摘要:

IN SCIENCE, AS IN LIFE, we humans make progress in fits and starts. When pressed, few successful scientists will say that they had a clear vision of the precise steps to be taken relative to their intended paths of investigation. Those who are responsible for the interpretation of research for the purpose of promulgating regulations for environmental protection also suffer alternating surges of certainty and uncertainty. This is not to say that scientists and administrators do not address their respective areas in a logical progression. Rather, it suggests that the process of developing an understanding of complex biological and social systems is, by nature, evolutionary. In science, we devote much time to rejecting alternative hypotheses in hopes that a properly constructed null will ultimately emerge and provide an understanding of some pattern or process. Because of the complexity of the problems in biological systems, the rejecting of alternatives frequently takes longer than we might like, especially for those responsible for developing protocols related to human-initiated changes to our world. Regardless of the fact that knowledge of our complex biological world takes time to accumulate, we are forced ever more often to develop regulations that balance environmental cost with economic return derived from biological communities that range from largely undisturbed to highly manipulated.

ISSN:0046-225X    

DOI:10.1093/ee/22.3.501

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

Within the field of biological control, there is a strategy that involves the attempt to control a native pest species with an exotic biological control agent. This strategy has been termed neoclassical biological control, and its ecological foundation differs markedly from other forms of biological control. Neoclassical biological control with a parasitic wasp and an entomophagous fungus from Australia is now being applied to rangeland grasshoppers in the western United States. Available evidence suggests that the costs of such a strategy greatly exceed the benefits. Although the probability of successful establishment may be low, if such an agent is established there are a number of possible nontarget impacts. Adverse effects include competitive suppression or extinction of both native biological control agents and nontarget acridids, which comprise the vast majority of extant grasshopper species. Suppression of nontarget acridids may result in loss of biological diversity, existing control of weed species, release of otherwise innocuous acridid species from competitive regulation, disruption of plant community structure, suppression of essential organisms vectored by grasshoppers, and disruption of food chains and other nutrient cycling processes. These impacts are particularly serious given that an established exotic agent is essentially permanent and spatially unbounded. Given that the value of the rangeland resource depends upon the largely unknown ecological processes that underlie its sustainable productivity, there are a number of management techniques that offer a greater probability of success with a markedly lower likelihood of ecological and economic disruption than does neoclassical biological control.

ISSN:0046-225X    

DOI:10.1093/ee/22.3.503

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

Studies of the response of natural enemies to vegetational diversity suggest that movement behavior plays an important role in determining natural enemy abundance in diversified agroecosystems. A simple mathematical model for the response of natural enemies to interplanted strip vegetation is developed based on the assumption that natural enemy movement can be represented as a diffusion process. Attractiveness of interplanted strips, resulting from strip vegetation having an abundance of resources, is represented by natural enemies having lower diffusion rates in the strips. Results of simulations with the model suggest that interplanted vegetation acts as a source of natural enemies when natural enemies colonize strip vegetation before crop germination, but acts as a sink when crop and interplanted vegetation germinate simulataneously. The magnitude of this effect varies with natural enemy mobility. Spatial patterns exhibited by natural enemies will be influenced by mobility and do not reliably indicate whether or not augmentation is occurring. There is a strong interaction between natural enemy mobility and experimental design, suggesting that the results of small-scale studies with agroecosystem diversification must be interpreted with caution. The ability of our model to account for much of the variability in natural enemy responses to diversification suggests that this variability may be caused by an interaction between natural enemy movement and system design rather than by fundamental differences in natural enemy behavior.

ISSN:0046-225X    

DOI:10.1093/ee/22.3.519

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

A study was conducted to determine if grasshopper stages of development could be used as indicators of nontarget arthropod activity on mixed-grass rangeland. Densities of grasshopper species, instars, and adults were estimated at several plots in northwestern South Dakota at weekly intervals throughout the summers of 1986 and 1987. At each plot, activities of nontarget arthropods were determined from pitfall and malaise trap catches. Factor analysis was used to relate activities of nontarget arthropods (Carabidae, Tenebrionidae, Meloidae, Lycosidae, Gryllidae, Formicidae, Ichneumonidae, Sphecidae, Pompilidae, and Asilidae) with densities of grasshopper species and stages of development. Nymphs of most dominant grasshopper species were associated with Carabidae, Lycosidae, Sphecidae, and Asilidae, all groups known to prey on grasshoppers. Adults were associated only with Tenebrionidae. These results suggest that insecticides applied to rangeland when most grasshoppers are middle to late instars will have a maximum impact on nontarget arthropods.

ISSN:0046-225X    

DOI:10.1093/ee/22.3.532

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

Influences of uncultivated corridors on rates of parasitism of the green cloverworm,Plathypena scabra(F.), in soybean agroecosystems were examined. Soybeans were planted in large experimental plots (0.45 ha); three plots contained corridors of successional old-field vegetation, three plots contained corridors planted in grasses, and three plots were left undivided. Treatments were arranged in a completely random design. No significant differences in larval parasitism were observed between treatments, and location (larvae collected near corridors, ≤5 m, compared with larvae collected farther from corridors, 6–11 m) did not have a significant effect on parasitism ofP. scabra larvae. Parasitism ofP. scabralarvae by the total parasitoid complex, byAleiodes nolophanae(Ashmead), and byCampylochaeta plathypenae(Sabrosky) generally increased in all treatments as the season progressed, but parasitism byC. plathypenaedeclined later in the season. Larval parasitism byCotesia marginiventris(Cresson) declined over time. Larval parasitism may have been related to spatial scale.

ISSN:0046-225X    

DOI:10.1093/ee/22.3.541

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

Genotypes of field-grown corn,Zea maysL., known to vary in their resistance to fall armyworm,Spodoptera frugiperda(J. E. Smith), were used in a study designed to examine the movement of neonate larvae. Movement of larvae was examined on corn plants at the midwhorl (the 8th leaf; V8) stage and the late-whorl (12th leaf; V12) stage. There was little difference in the movement of larvae when they were on resistant ‘MpSWCB–4’ compared with when they were on the susceptible genotype ‘Pioneer 3369A.’ However, larvae reached the feeding sites (whorl tissue) more quickly when they were placed on the younger (upper) leaves than when they were placed on the older (lower) leaves. When larvae were collected from resistant and susceptible genotypes 24, 48, and 96 h after artificial infestation, there were consistently fewer larvae on the resistant genotype only after 96 h. Populations of larvae decreased more rapidly when the plants were infested in the late-whorl stage than when the plants were infested in the midwhorl stage.

ISSN:0046-225X    

DOI:10.1093/ee/22.3.547

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

Timing and magnitude of corn earworm,Helicoverpa zea(Boddie), emergence was measured in a corn,Zea mays(L.), field near College Station, TX. Approximately 15,500H. zeaper hectare were produced, with 85% of the moths emerging in a 10-d interval. FeedingH. zeamoths were observed to be highly attracted to honeydew exudates of egrot,Claviceps paspali(F. L. Stevens&J. G. Hall) on infected florets of dallisgrass,Paspalum dilatatum(Poir.) in an adjacent pasture. Moths began feeding on the ergot at dusk. Feeding densities increased rapidly to peak at<1 h after sunset and then declined to relatively low levels by 2 h after sunset. Dissection analyses of sampled females showed that 95% were unmated, indicating that the characteristic age of the feeding moths was ≤1 d.

ISSN:0046-225X    

DOI:10.1093/ee/22.3.554

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

Cabbage maggot,Delia radicum(L.), populations from North Carolina (Fletcher and Scaly Mountain) and New York (Geneva and Highland) were surveyed to detect differences in the emergence pattern of flies from overwintered pupae. Populations from all locations consisted of different proportions of early- and later-emerging individuals. However, populations from New York consisted predominately of early-emerging individuals (≥90%), whereas populations from North Carolina were composed of a higher percentage of later-emerging individuals. Emergence patterns of F1progeny from crosses between early- and later-emerging flies from Scaly Mountain demonstrated that emergence traits were genetically controlled.D. radicumphenology studies in North Carolina suggested that temporal isolation of the two types was halted by an extended period of aestivation during the summer months, which subsequently allowed the two populations to interbreed during the autumn months. The relative proportion of early:late emergers appears to be unstable over time, which may be due to differential mortality factors operating when populations are temporally isolated or due to dominance or recessive factors governing earliness or lateness, or both.

ISSN:0046-225X    

DOI:10.1093/ee/22.3.559

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

Diapausing and nondiapausing adults of the southern green stink bug,Nezara viridula(L.), had supercooling points in the range from -10.4 to -11.7°C. Lethal exposure times of adult stink bug are given for -5.0, -7.5, and -10.0°C. No difference in cold tolerance was found between diapausing and nondiapausing stink bugs. Overwintering survival of confined adults at Charleston, SC, was high or 0 depending on severity of low temperatures.

ISSN:0046-225X    

DOI:10.1093/ee/22.3.567

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

Microhabitat preferences of three sympatric naucorids (Ambrysus circumcinctusMontandon,Limnocoris lutziLa Rivers, andCryphocricos hungerfordiUsinger) from the South Llano River of central Texas were evaluated in laboratory experiments. Each species was individually subjected to all paired contrasts produced from three substratum size classes (coarse gravel, small pebble, and small cobble). Within each contrast, three trials were conducted, each involving a different current velocity (slow, 6.6 ± 0.1 cm/s; intermediate, 9.8 ± 0.1 cm/s; and fast, 13.7 ± 0.5 cm/s). The gravel substratum was never preferred; moreover, preference in the pebble versus cobble contrast, when present, was only shown for the cobble substratum. Overall,A. circumcinctusexhibited consistent substratum preferences (cobble>pebble>gravel) independent of current velocity.C. hungerfordipreferred cobble over either gravel or pebble substrata; however, a synergistic effect between current velocity and substratum size was detected in the gravel versus pebble contrast. Finally,L. lutziexhibited the highest degree of velocity-dependent substratum selection. Laboratory analyses corroborated field investigations and offered insight into the influence of interacting abiotic variables on the microdistribution of Naucoridae.

ISSN:0046-225X    

DOI:10.1093/ee/22.3.571

出版商:Oxford University Press    

年代:1993

数据来源: OUP