摘要:

Abstract.1.Adelges cooleyi(Gil.) was rarely found in the top‐most whorl of shoots in its host plant Engelmann spruce.2. The survivorship of the fewAdelgesfundatrices which did colonize the top whorl was at or near zero for the 3 years in which survivorship was assessed, while survivorship in the bottom whorls was at least 60%.3. In contrast, when anAdelgesfundatrix did survive in the top whorl, her growth and reproductive output, and the growth of her progeny, the gallicolae, were at least double that of bottom whorl fundatrices.4. The distribution of fundatrices within spruce trees was strongly correlated (R2=0.934) with fundatrix fitness (=survivorship × fecundity × growth).5. We hypothesize that the vigorous growth of top whorl shoots promotesAdelgesgrowth and fecundity, but the earlier growth of these shoots results in low temperature mortality of fundatri

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1990.tb00806.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.1. An analysis of the number of ovarioles/ovary is presented for fourteen species ofDacusranging from broad generalists (D.tryoni(Frogg.)) to strict host specialists (D.aglaiaHardy). For eight species data on egg size and the incubation time of eggs is also presented. Interrelationships among these life history variables and their relationships to host specialization were examined.2. There was a broad positive relationship between the breadth of the natural host range (i.e. excluding cultivated fruits) and ovariole number (and hence potential fecundity). Highly polyphagous species had thirty‐five to forty ovarioles/ovary while the specialists ranged from eight to twenty.3.D.musae(Tryon), a specialist on banana, was an exception having an ovariole number similar to that of the most polyphagous species.4. There was no clear relationship between egg size and ovariole number across eight species, though monophages were not fully represented in this analysis. Among these eight species there was no significant relationship between wing length and egg length, nor was there any such relationship among individuals within species.5. There was considerable variation among species in the incubation time (at 25°C) for eggs, ranging from 24 h forD.cucumisFrench to 53 h forD.cacuminatus(Hering). This variation was only weakly related to egg size, thoughD.cucumisproduced the largest eggs of any species examined.6. Possible explanations for a relationship between potential fecundity and host range are discussed in terms of the balance between the abundance of host resources for generalists and their predictability for specialists. However, the observed relationship between ovariole number and host range must remain tentative, given that only fourteen species from one genus have been examined. Considerably more data is required for other dacines, for species in other tephritid subfamilies, and for other phytophagous insect groups to determine whether the relationship is generally applicab

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1990.tb00807.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.1. Mortality imposed on the leaf mining fly,Liriomyza commelinae(Frost) was studied at three spatial levels: (1) the leaf, (2) the stem, and (3) a metre quadrat of the food plant.2. Real mortality (R.M.) (death as a percentage of eggs laid) during development for five sites over 3 years (forty‐seven generations) was 96.3 + 1.9% ‐2.5% (±95% c.l.), due mainly to parasitoids and predatory ants, with a small component due to competition and other causes.3. Real mortality due to the parasitoid complex averaged 41.2%. It was not related to population density in leaves or stems but was positively dependent on density in one metre quadrats.4. Predation byCrematogaster brevispinosaMayr was 21.2% and was independent of population density at all spatial levels.5. Mortality due to other causes (e.g. competition and exposure to high temperature resulting from insolation) was positively dependent on the number of mines per leaf at three out of five sites studied and the number of mines per stem at two of the three sites studied; however, such mortality was independent of density per metre qua

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1990.tb00808.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.1. We classified the parasitoids of 185 British herbivorous insect species as being koinobionts (which should tend to be specialists) or idiobionts (potential generalists) to examine the influences of host feeding‐niche and foodplant type on the numbers of parasitoid species attacking individual host species.2. The majority of parasitoid species of exophytic hosts are koinobionts, whereas endophytic hosts support mainly idiobionts.3. Parasitoid assemblage size increases with host foodplant size and complexity; for endophytic hosts this is due to an increase in idiobionts on hosts on large plants, but for exophytic hosts it is the number of koinobionts that increases with foodplant size.4. Comparison of these patterns with those predicted under a competition hypothesis suggests that parasitoid communities associated with endophytic hosts may be commonly limited by interspecific competition, whereas those of exophytic hosts probably are no

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1990.tb00809.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.1. Members of a field population ofGryllus campestrisL. varied in their walking and calling activity. In both sexes, some individuals occupied burrows whereas others walked around in the observation area. Males at burrows could be either silent or calling.2. In the course of one summer, population density decreased and the initial balanced sex ratio changed to a large surplus of males.3. At high population density, there were equal numbers of non‐calling males at burrows, calling males at burrows and walking males, while walking females predominated over females at burrows. Non‐calling males at burrows achieved more encounters with females than did calling and walking males. Females met males by walking through the population and by waiting at burrows. Thus, calling and phonotaxis were not essential for mate finding and calling was less effective than previously thought.4. At low population density calling males predominated. Calling males at burrows achieved the most encounters with females. Females met males only by walking around in the population area. Calling was thus more important in mate finding than at high population density.5. Changes in sex ratio and population density may cause the flexibility in mate finding behaviour of individual crick

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1990.tb00810.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.1. Disappearance of different amounts of aphid ingested by three species of polyphagous predators, the carabidsBembidion lampros(Herbst) andNebria brevicollis(F.) and the staphylinidPhilonthus cognatusStephens, was monitored by a quantitative enzyme‐linked immunosorbent assay (ELISA). The effect on the rate of inactivation of prey antigens by the ingestion of subsequent, non‐aphid food was also studied.2. Antigen inactivation was significantly more rapid in the staphyilinid than in the carabids.3. No statistically significant differences were found in the rate of antigen inactivation between beetles which consumed only aphids and those which were given a different type of food after feeding on aphids; the detection period was longer in the former groups. A higher proportion of beetles with low levels of aphid antigen were found earlier in the latter group.4. The results did not unequivocally support the prediction derived from optimal digestion theory that beetles without continuous access to food would retain an initial meal longer than beetles with unlimited acc

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1990.tb00811.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.1. Nest thermoregulation follows a similar pattern inVespa simillimaSmith andV. tropicaL. There is a gradual decline in the daily fluctuations of nest temperature to a constant steady state which is maintained during the production of the first sexuals, followed by a sudden loss of stability at the end of the colony cycle.2. The larvae are not major producers of heat, as they are unable to raise their body temperature by more than 1–2°C above ambient. However, they act as heat reservoirs and providers of food in the form of larval secretions. This feeding may allow workers to raise their body temperature during non‐foraging periods.3. The adults are capable of raising their body temperature many degrees above ambient and the presence of even one adult, in this case aV.analisF. mother queen, was able to raise the nest temperature.4. Supplementary carbohydrate food promotes thermogenesis and enhances colony develop

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1990.tb00812.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.1. Young and mature leaves of a tropical legume,Inga edulis var. minutulaSchery, are strikingly different in secondary chemistry, especially condensed tannins, and leaf toughness.2. Bioassays with the two different leaf types indicate that leaf cutter ants,Atta cephalotes(L.), always find mature leaves relatively more acceptable than young leaves when selection was based on chemical cues.3. Since extracts of young leaves show greziter inhibition of fungal pectinases we suggest that leaf‐cutter ants are capable of distinguishing which leaf types are most suitable for the growth of their symbiotic fungus.4. However, mature leaves are 3 times tougher than young leaves and this prevents leaf‐cutter ants from harvesting the more suitable mature leaves.5. Consequently, bioassays which require cutting before leaf removal indicate that some colonies actually harvest more from the less suitable young leaves.6. We suggest that the quality of a colony's habitat may indicate whether a colony will harvest more of the less suitable young leaves. Colonies which are harvesting from highly suitable host plants avoid the tropical legumeI.eduliswhile those in poorer habitats acceptI.edulisbut, because of leaf toughness, mostly harvest the less suitable young lea

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1990.tb00813.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.1. Larvae ofTephritis conuraLoew (Diptera: Tephritidae) live gregariously in flower heads ofCirsium heterophyllum(L.) Hill (Cardueae). They are attacked by the endoparasitic waspsEurytomasp. neartibialisBoheman (Hymenoptera: Eurytomidae) andPteromalus caudiger(Graham) (Hymenoptera: Pteromalidae).2. The responses of the parasitoids to different host patch sizes were investigated from the analysis of field samples. At the host population level, overall probabilities of parasitism were independent of host numbers per flower head or showed a tendency to inverse density‐dependence for both parasitoid species.3. Measurements of ovipositor length inEurytomaandP.caudigerindicated that parts of the flower head constitute a structural refuge from parasitism.4. The accessibility of hosts in a flower head was found to differ markedly, depending on larval locations and flower head characters. In spite of this high variability, similar average percentages of larvae were accessible to the parasitoids in each patch size class.5. High variability of oviposition success in laboratory experiments can be explained by random locations of hosts in the flower head

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1990.tb00814.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.1. Insect–insectivore trophic relations were reviewed using presence–absence data from sixty‐one invertebrate‐dominated food webs and fifteen food webs from Briand's (1983) original forty web collection. From counts of prey links in higher taxa (orders, classes, phyla), six phyla and thirteen classes of non‐insect insectivores and fourteen orders of insect predators and prey were found.2. Detritus‐based habitats (phytotelmata, felled logs, carcasses, dungpads) harboured fewer orders of insects, that interact with other insects, than webs from grazer‐based (host plants, some galls) and mixed‐based systems (aquatic webs). Consumer–resource networks of higher insect taxa in these webs shared several features found in some species‐level biological networks: the trend was towards few pairs of strong asymmetrical links, several weak links and many null interactions.3. From counts of insect predator–insect prey links, hymenopterans as terrestrial predators and parasitoids interacted with the most number of higher insect taxa. Hymenopterans were also linked as prey more often than other terrestrial insects. In freshwater habitats, plecopterans were linked as predators more often than other aquatic taxa, whereas dipterans were listed as prey more often than other insects.4. Dipterans were linked in the diets of non‐insect insectivores from seven of eight common taxonomic classes. Arachnids were identified as insect predators by food web researchers in the largest number of webs, followed by passerine birds and cyprinodont fishes. From analysis of prey links at the ordinal level, predaceous insects were less polyphagous than other predators (other ectotherms and endotherms).5. Analysis of chain lengths, as expected, showed that insect prey occupied mostly lowermost trophic levels, non‐insect insectivores were found mostly at uppermost trophic levels, and predaceous insects were found mostly at intermediate trophic levels across most habitats.6. This analysis offers evidence that insects are not just occupying intermediate trophic levels in some communities. Indeed, some taxa feed at the upper ends of long food chains, for example eupelmids in galls, staphylinids in carcasses, and perli

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1990.tb00815.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY