摘要:

ABSTRACT.1The pteromalidTrichilogaster acaciaelongifoliae(Froggatt) causes galls to develop in the place of inflorescences during the reproductive phase of its hostAcacia longifolia(Andr.) Willd. (Fabaceae). After being introduced to South Africa during 1982 and 1983, this wasp reduced the reproductive potential ofA. longifoliaby>89% when only 50% of the branches on a tree were galled. In addition, vegetative growth of galled branches was reduced by 53% when the vacated galls had desiccated.2The wasp is able to manipulate its host so effectively because: (a) the dry mass of developing galls was significantly greater than that of the corresponding reproductive organs, peaking in spring (September) when galls were 25 times the mass of unfertilized inflorescences. (b) The large biomass diverted to gall production is accounted for by a high proportion (66–73%) of multiple‐chambered galls. The dry mass of multiple‐chambered galls was significantly greater than that of both single‐chambered galls and pods. (c) The extent of biomass diversion to gall production was relatively greater during the earlier part of the reproductive season, enhancing stress on the host. (d) The wasp sometimes forced the plant to produce up to 200% more galls per branch than the normal quota of inflorescences. This phenomenon, called forced commitment, further increases stress on the host plant. (e) Galls constituted up to 21% and 40% of the dry and wet biomass of above‐ground parts of infested trees, respectively. This caused breakage and mortality of large branches and stems. (f) Reproduction inA. longifoliahas been shown elsewhere to be so energy consuming that vegetative growth is strongly inversely related to pod production. Because the stress from galling byT. acaciaelongifoliaecoincides with and replaces reproduction with a greater stress, successful reduction of both reproduction and vegetative growth are achieved.3This biological control programme is the first in which a gall‐forming hymenopteran has been used to control a weed. Since the effects of gall‐formers are indirect compared with those of insects attacking vegetative plant parts, their potential as biocontrol agents has been underrated. This research provides ecologically based guidelines for the future selection o

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1988.tb00327.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

ABSTRACT.1Foraging routes of worker and queen bumble bees (Bombus kirbyellusCurtis) collecting nectar from flowers of the alpine sky pilot,Polemonium viscosumNutt., were followed and the corolla tube length, corolla diameter, floral scent, and number of flowers on plants visited or bypassed by bees were monitored. Additionally, the number and proportion of flowers visited per inflorescence and distance flown from each to the next were recorded. Queens and workers differed significantly in choice of flowers. However, intra‐inflorescence visitation rates and departure distances were similar between castes. Castes differed in the extent to which visitation reflected patch quality versus individual floral traits.2Both queens and workers failed to visit skunky‐flowered plants more often than they failed to visit sweet‐flowered ones, and preferred large over small inflorescences. However, queens visited large‐flowered plants more often than small‐flowered ones, while workers preferred flowers with shorter corolla tubes, regardless of their diameter. Although a number of studies have documented caste specialization on alternate species of host plants, ours is one of the first to show that morphological preferences promote comparable foraging differences between castes on monospecific plant resources.3Queens, once on a plant, responded to floral traits by probing more flowers on large inflorescences, as well as on those with broader floral form. Workers did not alter intra‐inflorescence visitation rate in response to floral traits.4For workers, no significant relationship was demonstrated between the likelihood of passing by a plant and the number of flowers probed on the previous inflorescence visited. Thus, workers appeared to accept or reject each plant ofP. viscosumindependently. However, queens passed by fewer plants when leaving rich inflorescences than poor ones. These results suggest that workers use only individual plant acceptability in choosing which plants to visit, whereas queens base plant choice on patch and individual attributes. Such differences between castes in foraging rules when exploiting the same floral resource have received little attention, and provide insights into the heterogeneity of harvestable reward distributions from the perspective of the forager

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1988.tb00328.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

ABSTRACT.1Larval performance of the leaf beetleParopsis atomariaOliver was determined for larvae raised on both new and mature leaves ofEucalyptus blakelyiMaiden. Larvae were transferred to mature leaves at different ages; control larvae stayed on new leaves through all instars.2Only larvae reared on new leaves through the third instar survived to pupate on mature leaves; developmental time was prolonged by 20% and pupal weight was reduced by 50% in these larvae compared with larvae reared entirely on new leaves. Almost all larvae died when transferred to mature leaves as first, second or third instars.3Low survival and slow development on mature leaves was mainly due to failure by larvae to feed. Larvae palpated leaves and could discriminate among leaf ages immediately, without biting into the leaf tissue.4New leaves had higher concentrations of oil and tannins than old leaves, while there were no significant differences in nitrogen concentrations in the two types of leaves. Mature leaves were more than 3 times tougher than new leaves, in terms of g mm−2of penetrometer force.5In drought yearsE. blakelyimay not produce sufficient new leaves to supply specialist herbivores with their preferred food resource. We infer that drought years reduceP. atomarialarval performance significantly, and influence the population dynamics of the insec

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1988.tb00329.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

ABSTRACT.1The relationships between number of species, abundance per species, and body length are examined for 859 species of beetles in samples of arthropods collected from ten Bornean lowland forest trees by insecticide fogging. Similar relationships are examined for different feeding guilds of these beetles, and for those beetles from different species of trees.2The data are used to construct four interrelated graphs, namely species: abundance, species: body length, population abundance: body length and total number of individuals: body length distributions.3In contrast to a number of previous studies, no consistent linear relationship between population density and body length was found for the Bornean beetles and it is suggested that, as in birds, the added dispersal ability of flight reduces critical population densities necessary for persistence in small species. Previous relationships between body weight and population abundance may also be artefacts of the way in which data were gathered.4Despite large samples, we failed to locate the mode in plots of the number of species in each abundance category (species: abundance distribution).5Species: body length and total number of individuals: body length plots were similar to those found in previous studies, although using data for Coleoptera alone may have produced a steeper decline in the total number of individuals as body size increases than is apparent in samples of all arthropods.6We present the first three‐dimensional graph relating numbers of species, body lengths and population abundances. The surface of this three‐dimensional relationship is relatively sim

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1988.tb00330.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

ABSTRACT.1There is a narrow hybrid zone between two chromosomal races of the grasshopperPodisma pedestris(L.) in the French Alps.2There are no gross differences in habitat across the zone, and a multivariate analysis of the vegetation composition detected no significant transition either.3The hatch and development rates ofPodismain hybrid populations were lower than those found in matched habitat types outside the zone.4The simplest explanation for the persistence of the parapatric distribution of the two races is that hybrid disadvantage is maintaining a tension zone between them.

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1988.tb00331.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

ABSTRACT.1Male spacing, aggression, and female visitation are described for a lek ofDrosophila cnecopleuraHardy within a Hawaiian rainforest. The lek was located at a single tree ofPisonia umbellifera, and the males present defended individual leaves as mating territories. Observations were made in October 1986 and April 1987.2Approximately twice as many males were present at the lek in October than in April. At both times, males generally perched on the lowest leaves in the lek. Individuals did not remain on particular leaves for long periods of time but frequently moved among different territories.3Males engaged in two types of aggressive encounters, face‐offs and chases, and in all encounters the resident displaced the intruder.4Females were sighted at the lek 0.69 times/h in October and 0.23 times/h in April. Most of the leaves visited by females were among the lowest in the le

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1988.tb00332.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

ABSTRACT.1The adaptive significance of multiple mating by femaleGryllus bimaculatus(De Geer) was investigated.2Multiple mating prevented the depletion of sperm stores and, therefore, maintained high hatching success. This may not, however, explain the high frequency of remating in this species.3Male‐derived egg stimulants known to be passed with sperm at mating increased the number of eggs produced only when females mated throughout their lifespans.4Spermatophore consumption appeared to provide nutrients which, while they did not increase the quantity of eggs, increased egg quality as indicated by weight. Females who consumed spermatophores had a greater hatching success.5While females may derive non‐genetic benefits from mating, these are apparently long‐term benefits; females must mate throughout their lives in order to accrue them.6Since the benefits of mating may not be derived from individual males, the spermatophores and their contents in this species are best considered as mating e

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1988.tb00333.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

ABSTRACT.1The butterflySandia xami(Reakirt) has a very clumped yearly pattern of oviposition on its food plantEcheveria gibbifloraD.C., and the mean number of eggs per plant is always very low.2Three features of host plants are highly associated with the probability of being oviposited upon: height of plant; degree of conspicuousness; and degree of isolation from conspecific plants.3The relative importance of these factors as predictors of the probability of oviposition change according to the time scale considered: height and conspicuousness are more important over short (weekly) time intervals whilst isolation takes precedence over longer (yearly) periods.4It is hypothesized that the clumped pattern of oviposition is responsible for the low numbers of the butterflies relative to their very abundant food plant.

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1988.tb00334.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

ABSTRACT.1Predation by birds, crawling arthropods (ants, harvestmen, spiders), and social wasps (Vespula) spp. on introduced stocks ofHeliothis virescens(Fabricius) larvae was investigated in a oak‐hickory forest canopy in northwestern Arkansas (U.S.A.).2Wasps,Vespula maculifrons(Buysson) andV.squamosa(Drury), removed over 90% of the larvae. Repeated visits to a feeding site by the same marked wasps accounted for removal of either a single larva or all larvae. Larvae pinned (punctured) to artificial leaves were selected over 70% of the time by wasps when compared to attachments that did not puncture larvae; however, unpunctured larvae were taken.3Crawling arthropods accounted for low levels of predation, and birds did not appear to prey on larvae. Apparently wasps removed larvae rapidly and efficiently, thereby depleting the feeding sites before other predators discovered the larvae.4Although attaching larvae to artifical hickory leaves provided an easy method for placing larvae into the forest canopy, a lower percentage of larvae were removed from these leaves compared to natural hickory leaves. Moving feeding sites did not influence the number of larvae take

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1988.tb00335.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

ABSTRACT.1The effects of predation on clutch size and egg dispersion in the codling mothLaspeyresia pomonella(L.) were experimentally studied in an orchard by recording survival of eggs glued onto different substrates.2Egg mortality due to sucking insects was readily distinguishable from that due to chewing insects.3In both the field and laboratory, females preferred to deposit eggs singly on the uppersides of leaves.4Eggs on the uppersides of leaves and on fruit survived significantly better than did those on the undersides of leaves or on twigs.5Egg losses were highest during the early part of the flight season.6The smallest (one egg) and largest (nine eggs) clutches, associated with one egg‐bearing leaf per twig, both suffered the lowest rates of predation. Factors selecting against oviposition on fruits and production of large clutch sizes are presented and discusse

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1988.tb00336.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY