are frequent.2. In aggressive encounters, there is an advantage in size and residency status.3. The costs associated with the two nesting strategies vary across geographically separated populations: nest digging incurs costs in terms of time, and these vary according to the hardness of the soil substrate; nest searching is variably costly in terms of risk of injury in aggressive encounters with nest‐owning females.4. Individual female wasps can switch between nesting strategies, and thus soil hardness, by affecting the cost of nest construction, affects the relative frequencies of the two nesting strategies within a population, favouring an increase in the searching strategy. This, in turn, affects the frequency and intensity of aggression between females at a nesting aggregation.5. Female body size is correlated with soil hardness. As aggressive encounters are more frequent in sites with hard soil substrates, there is increased selective advantage in having large body size at these sites.6. Body size is determined primarily by the availability of food resources during larval development, which is, to a degree, a function of the size of the adult female. There is a trade‐off between provisioning a few cells with many provisions in each, leading to the development of few but large adults, as opposed to many cells with few provisions, leading to many small offspring. The relative advantage of these two provisioning strategies is, at least in part, a function of the hardness of the soil substrate.
Microgeographic genetic structure and intraspecific parasitism in the antLeptothorax nylanderi
Authors: Foitzik S. , Heinze J. 
Published: March 2003

Summary1. Genetic colony structure of the small central European antLeptothorax nylanderiis affected strongly by ecological constraints such as nest site availability and intraspecific social parasitism.2. AlthoughL. nylanderiis generally monogynous and monandrous, more than a quarter of all nests collected in a dense population near Würzburg, Germany, contained several matrilines. As shown by microsatellite analysis, the average nest‐mate relatedness in these nests was 0.20. Genetically heterogeneous nests arise from nest take‐over by alien colonies or founding queens, a result of severe competition for nest sites.3. In summer, more than one‐third of all colonies inhabited several nest sites at a time. Polydomy appears to be rather limited, with two or three nests belonging to a single polydomous colony.4. Queens appear to dominate male production; only a small fraction (8%) of males was definitively not progeny of the queen present but might have been worker progeny or offspring of another queen.5. Strong evidence for heterozygote deficiency was found and a total of nine diploid males was discovered in two colonies. These findings suggest deviation from random mating through small, localised nuptial flights.
Reproductive development and maternal effects in the pine weevil Hylobius abietis
Authors: Wainhouse D. , Ashburner R. , Boswell R. 
Published: March 2003

Summary1. In a laboratory study of maturation feeding of female pine weevil Hylobius abietis on current and 1‐year‐old stem bark of transplants of Scots and Corsican pine, Norway and Sitka spruce, Douglas fir, and hybrid larch, the length of the pre‐oviposition period was influenced by the species on which weevils fed. The shortest pre‐oviposition period was on hybrid larch (11.8 days) and the longest on Douglas fir (15.5 days).2. The species on which weevils fed also affected fecundity but there was evidence of a species–year interaction. Over a period of 36 days, most eggs were laid by weevils feeding on current stem of Norway spruce and Corsican and Scots pine and fewest on current stem of Sitka spruce.3. Significant maternal effects on egg size were observed both in relation to female size and conifer species. The largest eggs were laid on Corsican pine and the smallest on Douglas fir, with no evidence of a trade‐off between number of eggs laid and their size.4. There was a positive relationship between egg and larval size and between larval size and survival on logs of four conifer species. Residual resistance mechanisms in the bark of recently cut stumps and larval competition are discussed briefly in relation to the importance of the observed maternal effects on weevil population dynamics.
Effects of gender and mating status on self‐directed dispersal by the whitefly parasitoidEretmocerus eremicus
Authors: Bellamy David E. , Byrne David N. 
Published: March 2003

Summary1. The impacts of gender and mating on short‐range (< 10 km) dispersal by the whitefly parasitoidEretmocerus eremicusRose and Zolnerowich (Hymenoptera: Aphelinidae) were examined. A fluorescent dust‐marking technique was also tested.2. In a vertical flight chamber, female flight duration was significantly longer than that of males, and unmated parasitoids flew for longer than mated parasitoids. The mean flight durations were: unmated females 34 min, mated females 10 min, unmated males 7 min, mated males < 1 min.3. The dispersal behaviour ofE. eremicuswas investigated in the field using fluorescent dust. Before doing so, it was determined in the laboratory that this dust did not affect flight behaviour, was retained over the length of the experiments, and allowed large samples to be processed quickly and inexpensively.4. In the field, traps were placed along annuli at 3, 5, 7, and 10 m from release points. Eighty‐seven per cent of the 4153 parasitoids captured were males. Sex ratios were near parity on release.5. The difference in dispersal characteristics between males and females may be resource based, suggesting that certain requirements were met within the field plots for males that were not met for females.6. Locally, males dispersed in a manner consistent with a simple diffusion model while females engaged in wind‐directed flight soon after leaving release sites. The fact that the genders exhibited dissimilar dispersal characteristics, supports the claim that insect flight, even by small species, can be self‐directed.
Body size as an estimator of production costs in a solitary bee
Authors: Bosch Jordi , Vicens Narcís 
Published: March 2003

Abstract 1. Body weight is often used as an estimator of production costs in aculeate Hymenoptera; however, due to differences between sexes in metabolic rates and water content, conversion of provision weight to body weight may differ between males and females. As a result, the cost of producing female progeny may often have been overestimated.2. Provision weight and body weight loss throughout development were measured in a solitary bee, Osmia cornuta (Latreille), to detect potential differences between sexes in food weight/body weight conversion.3. Male O. cornuta invest a larger proportion of larval weight in cocoon spinning, and presumably have higher metabolic rates than females during the larval period; however, this is compensated by a slightly longer larval period in females.4. Overall, body weight loss throughout the life cycle does not differ significantly between sexes. As a result, cost production ratios calculated from provision weights and from adult body weights are almost identical.5. The validity of other weight (cocoon, faeces) and linear (head width, intertegular span, wing length, cocoon length, and cell length) measures as estimators of production costs is also discussed.6. Valid estimators of production costs vary across species due to differences in sex weight ratio, cocoon shape, provision size in reference to cell size, and adult body size.
The use of artificial neural networks in ecological analysis: estimating microhabitat temperature
Authors: Bryant Simon R. , Shreeve Tim G. 
Published: March 2003

Abstract 1. The thermal environment at the scale in which most species exist is largely unknown, and thus the majority of physiological models is based on meteorological measures of ambient temperature.2. The use of artificial neural networks in ecological analysis is promoted by using them to model microhabitat temperature.3. The performance of conventional multiple linear regression is compared with that of artificial neural networks in predicting the temperature profiles of two different microhabitats using ambient temperature, solar radiation, and wind speed as input (independent) variables.4. In both cases, the artificial neural networks showed a lower mean absolute residual error than multiple linear regression (0.95 °C compared with 1.41 °C, and 0.29 °C compared with 0.50 °C) and a higher correlation (r2) between predicted and observed values (0.832 compared with 0.668, and 0.884 compared with 0.670).5. An artificial neural network developed to include a microhabitat patch description based on height within patch, substrate, and four classes of per cent vegetation cover performed well (r2 = 0.933, prediction error 95% confidence limits =± 2.5 °C).6. It is suggested that artificial neural networks are more appropriate than conventional regression‐based approaches for estimating microhabitat temperature.
Lack of evidence for reproductive isolation among ecologically specialised lycaenid butterflies
Authors: Nice C. C. , Fordyce J. A. , Shapiro A. M. , Ffrench‐Constant R. 
Published: March 2003

Abstract 1. The evolution of reproductive isolation between recently diverged or incipient species is a critical component of speciation and a major focus of speciation models. In phytophagous insects, host plant fidelity (the habit of mating and ovipositing on a single host species) can contribute to assortative mating and reproductive isolation between populations adapting to alternative hosts. The potential role of host plant fidelity in the evolution of reproductive isolation was examined in a pair of North American blue butterfly species, Lycaeides idas and L. melissa.2. These species are morphologically distinct and populations of each species utilise different host plants; however they share 410 bp haplotypes of the mitochondrial cytochrome oxidase subunit I (COI) gene, indicating recent divergence.3. Some populations using native hosts exhibited strong fidelity for their natal host plant over the hosts used by nearby populations. Because these butterflies mate on or near the host plant, the development of strong host fidelity may create reproductive isolation among populations on different hosts and restrict gene flow.4. Tests of population differentiation using allozyme allele frequency data did not provide convincing evidence of restricted gene flow among populations. Based on morphological differences, observed ecological specialisation, and the sharing of genetic markers, these butterflies appear to be undergoing adaptive radiation driven at least partially by host shifts. Neutral genetic markers may fail to detect the effects of very recent host shifts in these populations due to gene flow and/or the recency of divergence and shared ancestral polymorphism.
Immune expression in a damselfly is related to time of season, not to fluctuating asymmetry or host size
Authors: Yourth Christopher P. , Forbes Mark R. , Smith Bruce P. 
Published: March 2003

Summary1. Variation in immune responsiveness within and among species is the subject of the emerging field of ecological immunology. The work reported here showed that individuals ofLestes forcipatusRambur differ in their likelihood of mounting immune responses, and in the magnitude of those responses, against a generalist ectoparasite, the water miteArrenurus planusMarshall.2. Immune responses took the form of melanotic encapsulation of mite feeding tubes, occurred in the few days after host emergence, and resulted in mites dying without engorging. Such immune responses were more probable and stronger for hosts sampled later rather than earlier in the season. Such responses may act as selection affecting seasonal patterns of egg hatching and larval abundance of mites.3. Contrary to expectation, metrics of host size (wing length) and wing cell fluctuating asymmetry were not related to the likelihood of immune responses.4. The importance of season on immune expression of insects has not been explored in detail. These results suggest possible trade‐offs in allocation of melanin (or its precursors) to maturation versus immunity, and indicate the need for studies on the synergistic effects of weather and parasitism on host species that use melanotic encapsulation to combat parasites and pathogens.
Aphid population dynamics: does resistance to parasitism influence population size?
Authors: Hufbauer R. A. 
Published: March 2003

Summary1. Insect population size is regulated by both intrinsic traits of organisms and extrinsic factors. The impacts of natural enemies are typically considered to be extrinsic factors, however insects have traits that affect their vulnerability to attack by natural enemies, and thus intrinsic and extrinsic factors can interact in their effects on population size.2. Pea aphids Acyrthosiphon pisum Harris (Hemiptera: Aphididae) in New York and Maryland that are specialised on alfalfa are approximately two times more physiologically resistant to parasitism by Aphidius ervi Haliday (Hymenoptera: Braconidae) than pea aphids specialised on clover. To assess the potential influence of this genetically based difference in resistance to parasitism on pea aphid population dynamics, pea aphids, A. ervi, and other natural enemies of aphids in clover and alfalfa fields were sampled.3. Rates of successful parasitism by A. ervi were higher and pea aphid population sizes were lower in clover, where the aphids are less resistant to parasitism. In contrast, mortality due to a fungal pathogen of pea aphids was higher in alfalfa. Generalist aphid predators did not differ significantly in density between the crops.4. To explore whether intrinsic resistance to parasitism influences field dynamics, the relationship between resistance and successful field parasitism in 12 populations was analysed. The average level of resistance of a population strongly predicts rates of successful parasitism in the field. The ability of the parasitoid to regulate the aphid may vary among pea aphid populations of different levels of resistance.