摘要:

Grasshopper assemblages were examined at 30 sites in southcentral Idaho, representing various degrees and types of disturbance. These disturbances included heavy livestock grazing, wildfires, plowing, herbicide applications, and seeding of introduced perennial bunchgrasses, mainly crested wheatgrass. These disturbances resulted in the loss of sagebrush and native perennial grasses and has led to the establishment of exotic annual grasses and forbs on several sites. Grasshopper assemblages on sites dominated by annual vegetation were characterized by relatively high densities, low species diversity, and high proportions of species with broad diet breadths. Introduced perennial grass seedings were characterized by a high proportion of grass-feeding grasshopper species and high species diversity. Sagebrush–grass sites were characterized by lower grasshopper density and high species diversity. These results, obtained under generally low grasshopper densities, suggest that rehabilitation of annual grasslands with perennial grasses and shrubs, and protection of endemic plant communities, can contribute to more diverse grasshopper communities with lower proportions of pest species.

ISSN:1754-5692    

DOI:10.1093/ee/22.1.71

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

Nymphs of the deer tick,Ixodes damminiSpielman, Clifford, Piesman&Corwin, were studied in Westchester County, NY, to determine the seasonal mortality pattern and the potential for unfed nymphs to survive through the active season (May–August). Field-collected nymphal ticks were monitored in field exclosures, which prevented contact with mammals while not restricting habitat choice by ticks. In addition, nymphs were confined in small mesh packages and monitored in the field. In 1989, few (1.3%) ticks placed in exclosures in May–June survived until the end of August. The average mortality rate (proportion of ticks dying per day) in the exclosures was 0.04 ± 0.03 in 1989, 0.048 ± 0.03 in 1990. Ticks placed in mesh packages had 90% mortality after 46 d, 99% after 100 d, and 100% after 300 d. These results indicate that survival through the active season is rare in nymphalI. damminiin Westchester.

ISSN:1754-5692    

DOI:10.1093/ee/22.1.82

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

Euxesta stigmatisLoew, preferred silk tips for oviposition (P<0.5) over other parts of corn plants. Most oviposition occurred during daylight hours, but peaked between 1100 and 1800 hours (EST). Few eggs (12–17%) deposited at the leaf base completed development, whereas eggs laid inside the tassel did not develop. Highest percentage of adult emergence was from com ears (41–83%). Development from egg to adult was longer on seed corn,Zea maysL. ‘Pioneer’ 305, 35–37 d, than on sweet com, ZeamaysL. ‘Silver Queen’, 30–32 d. Development times did not vary with seasons or sex, but development of different stages of E. stigma tis was the shortest at 30°C (egg-adult, 28.2 d).

ISSN:1754-5692    

DOI:10.1093/ee/22.1.88

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

The water loss dynamics and humidity preference ofRhynehophorus cruentatus(F.) adults were investigated. Total body water averaged 47 ± 8% by mass, and cumulative loss increased with time at all humidities tested (0, 33, 63, and 100% RH) at 30°C. Death occurred more rapidly in low than in high humidities, at which time weevils had lost ≍50%of their total body water. Cuticular permeability of weevils calculated from exposure to 0% RH for 2 h was 39.5 ± 4.1 and 75.9 ± 8.1 μg cm−2h−1mmHg−1when surface areas were calculated using Meeh's formula and planimetry, respectively. When given a choice,R. cruentatusadults chose high over low relative humidity after exposure for 2 and 24 h.R. eruentatusadults are subject to desiccation under a drying environment and may use habitat location to conserve water.

ISSN:1754-5692    

DOI:10.1093/ee/22.1.93

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

Alternate feeding hosts of adult boll weevils,Anthonomus grandisBoheman, were studied in Tamaulipas, Mexico, by (1) isolating and identifying pollen grains from the alimentary tract of weevils caught in pheromone traps in Tamaulipas, Mexico, during 1985, 1986, and 1987; and (2) evaluating the potential importance of alternate host plants in the biology of the boll weevil by recording the survival rates, fat body accumulation and reproductive development of boll weevil adults when fed Rowers and buds of selected plant species. In total, 3,348 pollen grains of all kinds were isolated from 1,204 boll weevils captured in pheromone traps in central Tamaulipas. Of 406 individual weevils collected from October through May, 34.7% were found with some type of ingested pollen grains. Boll weevils with ingested pollen were found in every habitat in which traps were placed, although the percentage of weevils with ingested pollen varied between habitats and with distance from cultivated cotton. The mean number of pollen grains of all species per weevil was 12.9 ± 3.8 (mean ± SE) (n= 406), and several weevils were found with>200 ingested pollen grains. The ingested pollen grains were from fourteen identified plant families. The most commonly represented families were Compositae (29.9%), Leguminosae (14.6%), Malvaceae (5.3%), Gramineae (0.6%), and Fagaceae (0.6%). Adult boll weevils readily fed on the various noncotton plants (Compositae, Malvaceae, and Cactaceae) offered in field cages. Mean survival times of boll weevils were significantly greater when fed either pure pollen mixtures,Gossypium hirsutumL. buds (cotton),Opuntia lindheimeriEngelm. (Cactaceae) flowers, orAbutilon hypolecumGray (Malvaceae) than controls (water only). Fat body development of boll weevils fed these food sources was also significantly greater than controls. Polyphagous pollen feeding behavior may be an important survival strategy of the boll weevil in the absence of reproductive hosts, especially in tropical habitats where adult boll weevils may be active throughout the year.

ISSN:1754-5692    

DOI:10.1093/ee/22.1.99

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

The influence of leafhopper,Graminella nigrifrons(Forbes), gender and female mating status on the disease dynamics of leafhopper-transmitted maize chlorotic dwarf machlovirus was examined in a maize,Zea maysL., monoculture. Physical maps of disease incidence showed that diseased plants resulting from the release of males at the center of plots were less aggregated than for female treatments. Disease gradient slopes were compared after fitting the data to the log-logistic disease spread model. The release of males resulted in a mean disease gradient slope that was significantly more shallow than female treatments. Disease dispersion was further characterized using Lloyd's patchiness index, which yielded results that confirmed the analysis of disease gradients. These measures of dispersion also indicated a tendency for disease aggregation resulting from virgin females to be intermediate to males and mated females. Although the level of aggregation was most different for male and mated female treatments, there was no Significant difference between these treatments for overall disease incidence, indicating that the pattern of disease spread, but not overall disease incidence, was influenced. Whereas previous studies have focused on the role of host plant finding by leafhoppers as a determinant of individual movement behavior within a habitat, and consequently pathogen spread, our results suggest that an understanding of mating behavior may contribute to our understanding of plant disease dynamics.

ISSN:1754-5692    

DOI:10.1093/ee/22.1.109

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

We evaluated the importance of leaf size in determining oviposition choice (i.e., gall densities), gall (and larval) size, and larval survivorship for a population of leaf-galling sawflies,Pontaniasp. nr.pacificaMarlatt, on arroyo willow,Salix lasiolepisBentham. Our results did not support the hypothesis that female sawflies prefer to oviposit in developing willow leaves that will be larger when they are fully expanded. Although leaves with four to seven galls had bigger leaf areas than leaves with one to three galls, the size of the mature leaf did not appear to be an important factor determining which leaves were selected for oviposition among the leaves available. The data did not support the prediction that larger leaves producePontaniasp. galls (and larvae) that are substantially bigger than those on smaller leaves; gall size was only weakly correlated with leaf area (r≤ 0.253). We hypothesized that survivorship ofPontaniasp. larvae would be positively related to leaf size, but the result was opposite. In total, larval survival was weakly biased toward smaller leaves, primarily because of lower mortality from natural enemies. Mortality from two species of inquilines was positively related to leaf area, whereas mortality from two ectoparasitoids showed inconsistent relationships to leaf area. The absence of strong directional selection illustrates that it would be unlikely for female sawflies to evolve a leaf size choice strategy based on maximizing survival rates of their offspring.

ISSN:1754-5692    

DOI:10.1093/ee/22.1.116

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

The preference ofSchistocerca americana(Drury) for 40 potential host plants relative to bahiagrass,Paspalum notatum, was determined in two-choice and fourchoice tests. Although highly polyphagous,S. americanademonstrated clear preference and nonpreference for certain species. Host selection by small nymphs (instars 3 and 4), large nymphs (instal's 5 and 6), and adults was highly correlated. Host selection by spring-generation grasshoppers was highly correlated with summer-generation host preference. The presence of alternate hosts, especially nonpreferred species, resulted in modified host-selection behavior wherein grasshoppers were more discriminating in fourchoice tests than two-choice tests.

ISSN:1754-5692    

DOI:10.1093/ee/22.1.127

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

In caged choice experiments,Lymantria dispar(L.) larvae strongly preferredAcer saccharumMarsh. andFraxinus pennsylvanicaMarsh. trunks (44.3 and 43.3% of larvae, respectively) toBetula papyriferaMarsh. trunks (5.7%). When larvae were allowed to choose among the foliage of live seedlings of the same species, they preferredB. papyrifera(71.0%) overA. saccharum(14.3%) andF. pennsylvanica(0.7%). Trunk sections ofA. saccharumandB. papyriferawere wrapped around live seedlings of the same trees andF. pennsylvanicain six possible combinations of trunk and foliage species to evaluate the impact of trunk characteristics on host selection in the presence of foliage. The most preferred trunk-foliage combinations, in descending order of percentage larvae found on each, were as follows:A. saccharum-B. papyrifera(41.0%),B. papyrifera-B. papyrifera(19.0%),A. saccharum-A. saccharum(14.8%),B. papyrifera-A. saccharum(12.2%),A. saccharum-F. pennsylvanica(2.2%), andB. papyrifera-F. pennsylvanica(1.0%). Both trunk species and foliage species Significantly influenced larval choice. The effect of tree canopy size, as measured by leaf surface area, on the distribution of larvae was measured in a forest clearing where five replications of 17 tree species and cultivars were planted. The tree species ranged from highly susceptible (Malussp.) to highly resistant (Gleditsia triacanthosL.). The number of larvae per tree was explained well by the size of the leaf canopy for the six most preferred tree species and cultivars. This relationship did not exist for the remaining 11 species and cultivars of less preferred trees. Apparently, the size of preferred trees influences the distribution of gypsy moth larvae among them.

ISSN:1754-5692    

DOI:10.1093/ee/22.1.134

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

Starving fourth-instarAgrotis ipsilon(Hufnagel) for 4 d did not increase the propensity of 3-d-old moths to engage in long-duration (i.e., ≥1 h) continuous flights, or the duration of such flights, on flight mills. Adult diet (nothing, distilled water, or honey–water) did not significantly influence male flight propensity until 2 d of age or female propensity until 3 d of age. Male propensity to fly and flight profiles (flight duration, times of flight initiation and termination) seem to depend more upon the availability of liquids than carbohydrates, whereas female behavior is more dependent on a carbohydrate source. In all instances, the influence of both larval and adult diet stress on flight propensity and duration is negative. One would expect a positive effect if such stress factors act as cues that trigger a behavioral or physiological shift to a migratory phase. Instead, environmental factors that stress individuals seem only to decrease the already high propensity to make prolonged flights and decrease the duration of those flights.

ISSN:1754-5692    

DOI:10.1093/ee/22.1.141

出版商:Oxford University Press    

年代:1993

数据来源: OUP