摘要:

Computer simulation studies reported here examine potential for injury to alfalfa,Medicago sativaL., byAgromyza frontella(Rondani), the alfalfa blotch leafminer (ABL). A validated, physiological model of alfalfa growth, ALSIM 1 (Level 2), was modified to incorporate eight hypothesized mechanisms of injury by ABL. A phenological model forecasting occurrence of damaging stages of ABL was used to time simulated injury under nine weather regimes. Sensitivity of yield, quality (leaf fraction), and end-of-season root reserves to different types and degrees of injury were examined. Leaf mining by third instars had virtually no effect on yield during any harvest period under any weather conditions. Leaf fraction of harvested hay increased slightly. There was essentially no impact on end-of-season root reserves. Model results were insensitive to major qualitative changes in the way larval injury was represented. Simulated pinholing injury by adult female ABL had a greater effect. Greatest reduction in total yield (15%) occurred when pinholing was combined with low rainfall. Pinholing also significantly increased the leaf fraction of harvested hay but had little or no influence on end-of-season root reserves. Sensitivity analyses showed that ALSIM was more responsive to all types of damage during the period of ABL adult activity than during the period of larval mining. The model was most sensitive to changes in rates of photosynthesis and assimilate accumulation, and to a lesser degree to changes in level of soil moisture at which water stress was initiated and rate of evaporation from the canopy. During the period of ABL activity, the model was fairly insensitive to alteration of light absorption by the canopy and insensitive to changes in leaf area index and senescence rate of leaves. Cutting management (scheduling) was examined as a factor influencing simulated impact of ABL on alfalfa. Early harvest most often reduced percentage yield loss caused by ABL and reduced the already small effect of ABL on end-of-season root reserves.

ISSN:1754-5692    

DOI:10.1093/ee/16.3.575

出版商:Oxford University Press    

年代:1987

数据来源: OUP

摘要:

Sunflower moth,Homoeosoma electellum(Hulst), is a major pest of cultivated sunflower,Helianthus annuusL., in North America. Thirty perennial and 11 annual species ofHelianthusand several cultivars of sunflower were evaluated for resistance toH. electellumlarvae. Larvae feeding on sunflower inflorescences in laboratory and greenhouse bioassays performed significantly poorer on 14Helianthusspecies than on the cultivar hybrid ‘894’. In in vitro bioassays, nonpolar extracts fromH. annuus, Helianthus argophyllusTorrey&Gray,Helianthus ciliarisDC, andHelianthus petiolarisssp.petiolarisNuttall caused significant lengthening of larval stadia and retarded larval growth. Larvae feeding on purified sesquiterpene lactones and diterpenes fromH. argophyllus,H. ciliaris, Helianthus angustifoliusL., andHelianthus mollisLambert in a wheat-germ diet at 0.1–1.0% concentration experienced high mortality, retarded growth, and an extended developmental period. The sesquiterpene lactone 8 β-sarracinoyloxycumambranolide isolated from glandular trichomes on anthers ofHelianthus maximilianiSchrader was toxic to young larvae in bioassays. Two mechanisms givingHelianthusresistance to seed injury by larvae ofH. electellumare terpenes in the florets and phytomelanin in the pericarp of seeds.

ISSN:1754-5692    

DOI:10.1093/ee/16.3.586

出版商:Oxford University Press    

年代:1987

数据来源: OUP

摘要:

The functional response ofLeptopilina boulardiBarbotin et al. to variations in density of its major natural host,Drosophila melanogasterMeigen, was examined in the laboratory. A behavioral criterion was used to assess attempts by parasitoid females to leave experimental arenas; a patch visit was considered terminated whenever a searching female left the host medium for over 5 min. The results demonstrate density-dependent oviposition behavior inL. boulardi, apparently stemming from a tendency by parasitoid females to spend longer periods of time in patches containing higher densities of hosts, and to emigrate quickly from patches of low host density. However, the form of the functional response was ambiguous. Allowing parasitoid search times to vary among patches changes the spatial frame of functional response measurements and complicates their interpretation; a number of these complications are discussed.

ISSN:1754-5692    

DOI:10.1093/ee/16.3.593

出版商:Oxford University Press    

年代:1987

数据来源: OUP

摘要:

The thermal environment of the screwworm larva was studied under natural and mass-rearing developmental conditions. A}rtificially infested ovine and bovine experimental hosts were used to monitor larval (myiasis wound) and rectal temperatures over the course of parasite development. Temperatures in infestations in ovine wounds increased from mean initial values of 37 to near 41°C after 2 d, then decreased slowly for 3 d to 40°C as larvae matured. Wound temperature was positively related to larval density in the wound, but larval development rates were negatively related to density. Ovine hosts, but not bovine, became febrile in response to infestation, effectively increasing mean wound temperatures approximately 1°C in large infestations. In bovines, temperatures throughout the developmental period followed patterns similar to those in ovines, but were approximately 2°C lower. Temperatures in mass-rearing conditions, with minimal exogenous temperature control, showed that larvae can maintain temperatures above ambient and within a narrow range. Under such conditions they simulate the natural host's thermal environment during all but the final 36–48 h of development, when temperatures descend rapidly to as low as 32°C. Periodic feedings at late stages may abruptly alter temperatures for short periods. Implications of the role of temperature in the evolution of the screwworm from a carrion-feeding ancestor, and as a stress factor in mass rearing, in terms of present mass-rearing techniques, are discussed.

ISSN:1754-5692    

DOI:10.1093/ee/16.3.599

出版商:Oxford University Press    

年代:1987

数据来源: OUP

摘要:

Polyvinyl chloride (PVC) substrates molded in forms shaped as rods, thin blocks, and surrogate moths were developed to releaseHeliothis virescenssex pheromone. Bioassays of various colors of the PVC substrate impregnated with pheromone components run in central and south Texas showed that black molded baits were most effective. Formulation of the pheromone components in the black PVC substrate prolonged the attractiveness and efficiency of these baits compared with those of other colors and laminated plastic dispensers. Bioassays showed that 6 µl of V-2 (Z-11-hexadecenal:Z-9-tetradecenal [14.6:1]), incorporated in the black PVC block- or surrogate moth-shaped dispensers performed best for 2-wk periods compared with three other pheromone blends composed of four additional components. Dissipation rate of the V-2 components from the black PVC substrate was regulated at a highly consistent rate, and the initial emission ratio of the two compounds was more precisely maintained than that emitted from laminated plastic dispensers. Techniques were developed to produce black PVC V-2 dispensers cut from thin, polymerized vinyl chloride sheets at the rate of 690 baits per hour. High production rate and product consistency in the quality of the PVC dispensers were assured by the simplicity of fabrication methods developed.

ISSN:1754-5692    

DOI:10.1093/ee/16.3.605

出版商:Oxford University Press    

年代:1987

数据来源: OUP

摘要:

Artificially inoculated spider mite foci increase in size at an exponential rate. Productivity was greatest on plants farthest from the center of each focus. Timing of initial infestation was shown, both experimentally and through simulation, to affect ultimate yield of cotton: the earlier the initiation of infestation, the lower the yield. These results as well as those of other researchers indicate that the tolerance of cotton to mite infestations increases with crop maturity.

ISSN:1754-5692    

DOI:10.1093/ee/16.3.614

出版商:Oxford University Press    

年代:1987

数据来源: OUP

摘要:

The quantitative and qualitative losses in stored corn infested byProstephanus truncatus(Horn), and stored for 20 wk at 30°C and 70% RH, were compared with those ofRhyzopertha dominica(F.). Treatments included insect-infested whole corn, uninfested whole corn plus ground corn (dockage), and uninfested whole corn. The quality assessment criteria included adult insect number, dust weight production, seed moisture content, changes in seed fat acidity value, germination, and microfloral infection of seeds. Both insect species multiplied quickly, withP. truncatuspeaking at 880 adults per 120 g corn by week 14, then declining slightly because of an exhausted food supply.R. dominicanumbers increased to 550 adults per 120 g corn by week 14 and 1,300 adults per 120 g corn by week 20.P. truncatusdust production was significantly different from that forR. dominica(P<0.005). Infested treatments had significantly different seed moisture content, fat acidity values, and bacterial infection of seeds compared with controls (P<0.005). Seed germination was significantly reduced for both species compared with controls (P0.05); only theP. truncatustreatment showed a difference in infection byAspergillus glaucusgroup with a decrease after week 11 (P<0.005).

ISSN:1754-5692    

DOI:10.1093/ee/16.3.618

出版商:Oxford University Press    

年代:1987

数据来源: OUP

摘要:

Within-plant distribution ofHeliothis zea(Boddie) F3generation eggs was determined from soybean samples,Glycine max(L.) Merrill, taken from fields in eastern North Carolina. Numbers of eggs on 22 and 29 plant parts during 1980 and 1981, respectively, were recorded.X2tests of homogeneity for the proportion of eggs on each part tested across fields of different phenologies within each date indicated that these proportions changed from field to field. Based on the proportion of eggs per plant part or the frequency of occurrence of each plant part, the preferred oviposition sites were both the upper and lower trifoliates; however, terminals were the most preferred on the basis of the proportional area represented by each plant part.

ISSN:1754-5692    

DOI:10.1093/ee/16.3.625

出版商:Oxford University Press    

年代:1987

数据来源: OUP

摘要:

Quantitative studies were conducted to evaluate comparative responses of two alternate hosts,Cadra figulilella(Gregson) andEphestia elutella(Hübner), to a suspension of two nonoccluded viruses ofAmyelois transitella(Walker). Instar, weight of larvae with chronic disease, and comparative mortality of neonate larvae were determined. Although all tests indicated that the alternate hosts were highly resistant to the viruses, larvae ofA. transitellaremained highly susceptible to suspensions of virus from the alternate hosts after five serial passages.

ISSN:1754-5692    

DOI:10.1093/ee/16.3.630

出版商:Oxford University Press    

年代:1987

数据来源: OUP

摘要:

A Mexican race ofOplomus dichrous(Herrich-Schaeffer) was collected in September 1983 and brought to the United States for evaluation as a biological control agent of Colorado potato beetle (CPB),Leptinotarsa decemlineata(Say). Predator development was negligible between 12 and 15°C and optimum from 28 to 33°C. Development for one generation (egg to egg) at 25°C requires ca. 1.5-fold longer than that of CPB. In field-cage studies, 95% control was attained with a release ratio of ca. oneO. dichrousadult to 40–50 CPB eggs. It is unlikely that this predator will successfully overwinter in the Northeast. Considering its relatively low population growth rate in cool climates, it apparently has little potential to control CPB in the Northeast, although it may be of importance in warmer climates.

ISSN:1754-5692    

DOI:10.1093/ee/16.3.633

出版商:Oxford University Press    

年代:1987

数据来源: OUP