bluuebunny/crossref_metadata_2025_split huggingface dataset:
Females of the European beewolf preserve their honeybee prey against competing fungi
Authors: Strohm Erhard , Linsenmair K. Eduard 
Published: March 2003

Summary1. Females of the European beewolf Philanthus triangulum (Hymenoptera, Sphecidae) provision brood cells with paralysed honeybees as larval food. Because brood cells are located in warm, humid locations there is a high risk of microbial decomposition of the provisions. Low incidence of fungus infestation (Aspergillus sp.) in nests in the field suggested the presence of an anti‐fungal adaptation.2. To test whether the paralysis caused the protection from fungus infestation, the timing of fungus growth on bees that were freeze‐killed, paralysed but not provisioned, and provisioned regularly by beewolf females was determined. Fungus growth was first detected on freeze‐killed bees, followed by paralysed but not provisioned bees. By contrast, fungus growth on provisioned bees was delayed greatly or even absent. Thus, paralysis alone is much less efficient in delaying fungus growth than is regular provisioning.3.Observations  of beewolves in their nests revealed that females lick the body surface of their prey very thoroughly during the period of excavation of the brood cell.4. To separate the effect of a possible anti‐fungal property of the brood cell and the licking of the bees, a second experiment was conducted. Timing of fungus growth on paralysed bees did not differ between artificial and original brood cells. By contrast, fungus growth on bees that had been provisioned by a female but were transferred to artificial brood cells was delayed significantly. Thus, the treatment of the bees by the female wasp but not the brood cell caused the delay in fungus growth.5. Beewolf females most probably apply anti‐fungal chemicals to the cuticle of their prey. This is the first demonstration of the mechanism involved in the preservation of provisions in a hunting wasp. Some kind of preservation of prey as a component of parental care is probably widespread among hunting wasps and might have been a prerequisite for the evolution of mass provisioning.
What causes male‐biased sex ratios in mature damselfly populations?
Authors: Stoks Robby 
Published: March 2003

Summary1. Several hypotheses to account for biased sex ratios in mature insect populations were tested by monitoring two field populations of the damselfly Lestes sponsa and by performing experiments in field cages. The population sex ratios are heavily male biased in this species.2. The observed sex ratio at emergence was even and both sexes emerged synchronously. Females had longer maturation times but these were insufficient to explain the observed sex ratio shift.3. Mass increases during maturation were consistently larger in females. In agreement with this, immature females made more flights per unit of time, which should make them more vulnerable to predation, however maturation probabilities were lower in females only in one field cage experiment. This inconsistency may be due to long bad weather conditions. Interestingly, predators reduced mass increase and this reduction was larger in females than in males.4. Calculations based on the sex specific maturation times show that only slightly lower daily survival probabilities during maturation in females are enough to generate the observed sex ratio shift.5. Mature survival was higher in males than in females in one field population but not in another, indicating that this cannot be a general mechanism causing the sex ratio. A higher maturation probability in males is therefore the most plausible mechanism causing the sex ratio shift in damselfly populations.
The role of resources and natural enemies in determining the distribution of an insect herbivore population
Authors: Williams Iain S. , Jones T. Hefin , Hartley Susan E. 
Published: March 2003

Summary1. Both resources and natural enemies can influence the distribution of a herbivore. The ideal free distribution predicts that herbivores distribute themselves to optimise utilisation of resources. There is also evidence of herbivores seeking out refuges that reduce natural enemy attack (enemy‐free space). Which of these theories predominates in a thistle–tephritid Terellia ruficauda (Diptera: Tephritidae)–parasitoid interaction is examined.2. The plant, Cirsium palustre, had a contagious distribution approximated by the negative binomial distribution. Terellia ruficauda foraged preferentially and oviposited on isolated plants although its larvae gained neither nutritional benefit nor reduced natural enemy pressure from such behaviour.3. Parasitoids of T. ruficauda foraged and oviposited more frequently on isolated than on crowded T. ruficauda, resulting in inverse density‐dependent parasitoid attack at all spatial scales examined. Neither the herbivore nor natural enemies distributed themselves according to the predictions of the ideal free distribution and the herbivore did not oviposit to reduce natural enemy attack.4. Extrapolating from the theoretical predictions of the ideal free distribution and enemy‐free space to the field requires considerable caution. Terellia ruficauda and its parasitoids appear to select their oviposition sites to spread the risk of losses through factors (e.g. mammal herbivory) that may damage dense clusters of C. palustre.
An adaptive benefit of facultative coprophagy in the German cockroach Blattella germanica
Authors: Kopanic Robert J. , Holbrook Glenn L. , Sevala Veeresh , Schal And Coby 
Published: March 2003

Summary1. A possible adaptive benefit of coprophagy was investigated in nymphs of the German cockroach Blattella germanica (L.).2. Newly ecdysed first instars, given no source of food other than conspecific faeces, survived significantly longer than first instars deprived of faeces. The faeces of adult males and females may be of different quality, however, because nymphs given female faeces were more likely to moult into the second stadium than nymphs given male faeces.3. In contrast to first instars, second instars provided adult faeces survived only slightly longer than starved counterparts. Faecal feeding is therefore stage‐specific, as is the benefit derived from it.4. The relationship between the nutrient composition of faeces and the survival of nymphs was also examined. First instars fed the faeces of adults that had been maintained on a high (50%) protein diet, died more slowly than first instars fed the faeces of adults that had been maintained on medium (22.5%) and low (5%) protein diets. Chemical analysis of faeces showed that the concentration of protein in adult faeces increased with the level of protein in the diet. Moreover, food choice assays showed that first instars, unlike adults, ingested more of the high‐protein diets.5. These data support the idea that coprophagy is a stage‐specific adaptive behaviour that permits first instars to moult into the second stadium with minimal foraging.
Habitat and weather affect reproduction and size of the dung beetleAphodius fossor
Authors: Vessby Karolina 
Published: March 2003

Summary1. The influence of sun exposure and moisture on reproduction and size of a north temperate dung beetleAphodius fossorwas investigated. Adult beetles were added to cow pats that were either shaded or exposed and treated with different watering regimes.2. After 26 days, more eggs and larvae were recovered from shaded and wetter pats than from exposed and drier pats.3. At the end of the experiment, more beetles had developed in shaded and wetter pats, and these beetles were larger than those from exposed and drier pats.4. There was no between‐treatment difference in the ratio between adults in final sampling and larvae in first sampling.5. It was concluded that exposure and moisture can influence both reproduction and size ofA. fossor. It is suggested that weather may be a factor regulating reproduction inAphodiusnot only through heat‐ or drought‐induced mortality, as suggested earlier, but also by limiting the time available for egg laying. Further studies are needed to clarify this suggestion.
Discrimination against previously searched, host‐free patches by a parasitoid foraging for concealed hosts
Authors: Hoffmeister T. S. , Gienapp P. 
Published: March 2003

Summary1. The foraging behaviour of the parasitoid wasp Halticoptera laevigata Thomson (Hymenoptera: Pteromalidae) was studied. This wasp attacks the first‐instar larvae of the fruit fly Myoleja lucida Fallén (Diptera: Tephritidae) within honeysuckle Lonicera xylosteum L. (Caprifoliaceae) fruits. It was hypothesised that, to forage efficiently, wasps should be able to maintain a systematic or at least non‐random search pattern on the level of the microhabitat, i.e. branches with fruits, and/or be able to recognise previously searched fruits.2. Comparisons of observed patch visitation patterns on branches bearing uninfested fruits with expected values for systematic and random visitation patterns indicated that H. laevigata wasps visit patches randomly and do not avoid visiting host‐free patches that they have visited previously.3. While wasps did not alter their search effort on uninfested fruits searched previously by conspecifics, they searched for much shorter times and probed less frequently for hosts on uninfested fruits that they had searched previously.4. The results indicate that H. laevigata wasps engage in partially systematic search and increase their search efficiency through the recognition of self‐searched fruits. The reasons why partial rather than fully systematic search should be adaptive in this parasitoid are discussed.
Senescence of immune defence in Bombus workers
Authors: Doums Claudie , Moret Yannick , Benelli Elmar , Schmid‐Hempel Paul 
Published: March 2003

Abstract 1. Senescence in workers of social insects is a particularly intriguing life‐history trait as the future fitness of workers relies primarily on age‐dependent survival rate. The pattern of senescence of immune defence traits was investigated under laboratory conditions in workers of two bumble bees: Bombus terrestris and B. lucorum.2. In both species, there was a significant decrease with age in the ability to encapsulate a foreign object (a global measure of the efficiency of immune systems). This pattern of senescence was observed in all colonies in B. terrestris (seven) and B. lucorum (eight) assayed, even though, for the latter, there was some heterogeneity among colonies.3. In B. terrestris, two other measures of immune defence were taken: the relative percentage of fat body in the abdomen and the concentration of haemocytes (the immune defence cells). The quantity of fat body increased only slightly with age and there was no effect for the concentration of haemocytes. Interestingly, the concentration of haemocytes decreased strongly after an encapsulation response, regardless of the age of workers.4. The importance of the senescence pattern observed for the immune defence traits is discussed in the context of the social biology of workers.
Dung feeding in adult scarabaeines (tunnellers and endocoprids): even large dung beetles eat small particles
Authors: Holter P. , Scholtz C. H. , Wardhaugh K. G. 
Published: March 2003

Abstract 1. The maximum size of ingested particles was determined in 15 species of adult dung beetle (Scarabaeidae: Scarabaeinae) by mixing small latex or glass balls of known diameter into the dung used as food. Twelve species (tribes Coprini, Onitini, Oniticellini, and Onthophagini) were tunnellers (making dung stores for feeding and breeding in the soil below the pat) and three species (tribe Oniticellini) were endocoprids (feeding and breeding in the dung pat itself).2. The test species, covering a wide range of body size (fresh weights 0.05–7.4 g), ingested minute particles only (maximum diameter 8–50 µm), and there was a statistically significant but numerically small increase in particle size with body weight.3. When the effect of body size was taken into account, taxon (tribe), ecological group (tunneller/endocoprid), and dung preference (coarse/fine) had no significant effect on the size of ingested particles.4. Tests using two tunnelling species did not indicate that beetles use their mandibles to grind dung particles prior to ingestion.5. The results suggest essentially the same feeding mechanism in all adult tunnelling or endocoprid scarabaeines that eat fresh dung. Larger, indigestible plant fragments are avoided by filtration, and ingestion is confined to very small particles of higher nutritional value.
Patterns of pollen feeding and habitat preference among Heliconius species
Authors: Estrada Catalina , Jiggins Chris D. 
Published: March 2003

Abstract 1. The ecological circumstances that precipitate speciation remain poorly understood. Here, a community of Heliconius butterflies in lowland Panama was studied to investigate patterns of pollen use, and more specifically the ecological changes associated with the recent divergence of Heliconius melpomene (Linnaeus) and H. cydno (Doubleday).2. Considering the seven commonest Heliconius species in the community, 32 types of pollen or spore were encountered in pollen loads but only five pollen species were common. Systematic exploitation of pollen was therefore confined to a small proportion of the flowers visited.3. Most of the variation in pollen load composition between individuals was explained by differences in collecting locality. The exception was Psiguria, which was used in all habitats by the melpomene/hecale clade far more than by the erato/sapho clade. This may suggest an ancestral switch within Heliconius towards increased reliance on Psiguria pollen.4. Heliconius cydno and H. melpomene differed significantly in pollen load composition for three of the five most commonly collected pollen species. This is most probably explained by differences in habitat preference; H. melpomene and its co‐mimic H. erato are found in open habitat while H. cydno and its co‐mimic H. sapho are found in closed‐canopy forest.5. As melpomene and cydno are known to hybridise occasionally, such differences in adult microhabitat contribute to pre‐mating isolation. Habitat divergence between H. cydno and H. melpomene, which is associated with changes in mimicry, must have played a role in their recent speciation.
Dynamics of springtail and mite populations: the role of density dependence, predation, and weather
Authors: Ferguson Steven H. , Joly Damien O. 
Published: March 2003

Abstract1. Ecological theory suggests that density‐dependent regulation of organism abundance will vary from exogenous to endogenous factors depending on trophic structure. Changes in abundance of soil arthropods were investigated at three trophic levels, springtails (Collembola), predaceous mites (Acari), and macro‐arthropods (spider, adult and larval beetles, centipedes). Predictions were that springtails are predator regulated and mites are food limited according to the Hairstonet al. (1960) model, which predicts alternating regulation by competition and predation from fungi to springtails to mites to macro‐arthropods. The alternate hypothesis was based on the bottom‐up model of trophic dynamics, which predicts that each trophic level is regulated by competition for resources.2. The relative contributions to springtail and mite population dynamics of endogenous (i.e. density‐dependent population growth related to food availability) and exogenous (i.e. predation and weather) factors were tested using time‐series analysis and experimental manipulation of water conditions. Box patterns were distributed within an aspen forest habitat located in the Canadian prairies and surveyed weekly from May to September 1997–1999. Each box depressed the leaf litter, creating a microhabitat island for soil arthropods that provided counts of invertebrates located immediately beneath the boxes.3. Strong evidence was found for endogenous control of springtail and mite numbers, indicated by a reduction in population growth related to density in the previous week. Contrary to predictions, no evidence was found for regulation of springtail numbers by mites, or for regulation of mite numbers by macro‐arthropods. Springtail population growth rate was related positively to current springtail density (8 and 23% variation explained) and related negatively to 1‐week lagged density (85 and 58%), and related negatively to temperature (5 and 5%) for time‐series data and for experimental addition of water respectively. Mite population growth rate was related positively to current mite density (54%) and temperature (4%), and negatively to 1‐week lagged mite density (20%) and precipitation (6%) for time‐series analysis. For experimental addition of water, mite growth rate was related positively to current mite density (44%) and temperature (5%), and negatively to 1‐week lagged density (11%). Results differed from the Hairstonet al. (1960) model predictions but were consistent with a bottom‐up view that springtail and mite populations were regulated intrinsically by competition for food and secondarily by temperature as a function of reproduction.
Allee effect in larval resource exploitation in Drosophila: an interaction among density of adults, larvae, and micro‐organisms
Authors: Wertheim Bregje , Marchais Julien , Vet Louise E. M , Dicke Marcel 
Published: March 2003

Abstract 1. Aggregation pheromones can evolve when individuals benefit from clustering. Such a situation can arise with an Allee effect, i.e. a positive relationship between individual fitness and density of conspecifics. Aggregation pheromone in Drosophila induces aggregated oviposition. The aim of the work reported here was to identify an Allee effect in the larval resource exploitation by Drosophila melanogaster, which could explain the evolution of aggregation pheromone in this species.2. It is hypothesised that an Allee effect in D. melanogaster larvae arises from an increased efficiency of a group of larvae to temper fungal growth on their feeding substrate. To test this hypothesis, standard apple substrates were infested with specified numbers of larvae, and their survival and development were monitored. A potential beneficial effect of the presence of adult flies was also investigated by incubating a varying number of adults on the substrate before introducing the larvae. Adults inoculate substrates with yeast, on which the larvae feed.3. Fungal growth was related negatively to larval survival and the size of the emerging flies. Although the fungal growth on the substrate was largely reduced at increased larval densities, the measurements of fitness components indicated no Allee effect between larval densities and larval fitness, but rather indicated larval competition.4. In contrast, increased adult densities on the substrates prior to larval development yielded higher survival of the larvae, larger emerging flies, and also reduced fungal growth on the substrates. Hence, adults enhanced the quality of the larval substrate and significant benefits of aggregated oviposition in fruit flies were shown. Experiments with synthetic pheromone indicated that the aggregation pheromone itself did not contribute directly to the quality of the larval resource.5. The interaction among adults, micro‐organisms, and larval growth is discussed in relation to the consequences for total fitness.
Do leaf shelters always protect caterpillars from invertebrate predators?
Authors: Jones Meg T. , Castellanos Ignacio , Weiss Martha R. 
Published: March 2003

Abstract 1. All larval instars of Epargyreus clarus, the silver‐spotted skipper, construct and inhabit leaf shelters that are presumed to protect them from predator attack.2. Shelters effectively protected the larvae against foraging Crematogaster opuntiae ants and naive Polistes spp. wasps in laboratory tests, but did not protect them from predators, largely vespid wasps, present in the field.3. A range of factors, including type of predator, learning ability, and experience level, may determine the effectiveness of leaf shelters as protection from predators.
Ontogenetic shifts in competitive interactions and intra‐guild predation between two wolf spider species
Authors: Balfour Robert A. , Buddle Christopher M. , Rypstra Ann L. , Walker Sean E. , Marshall Samuel D. 
Published: March 2003

Abstract.1. The wolf spiders (Araneae: Lycosidae)Hogna helluo(Walckenaer) andPardosa milvinaHentz co‐occur in soybean fields of south‐west Ohio, U.S.A. As adults,Hognais the larger species and has the competitive advantage in most interactions; due to differing phenologies, however, their size‐classes frequently overlap and as such there is potential for shifts in competitive ability and intra‐guild predation. The hypothesis that competitive interactions and intra‐guild predation will favourPardosawhenPardosais similar‐sized, or has a size advantage overHogna, was tested in laboratory and field experiments.2. Studies in laboratory arenas, pairing similar‐sized individuals of these species andHognaspiderlings with larger spiders of both species, revealed that intra‐guild predation seldom occurs with similar‐sizedHognaandPardosa, howeverPardosawill consume smallHognaindividuals in laboratory arenas.3. Field experiments involved stocking high densities (50 m–2) ofPardosaandHognain enclosures placed in soybean fields. In experiments with spiders of similar size, no interspecific effects were uncovered, but an intraspecific effect was found forPardosaas its survival and weight gain were lower in the presence of more conspecifics. LargeHognaorPardosahad no effect on the survival or weight gain ofHognaspiderlings.4. AlthoughHognais a better competitor as an adult, it has no advantage overPardosawhen their size‐classes overlap, andPardosaeffects onHognamay be inconsequential under field conditions. Therefore, the co‐existence of these species is fostered by the fact that there are few negative interspecific interactions during their ontogeny.