摘要:

Abstract.1. The bole of a Norway spruce,Picea abies(L.) Karst., was cut in 25 cm sections and infested in the laboratory with 2 or 8 females/dm2ofIps typographus(L.) and an equal number of males.2. One log of each beetle density was dissected every second day, beginning 2 days after female introduction.3. The oviposition rate was highest at the beginning of the breeding period for both densities and then declined, especially at the high density. Residence time is a useful approximation for the number of laid eggs in the beginning of the oviposition period or when the density is low.4. Final gallery length and egg number per gallery were on average significantly smaller at density 8 than at density 2.5. Linear relationships between total gallery length and number of egg niches were found to be similar for the two densities.6. An estimate of the egg to adult mortality at different densities was found by using data from a field study that related gallery length to breeding density in attacked living trees, together with published relationships between density and egg niches or emergence of new adults.7. It was concluded that both decreased oviposition rate and earlier re‐emergence at higher densities contribute to a declining oviposition with increasing density. The final offspring production is futher reduced by lower survival due to larval competition as density increase

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1990.tb00777.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.1. The patterns of host‐feeding and oviposition were examined inAphelinus asychisWalker, which had been provided with second‐instar pea aphids as hosts.2. Female wasps responded to increasing host density (between one and forty aphids for 24 h) with an increasing tendency to oviposit rather than to feed. Superparasitism occurred at all aphid densities, even when unparasitized aphids were available.3. Aphids intended for feeding were paralysed and died. Wasps did not feed on and oviposit in the same aphid.4. Feeding to satiation lasted between 4 min and 42 min. Females that had starved for ≰18 h generally deposited one or more eggs before feeding again, while the reverse was true in wasps that had starved for 21 h.5. The host‐feeding behaviour ofA. asychisis determined by a female's nutritional status. At low rates of host encounter, the anhydropic eggs may be resorbed. This reproductive strategy conforms to the destructive non‐concurrent type among the Hy

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1990.tb00778.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.1. On a study farm in Hampshire where large blocks of cereal fields had the pesticide inputs on their headlands experimentally and selectively reduced (the practice known as ‘conservation headlands’), numbers of butterflies were monitored over 4 years by using transect counts.2. Consistently more butterflies were seen flying over field edges sprayed under the conservation headland regime compared to those that were fully sprayed.3. A comparison of changes in butterfly abundance on the study farm containing conservation headlands with data from the National Butterfly Monitoring Scheme indicated that population increases in some species may result from the use of conservation headlands.4. The implications of resource provisioning and the potential reduction of spray drift into field‐margin habitats are discussed in relation to farmland butter

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1990.tb00779.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.1. We tested the hypothesis that survival and sources of mortality of the leaf‐folding sawfly (Phyllocolpasp.) varied significantly among host plants of the arroyo willow (Salix lasiolepisBent ham).2. Survival of the leaf folder differed among field and potted willows in a common environment in two of three cases, and sources of mortality differed among plants in four of five cases.3. Egg mortality differed among field plants but not among the potted willow plants.4. Larval mortality and parasitism differed among field and potted willows in 2 years, and appeared to be compensatory mortality sources.5. Leaf folder density among plants was not generally correlated with percentage of leaf folds with no egg (galls formed but no subsequent oviposition), percentage survival, or percentage mortality, indicating a general lack of density dependence.6. The proportion of folds with no egg oviposited differed significantly among field and potted plants, and was only correlated with survival or sources of mortality in one of three years.7. The data support the hypothesis that host plant genotype affects the interaction of the leaf folder with its natural enemies, and thus represents a three trophic level interactio

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1990.tb00780.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.1. A laboratory competition experiment is described in which the growth and development rates of larvae of the damselflyIschnura elegans(Lind.) were measured over an entire instar.2. Two larval instars which commonly occur together in the field were used in the experiment; they were maintained with a superabundance of prey and either larvae from the same or the larger/smaller instar.3. Small larvae suffered increased development times and decreased size increases at the moult in the presence of large larvae but similar interference effects were not evident when these smaller larvae were in the presence of other small larvae.4. Development time and size increases of large larvae were not significantly affected by the presence of small larvae.5. Irrespective of the instar combinations investigated, interference effects were reduced when there were more perches available, although in only a few cases was this reduction significant.6. The consequences of the asymmetric competition reported in the experiment for the study of lifetime reproductive success in damselflies are discussed. Late emerging adults may incur reduced reproductive success.

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1990.tb00781.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.1. Host plant preference experiments were conducted with closely related taxa of the aphid genusCryptomyzus.Males, and presexual morphs (sexuparae and gynoparae), were used to determine the impact of host plant choice on reproductive isolation. In the case of host‐alternating species these morphs are migratory and so will select the host plant.2. Host plant preference of two closely related taxa ofC. alboapicalis(Theobald) was found to promote their reproductive isolation. The preference of sexuparae of these monoecious taxa was more pronounced than that of the males.3. Host plant preference and subsequent production of oviparae showed thatC. galeopsidis(Kaltenbach) consists of two host races restricted toRibes rubrumL. andR. nigrumL., respectively. The existence of clones, intermediate in their preference and reproductive performance on these plants, suggests that hybridization occur

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1990.tb00782.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.1. The effect on growth and survivorship of the number ofHalisidota caryae(Harris) caterpillars in groups feeding on three taxonomically distinct hosts was examined experimentally in the field.2. Caterpillars grew more rapidly and survived better in larger sized groups than in smaller sized groups.3. Caterpilliars grew more rapidly and survived better onCarya ovata(Koch) than onHamamelis virginiana(L) orQuercus velutina(Lam.).4. There were equal numbers of invertebrate predators on groups of different sizes and thus larger groups had significantly fewer predators per caterpillar than did smaller groups.5. Invertebrate predators accounted for at least a 10% daily decrease in survivorship.6. Local movement reduced predation because moving groups had fewer predators than did stationary groups.

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1990.tb00783.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.1. In a previous study,Orius tristicolor(White), a generalist predator of soft‐bodied insects and mites, invaded patches with a mixed plant assemblage at a faster rate than it did single‐species stands. This study was designed to determine experimentally the underlying mechanisms of predator movement patterns that cause more intense colonization of crop mixtures.2. Plots were established in a randomized complete block design. Treatments reflected different components of mixed crop patches: species richness, plant density, colour contrast, structural complexity, and volatile plant compounds.3.O. tristicolorcolonists were more abundant on squash intercropped with corn and cowpea than in squash monocultures even though early season prey densities were similar. Initial accumulation of the generalist predator was also higher in densely planted monocultures and in monocultures with artificially enhanced structural complexity than in normally‐spaced squash monocultures.4. Therefore, mechanisms underlying rates of predator colonization in a stand initially depended upon aspects of plant architecture and density and were independent of prey density and plant diversity.O. tristicolordensities at the end of the colonization period, however, were greater on squash (Cucurbita pepoL.) in polyculture than in any other treatment.5. These results suggest that attributes of the vegetation can influence the colonization rates of interacting organisms on different trophic levels and thus can alter predator‐prey interactions and the development of community st

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1990.tb00784.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.1. Intraspecific aggression between termite major workers was used to obtain estimates of foraging distances for threeMicrotermesspecies in Sudan.2. Maximum foraging distance recorded forM.sp. nralbopartitus(Sjöstedt) in Khartoum was 11.3 m, giving an estimated minimum colony area of 100 m2. This is probably an underestimate. In the Tokar Delta, individuals from single colonies ofM. najdensisHarris were encountered up to 42 m apart, giving a colony area of 1390 m2.3. Intraspecific aggression could not be used reliably to distinguish members of different colonies ofM. lepidusSjöstedt. Soil barrier formation between groups of workers in petri dishes may be of use as a supplementary technique, especially for species showing no clear aggression.4. Experiments on isolated laboratory colonics ofM.sp. NrlepidusSjöstedt, established from alates collected in Khartoum, further confirmed the value of inter‐colony aggression for indicating colony identity.5. The complications introduced into estimation of subterranean termite foraging areas by overlap and interdigitation of colonies are discu

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1990.tb00785.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.1. Twenty‐three nests of the submissive antFormica fuscaL. were sampled in two adjacent territories of the dominant wood antFormica polyctenaFörst. The nests were dug up at different distances from the wood‐ant mounds. Distance is assumed to be inversely related to the extent of disturbance ofF. fuscabyF. polyctena.2. Colony success ofF. fuscawas assayed by counting the numbers of workers (colony size), and worker and sexual offspring in a nest. For individual size, the head width and dry weight of fifty workers per nest were measured.3. Colony size correlated positively with the numbers of worker and sexual offspring in one territory, but only with worker offspring in the other.4. Distance from the wood‐ant mound correlated positively with colony size and numbers of worker and female offspring in one territory. In the other territory distance correlated positively with number of females, but negatively with number of worker offspring. No significant correlations between distance and the size measurements were obtained.5. Because of its nonaggressive behaviourF. fuscamay nest fairly close to a wood‐ant mound but is likely to show reduced abundances in terms of nest density and forager number, and, ultimately, lowered

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1990.tb00786.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY