摘要:

Abstract.1We report on the mating system of a field population of the parasitic wasp,Bracon hebetor, on a corn pile infested by the Indian meal moth,Plodia interpunctella.We demonstrate that the mating system is based upon male scramble competition polygyny with male aggregations on high places on the corn.2The sex ratio among adults was greater than 80% males on the surface of the corn, whereas below the surface the sex ratio was less than 45%. Males actively courted females on the surface, but there were no aggressive interactions among males during courtship or mating.3Approximately 20% of the females found on the surface of the corn had no sperm in their spermathecae, regardless of age, but the numbers of unmated females decreased later during the day.4In laboratory studies we showed that females from this population oviposit a female biassed sex ratio, and that only 14% of females were mated before dispersing from their place of emergence.5Thus sib‐mating is unlikely in this gregarious parasitoid. This outcrossing mating system probably arose because of severe inbreeding depression thatB.hebetorsuffers via a sex locus: diploids that are heterozygous at the sex locus develop into females, but homozygous diploids are male and are generally inviable. The female biassed sex ratio may have evolved inB. hebetorin response to males being the more expensive sex, females dispersing more frequently from the population than males, or a fraction of females remaining unmated in the populatio

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1992.tb01032.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.1Several attributes of foliage were measured from the Australian rainforest treeArgyrodendron actinophyllumEdlin (Sterculiaceae). These were related to estimates of abundance per leaf area of the most common arthropod guilds and families sampled with restricted canopy fogging.2When all these arthropod groups were considered, much of the overall variance in arthropod spatial distribution could be attributed to leaf age characteristics, arthropod aggregation patterns, arthropod activity and distance to tree trunk.3The fraction of variance which could be specifically explained by foliage attributes such as nitrogen‐, water‐ and fibre‐content, specific leaf weight, and epiphyll load was small for most arthropod groups (usually<30%). However, an index of food quality explained a higher proportion of variance (50%) in the abundance of phloem‐feeders. Leaf size and foliage compactness did not influence significantly the abundance of any arthropod group.4Most herbivores were more abundant on young foliage than on mature leaves. With the exception of Corylophidae and Chrysomelidae, which were more abundant in the lower and upper canopy respectively, arthropod stratification was not conspicuous within the inner core of tree crowns.5The results firstly emphasize the distribution of young foliage as a key factor affecting the abundance of many herbivores and, secondly, the importance of the local illumination regime for host leaf production and its indirect effects on the spatial distribution of arboreal art

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1992.tb01033.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.1For the understanding of the influence of natural selection on the persistence of host selection behaviour in populations ofDrosophilaparasitoids it is important to know whether parasitoids will become time‐ or egg‐limited. We investigated whether theDrosophilaparasitoidLeptopilina clavipes(Hartig) meets egg‐ or time‐limited conditions in the field.2To this end the following aspects of the parasitoid's life were studied: egg load at emergence, travelling velocity between patches, patch residence times, oviposition rates and life expectancy. Together with the results from earlier studies on host and patch distributions, this formed the input of a ‘Monte Carlo’ simulation model, in which the life history of an individual parasitoid can be traced.3The simulations revealed that under the conditions found in the field 12.9% of the parasitoid population is egg‐limited. The model was also run for a number of scenarios which reflect ‘good’ or ‘bad’ circumstances. In most cases a significant proportion of the parasitoid population proved to be egg‐limited.4For the measurement of travelling velocities and patch residence times a marking method, especially applicable to small‐sized parasitoids such asL.clavipes, is described. Marking did not affect survival, host habitat location or host detection rate. Parasitoids were found to be attracted to the odour of fruit‐bodies ofPhallus impudicus, the most important breedi

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1992.tb01034.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.1We investigated the effect on egg hatch of exposure to: (1) varying larval density, and (2) larval contact inAedes triseriatusSay (Diptera: Culicidae). For 2 days in the laboratory we submerged eggs into a treehole water medium containing 0 (control), 4, 12 or 24 larvae that could either contact the eggs directly or were separated from them by a screen. Following treatment, abundance of microorganisms on the egg surfaces, a food source for newly hatched larvae and a proposed hatching stimulus, was assessed by counts made from serial dilutions of samples.2We discovered a complex hatching response to larval contact and to larval density, and an interaction between these two factors in their effect on microbial growth. Hatching was inhibited in the 0‐larva control, even though microorganisms grew abundantly on the eggs. Hatch rate, as well as microbial counts, were high for eggs in direct contact with 4 larvae. As density increased in the larval contact treatment, microorganisms disappeared from the egg surfaces and hatch rate declined.3When protected from larval grazing, eggs supported numerous microbial colonies irrespective of larval density. In contrast to the contact treatment group, egg hatch increased with increasing larval density. These observations suggest that the combination of microbial growth and a larval factor stimulates hatch. This hatching response may have evolved because both abundant microorganisms and numerous larvae reflect a habitat of good qualit

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1992.tb01035.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.1Food demands of the predatory carabidNotiophilus biguttatusF. and their fulfilment were studied in the laboratory and field.2In the laboratory, larval consumption, growth, adult body size and egg production were established for different regimes of temperature and food, the springtailOrchesella cincta.3Temperature strongly influenced feeding rate of larvae and adults and consequently growth and oviposition rates. Accordingly, growth rate and ovi‐position rate increased with prey supply.4Prey supply also had an effect on fat content, but the number of ripe eggs in the ovaries was related neither to temperature nor to prey supply.5Adult body size was affected by temperature during the larval period but more so by food supply.6Dissection of field fresh females showed them to bear eggs for the whole year, except in late winter/early spring and in July.7Fat content was low in spring and, from July on, high in summer and autumn. Survivorship during starvation differed widely between samples and seemed to be related to reproductive status rather than to fat content.8Samples of beetles and springtails from eleven pine plantations revealed for the beetles significant differences in fat content and body size, the latter ranging between the maximum and minimum value obtained in the laboratory.9Conclusions about food limitation based on body size and fat content were not corroborated by a relationship of these indices with springtail densit

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1992.tb01036.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.1In nest‐building wasps there is a continuum from species that provision each offspring cell with one large prey item (single provisioning) to species that provision each cell with many small items (multiple provisioning). The significance of number of prey per cell was examined during two seasons inAmmophila sabulosa(L.), a species that provisions between one and five caterpillars per cell.2There was no difference between the total weight of prey in singly‐provisioned and multiply‐provisioned cells: individual caterpillars placed in multiply‐provisioned cells were smaller.3Small caterpillars were captured and transported to the nest faster than large ones.4If the first prey provisioned was large, the cell was usually then permanently closed. If the first prey was small, additional prey were captured, and females appeared to become more selective: additional prey were rarely large.5It is suggested that the flexible provisioning strategy used byA.sabulosaallows a wide range of prey sizes to be utilized without affecting maternal control of offspring size and sex. This could be important when available prey sizes vary temporally and spatially.6There was a male‐biased first generation investment ratio. Female‐producing cells were provisioned with a higher total prey weight than male‐producing cells, and conversion of prey weight to adult weight was more efficient for females.7Total prey weight provisioned is probably a good indirect measure of parental time investment inA.sabulosa.Other measures, particularly number of prey provisioned, will be

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1992.tb01037.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.1The daily activity pattern and aspects of the thermal biology are described for the day‐flying hawkmoth,Macroglossum stellatarumL. (Lepidoptera: Sphingidae), while foraging at a flowering population ofLavandula latifolia(Labiatae) under the dry‐hot summer conditions of a southeastern Spanish locality.2The average abundance ofM.stellatarumremained fairly constant from sunrise to about 17.00 hours (GMT), and a distinct peak occurred in the evening (18.00—20.00 hours).3Foraging took place over a broad range of microclimatic conditions, as described by air temperature (Ta; range 19‐36°C) and solar radiation (IR; range 1–1025 Wm‐2).4The thoracic temperature (Tth) of insects remained within relatively narrow limits (39–46°C), with the highest values occurring around noon. Variation inTthmainly reflected differences inTabetween foraging sites and times.Tthwas nonlinearly related toTa, the rate of increase ofTthwithTadecreasing with increasingTa.5The unusual tolerance of highTthexhibited byM.stellatarum, and its enhanced thermoregulatory capacity at highTa, enable this species to withstand the severe environmental conditions faced during diurnal foraging in the Medit

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1992.tb01038.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.1Delia flavifronsZetterstedt (Diptera: Anthomyiidae) visits flowers ofSilene vulgaris(Moench) Garcke (Caryophyllaceae), where the adults feed, mate, lay their eggs, and the larvae feed on developing seeds. The objective of the study was to examine how an ovipositing female fly assures a food resource for her progeny.2Ovipositing females preferred young, non‐pollinated flowers over older pollinated ones. The flies did not pollinate the flowers and survival of the larvae depended on the flowers being pollinated by moths.3Flowers containing fly eggs were pollinated more often than expected from chance, probably as a result of both flies and moths visiting particular flowers.4Eggs were laid singly, and multiple oviposition occurred randomly. Although most eggs hatched, only about half produced larvae that made their way into the fruits. As a result, the probability of competition arising from multiple oviposition may be reduced to such an extent that selection does not favour females that avoid flowers with conspecific eggs.5Moth larvae of the noctuid genusHadenaalso feed on the seed pods ofS. vulgarisand will kill any fly larvae they encounter. However, there was no deviation from random oviposition by the flies in relation to eggs laid by the moths, but the competitively weaker fly usually started to lay eggs towards the end of the moth's egg‐laying period.6The relationship betweenDelia flavifronsandSilene vulgarissuperficially parallels that for known pollinator/predator systems, but floral adaptations to hypothetically pollinating flies seems not to have taken pl

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1992.tb01039.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.1The plant‐to‐plant movement of the corn leafhopper,Dalbulus maidisDelong&Wolcott, and the spread of the leafhopper‐borne maize rayado fino virus were investigated in four patterns of maize(Zea mays)dispersion.2D. maidiswas less abundant and the spread of the virus was slower in dense stands of maize than in sparse stands.3When plant density was held constant, leafhoppers were more abundant in maize stands with relatively equidistant plant spacing (uniform dispersion) than in stands with densely‐sown rows (linear dispersion) or double‐sown hills (clumped dispersion), but there was no difference in virus incidence among these plant dispersion patterns.4Leafhoppers were less likely to move to adjacent plants in uniform plant dispersion patterns than in either linear or clumped dispersion patterns. This result may explain the lack of higher virus incidence in uniform stands, despite higher leafhopper abundance.5Leafhopper movement was consistent with a simple rule: the shorter the distance to the next adjacent plant, the more likely a leafhopper is to move between plants.6These results demonstrate that host plant dispersion can affect the abundance and behaviour of highly mobile herbivorous insects even when plant density is

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1992.tb01040.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.1Among‐population differences in pupal mass were studied in a geometrid,Epirrita autumnata.SomeEpirrita autumnatapopulations regularly reach outbreak densities while others are never known to do so. Because adults do not feed, pupal mass of females correlates strongly with fecundity.2Larvae were collected from twelve field sites. Ten of our sample populations originated within the outbreak range of the species and represented different phases of outbreaks. Two populations originated outside the outbreak range.3Pupal mass of field‐collectedE. autumnatavaried significantly among populations. The peak phase populations had the smallest pupae and the biggest were found in low density populations outside the outbreak range.4Offspring of moths from each population were reared under identical conditions in two larval densities. Significant differences were not found in pupal mass among populations. That is, the inherent size, correlated with fecundity of moths, was not different between populations originating within and outside the outbreak range, nor among collections from different densities or phases of the outbreaks.5Rearing density did not interact in a consistent way with population.6As far as size and fecundity are concerned, the results do not support Chitty's hypothesis that differences in genetic composition of the population at low and high density phases generate cyclic fluctuations of population density.7Because no hereditary or maternal differences were found in size and fecundity betweenE.autumnataoriginating within and outside the outbreak range, variation in reproductive capacity cannot explain why outbreaks occur only in some populati

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1992.tb01041.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY