摘要:

The critical photoperiod for diapause induction was determined in the laboratory and validated in the field forDiolcogaster facetosa(Weed), a parasite of the green cloverworm. In the laboratory at constant 24°C, as well as in the field under natural conditions, the critical photoperiod for diapause induction is between 13:11 and 14:10 (L:D). Second instars are sensitive to diapause-inducing photoperiods, and diapause occurs in the final instar after it has emerged from the host and spun a cocoon. Study of diapausing individuals from the field during autumn and winter indicated that photoperiod has only a minor role, if any, in diapause maintenance or termination. The date of diapause termination was not determined, but the combination of diapause development and postdiapause development had not been completed in the field by the spring equinox.

ISSN:1754-5692    

DOI:10.1093/ee/20.1.65

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Acyrthosiphon kondoiShinji is a major pest of alfalfa (Medicago sativaL.). Susceptible seedling plants are killed byA. kondoi, and established plants suffer yield loss by stunting. Information is meager on the influence ofA. kondoiinfestation or host plant resistance on forage quality of alfalfa leaves and stems. In a controlled environment, the forage quality (including phenolic monomers)of alfalfa germplasms KS153P4 and KS153BA3P4 (susceptible and resistant toA. kondoi, respectively) with and withoutA. kondoiinfestation was compared. Leaves infested withA. kondoihad lower concentrations of crude protein and true in vitro digestible dry matter (TIVDDM) than uninfested leaves of controls, but infested stems had higher crude protein concentration. Stems and leaves infested withA. kondoihad higher neutral detergent fiber concentrations than did those of uninfested controls. Infested stems of KS153BA3P4 had more syringic acid than did infested stems of KS153P4 and uninfested controls. However,A. kondoiinfestation did not alter TIVDDM or digestible neutral detergent fiber of stems. TheA. kondoi-resistant KS153BA3P4 had more neutral detergent fiber in leaves but lower TIVDDM and digestible neutral detergent fiber in stems than susceptible KS153P4. Infestation of alfalfa for short time periods byA. kondoidecreased the nutritive value of leaves and stems.

ISSN:1754-5692    

DOI:10.1093/ee/20.1.71

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Dung from cattle treated with sustained-release boluses containing either methoprene or diflubenzuron was bioassayed biweekly for 27 wk with the horn fly,Haematobia irritans(L.); two species of dung-burying beetles,Onthophagus gazella(F.) andSisyphus rubrusPaschalidis; and two species of dung-inhabiting predators,Philonthus flavolimbatusErichson andP. longicornisClark. When reared on dung from a steer treated with the methoprene bolus, emergence of adult horn flies was reduced 37.5–99.4% during the first 25 wk and 8.3% at 27 wk when compared with emergence of horn flies reared on untreated dung. Adult horn fly emergence, when reared on dung from a steer that received the diflubenzuron bolus treatment, was reduced 82.9–100% over a 21-wk period, but there was no reduction at 27 wk. Emergence of adultO. gazellaandS. rubrusfrom brood balls made with dung from a steer treated with a diflubenzuron bolus was reduced for 7 wk after treatment. Dung from the methoprene-treated animal had no apparent effect on the reproduction of either dung beetle species. There was no apparent effect onP. flavolimbatusandP. longicorniswhen reared on dung from steers treated with either methoprene or diflubenzuron.

ISSN:1754-5692    

DOI:10.1093/ee/20.1.77

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Compared with green plants, variegated plants compensated for the reduced photosynthetic efficiency of each leaf by producing more leaf area per unit of biomass. This altered growth pattern indicates that nutrients must be more mobile in variegated plants to support the new leaf growth. The movement of plant nutrients, such as nitrogen, has been linked to the performance of several phloem feeding insects. The fecundity of two phloem feeding insects was examined to determine if factors that increased nitrogen movement could improve their performance. The fecundity ofUnaspis euonymiandAphis fabaewas observed, respectively, on stems and leaves of variegated and greenEuonymus japonicavar.aureus.Fecundity of both phloem feeders was improved on the variegated plants. In addition to examining interplant variation in suitability, intraplant variation was examined forA. fabae.Young variegated leaves provided the most suitable substrate for this insect. These data suggest that horticulturally important attributes such as variegation can affect the susceptibility of ornamental plants to insect pests. Variegation alters normal patterns of growth and nutrient transport in a manner that suggests an increased flux of mobile nutrients. These changes are likely to enhance the fecundity of associated sucking insects such as aphids and scales.

ISSN:1754-5692    

DOI:10.1093/ee/20.1.83

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

The seasonal and spatial distributions of dung-feeding scarabs in an open pastureland and in wooded (holm oak) pastureland in a typical Mediterranean area of the western part of the Iberian Peninsula (Salamanca) were compared. Six pitfall traps baited with bovine dung were placed in each habitat according to a model by J. P. Lumaret. Only beetles in the families Scarabaeidae and Geotrupidae were studied because they are the most important agents in the elimination of cattle dung from the soil surface. Weekly trapping for 1 yr produced 6,909 specimens. Of the 18 species found, the largest beetles and biomass were concentrated mainly in the wooded habitat, especially in the summer. This constitutes a problem for dung removal because large amounts of dung remain in open pasturelands, possibly resulting in the impoverishment of such areas.

ISSN:1754-5692    

DOI:10.1093/ee/20.1.90

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Rotting fruit exposed to the red imported fire ant,Solenopsis invictaBuren, was consumed by the ants, which successfully prevented colonization by other decomposer arthropods. When fire ants were excluded, the fruit was colonized by large numbers of several species of Diptera (Drosophilidae and Tephritidae) and Coleoptera (Nitidulidae and Staphylinidae), as well as small numbers of parasitic Hymenoptera and other arthropods. When rotting fruit was colonized by these decomposer arthropods and then exposed toSolenopsis invicta, the remaining fruit and the fruit colonizers were consumed by the ants. The data demonstrate that fire ants rapidly locate and recruit to rotting fruit where they consume other decomposer arthropods, exclude invasion by other decomposer arthropods, and use the decomposing resource themselves.

ISSN:1754-5692    

DOI:10.1093/ee/20.1.98

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Complete recovery of ‘Zinfandel’ grapevines from damage by Willamette spider mite,Eotetranychus willamettei(McGregor), required 2 yr. For vines that previously had experienced the highest level of mite damage (1,347 mite-days), a significant reduction of 14.9% in total yield per vine was detected within the first year of recovery. However, no significant reductions were noted in vegetative growth, mean berry size, or number of fruit clusters per vine (P>0.05). Yield depressions after 2 yr of infestation were not greater than after a single year of infestation. No significant differences were found for any parameter measured within the second year of the study. A graphic model is presented to illustrate the potential effects of differential recovery rates and duration of recovery from damage by pests of perennial crops on the determination of economic injury levels. Increases in total recovery time and decreases in rate of recovery resulted in lower predictions for economic injury levels for fixed control costs. Failure to consider recovery rate and duration is hypothesized to result in the underestimation of crop losses due to indirect feeding damage.

ISSN:1754-5692    

DOI:10.1093/ee/20.1.104

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Benthic macroinvertebrate colonization of 12 0.04-ha experimental ponds was studied for 1 yr. The ponds were filled in late January 1988 and artificial substrate samples were retrieved at 4-wk intervals from 25 February 1988 to 25 February 1989. The first organisms (Chironomusand Ceratopogonidae) were collected in the first set of samples 4 wk after filling. The colonization sequence was Diptera (primarily several genera of chironomids), followed by Coleoptera, Ephemeroptera, and Odonata. The arrival of taxa corresponded to adult flight periods. Noninsect taxa (Oligochaeta, Nematoda, Amphipoda) were collected in relatively low numbers late in the year. Twenty-nine taxa were collected, 13 of which were present in all 12 ponds. Mean number of taxa, diversity, and evenness increased rapidly during the first 7 mo, but never became very high. Mean density increased slowly throughout the spring and summer to about 200 individuals per sampler and then increased rapidly during the autumn to about 600 individuals per sampler. Community structure was dominated by Chironomidae (≈85%) and Ephemeroptera (≈9%). Trophic function was dominated by detritus-feeding collectors (≈79%). Factors that influenced the structure and function of the new experimental ponds appeared to be: lack of connection to colonized waters, small size, and simple, homogeneous habitat and food resources.

ISSN:1754-5692    

DOI:10.1093/ee/20.1.110

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Potato leafhopper,Empoasca fabae(Harris), is a major pest of spring-planted alfalfa (Medicago sativaL.). In two experiments, an alfalfa monoculture and an intercrop (mixture of alfalfa and oat,Avena sativaL.) were evaluated for their potential for reducing leafhopper densities. The 1988 experiment tested the effects of the intercrop and leafhopper control, whereas the 1989 experiment tested the effects of weed control and two oat cultivars differing in stature. Leafhopper density (number per square meter and number per 100 alfalfa stems) and various plant parameters were measured in both experiments. Adult leafhopper densities per square meter were reduced an average of 82.6% in 1988 and 77.3% in 1989, and densities per 100 stems were reduced an average of 64.7% in 1988 and 54.5% in 1989, in the intercrop compared with the alfalfa monoculture. Nymph densities per square meter were reduced an average of 85.5% in 1988 and 89.5% in 1989, and densities per 100 stems were reduced an average of 74.8% in 1988 and 82.7% in 1989, in the intercrop compared with the alfalfa monoculture. The intercrop was characterized as having reduced alfalfa biomass, reduced alfalfa stem density, reduced alfalfa maturity (1989 only), increased alfalfa stem length (1989 only), reduced weed biomass, and increased shading of alfalfa in comparison with alfalfa monoculture. Thus, factors that may cause the observed reduction in leafhopper density may be associated with the host plant or the habitat condition. The study corroborates other studies that have shown reduced potato leafhopper densities in grass–legume mixtures, and suggests that an oat-alfalfa intercrop may reduce the need for responsive tactics for leafhopper management on spring-planted alfalfa compared with the need in alfalfa monoculture.

ISSN:1754-5692    

DOI:10.1093/ee/20.1.118

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Samples (0.5 m2) were taken from the South Llano River, Kimble County, Tex., to determine inter- and intraspecific differences in microhabitat association for the three most abundant species of Naucoridae. Various aspects of substratum condition, current speed, temperature, depth, as well as complex key hydraulic features, were used to characterize the microhabitat for each sample. Eight species of naucorids occur in the river; however, onlyAmbrysus circumcinctusMontandon,Cryphocricos hungerfordiUsinger, andLimnocoris lutziLa Rivers occurred with sufficient frequency in our samples to allow statistical analysis. None of the three species exhibited age-related differences in microhabitat association based on multivariate analysis of variance (MANOVA), and none of the examined abiotic variables yielded significant differences between nymphs and adults when analyzed from a univariate perspective except Froude number forL. lutzi. BothA. circumcinctusandC. hungerfordiexhibited highly significant differences (MANOVA) in abiotic characteristics between quadrats of occurrence and nonoccurrence. Results of individual analyses of variance (ANOVAs) indicated that 9 of the 10 abiotic variables were significant forA. circumcinctusand 8 forC. hungerfordi. In contrast, quadrats whereL. lutzioccurred could not be distinguished from those in which it was absent based on MANOVA, and only two abiotic variables exhibited significance in the ANOVAs. Associations between age groups (nymphs and adults) within a species and between all possible species pairs (combined age groups) also were evaluated with contingencyX2tests using presence-absence data and with Pearson's product–moment correlations using density data. In all cases, significant negative associations were not detected, suggesting that neither age groups nor species exhibit microhabitat segregation. Discriminant function analysis for each species supported MANOVA results on presence–absence data. Separate multiple step-up regressions were used to evaluate which abiotic factors were most related to the density for each species. Significant variables included mean current speed, which accounted for 23.8% of the variation in density ofA. circumcinctus; rock standard error of the mean, which accounted for 43.1% of the variation in density ofC. hungerfordi; Froude number and depth range, which together accounted for 39.0% of the variation in densitiy ofL. lutzi. In summary, each common naucorid clearly shows microhabitat associations, but the evidence of interspecific differences is indirect.

ISSN:1754-5692    

DOI:10.1093/ee/20.1.127

出版商:Oxford University Press    

年代:1991

数据来源: OUP