摘要:

Abstract.1We tested the hypothesis that females of the egg parasitoid,Trichogramma minutumRiley (Hymenoptera: Trichogrammatidae), could adjust their fecundity schedule according to host availability and that there was a negative correlation between reproduction and survival in these wasps.2Newly‐emerged females were provided with an unlimited or limited number of hosts in the first trial and with either unlimited, limited or zero hosts in the second trial.3When hosts were unlimited, wasps had the highest rate of reproduction in the first day, which decreased dramatically thereafter. When hosts were limited, wasps from the two trials differed in their response. In Trial I, females with limited hosts had lower first‐day fecundity than, and the same subsequent‐day fecundity as, those with unlimited hosts. However, in Trial II, females with limited host had a lower first‐day but a higher subsequent‐day fecundity than those with unlimited hosts. This indicates variation inTrichogramma's ability to shift its fecundity schedule in response to host availability.4There was a positive (rather than a negative) correlation between reproduction and survival. Wasps that oviposited (in host‐unlimited treatment) had greater longevity than those that could not (in host‐unavailable treatment).5The sex ratio of the progeny produced by wasps in both host‐unlimited and limited treatments shifted gradually from a female to a male bias as the wasps aged.6We consider the ability of parasitoids to adjust their fecundity schedule as an adaptation to changing host resources and discuss our findings with regard to theories of life hi

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1993.tb01102.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.1Many species of birch‐feeding Lepidoptera make leaf‐shelters by tying leaves together with silk. Several species, or several instars of a single species, may be found together within a single leaf‐shelter.2Shelters made in June by the birch tube‐makerAcrobasis betulella(Pyralidae) are colonized throughout the season by other Lepidoptera. ArtificialA.betulellashelters, made by tying leaves together with string, were colonized at a greater rate than nearby control foliage, indicating that secondary species are indeed responding to the presence of the shelter, and not to some other aspect of plant quality.3Several species in the families Oecophoridae, Gelichiidae and Stenomidae make ‘leaf‐sandwiches’ by tying two leaves together; these are later colonized by oviposition from adultA.betulella.Artificial sandwiches made by joining leaves together with paperclips were colonized by several species of sandwich‐makers, as well as byA.betulella.Colonization occurred mainly via oviposition, although some sandwiches may have been colonized by wandering larvae.4First instarA.betulella, which cannot form their own shelter, enjoyed greater survivorship when placed in artificial leaf‐sandwiches than when placed on leaves w

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1993.tb01103.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.1In nature, interference amongAnagrus delicatus(Hymenoptera: Mymaridae) parasitoids reduced the per‐capita number of hosts parasitized. Interference increased with parasitoid density.2Anagrus delicatusdid not avoid parasitizing hosts that had recently been parasitized by conspecific wasps. Evidence indicated that this superparasitism was largely a random process, increasing with the ratio of parasitized to unparasitized hosts.3Individual parasitoid efficiency, the number of hosts killed per wasp per unit time, decreased with increasing wasp density. This occurred whether wasps searched the patch together (simultaneously) or one by one (sequentially), and was the result of an increase in time spent superparasitizing hosts at higher wasp density. This is known as indirect mutual interference.4Increasing numbers of parasitoids together on the same patch caused a significant decline in the rate and per‐capita number of hosts parasitized. However, there was not a correspondent decline in searching efficiency with increasing wasp density (i.e. no direct mutual interference).5These forms of parasitoid density dependence should contribute to the stability of the host—parasitoid intera

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1993.tb01104.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.1The fitness consequences of superparasitism for a solitary parasitoid depend on whether the host was first parasitized by itself (‘self‐superparasitism’) or a different individual (‘conspecific superparasitism’). Self superparasitism is usually expected to be avoided.2A.pandensfemales showed no difference in their probability of superparasitism between self‐parasitized and conspecifically‐parasitized hosts. The probability of superparasitism decreased as time from the laying of the first egg in a host increased, from about 0.29–0.46 at a time interval of 1 h to 0.10–0.14 at 72 h.3The egg distribution of wasps foraging alone on a patch showed significant avoidance of superparasitism, but that of wasps foraging in the presence of conspecifics was not significantly different from a random distribution. This suggests that wasps switch from avoidance of superparasitism when alone to acceptance of all hosts when in a group.4When wasps foraged in a group, the hosts had many more ovipositor puncture marks than when wasps foraged singly. This suggests that either hosts were attacked several times per encounter, or that the wasps' encounter rate with hosts was much higher when in a group. If the latter is true, it is possible that, although the egg distribution suggested a higher rate of superparasitism when wasps foraged in a group, the ratio of acceptances to contacts of parasitized hosts may in fac

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1993.tb01105.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.1The possible effects of the inclusion of ‘tourist’ species have been the cause of some concern in investigations of interspecific relationships between abundance and body size.2Data for adult beetles (Coleoptera) from oak trees in Britain are used to investigate the relationship of abundance to body size when tourists are and are not included.3For this particular assemblage, tourists do not fundamentally alter the basic statistics of the relationship between abundance and body size. However, they are not a random sample of the beetle assemblage. They have lower abundances and are also of smaller body size than other spec

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1993.tb01106.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.1Evolutionary pressure should select for efficient foraging strategies, within the constraints of other selective forces. We assess the mechanisms underlying flower choice in the butterfly,Pieris napi(L.), which as an adult forages for nectar. Experiments were carried out on a laboratory colony, using artificial flowers of two colours, and replicated on two successive generations.2When nectar was freely available from all flowers, equal numbers of butterflies visited each colour, but individual butterflies exhibited flower constancy, showing a strong preference for one colour or the other.3Following 3 day conditioning periods in which nectar was available from flowers of one colour only, butterflies responded by developing a preference for this colour, which persisted when both flower colours were refilled. This preference could subsequently be switched to the other flower colour following a further 3 days of conditioning. These are interpreted as adaptive (learned) responses, which would have obvious selective benefits in the field, enabling butterflies to avoid flower species which experience has shown are poor sources of nectar, and to adapt to temporal and spatial changes in nectar availability.

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1993.tb01107.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.1An analysis of published data and a mathematical model of the population dynamics of introduced parasitoids were used to explore the possibility that biological control introductions fail because an Allee effect drives small, introduced populations extinct. Such an Allee effect would arise because low densities, resulting from dispersal into a new environment, lead to failure to mate, which leads to a male‐biased sex ratio, which, if extreme enough, could cause population extinction.2For chalcidoids, ichneumonoids and tachinids, the proportion of parasitoid populations that established when introduced for control of lepidopteran pests increased with the number of parasitoids per release, the total number released, and the number collected when each variable was analysed separately. For chalcidoids alone, establishment increased with the number of releases for this variable analysed separately. However, stepwise logistic regression of establishment on these variables included only the total number released for chalcidoids and the number per release for ichneumonoids and tachinids. This suggests that an Allee effect may limit the establishment of introduced parasitoids more than stochastic environmental variation or lack of genetic variation.3A reaction‐diffusion model of parasitoid introductions was developed, which included mate finding, dispersal, reproduction and survival. Sensitivity analysis showed that the critical number of females needed to establish a population decreased hyperbolically as mate detection distance and net reproductive rate were increased, but the critical number increased linearly as mean‐square displacement was increased. The critical number of females did not change when the gross distance traversed per generation was varied. This was because increased area searched by males compensated for increased displacement. Changing from virgin females producing all males (arrhenotoky) to virgin females producing no progeny increased the critical number of females by over 30%.4The analysis of past introductions and the sensitivity analysis of the reaction‐diffusion model both suggested a threshold of about 1000 insects per release to ensure establishment of introduced parasitoids. The implications of our results for the design of biological control introductions are discussed. Limitations in retrospective analyses and current knowledge indicate the need for an experimental approach to introd

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1993.tb01108.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.1The patterns of herbivory by leaf miners on the shrubOchna ciliatagrowing on Aldabra Atoll were studied in relation to browsing by feral goats and exposure to the tropical sun versus shading.2Damage due to both tunnelling (Diptera) and ‘blotch‐making’ (Lepidoptera) leaf miners was statistically greater on trees that had been browsed and on those that received more extensive exposure to the sun.3Effects of exposure and browsing were additive, as evidenced by the lack of statistical interaction between these factors.4There was a significant negative correlation between the numbers of tunnelling and blotch‐making miners in trees that had been browsed, but not in unbrowsed trees.5Three geographical areas were sampled to test whether the effects of browsing on leaf mining were invariant or influenced by as yet unknown environmental factors. A statistically significant interaction between browsing and geographical region indicated that, while browsed trees had significantly more mines whatever the habitat, the extent of this effect differed across the h

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1993.tb01109.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.1A priori, there are no obvious reasons why patterns should exist in the frequency of density dependence across insect orders. However, orders may reflect related factors which influence population regulation (e.g. life‐history patterns and ecology) and are difficult to quantify. The frequency of occurrence of density dependence is compared in 171 time series (of ten or more generations) from Lepidoptera, Hemiptera, Diptera, Odonata, Hymenoptera and Coleoptera.A posterioriattempts are made to identify the cause of observed patterns.2Buhner's (1975) test found non‐delayed density dependence more frequently in Odonata than Lepidoptera and Hymenoptera, which in turn showed non‐delayed density dependence more frequently than Diptera, Hemiptera and Coleoptera. Similarly, detection was greater for Odonata than other orders using Dennis&Taper's (1993) test for density dependence and Crowley's (1992) test for attraction. Varley&Gradwell's (1960) test found density dependence less frequently in Hemiptera than other orders. These differences were independent of time series length, temporal trends and numbers of generations per year.3The reasons for observed patterns in detection of density dependence (and attraction) in insect orders are not clear; however, plausible explanations are differences in: (i) intrinsic growth rate, which is correlated with body size (although evidence to support this hypothesis is weak); (ii) the sampling method used; or (iii) whether individuals come from a single population or many populations.4Using Turchin's (1990) test, delayed (lag 2) density dependence was detected most frequently in Hymenoptera, which often show delayed diapause or are parasi

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1993.tb01110.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.1Crawling predators were excluded from bamboos attacked by three species of chrysomelid leaf miner in two plots of tropical dry forest in Costa Rica.2The percentage of predated mines declined from an average of 61 % to an average of 29% in plots where crawling predators had been excluded. There were concomitant increases in successful beetle emergence and in the numbers of beetles attacked by parasitoids.3The probability of a miner that had escaped predation being attacked by a parasitoid was the same in experimental and control treatments, indicating that the risks of predation and parasitism are statistically independent.4The results were consistent across species and plots with the exception of one species in one plot where emergence was lower in the exclusion treatment than in the control because of very severe parasitoid attack. This result is unexplained.5Limited observations, and evidence from the type of damage observed on predated mines, suggest that the most important crawling predators are ants.

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1993.tb01111.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY