摘要:

Considerable genetic variation in virulence, fecundity, and adult weight was found between and within clones of greenbug,Schizaphis graminum(Rondani), populations near Davis, Calif. Eight clones were established from individual apterous aphids collected from four fields within 50 km of each other. Aphids from these clones differed in their ability to damage wheat variety ‘TAM 107’ and in their weight and fecundity on several sorghum varieties. Based on these differences, the clones could be separated into four distinct groups. Lineages of four clones, maintained for 14–16 successive generations by selecting either large or small aphids, differed in their fecundities. These differences could not be explained by maternal effects. If biotypes of the greenbug are determined by the damage they cause to particular plant varieties, as recently proposed, then clones that differ in fitness traits such as fecundity and weight cannot be considered different biotypes. However, to develop strategies for reducing the rate of aphid adaptation to resistant varieties, we must understand such variation in fitness on a local scale, information that is not obtained in general biotype surveys.

ISSN:1754-5692    

DOI:10.1093/ee/20.3.757

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Although experienced modelers are usually aware of the dangers and benefits of the use of models in applied entomology, many scientists who may use models are not. Although some remain skeptical that models serve any useful purpose, others have unrealistic expectations about the information that models can provide concerning a particular problem. Models are often incorporated in the decision-making framework of expert systems in which their limitations may be hidden. Government spending cuts and cost recovery policies in some countries force vigorous promotion of management systems by scientific advisory staff. Such uses can lead to unreasonable claims and expectations about the realism of answers provided by models. Here, the definition of a model is reviewed, a brief history of model uses in ecology is presented, and the limitations of such uses are discussed. In pest management, the very real benefits and dangers of using models will not be fully appreciated until objectives are clarified and limitations of specific models are discussed openly in published work.

ISSN:1754-5692    

DOI:10.1093/ee/20.3.768

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Cumulative effects of constant temperature (15–35°C) and relative humidity (50–90%) on longevity and total duration of the life cycle ofOoencyrtus papilionisAshmead, a common egg parasite of the sugarcane pest,Pyrilla perpusillaWalker, were determined. The influence of temperature on the longevity and developmental period of the egg parasite was highly significant, and relative humidity also produced marked differences in longevity and life cycle duration. Average longevity of males decreased from 4.15 to 1.22 d and that of females from 10.39 to 1.68 d in response to increasing temperature from 15 to 35.5 ± 1.5°C. Mean life cycle duration also declined from 40.68 to 9.28 d as the rearing temperature increased from 15 to 30 ± 1.5°C. No development occurred within the host eggs at or above 32.5°C.

ISSN:1754-5692    

DOI:10.1093/ee/20.3.774

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Cantharidin contents were determined for fourEpicautaspecies abundant in northeast Kansas alfalfa fields.E. occidentalis(Werner) andE. pennsylvanica(DeGeer) typically contained much cantharidin (198–266μg/beetle), representing nearly 1% of their dry body weight, significantly more toxin than possessed byE. fabricii(LeConte) andE. pestiferaWerner. Two species also exhibited significant intersexual differences in cantharidin content.E. occidentalismales had almost four times more cantharidin than females. In contrast, femaleE. pennsylvanicacontained approximately six times as much of the substance as males. Three bales of alfalfa hay were collected from an area of a field infested with a swarm ofE. occidentalisat the time of harvest. Blister beetles were recovered from 91% of the mechanically produced sections of compressed hay (commonly known as flakes) from these bales. Although the contamination in only one flake of hay approached a calculated lethal level of 25 mg/kg forage, these data indicate that an encounter with a single blister beetle-contaminated flake of hay in the toxic range is quite possible, albeit infrequent. Flakes of field-collected hay, contaminated at the highest observed levels, could provide a lethal dose of cantharidin to horses weighing 125–500 kg.

ISSN:1754-5692    

DOI:10.1093/ee/20.3.776

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

The epicuticular lipids of alfalfa (Medicago sativaL.) were analysed by gas chromatography to determine if differences exist between plants with varying degrees of resistance to spotted alfalfa aphids,Therioaphis maculata(Buckton). Leaf surfaces of some resistant plants were found to have as much as 50% more wax esters than did those from plants that were susceptible to spotted alfalfa aphids. This difference was found in one set of sibling plants, which had been selected for spotted alfalfa aphid resistance, but not in a resistant plant population with a wider genetic base. Amounts of epicuticular lipids were found to be similar for leaves of the same age from stems of the same plant and from plants with similar genetic backgrounds which were grown under the same conditions.

ISSN:1754-5692    

DOI:10.1093/ee/20.3.781

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Photoperiod influenced nymphal development and diapause induction in a laboratory culture ofOrius insidiosus(Say). At 20°C, development of nymphs was significantly faster at a photoperiod of 10:14 (L:D) than at 12:12, 13:11, 14:10, or 15:9. Subsequently, diapause induction exhibited a typical long-day response; nearly 100% of adult females entered reproductive diapause when reared under short photoperiods (10:14 [L:D]), whereas at longer photoperiods (12:12, 13:11, 14:10, 15:9 [L:D]), fewer insects initiated diapause (56.8, 29.7, 5.3, 12.9%, respectively). The critical photoperiod fell between 12:12 and 13:11 (L:D). Duration of the preoviposition period was inversely related to photoperiod.

ISSN:1754-5692    

DOI:10.1093/ee/20.3.786

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Results are reported on the survival patterns of newly emergedTenebrio molitorL. reared in nutrient media supplemented with 0.125, 0.25, or 0.5% sodium selenite. One group was transferred to sodium selenite-containing medium after 1 wk in control medium, and another group was transferred after 1 wk from sodium selenite medium to control ration. Survival percentages and slope of survival curves are compared with control values. Results demonstrate a pronounced toxic effect of selenium which appears to be residual in those beetles transferred from the medium-containing selenium. OtherT. molitorwere reared in sodium selenite-containing media and, on days 3, 7, and 11, beetles were killed and the selenium content (ppm/mg tissue) of Malpighian tubules, digestive tract, and reproductive tracts were determined using fluorometric analysis. Results are reported correlating selenium content in the different organs to time of exposure to selenium and to concentration of sodium selenite in the incubation media. Malpighian tubules appeared to accumulate the greatest amount of selenium, the digestive tract was second, and the reproductive tissues accumulated the least amount of selenium. There appeared to be a direct dose accumulation relationship for Malpighian tubules but not for digestive or reproductive tissues; at the 0.25 and 0.5% treatments, no statistically significant differences were noted in the amounts of selenium that were present.

ISSN:1754-5692    

DOI:10.1093/ee/20.3.790

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

In the northern part of its range in North America, the Hessian fly,Mayetiola destructor(Say), has one generation each year and overwinters in diapause. In the southern part of its range, it may have six generations each year, and does not overwinter in diapause; however, its summer development is interrupted by an aestival period. Between these two extremes, the number of generations varies with geographical location and prevailing climatic conditions, and the species usually diapauses and aestivates each year. Laboratory aestivation can be induced by high temperatures (daily thermocycles ranging from 17 to 36°C), and terminated by exposure to four or more consecutive days at 21.1°C. Diapause was terminated at 21.1°C in about the same number of days of exposure to daylengths of 8:16 or 16:8 (L:D), suggesting that photoperiod is less important than temperature. Extremely high Indiana temperatures during the summer of 1988 induced a more intense aestivation, and its termination was delayed in the field. Many eggs were laid on wheat that fall after the Hessian fly-free date, and a very mild winter followed, resulting in the largest spring fly infestation recorded in the last 24 yr. A large percentage of aestival puparia submerged under water for weekly intervals up to seven weeks delayed pupating by the duration of time that they were submerged, suggesting that a higher titer of oxygen might be necessary to break aestivation.

ISSN:1754-5692    

DOI:10.1093/ee/20.3.795

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Cabbage plants were sprayed in the field with a butanol extract ofErysimum cheiranthoides, a wild crucifer normally rejected by ovipositingPieris rapae(L.) because of the presence of deterrent cardenolides in the foliage. Extract-treated plants received significantly fewer eggs than did solvent-treated control plants, both in field plots sprayed weekly and exposed to a natural butterfly population, and in 24-h experiments exposing plants to artificially concentrated wild butterfly populations in a large outdoor screen cage. The level of deterrence varied over time, perhaps because of susceptibility of the water-soluble deterrents to wash-off by rain water. Nevertheless, wild butterflies responded to theErysimumdeterrents in a fashion similar to that observed in earlier greenhouse experiments conducted with laboratory-reared butterflies. These results provide additional support for the hypothesis that host plant selection depends on a balance of both positive and negative stimuli. The results also suggest that protection of plants by deterrents may be possible in the field over short periods of time.

ISSN:1754-5692    

DOI:10.1093/ee/20.3.802

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Grasshopper (Orthoptera: Acrididae) density and species composition were monitored in three southwestern Montana grazing areas. Periodic comparisons were made of percent cover, percent crude protein, percent water content, and total phenolics for grasses grazed by cattle versus grasses protected from grazing. Grasshopper densities and composition differed in three areas. Grazing reduced vegetative cover, accompanied by increases in ground litter and patches of bare ground. Plant nitrogen and water content decreased during the spring and then increased in late summer following rains. Phenolics levels were independent of grazing and weather fluctuations. Changes in grasshopper nymph densities roughly corresponded to springtime decreases of crude protein and water content in grasses. Nymphal mortality was inversely related to density. Grazing, weather, or changes in plant chemistry had little effect on grasshopper parameters of this study.

ISSN:1754-5692    

DOI:10.1093/ee/20.3.807

出版商:Oxford University Press    

年代:1991

数据来源: OUP