摘要:

Abstract.1Unlike most parasitoids, tachinid flies of the tribe Ormiini use sound to locate their hosts. Although thought to exert selection pressure on their host's calling behaviour, little is known about the biology of ormiines. Accordingly, this study reports the biology and impact of the ormiineHornotrixasp. upon calling males of the univoltine bushcricketSciarasaga quadrataRentz in south‐western Australia.2Populations of adultS.quadratawere monitored in the field over two successive calling seasons. Females, which do not call, were not parasitized byHornotrixasp., but the risk of parasitism for males increased as the 3‐month calling season progressed. Parasitism did not commence untilc. 2 weeks into the calling season, but by the end of the season up to 87% of surviving males were parasitized.3Parasitized males lived for 14 days and were found singing until their penultimate evening before death in the field. Unparasitized males lived on average 69 days and a maximum of 119 days.4Multiparasitism of hosts was common, with up to sixteen fly larvae found within parasitized males. The number of fly larvae within hosts significantly increased at the end of the season. However, successful emergence of fly larvae from hosts, as well as pupal size, significantly decreased as more than one fly larva developed within the host.5Hornotrixasp. has a long pupal duration of 30–31 days at 20°C. As a consequence, only one complete fly generation, which overwinters in the pupal stage, is likely within each host generation.6No evidence for differential (size‐bias) mortality byHornotrixasp. on maleS.quadratawas found. The size of parasitized and unparasitized males collected in the field was not significantly different.7It is concluded thatHornotrixasp. is a significant mortality factor acting on the survival of adult maleS.

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1995.tb00435.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.1The distribution of the body sizes of British aphids is right‐skewed on a logarithmic axis, as in other taxa. Over the size range 2–5 mm there is a marked decrease in numbers of species with increase in size, which on a log log scale has an exponent of ‐3, The exponent for the right‐hand side of the size distribution of British plants is ‐0.7.2The sizes of sixty‐eight species of the genusAphisare weakly correlated with the size of their respective host plants.3An aphid's size is strongly correlated with the length of its proboscis, which indicates the depth to which it has to probe plant tissues in order to feed.4On average, trees host more species of aphids than either shrubs or herbaceous plants, which appears to be associated with the relative surface area of specific plant structures. The surface area of plants is mainly made of leaves and most species of aphids are leaf feeders. The largest and least numerous species of aphids feed on the branches and trunks of trees, the proportional cover of which is less than that of leaves.5Taking into account all the above observations, a functional explanation in terms of the relative surface area of specific plant structures is offered to account for the size diversity curv

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1995.tb00436.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.1We tested the hypothesis that biased sex ratios in the aphidiid parasitoid,Aphidius ervi, are the result of sex‐specific mortality of immatures due to hyperparasitism. The solitary hyperparasitoid,Dendrocerus carpenteri, deposits its eggs on the prepupa or pupa of the primary parasitoid after its pea‐aphid host is mummified.2In dichotomous choice tests, females ofD.carpenteriaccepted immatures of both sexesof A.erviwith equal frequency. Independent of the sex of the primary parasitoid, the probability of a mummified pea aphid being hyperparasitized did not differ between large (adult at the time of death) and small (fourth nymphal instar) mummies.3As predicted by‘host quality’models of offspring sex allocation,D.carpenteriproduced a higher proportion of female than male offspring in large mummies. These laboratory results were supported by field data.4Because hyperparasitism byD.carpenteriis random with regard to host sex, it should have no influence on optimal sex allocation by the primary par

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1995.tb00437.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.1We tested the effects of food, in the form of leaf litter, and density on population growth and fitness correlates of the tree hole mosquitoAedes triseriatus. Our field experiment used a 2 x 2 randomized block design, with three holes as blocks. In cages within three holes, we manipulated densities ofAedes triseriatuslarvae, and presence of leaf litter. Our laboratory experiment used a 2 x 3 factorial design in which we also manipulated densities of larvae and availability of leaf litter within similar cages (inside, outside, or absent). For both experiments we determined effects on survival, days to and mass at eclosion of both sexes, and a composite index of population performance λ′, that estimates finite rate of increase.2In the field experiment, we found significant and large effects of leaf litter and of density on the performance ofA. triseriatus. The effect of density did not depend on leaf litter availability. We documented significant variation among tree holes for most correlates of fitness. Often, the effects of treatments varied significantly depending on the tree hole tested.3In the laboratory experiment we found significant effects of density and litter, and that direct browsing on leaf litter is necessary for the effect of litter on performance ofA. triseriatus. In the laboratory, the negative effect of increased density was dependent on leaf litter availability.4Our results demonstrate that leaf litter has important effects on population performance of tree hole mosquitoes in natural tree holes. Direct browsing on the surface of leaf litter is the most likely mechanism by which litter enhances population growth. The impact of litter on populations varies among tree hol

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1995.tb00438.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.1Local dispersal and philopatric behaviour of the alpine grasshopper,Podisma pedestris, were studied at two sites in the Alpes Maritimes using a new mark—release—resight technique featuring markingin situ, and multiple resighting without handling. The time‐consuming nature of the design was justified by the quantity and quality of the data yielded.2Philopatry is defined independently of any concept of home range as a phenomenon by which movements over longer periods are less than would be expected by extrapolation of measures over shorter periods.3By this definition, the grasshoppers are shown to exhibit philopatry. Nymphs comprise two heterogenous classes of those which move little and those which move considerable distances.4Daily dispersal estimates were obtained from movements of 1055 nymphs and adults at one site, and of 593 adults at another.5Differences are demonstrated in daily dispersal distances for age, sex and site combinations.6Some differences in microhabitat preference were observed.7The findings are compared with previous measurements of dispersal in this species, and the merits of the new technique are disc

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1995.tb00439.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.1Foraging for bloodmeals is the most frequently recurrent and probably the most targetable of all activities that render tsetse vulnerable to interception with static trapping devices.2Surgical monitoring of the rnidgut every 24 h during three successive days of food deprivation, showed that a full bloodmeal, irrespective of its size or source, vacated the rnidgut of both sexes ofGlossina pallidipesAusten in eight progressive stages.3Probing responsiveness in both sexes increased exponentially during the first four stages of their midgut evacuation, reaching a peak between stages 3 and 5. Thereafter it decreased, also exponentially.4MostG.pallidipescaught by NG2G traps baited with cow urine and acetone had midguts in the last three stages (6–8) of bloodmeal evacuation. The same was true of the majority of those that failed to feed on a calf shortly after entrapment.5The implications of the foregoing for tsetse foraging activity and trappability as well as for the potency of cattle urine and acetone as odour‐bait for tsetse are discus

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1995.tb00440.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.1In Kenya, the aphidCinara cupressi(Buckton) has an aggregated distribution across individuals of its host plant, the Mexican cypress,Cupressus lusitanica(Mill).2There are significant differences in host plant quality:C.cupressinymphs transplanted onto cypress trees with low aphid infestations are significantly less likely to establish than aphids transplanted onto trees with high aphid infestations.3Given that some transplanted nymphs establish, the previous level of infestation does not influence aphid survival.4Evidence for local adaptation to individual plants was not found: nymphs transplanted to the trees from which their parents were collected neither established more readily nor showed lower mortality than those transplanted to other trees with similar levels of infestation. Therefore the variation in host plant quality has not led to the development of local adaptation to particular host plants.

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1995.tb00441.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.1Life tables and rates of parasitism were tabulated from mud nests built byTrypoxylon politum(Hymenoptera: Sphecidae) at nine different nesting sites from Missouri and Mississippi.2Most developmental mortality occurred either during the first two instars of development, or during the inactive prepupal phase. The majority (76%) of deaths were caused by insect parasitoids and cleptoparasites. Levels of parasitism and survivorship varied among nesting sites, and among locations within the two sites surveyed at a fine spatial scale.3Total developmental mortality,K, was positively associated with the number of hosts (immatureT.politum) per site. Within one of two sites sampled at a fine spatial scale,Kwas negatively associated with the local density of hosts. Levels of total parasitism were positively associated with host population size, and negatively associated with local host density within one of the two sites sampled at a fine spatial scale.4Levels of parasitism byMelittobia(Hymenoptera: Eulophidae) were positively associated with the number of hosts per site, but negatively associated with the local density of hosts within sites.Melittobiaparasitism was also negatively associated with the local density of old nesting material within sites.5Parasitism byMelittobiawas a function of both the numbers of nests per quadrat and the mean nest size per quadrat at one of the two sites surveyed at a fine scale. At the other site, parasitism byMelittobiawas a function of mean nest size per quadrat.6The life cycle and nesting behaviour ofT.politum, in relation to the regulation of its numbers, is discussed.

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1995.tb00442.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.1The effects of climate and body size on male behaviour were examined in the solitary beeAnthophora plumipes(Hymenoptera: Anthophoridae), which shows resource‐based polygyny at floral food sources in Britain in spring.2Larger males are able to fly at lower temperatures than smaller males, and can therefore court females under conditions in which smaller males cannot fly. This is predicted from patterns of endothermic ability at low temperatures already demonstrated within this species.3Video analysis of male competition for opportunities to initiate courtship with tethered females showed that larger males are also competitively superior, and can displace smaller males from favoured flight positions immediately behind females.4The mating system shown by maleA plumipesis strongly dependent on male density. At low densities, males show exclusive territoriality at floral sources. As male density increases, this strategy is abandoned in favour of patrolling with considerable spatial overlap between males, and opportunistic Polygyny.5Despite high endothermic abilities, male behaviour is highly dependent on weather, and particularly ambient temperature. Males bask in the early morning and maintain high thoracic temperatures. Temperature data from freshly killed bees show that thoracic warming from solar sources effectively doubles the thermogenic power generated by the bee alone at low ambient temperatures.6Male strategies inA.plumipesare compared to female responses to climate. Having controlled for differences in body size there is no difference in endothermic abilities between the sexes. Males do not, however, fly under conditions in which females of the same size would remain active. These results are discussed in the light of differential dependence of reproductive success on flight activity for the two sexe

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1995.tb00443.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.1We compared the effects of plant genotype and local environment on population densities of a community of coastal insect herbivores in west‐central Florida. Reciprocal transplants of four genotypes of three species of coastal plants,Borrichia frutescens, Iva frutescensandLimbricata, were made in July 1992 between a series of off‐shore islands.2For each plant species, phytophagous insects with a wide range of feeding modes including gall‐makers, stem borers, leaf miners and sap suckers were affected more by local environment than by plant genotype. Whereas host genotype had a significant effect on the population densities of gall‐makers onB.frutescensin the spring of 1993, no significant effect on the denrities of any other insect species was found and the effect on the gall‐makers onBorrichiadisappeared in the summer, 1 year after the transplants had been made. In our study, local environment had by far the greatest effect on insect population densities among islands. This is an unusual result because in other studies over 80% of the insect species examined have been affected by plant genotype (Karban, 1992). This result is consistent with that reported by Stiling (1994), who censused populations of two phytophagous insects on reciprocal transplantr otBorrichiain north Florida.3Local environment also had an effect on insect population densities within islands. This result contrasts with similar studies performed in north Florida (Stiling, 1994), where population densities did not differ within areas, and underlies how some biotic processes may change with in the same community even over relatively small changes in spec

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1995.tb00444.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY