摘要:

Abstract.1. In laboratory experiments,R.fagimade feeding holes in eighteen tree and shrub species, including beech, from seven plant families but few plants other than beech were eaten to any extent.2. Overwintered adult weevils preferred beech to all these eighteen plants in spring.3. Hawthorn and raspberry were the most acceptable plants if beech was not available at this time.4. Field collected weevils from hawthorn had partly developed oocytes in early April, prior to beech bud burst.5. New generation weevils sought alternative food sources in late June and July; raspberry was preferred to the youngest available beech leaves at this time.

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1978.tb00925.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract.1. The causes and incidence of mortality in populations of the yew gall midgeTaxomyia taxiat Kingley Vale, West Sussex, are described in relation to the various life cycles of the midge.2. Life table analysis of populations studied for 10 years indicates that the key factor in mortality is failure to achieve maximum fecundity, although in 1‐year life cycles parasitism byMesopolobus diffinisis equally important. Densities and mortality vary considerably between different life cycles, and no regulation has been firmly established.3. Interactions between the host populations and their parasites are complex and as yet not fully analysable, but the pattern of parasitism seen may explain some of the complex life history pattern of the host. The existence of long‐term cycles of host and parasite densities are predic

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1978.tb00926.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract.1. The densities of the hymenopteran parasitesTorymus nigritarsusandMesopolobus diffinisare determined mainly by the density of available hosts,Taxomyia taxi.2. Area of discovery ofT.nigritarsusis negatively related both to density of available hosts and to the density of searching parasites. Implications for the foraging strategy ofT.nigritarsusare discussed.3.Mesopolobus diffinispreferentially parasitizes hosts in the small 1‐year galls. This and other evidence suggests that not all galls are equally available for parasitis

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1978.tb00927.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract.1. From published data on the rate of build‐up of insecticide resistance in wild populations ofAnopheles culicifaciesandAn.stephensi, calculations have been made of the coefficients of selection which would be required to produce these rates of evolution. It is assumed in turn that the resistances might be effectively dominant, recessive or intermediate.2. The results in the case of DDT resistance inAn.culicifaciesindicated that the fitness of resistant individuals was 1.28–1.51 × that of susceptibles.3. Published data have also been examined with reference to the reversions towards susceptibility which occurred when spraying has been withdrawn. The coefficients of selection against resistance, which would be required to produce the observed rates of reversion, have been calculated. In the case ofAn.culicifaciesand DDT these coefficients were found to be inversely related to the initial frequency of the susceptibility gene.4. The coefficients of selection have been used to assess the feasibility of inhibiting the evolution of resistance by spraying different insecticides in the alternate sectors of a grid pattern and/or periodically releasing susceptible males. If the proportion of migrants from sector to sector were 15–30%, a “grid” system would considerably reduce the rate of evolution of resistance, but to prevent resistance from ultimately building up to high levels periodic releases would also be required. These releases need not be frequent (approximately during one month each year) if resistance is effectively recessive in

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1978.tb00928.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract.1. The spatial distribution of both adult apterous and nymphalM.persicaewas related to the “age” of the leaf.2. This distribution was bimodal and was maintained even on rapidly “ageing” leaves by frequent emigration.3. The spatial distribution was also found to change between regions of a leaf, the densest populations occurring at the base of all leaves, but with the populations most evenly distributed on the young and old leaves.4. The spatial distribution also changed during the nymphal period, the youngest nymphs being found predominantly on the lamina, the fourth instar and adults on the largest available veins.5. On rapidly growing plants, individualM.persicaemay move to a new feeding site as frequently as every 24–48 h.6. Some of the causes and consequences of this frequent dispersal are

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1978.tb00929.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract.1. In coastal Kenyan forests the most productive breeding habitats ofEretmapodites subsimplicipesare rain‐filled fruits of the Apocynaceae and Loganiaceae cast off by monkeys.2. Water incubated in fruit husks stimulates females to oviposit, but a sympatic congenerEretmapodites quinquevittatus, never found in fruits, prefers tap water.3. Thus, chemical discrimination of oviposition site may promote the micro‐habitat separations observed in nat

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1978.tb00930.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract.1. Ovipositional responses of an efficient gregarious ectoparasite (Aphytis holoxanthus) to increasing densities of its host (the Florida red scale,Chrysomphalus aonidum, Homoptera: Diaspididae) were studied in a laboratory system.2. The female parasite may lay one to several eggs at each encounter with a host.3. As host density increased, the number of eggs laid by the female parasite during the experimental period increased at a decreasing rate. This type of functional response resulted in less parasitism at higher host densities.4. As host density increased, the number of eggs laid per encounter decreased. This behavioural response partially compensated for the decrease in parasitism.

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1978.tb00931.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract.1. The role of the host plant,Acacia karroo, in the population dynamics of the indigenous non‐pest psyllid,Acizzia russellae, was investigated.2. Population levels ofA.russellaein early summer were almost 10 times greater on the regenerative foliage of pruned trees (cut back in spring) than on normal trees. During late summer and winter, populations declined far more slowly on pruned trees, so that very much higher numbers of psyllids were maintained on these trees through to the next spring. This finding, and others, suggest that natural enemies and climate are not major determinants in the population dynamics of this insect under normal conditions in the field.3. Laboratory measurements of several chemical and physical characteristics of the foliage of pruned and normal trees did not reveal any differences which would account for the observed effects.4. Measurements of organic nitrogen concentrations in the leaves of normalA. karrootrees in the field showed significant correlations between psyllid numbers and leaf nitrogen, but only during summer in November and January.5. Psyllid performance in the laboratory (duration of life cycle, egg production, and dry weight of emergent females) was significantly better for psyllids reared on plants containing high amino nitrogen.6. It is suggested that the availability of quantities of suitably high quality nutrients in the leaves of prunedA. karrootrees explains the “epidemic” population levels achieved by the psyllid on pruned plants. It seems that characteristics of the host plant impose the major limitation on psyllid population growth, which may explain the permanent low endemic population levels of this insect in the

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1978.tb00932.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract.1. Histological sections of tree roots on which periodical cicada nymphs of both the 17‐year and the 13‐year race arid various instars had fed showed that salivary sheaths made by the nymphs ended in xylem vessels.2. Because no salivary sheaths were found in phloem cells, this observation indicates that cicada nymphs are xylem feeders throughout their developmental period.3. The habit of feeding on xylem fluid, which is extremely dilute, may explain why periodical cicada nymphs require so many years (13 or 17) to mature. It may also explain why they excrete amino acids rather than sugars, as phloem feeders

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1978.tb00933.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract.1. The population of the lycosidTrochosa terricolaThorell was sampled from April 1973 to August 1975 at Weeting Heath NNR, a Breckland grass heath.2. Four sampling methods were compared for efficiency. Hand searching gave density estimates between 38.3 and 70.1% of heat extraction.3. The temperature range in the sward at +1 cm was –5°C to 39°C with January and July means of 3.2°C and 17.4°C.4. Eight male and nine female instars were determined and the life cycle extended over 2 or 3 years.5. Adults were nocturnal but the juveniles diurnal. An annual diplochrone activity pattern was observed for adult males.6. The horizontal distribution within the sward was aggregated, the structure and microhabitat being important determining factors. The population density was greater in moist, youngFestucaspp. tussocks. An equation relating population density to habitat characteristics was derived.7. The overall population density ranged from 14.0 m‐2to 76.0 m‐2and was maximal in autumn after breeding. The population biomass was greatest during autumn (291.2 mg d.wt m‐2).8. Mean number of juveniles emerging from an egg sac was 77.3 (first sac) and 38.0 (second sac). The natality in 1973 was 66.8 individuals m‐2.9. The survivorship curve until maturity varied between types I and III in different years.10. The population dynamics were compared and are discussed in the light of other data. The variable population characteristics suggested that Den Boer's “spreading of risk” theory applied to theT.te

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1978.tb00934.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY