摘要:

Comparisons of the suitability of different tree species as food for the gypsy moth,Lymantria dispar(L.), have usually been based on measurements of larval growth on foliage samples taken from few tree individuals at single field sites. By rearing gypsy moth larvae on five tree species (three preferred [all oaks] and two marginal) at sites located in three physiographic regions, we tested whether differences in suitability among tree species can vary from location to location. Relative suitabilities did not vary among locations for weight of female pupae or development time of male larvae, but there were some differences for weight of male pupae and development time of female larvae. These tree species × location interactions, however, accounted for little of the overall variability in gypsy moth pupal weight and development time on the three oak species. The largest sources of variation, aside from sex, were differences among larvae on the same tree and differences among trees of the same species. Some factors that were controlled for in this study, such as tree size (trunk diameter was positively correlated with weights of male and female pupae), phenology, extent of defoliation, and genetic differences among gypsy moth populations, may contribute to differences in the relative suitability of tree species among naturally occurring sites of infestation. Nevertheless, results of this experiment suggest that in studies of relative suitability, sampling replicate trees within species is more crucial than including multiple study sites.

ISSN:1754-5692    

DOI:10.1093/ee/19.5.1344

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

The effects of vegetation structure and tidal flooding on the organization of a spider community were studied along an elevational gradient in an intertidal marsh. High marsh habitats were dominated by the grassSpartina patens(Ait.) Muhl., a species characterized by a low, matted profile and a complex layer of thatch. Another grass,Spartina alternifloraLois., is more upright in structure, has a poorly developed thatch layer, and abounds in habitats that extend from the high marsh to much lower elevations. Along this elevational gradient, the structure ofS. alterniflorachanges from a short form on the high marsh to a tall form on the low marsh, and the frequency and duration of tidal flooding increases. Although more robust in structure during the summer months, the tall-form habitat ofS. alterniflorais selectively destroyed and defaunated during the winter by shifting ice and storms and must be recolonized by spiders every spring from the more protected overwintering short-form habitat ofS. alternifloraon the high marsh. In all, 21 species of resident spiders were sampled from the two grasses. The community of spiders inS. patenswas less diverse than inS. alternifloraand consisted mostly of hunting spiders (Lycosidae, Gnaphosidae, Clubionidae, Thomisidae, Philodromidae, and Salticidae), which were more abundant in this low-profile grass. Web-building spiders (Dictynidae, Linyphiidae, Araneidae, and Tetragnathidae), which were rare inS. patens, occurred commonly in the more upright structuredS. alterniflorabecause of the abundance of sites for web attachment. Down the elevational gradient from short-form to tall-formS. alterniflora, the abundance of most hunting spiders and several web-building species decreased and was associated with an increase in the frequency and duration of tidal flooding. Winter defaunation of tall-formS. alternifloracontributed further to the depauperate spider community in this low marsh habitat. Thus, vegetation structure and elevational factors act in concert to influence the distribution, abundance, and community structure of spiders in intertidal marshes.

ISSN:1754-5692    

DOI:10.1093/ee/19.5.1356

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

In Guatemala, 1,137 fruit samples weighing 3,912 kg from 30 host plants had a meanC. capitatainfestation of 1.58 (range, 0.1–382.9) pupae/kg and 20.18 (range, 0.1–447) forAnastrephaspp. from 1980 to 1983.A. ludenswas the most abundant and was found from 10 to 2,000 m elevation. Ranking of host fruits revealed thatC. capitatainfested mostly introduced temperate zone fruits andAnastrephaspp. mostly the tropical fruits. Infestation was inversely correlated with the numbers of mature fruits available on the trees and positively correlated with altitude up to 2,000 m forC. capitataandA. ludens, as well as with host plant biomass forC. capitata. An infestation sequence showed the preference ofC. capitatafor the fruits present in the field. Diversity of host plant infestation ofAnastrephain different regions of South and Central America and the economic importance of both genera in Guatemala are discussed.

ISSN:1754-5692    

DOI:10.1093/ee/19.5.1371

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

The importance of long-distance dispersal is recognized in the recolonization of disturbed habitats, but little is known about how migrant spiders respond to the various features of their atmospheric environment. Many spiders balloon by silken threads on wind currents for long distances and thus disperse to new habitats. Previous authors have focused on the meteorological conditions responsible for the initiation of spider ballooning. However, the meteorological conditions necessary for spiders to remain aloft on wind currents are less well known. During the fall and spring in east Tennessee, airborne spiders were collected from sticky traps extended from a 45-m tower at five heights throughout the forest canopy. Climatological data were collected continuously from the tower throughout the study. The results indicate that the most important meteorological factors affecting ballooning are abrupt changes in daily air temperature, maximum difference between dew point and air temperatures, and low wind fluctuations. For the fall, the highest percentage of spiders collected was at 22 m, immediately above the forest canopy, and for the spring, the highest catches were at 33 and 44 m. These results are correlated with sizes and taxa of animals trapped (i.e., more spider taxa with small body size ballooned in the spring than in the fall).

ISSN:1754-5692    

DOI:10.1093/ee/19.5.1381

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

The ground beetle (Coleoptera: Carabidae) communities associated with cropping systems of spring wheat under various tillage regimes were investigated at two locations in the Northern Great Plains during 1986 and 1987. Forty species of Carabidae were collected. More specimens were collected at Minot, N. Dak., but greater species richness occurred at Williston, N. Dak. Only 14 species accounted for ≥1% of the total number carabids collected.Harpalus pennsylvanicusDe Geer was the only species that was shared between locations, accounted for ≥1% of the total number of carabids, and was consistent across cropping and tillage systems. AlthoughHarpalus fallaxLeConte was shared between locations and accounted for ≥1% of the total number of carabids, it was not consistent across cropping and tillage systems. The Sorenson similarity index values at Minot were higher especially for the same cropping system. At Williston, the index values were lower, reflecting greater heterogeneity between treatments. Generally, lower numbers of individuals of a given species were found in cropping systems associated with conventional tillage. However, cropping system may have altered communities to higher degree than the tillage regime.

ISSN:1754-5692    

DOI:10.1093/ee/19.5.1388

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

Forage consumption and destruction rates of fourth and fifth nymphal instars and adult male and female ofDichroplus pratensisBruner were measured, and the forage loss caused by a population of this species inhabiting a natural grassland of La Pampa province, Argentina, was estimated. Consumption increased from fourth to fifth instar. From fifth instar to prereproductive adults, the amount eaten increased further in females but did not increase significantly in males. Then it dropped during the reproductive period in both sexes. Consumption rates (mg/individual/day) were 16.31 and 25.78 in fourth and fifth instars, 48.07 and 30.30 in the prereproductive females and males, and 8.33 and 7.27 in the reproductive females and males, respectively. Destruction rates were 3.87 and 12.34 in fourth and fifth instars, 6.73 and 8.53 in the prereproductive females and males, and 3.20 and 3.28 in the reproductive females and males, respectively. A higher proportion of the food removed by the male is not consumed, but is left to accumulate as litter. The forage loss caused by the population ofD. pratensiswas 274.32 kg/ha.

ISSN:1754-5692    

DOI:10.1093/ee/19.5.1392

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

Developmental rates from egg to adult for a uniparental race ofEncarsia perniciosi(Tower), an endoparasitoid of the San Jose scaleQuadraspidiotus perniciosus(Comstock), were determined using first instar hosts at 20°C, and using second instar hosts at 15, 20, 25, 28, 29.5, and 31°C under a regime of 16:8 (L:D) photoperiod. Parasitoids developed in male and female San Jose scale. Development rate was highest in male second instars, intermediate in females second instars, and lowest in first instar nymphs. Temperature versus development rate data were used to estimate parameters for both linear and nonlinear models of parasitoid development in male, female, and male and female hosts combined. Simulated adult flight peaks, based on linear and nonlinear models, were compared with peaks of adult parasitoid activity in three orchards during 1986 and 1987, and adult activity was measured using San Jose scale pheromone-baited and colored sticky traps. Modeled peaks agreed well with the spring flight peaks (F2and F3), but were generally earlier than peaks occurring during the summer generations (F4and F5) and later than those of autumn generations (F6and F7). The linear model for parasitoids developing in male and female hosts combined simulated 8 of 13 parasitoid peaks within ±7 d, whereas the nonlinear model was accurate for 7 of 13 peaks. Up to seven parasitoid flight periods per season were detected.

ISSN:1754-5692    

DOI:10.1093/ee/19.5.1396

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

Vertical distribution, aggregation behavior, and longevity of larvae ofBoophilus microplus(Canestrini) were studied in hollow nylon mesh cylinders (85.1 by 2.54 cm), in smaller tubes (8 by 2.5 cm) at 0, 15.24, and 66 cm, and on guineagrass (Panicum maximumJacq.) plants in open shadehouses in Puerto Rico. The maximum period of larval longevity from egg eclosion to death at 0, 15.24 cm, 66 cm, free in cylinders, and free on plants was 58, 85, 90, 78, and 130 d, respectively. Vertical distribution of larvae free in cylinders ranged from 0 to 85.1 cm, with most observed in small aggregations between 15 and 85.1 cm. Before larval death, the number of aggregations and the number of larvae in each aggregation declined from a mean of 8 and 75 to 1 with 12 larvae.

ISSN:1754-5692    

DOI:10.1093/ee/19.5.1403

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

Flight initiation threshold temperatures for agitated and undisturbed adult armyworms,Pseudaletia unipuncta, were measured. A predefined sequence of disturbances was applied to individual moths in an empty environmental chamber at various constant temperatures. With this agitation, the minimum flight threshold observed was 4°C, and the majority of moths could initiate flight at 10°C or above. A linear trend was noted between the log of duration of preflight wing shivering and ambient temperature. There were no detectable interactions with the sex or age of moths. Undisturbed moths were placed on oat seedlings at various constant temperatures under the photoperiodic conditions of rearing and left overnight. The presence of wing scales on a surface coated with Tanglefoot indicated flight. Flight was indicated at a minimum of 8°C. Flight maintenance thresholds were determined by lowering the temperature in a small tubular enclosure containing a single flying moth. Thresholds averaged 5.0°C for females and 3.9°C for males, with a minimum observed threshold of −l°C. No significant interactions with moth age or relative humidity at testing were noted.

ISSN:1754-5692    

DOI:10.1093/ee/19.5.1410

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

Life tables were compiled for two generations of the banded sunflower moth,Cochylis hospesWalsingham (Lepidoptera: Tortricidae), a univoltine pest of sunflower. Mortality of eggs and four instars in sunflower capitula was 8.9% for the 1986–1987 generation and 11.9% for the 1987%1988 generation.Orius tristicolorWhite (Hemiptera: Anthocoridae) preyed upon eggs and some first instars desiccated beneath involucral bracts. Mortality of fifth instars and pupae overwintering in the soil was 98.5% for the 1986–1987 generation and 94.8% for the 1987–1988 generation. Ground beetle (Coleoptera: Carabidae) predation reduced populations of overwintering larvae and pupae by 39.6% in 1986–1987 and 44.0% in 1987–1988.Glypta prognathaDasch (Hymenoptera: Ichneumonidae) parasitism reduced populations by 8.0% in 1986–1987 and 18.2% in 1987–1988. Although approximately 50% of fifth instars were parasitized, most fifth instars were consumed by predators before parasitoids emerged.

ISSN:1754-5692    

DOI:10.1093/ee/19.5.1418

出版商:Oxford University Press    

年代:1990

数据来源: OUP