bluuebunny/crossref_metadata_2025_split huggingface dataset:
Scramble competition in the southern pine beetle, Dendroctonus frontalis
Authors: Reeve John. D. , Rhodes Douglas J. , Turchin Peter 
Published: March 2003

Abstract.1. The nature of intraspecific competition was investigated in the southern pine beetle, Dendroctonus frontalis, a highly destructive pest of pine forests in the southern U.S.A. Data were analysed from an observational study of naturally‐attacked trees, and from field experiments where attack density was manipulated by adding different numbers of beetles to caged trees.2. The effect of attack density on gallery construction, oviposition, brood survival, and the overall rate of increase was examined, and a flexible model of intraspecific competition used to classify the type of competition (contest or scramble) at different points in the life cycle.3. The results of these analyses suggest that contest competition occurs during gallery construction and oviposition, in accord with previous work on D. frontalis. Strong scramble competition occurs later on in development, however, and the overall competitive process is better characterized as scramble competition, similar to other bark beetles. Trees with attack densities sufficiently high to produce significant competition are common in the field.
Plant cues influence searching behaviour and parasitism in the egg parasitoid Trichogramma nr. brassicae
Authors: Bjorksten Tracey A. , Hoffmann Ary. A. 
Published: March 2003

Abstract.1. The effect of experience of plant cues at emergence on searching behaviour and parasitism was investigated in two strains of Trichogramma nr. brassicae (Hymenoptera: Trichogrammatidae).2. Wasps reared on Sitotroga cereallela were allowed to emerge on a tomato plant or in a vial, with or without food. For one of the strains, females emerging on tomato searched significantly longer on a tomato seedling than females emerging in a vial.3. The experience effect lasted between 1 and 2 days. It involves associating plant stimuli with the remains of the host, because females emerging from their host on a tomato plant had an increased searching response to tomato, but females transferred to the plant immediately after emergence did not.4. The effect of emergence environment on parasitism of the host Helicoverpa punctigera on tomato and lettuce seedlings was tested. Wasps were allowed to emerge on seedlings of tomato or lettuce, or in an empty vial. For one strain, females experienced with tomato at emergence parasitized significantly more hosts on tomato than did females emerging on lettuce or in a vial. Parasitism on lettuce was not influenced by the treatments.
Mortality rate, reproductive output, and trap response bias in populations of the blowfly Lucilia sericata
Authors: Hayes E. J. , Wall R. , Smith K. E. 
Published: March 2003

Summary1. The ages of 877 females of the blowfly Lucilia sericata, collected from two farms in south‐west England between May and September 1996, were determined using a combination of ovarian dissection and wing fray analysis.2. Using survivorship analysis, the mortality rates over the entire field season were estimated to be 2.2 and 1.9% per day‐degree at the two farms, respectively. These gave a mean life expectancy of 46 and 53 day‐degrees, and a lifetime reproductive output of 130 and 172 eggs per female.3. The mortality rate remained relatively constant over time, with one exception, the first sample of the season when no older flies were present, indicating that underlying changes in demography (emergence and senescence of generations) over the field season were not sufficient to affect the rates calculated by survivorship analysis.4. The response of L. sericata to liver‐baited traps was affected strongly by age and reproductive status, with gravid females and females in the early stages of ovarian development being most markedly over‐represented relative to other age categories.
Intrinsic and extrinsic competitive interactions between two larval parasitoids of Heliothis virescens
Authors: De Moraes Consuelo M. , Cortesero A. M. , Stapel J. O. , Lewis W. J. 
Published: March 2003

Summary1. Competition between parasitoid species may be a key factor in the community dynamics of plant–herbivore‐parasitoid systems and is an important consideration in the selection and management of effective biological control agents.2. Interspecific competition can occur between adult parasitoids searching for hosts (extrinsic competition) and between multiple parasitoid larvae developing within a single host individual (intrinsic competition). A model system comprising the lepidopteran pest Heliothis virescens and two key hymenopteran endoparasitoids, Microplitis croceipes and Cardiochiles nigriceps, was employed to explore parasitoid host‐location strategies and the consequences of intrinsic and extrinsic competitive interactions between parasitoid species.3. The less specialised of the two parasitoids, M. croceipes, was found to have a shorter hatching time and to dominate intrinsic competition, except when its oviposition followed that of the more specialised parasitoid, C. nigriceps, by 16 h or more. This interval corresponded to the differential in hatching time between the two species.4. Cardiochiles nigriceps, however, displayed superior host‐searching efficiency that may compensate for its disadvantage in intrinsic competition. This parasitoid was more effective at detecting host infestation sites via airborne odours and at locating and attacking early instar host larvae than was M. croceipes.
Contrasting diel activity and feeding patterns of four species of carnivorous stoneflies
Authors: Elliott J. M. 
Published: March 2003

Summary1. The hypothesis under test was that larvae of Dinocras cephalotes (Curtis), Perla bipunctata Pictet, Isoperla grammatica (Poda), and Perlodes microcephalus (Pictet) differed markedly in their diel activity and feeding patterns. Mature larvae collected about 1 month prior to adult emergence were used either for gut analyses or for observations of their activity and feeding patterns in three stream tanks with natural substrata and glass bottoms, so that activity could be observed above and below the substratum. A dull red light was used for observations in the dark. Food (larvae of Ephemeroptera, Simuliidae, and Chironomidae) was provided in excess.2. Larvae for gut analyses were taken 1 h before dusk or dawn (n = 30 larvae per species for each day or night sample). The only species with food in the gut for the day samples was P. microcephalus. All species fed at night, the mean number of prey per larva being very similar for D. cephalotes, P. bipunctata, and I. grammatica but significantly higher for P. microcephalus. Most prey were insect larvae, especially Simuliidae and Chironomidae.3. Diel activity patterns of single larvae differed interspecifically but not intraspecifically. Larvae of D. cephalotes and P. bipunctata were rarely active during the day; their activity increased at dusk and decreased at dawn, and was highest during the night; their success at prey capture was highest at dusk and dawn, with an ambush rather than a search strategy. Isoperla grammatica was rarely active during the day, most active at dusk and dawn when prey capture was highest, using a search strategy, and less active for the rest of the night. Perlodes microcephalus was active during the day, but only below the substratum, and very active from dusk to dawn with a high prey‐capture success, using a search strategy. These experiments provided support for the hypothesis under test. The discussion concludes that the results could also help to explain known differences in growth rate and the length of the life‐cycle in these four species.
Consequences of foundress aggregation in the brown citrus aphid Toxoptera citricida
Authors: Michaud J. P. , Belliure B. 
Published: March 2003

Summary1. A field study was conducted in which colonies of Toxoptera citricida (Kirkaldy) were initiated with different numbers of foundresses on ungrafted citrus trees var. ‘Carrizo’ within an existing citrus grove in central Florida.2. The growth rate, longevity, and final size of T. citricida colonies were all positively correlated with number of foundresses.3. Colonies initiated by many foundresses produced alatae earlier than those initiated by fewer foundresses.4. Nymphal developmental time was reduced in colonies initiated by more foundresses but the mean number of grand‐progeny per foundress was lower when only surviving colonies were compared.5. The longevity of foundresses was unaffected by their number but foundress fecundity and nymphal survival decreased as foundress number increased.6. The most abundant natural enemies were Diptera: Syrphidae, primarily Pseudodorus clavatus (F.), and Chamaemiidae (Leucopis sp.), followed by Coleoptera: Coccinellidae, primarily Cycloneda sanguinea (L).7. Colonies initiated with more foundresses attracted more oviposition by dipteran predators than did colonies initiated with fewer foundresses.
Variation in predation costs with Chiastocheta egg number on Trollius europaeus: how many seeds to pay for pollination?
Authors: Jaeger Nicolas , Pompanon François , Després Laurence 
Published: March 2003

Summary1. In obligate plant/seed parasite–pollinator mutualisms, the plant is exclusively pollinated by an insect whose larvae are specific seed predators. Hence, outcomes of the interaction for the plant can vary with the number of eggs laid and the number of seeds eaten per larva.2. In the work reported here, predation by Chiastocheta larvae on seeds of Trollius europaeus was analysed as a function of the number of eggs laid on the flower. Flowers with an increasing number of eggs were bagged in three populations and seeds were counted after the end of larval predation, in order to assess whether there was competition among larvae.3. Seed predation on single‐egg flowers was high and variable (mean per population ranging from 15 to 40% of the developed seeds). Seed predation increased weakly with increasing egg load and was lower than gross seed production (always < 85%) whatever the number of eggs laid. This corresponds to a strong decrease in seed consumption per larva with increasing egg load, i.e. severe larval competition for resources.4. The results suggest that both interference among Chiastocheta larvae and carpel dehiscence may protect T. europaeus seeds from total predation. Estimates of seed predation based on egg load observed in 20 natural populations in the French Alps typically ranged from 30 to 60%. The interaction was always beneficial for the plant and there was no risk of total seed destruction by Chiastocheta larvae, favouring stability of the mutualism.
Past attacks influence host selection by the solitary bark beetle Dendroctonus micans
Authors: Gilbert Marius , Vouland Gérard , Grégoire Jean‐Claude 
Published: March 2003

Summary1. A spatio‐temporal study of host selection and local spread of a solitary bark beetle attacking live spruce Dendroctonus micans (Kugelann) was carried out using a combination of standard statistical methods, geostatistical analyses, and modelling. The study was based on data from three plots (150–300 trees, 0.3–1 ha) from 1978 to 1993. All trees were mapped and successful and abortive bark‐beetle attacks on each tree were counted annually. Because the attacked trees usually survived, temporal attack patterns as well as spatial patterns could be analysed.2. The distribution of successful insect attacks on the trees was slightly aggregative, indicating some degree of choice rather than totally random establishment.3. The level of yearly individual attacks per tree was very stable, suggesting that D. micans usually leave the host in which they develop.4. The attacked trees were distributed randomly in the plots; at the study's spatial scale, the insects dispersed freely throughout the plot (no spatial dependence).5. On the other hand, time dependence was strong; some trees were attacked repeatedly while others were left untouched.6. Among a choice of scenarios (random attack, fixed variability in individual host susceptibility, induced host susceptibility following random attack), the best fit was obtained with the model involving induced individual host susceptibility. This type of relation to the host tree contrasts strongly with patterns generally described in host–plant relationships (including gregarious, tree‐killing bark beetles), where local herbivore damage results in induced resistance.7. These results suggest that the first attacks in a new stand are made at random, that all or most of the beetles emerging from a tree disperse and resample the stand, and that they settle preferentially on trees that were colonised successfully by previous generations.
Resource availability and population dynamics of Nicrophorus investigator, an obligate carrion breeder
Authors: Smith Rosemary J. , Merrick Melissa J. 
Published: March 2003

Summary1. Food resources for rearing young may influence insect populations. This is particularly true for insects that breed obligately on rare, ephemeral resources such as dung, fungi, or carrion.2. Beetles in the genus Nicrophorus bury small vertebrate carcasses for rearing their young. Studies reviewed by Scott (1998) have found a positive relationship between carcass mass and total brood size. It is likely that access to carcasses suitable for breeding, and not food or mates, limits reproduction in both male and female Nicrophorus. Thus, small mammal densities could determine Nicrophorus population sizes.3. The work reported here examined the relationship between Nicrophorus investigator (Coleoptera: Silphidae) population size and small mammal abundance at two sites over a 4‐year period.4. Nicrophorus investigator buried and reared young on all the native small rodent species trapped at two sites in south‐western Colorado, U.S.A. (Peromyscus maniculatus, Microtus montanus, Zapus princeps, Tamias minimus, Thomomys talpoides). They preferred to bury and reproduce on rodent carcasses weighing between 16 and 48 g; rodents of this size represented 82% of captures.5. Population sizes of N. investigator and small rodents were estimated simultaneously using mark‐recapture censuses over a 4‐year period. Considering only rodents within the size range used by N. investigator, the estimated small mammal biomass per hectare in one year and the beetle population size in the following year were correlated significantly.
Jasmonate‐mediated induced plant resistance affects a community of herbivores
Authors: Thaler Jennifer S. , Stout Michael J. , Karban Richard , Duffey Sean S. 
Published: March 2003

Summary1. The negative effect of induced plant resistance on the preference and performance of herbivores is a well‐documented ecological phenomenon that is thought to be important for both plants and herbivores. This study links the well‐developed mechanistic understanding of the biochemistry of induced plant resistance in the tomato system with an examination of how these mechanisms affect the community of herbivores in the field.2. Several proteins that are induced in tomato foliage following herbivore damage have been linked causally to reductions in herbivore performance under laboratory conditions. Application of jasmonic acid, a natural elicitor of these defensive proteins, to tomato foliage stimulates induced responses to herbivory.3. Jasmonic acid was sprayed on plants in three doses to generate plants with varying levels of induced responses, which were measured as increases in the activities of proteinase inhibitors and polyphenol oxidase.4. Field experiments conducted over 3 years indicated that induction of these defensive proteins is associated with decreases in the abundance of all four naturally abundant herbivores, including insects in three feeding guilds, caterpillars, flea beetles, aphids, and thrips. Induced resistance killed early instars of noctuid caterpillars. Adult flea beetles strongly preferred control plants over induced plants, and this effect on host plant preference probably contributed to differences in the natural abundance of flea beetles.5. The general nature of the effects observed in this study suggests that induced resistance will suppress many members of the herbivore community. By linking plant biochemistry, insect preference, performance, and abundance, tools can be developed to manipulate plant resistance sensibly and to predict its outcome under field conditions.
Survival rates in a natural population of the damselfly Ceriagrion tenellum: effects of sex and female phenotype
Authors: Andrés Jose A. , Rivera Adolfo Cordero 
Published: March 2003

Summary1. Ceriagrion tenellum females show genetic colour polymorphism. Androchrome (erythrogastrum) females are brightly (male‐like) coloured while gynochrome females (typica and melanogastrum) show cryptic colouration.2. Several hypotheses have been proposed to explain the existence of more than one female morph in damselfly populations. The reproductive isolation and intraspecific mimicry hypotheses predict greater survival of gynochrome females, while the density dependent hypothesis predicts no differential survival between morphs.3. Mature males had greater recapture probability than females while the survival probability was similar for both sexes. Survival and recapture rates were similar for androchrome and gynochrome females.4. Gynochrome females showed greater mortality or migration rate than androchrome females during the pre‐reproductive period. This result is not predicted by the above hypotheses or by the null hypothesis that colour polymorphism is only maintained by random factors: founder effects, genetic drift, and migration.
Gut content analysis and a new feeding group classification of termites
Authors: Donovan S. E. , Eggleton P. , Bignell D. E. 
Published: March 2003

Summary1. Gut content analysis of termites was undertaken using microscopical techniques. The 46 study species covered the entire range of taxonomic and feeding forms within the Order.2. Inter‐specific gut contents data were analysed using principal components analysis, placing species along a clear humification gradient based on variations in the amount of silica and plant tissue fragments in the gut.3. Redundancy analysis was used to find morphological correlates of the observed variation in gut contents. A total of 22 morphological characters (out of 45 candidate characters) were correlated significantly with the gut contents.4. Three of the 22 significantly correlated characters unambiguously defined feeding groups, which were designated groups I to IV in increasing order of humification of the feeding substrate. Group I contains lower termite dead wood and grass‐feeders; group II contains Termitidae with a range of feeding habits including dead wood, grass, leaf litter, and micro‐epiphytes; group III contains Termitidae feeding in the organic rich upper layers of the soil; group IV contains the true soil‐feeders (again all Termitidae), ingesting apparently mineral soil. These groupings were generally supported statistically in a canonical covariance analysis, although group II apparently represents termite species with a rather wide range of feeding habits.5. Using existing hypotheses of termite phylogenetic relationships, it seems probable that group I feeders are phylogenetically basal, and that the other groupings have arisen independently on a number of occasions. Soil‐feeding (i.e. group III and group IV feeding) may have evolved due to the co‐option of faecal material as a fungal substrate by Macrotermitinae‐like ancestral forms. As a consequence, these forms would have been constrained to build nest structures from soil and would therefore have passed at least some soil through their guts.
Reproductive allocation within a polygyne, polydomous colony of the antMyrmica rubra
Authors: Walin Laura , Seppä Perttu , Sundström Liselotte 
Published: March 2003

Summary1. Ant colonies commonly have multiple egg‐laying queens (secondary polygyny). Polygyny is frequently associated with polydomy (single colonies occupy multiple nest sites) and restricted dispersal of females. The production dynamics and reproductive allocation patterns within a population comprising one polygyne, polydomous colony of the red antMyrmica rubrawere studied.2. Queen number per nest increased with nest density and the number of adult workers increased with the number of resident queens and with nest density. This suggests that nest site limitation promotes polygyny and that workers accumulate in nest units incapable of budding.3. Nest productivity increased with the number of adult workers and production per queen was independent of queen number. Productivity increased with nest density, suggesting local resource enhancement. This shows that productivity can be a linear function of queen numbers and that the limiting factor is not the egg‐laying capacity of queens.4. The total and per capita production of reproductives decreased towards the periphery of the colony, suggesting that the spatial location of nest units affects sexual production. Thus nests at the periphery of the colony invested more heavily in new workers. This is consistent with earlier observations in plants and could either represent investment in future budding or increased defence.5. The colony produced only five new queens and 2071 males, hence the sex ratio was extremely male biased.
Hosts as habitats: faunal similarity of phytophagous insects between host plants
Authors: Frenzel Mark , Brandl Roland 
Published: March 2003

Summary1. Published lists on the phytophages recorded on 86 cabbage plant species (Brassicaceae) and 30 thistle species (Cynaroideae) were used to investigate patterns in the faunal similarity of phytophages. This was done by calculating the Jaccard index and a standardised index of similarity between pairs of host species using presence/absence data.2. The faunal similarity measured as Jaccard indices indicated that pairs of cabbage hosts share on average 36% of phytophagous species whereas pairs of thistle hosts share only 10%.3. The faunal similarity between two host species increased with the taxonomic affinity of hosts. This increase was more pronounced in thistles than in cabbage plants.4. Irrespective of the taxonomic affinity of hosts, in the cabbage plants the faunal similarity of endophages was lower than in ectophages. In contrast, in the thistles faunal similarity differed only between endophages and ectophages for hosts of the same genera.5. Differences in the patterns of faunal similarity between the two host taxa may be due to idiosyncratic characteristics of the plant taxa, e.g. the unique chemical properties of the cabbage plants and the resource‐rich flower heads of thistles.