摘要:

Previous studies indicate that North American gypsy moth,Lymantriadispar (L.), populations are driven by a numerically bimodal replacement rate model: Nt+1/Nt=f(N), wheref(N) is bimodal, resulting in two equilibrium densities. Under this theory, populations are regulated about a low density equilibrium for many years until some perturbation (usually mass immigration) elevates populations to high densities, where they are regulated about a high-density equilibrium until crashing. In this paper, the evidence for and against numerical bimodality in gypsy moth populations is reviewed. The Melrose Highlands data (egg mass densities at 83 plots in New England from 1910 to 1931) were reexamined. These analyses indicated bimodality inf(N) when data were expressed as yearly means of several plots in a zone ≍30 km in diameter, but there was no clear evidence of bimodality in the dynamics at individual plots. Density fluctuations in these relatively small plots (0.07 ha) were instead dominated by apparently random effects. It is hypothesized that short-range dispersal dominates the dynamics of populations at these spatial scales. These results illustrate the importance of spatial scale in the characterization of ecological processes.

ISSN:1754-5692    

DOI:10.1093/ee/21.2.221

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

The parasitoid complexes of tortricoid (Lepidoptera: Tortricoidea) hosts were investigated to determine the component parasitoid guilds, the utilization of these guilds, and the host ranges of the parasitoid taxa. This provided an alternative, mOt;e detailed perspective on the structure of parasitoid complexes than the approach pioneered by Askew&Shaw (1986). The component parasitoid guilds are defined by three parameters: the host stage attacked, the mode of parasitism (ecto- or endoparasitism), and the form of parasitoid development (continuous or protracted). Characteristics of the 11 guilds of parasitoids of tortricoid hosts are presented in detail. Tortricoid hosts support a parasitoid complex of ≍9 species, with notable similarity in the utilization of parasitoid guilds in both the Nearctic and Palearctic regions. The complexes are dominated by koinobiont larval endoparasitoids and idiobiont pupal parasitoids. The host range of tortricoid parasitoids show some broad support for Askew&Shaw's (1986) hypothesis that parasitoid lifestyle can be used as a practical indicator of the breadth of the host ranges of parasitoids. However, the extent of exceptions indicate that the hypothesis cannot be accepted for parasitoid complexes in general and point to the importance of both parasitoid taxon and the host stadium attacked in influencing parasitoid host ranges. The relative merits of parasitoid guilds and parasitoid lifestyles as concepts in the analysis of parasitoid complexes are discussed.

ISSN:1754-5692    

DOI:10.1093/ee/21.2.230

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Modified screen mesh versions of the Hartstack pheromone trap were placed within and adjacent to fields of potato, corn, and cotton to investigate the effect of trap placement on male capture during the first, second, and third flights ofOstrinia nubilalis(Hübner). During the first flight in 1988, traps within potato fields captured greater numbers of males than traps outside of the field in the grass border. In 1990, total captures were few and capture rates were equal between locations. Weekly trap captures within the field were significantly correlated with weekly egg mass numbers sampled in the field in 1990. During 1989 and 1990, traps within cornfields at ear level captured greater numbers of second-flight males than traps in the field at canopy height and traps in the field border. Weekly trap captures within the field at ear and canopy level and adjacent to the field were significantly correlated with egg masses. In cotton, traps within the field captured more males than traps outside the field during 1988 and 1989, and captures were equal between locations in 1990. These results confirm that in North Carolina,O. nubilalismales seek mates both within and outside of field boundaries and indicate the potential merit of trap placement within the field.

ISSN:1754-5692    

DOI:10.1093/ee/21.2.240

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Natural oak regeneration is poor in Missouri's oak-hickory forests. The potential of the Asiatic oak weevil,Cyrtepistomus castaneus(Roelofs), to affect Missouri's oak resource was addressed. The spatial dispersion and density of the adult Asiatic oak weevil was investigated in a Missouri oak-hickory forest in relationship to the density of oaks, the preferential food source of this insect. The spatial dispersion pattern of emerging adult weevils was contagious and was defined by the negative binomial distribution in five of nine trapping areas. Oak stem densities within the trapping area of each plot were positively correlated with Asiatic oak weevil emergence density estimates in 1985. In 1986, Asiatic oak weevil catches in individual traps were not correlated with oak stem density associated with each trap when traps were placed 3 m apart. However, Asiatic oak weevil catches were significantly correlated with oak stem density associated with individual traps when traps were placed 30 m apart. Cluster analysis of the vegetation associated with individual traps in 1986 revealed the vegetation to be homogeneous in the area where the traps were placed 3 m apart and the vegetation to be more heterogeneous when traps were placed 30 m apart.

ISSN:1754-5692    

DOI:10.1093/ee/21.2.247

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

A Leslie model was developed for the population dynamics of corn earworm in soybean. In the model, survival rates are affected by predation, cannibalism, and chemical applications. The developmental transition probabilities in the Leslie model were obtained from experimental cumulative distributions. Corn earworm,Helicoverpa zea(Boddie), influx density is affected by crop growth stage and the attractiveness of the crop to moths. Analytic models for components of survival, for crop development, and for influx of adult moths were parametrized from process-level simulations, supplemented by field and laboratory observations. In these models, components are represented by continuous functions, which are at least piecewise analytic. The resulting Leslie model therefore lends itself more conveniently to study of the qualitative behavior of the system, to the design of sensitivity analyses, to incorporation into decision making and management models, and to study of the effects of parameter uncertainty.

ISSN:1754-5692    

DOI:10.1093/ee/21.2.253

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Soybean,Glycine max(L.) Merr., resistance to insects has been shown to vary with planting date and leaf age. This study determined effects soybean genotype, planting date, and leaf age had on feeding behavior of corn earworm,Helicoverpa zea(Boddie). Soybean genotypes ‘Cobb’ (susceptible) and ‘GatIR81-296’ (resistant) were planted early (29 May) and late (28 June) in 1989 in the field. Trifoliolate leaf samples from the top, middle, and bottom one-third of the plant were sampled four times throughout the season. Leaves were arranged in a free-choice fashion and presented to third-instarH. zeain the laboratory. Leaf area removed was calculated with a computer-based leaf area analysis system. Larvae preferred ‘Cobb’ over ‘GatIR81-296’ in each sampling date. Leaves from the late planting had greater leaf area removed on the first two sampling dates compared with leaves from the early planting (15.8 versus 11.7 and 34.5 versus 22.9 cm2), but leaves from the early planting had more leaf area removed compared with leaves from the late planting on the last two sampling dates (30.9 versus 22.7 and 21.3 versus 16.2cm2). Thus,H. zeaexhibited a bimodal feeding preference for early- and late-planted soybean. Older leaves (middle or bottom one-third) of all plants were typically preferred over younger ones (top one-third) throughout the season. Because resistance may vary during plant development, an accurate identification of soybean resistance should be done only with genotypes at a similar stage of development.

ISSN:1754-5692    

DOI:10.1093/ee/21.2.264

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Thirteen localPelargonium×domesticumcultivars were evaluated for greenhouse whitefly,Trialeurodes vaporariorum(Westwood), preference. Some morphological and physiological characteristics of these cultivars were measured to determine their influence on greenhouse whitefly adult preference. Host plant characteristics and greenhouse microclimate accounted for 37.8 and 11.8% of the total whitefly adult distribution variability measured 62 h after the adults had been released. In the variability accounted for by the host plant, 26.5% was attributed to differences between cultivars and the rest (8.0%) to the leaf developmental stage. Hairiness and leaf size were correlated with whitefly adult distribution; the less hairy ones and those with larger leaves were the preferred cultivars. The other host plant characteristics that were measured (thickness of adaxial epidermal cuticle, fresh-dry weight relationship, and soluble sugars and protein) were not related to greenhouse adult preference. Egg laying was not significantly different in each cultivar.

ISSN:1754-5692    

DOI:10.1093/ee/21.2.269

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Field hatch of gypsy moth,Lymantria dispar(L.), is an important population parameter of interest to both managers and researchers. It has been problematic to quantify hatch in the field without affecting its outcome. A method for quantifying hatch after it has naturally occurred in the field is presented. This technique uses a previously developed regression model for estimating fecundity, coupled with a count of unhatched eggs, to calculate the proportion of hatch. Hatch estimates were regressed against known hatch from a laboratory population to test the performance of the method (r2× 0.90,p× 0.0001). The method can be used to estimate first-instar hatch on an individual egg-mass basis or for a population.

ISSN:1754-5692    

DOI:10.1093/ee/21.2.276

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Mirna-type earth mounds up to ≍1.5 m in height and ≍20 m in diameter occur in densities of up to 20–25 per hectare in a seasonally waterlogged grassland area in southern Buenos Aires Province, Argentina. Fossorial mammals are absent from the site, but the black fire ant,Solenopsis richteriForel, is abundant. These ants construct epigeal nests averaging 20 cm in height and 60 cm in diameter and formed of excavated soil. Colonies ofSolenopsisalso construct extensive subsurface tunnels outward from the colony to gain access to foraging areas. This pattern of tunneling leads to horizontal translocation of soil toward the colony sites. It is postulated that when colonies of these ants become located consistently in elevated, better-drained microsites in landscapes that are seasonally waterlogged or flooded, soil translocation gradually results in large earth mounds. Such mounds occur at several locations in Buenos Aires Province and appear to be characteristic of poorly drained pampean grasslands. This phenomenon is similar to that produced by several groups of fossorial rodents as well as by certain fungus-gardening termites in Africa.

ISSN:1754-5692    

DOI:10.1093/ee/21.2.281

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Within-plant distribution ofHelicoverpa zea(Boddie) on soybeans,GLycine max(L.) Merrill, was investigated from 1980 to 1986. The distribution of larvae upon plant parts was evaluated based on the number on each plant part and on the number adjusted for the surface area of each plant-part. Distribution of larvae changed with larval size. The proportion of larvae, based on the number per plant part, was highest on rolled leaves for small larvae, but was highest on open leaves for large larvae. Distribution of larvae adjusted for the area of plant parts was most dense on rolled leaves, flowers, and pods. Plant phenology affected larva distribution because flowers and pods were unavailable in some plant growth stages. Larvae were observed feeding on all plant parts, but larvae found on stems were predominantly moving rather than feeding.

ISSN:1754-5692    

DOI:10.1093/ee/21.2.287

出版商:Oxford University Press    

年代:1992

数据来源: OUP