摘要:

The influence of different temperatures (from 26 to 39.5°C) and relative humidities (40 and 70%) on the development ofVarma jacobsoni(Oudemans) was studied by placing newly capped and parasitized worker bee broods into thermostatically controlled chambers. In one set of experiments the temperature was kept constant, and in the second set, the parasitized worker broods were placed at a temperature of 40,41, or 42°C for a time varying from 0 to 24 h and then returned to 32.5°C. The optimal temperature for development of the mites was between 32.5 and 33.4°C, which corresponds to the brood temperature ofApis melliferaL. Above 36.5°C, reproduction of varroa females was significantly reduced, and above 38°C, mites began to die without reproduction. Jumps of temperature were unfavorable to the development of the mites. The regulation of brood temperature by bees and occasional temperature peaks may be key factors in resistance of honey bees to varroa mites.

DOI:10.1093/ee/19.6.1780

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

The relationships between grasshopper densities and climatic variables in southern Idaho were examined using historical grasshopper survey records from 1950 to 1980. Mean annual grasshopper densities were calculated from grasshopper counts made within a 20-km radius of each of 26 weather stations spanning the Snake River plains and adjacent areas. The mean annual densities for each location were averaged to yield 27-yr mean grasshopper densities. Maximumr2improvement regression techniques were used to select average weather factors that were correlated with grasshopper densities. The average November precipitation and mean April temperature proved to be the best indicators of the mean grasshopper density for a location, accounting for 92% of the variation in the 27-yr mean densities. The relationships of temperature and precipitation to annual grasshopper population fluctuations were analyzed at 15 locations. Most of the mean monthly temperature variables included in the regression equations were positively correlated with grasshopper densities, except for November, December, and January mean temperatures, which were negatively correlated with grasshopper densities in the following year. Precipitation variables included in the regression models were positively correlated with grasshopper densities at nearly all locations. Precipitation appears to be an important factor driving grasshopper population dynamics in southern Idaho, possibly by its effect on vegetation quality and quantity.

DOI:10.1093/ee/19.6.1786

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

The responses ofMaruca testulalis(Geyer) larvae, which favor or hamper its colonization of a plant, were studied on three cowpeaVigna unguiculata(L.), Walpers, cultivars, ‘VITA l’ (susceptible), ‘VITA 5’ (moderately resistant), and ‘TVu 946’ (resistant). Larval responses studied were orientation, feeding, utilization of ingested food, and development. Attraction and arrest–stay of first instars to the plants indicated that orientational nonpreference of the larvae contributed to the resistance of ‘TVu 946’ and ‘VITA 5’ cultivars toM. testulalis. Results from studies on food intake, utilization of ingested food, larval growth, and development indicated that antibiosis was also partly involved in the resistance of ‘TVu 946’ and ‘VITA 5’ stems and pods.

DOI:10.1093/ee/19.6.1792

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

AdultCoecinella septempunetataL. were placed on grain sorghum plants,Sorghum bicolor(L.) Moench, at four growth stages with one of three greenbug,Schizaphis graminum(Rondani), densities under laboratory and field conditions. Greenbug predation and dislodgment rates for adults and nymphs were recorded during a 1-h observation period or until ∼75% of the greenbugs were either consumed or dislodged. Greenbug nymphs were consumed at 4 and 1.3 times the rate of adults in laboratory and field tests, respectively. Adult greenbugs were 1.8 times and nymphs were 1.3 times more likely to be dislodged than consumed under laboratory conditions. In field tests, adults and nymphs were dislodged 5 and 4 times more often, respectively, than they were consumed. The number of greenbugs consumed/min in laboratory and field tests increased with plant stage and density with the exception of the bloom plant stage. The number of greenbugs dislodged for each consumed was directly related to prey density and plant stage. Evaluation of predator efficacy using only the number consumed may underestimate the effect of predation on greenbugs due to the dislodgment behavior. Dislodgment allows greenbugs to escape immediate predation, but may expose them to increased risk from other biotic and abiotic mortality factors.

DOI:10.1093/ee/19.6.1798

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

During a 3-yr study, we investigated the effects of grapevine,Vitis viniferaL., irrigation management on the abundance of the western grape leafhopper,Erythroneura elegantulaOsborn and a variegated grape leafhopper,E. variabilisBeamer, at two locations in the San Joaquin Valley of California. Irrigation treatments ranged from 40 to 120% replacement of the expected nonstressed crop evapotranspiration (EToc). Densities of both species were significantly lower on vines in the low irrigation treatments (0.4, 0.6, and 0.8 EToc), than on vines that received maximum water allotments (1.0 and 1.2 EToc). Leafhoppers tended to be more numerous on the shaded side of the vines than on the sunlit side.E. elegantulaattained a maximum average density of 15 nymphs per leaf at Westside in 1984, whereas a maximum of 23 nymphs per leaf was recorded forE. variabilisat Kearney. There was greater variation in leafhopper densities in response to irrigation treatments at Westside than at Kearney, an effect believed to be the result of differential water holding capacities of the respective soils at each location. Restricted available water can affect vine water status and alter characteristics of the microenvironment, including canopy temperature and humidity. Both transient and long-term irrigation effects can contribute to fluctuations in leafhopper abundance.

DOI:10.1093/ee/19.6.1803

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

Relay intercropping soybean,Glycine max(L.) Merr., into winter wheat,Triticum aestivumL., is an alternative to double cropping soybean following winter wheat in the more northern latitudes of the United States. Because increased crop diversity affects arthropod populations, a study was conducted to determine if a wheat–soybean cropping system might have an effect on the potato leafhopper,Empoasca fabae(Harris), a pest of soybean. Two soybean isolines differing in their pubescence (pubescent and glabrous) were grown in monoculture and a relay intercropped system during 1987 and 1989. Potato leafhoppers were sampled with a D-Vac sampling apparatus throughout the summer. In these years, leafhopper populations were extremely high, and potato leafhopper damage was severe on glabrous soybean grown in monoculture; whereas numbers of leafhoppers were moderate and damage was absent on pubescent soybean in monoculture. Potato leafhoppers were virtually nonexistent before wheat harvest on the pubescent and glabrous soybean that were relay intercropped; no damage to either isoline was evident. Following wheat harvest and removal of wheat straw, potato leafhoppers entered those plots, causing damage to the glabrous soybean. During the time period when wheat was present, both soybean isolines were protected from feeding by potato leafhopper. The ramifications for potato leafhopper control on soybean and other crops is discussed when a companion grass crop is grown.

DOI:10.1093/ee/19.6.1810

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

Oriental fruit fly,Dacus dorsalisHendel, and melon fly,Dacus cucurbiataeCoquillett, population dynamics from 1987 to 1989 were determined from fruit collections and male trap captures in an agricultural area. The major oriental fruit fly hosts were wild strawberry guava,Psidium cattleianumSabine, and common guava,Psidium guajavaL., outside the crop area; the major melon fly hosts were cultivated truck crops on farms. Abundance of oriental fruit fly and melon fly throughout five major habitats (upland guava shrub, lowland guava shrub, java plum forest, ironwood forest, and farms) was associated with oriental fruit fly abundance in guava areas and melon fly abundance on farms, respectively. During periods of peak guava abundance, numbers of oriental fruit fly increased on farms; during periods of peak crop production, melon fly increased in habitats surrounding farms. These findings are discussed with respect to placement of fruit fly traps for population monitoring and development of pest management strategies.

DOI:10.1093/ee/19.6.1820

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

The pales weevil,Hylobius pales(Herbst), and the pitch-eating weevil,Pachylobius picivorus(Germar), are pests of plantation pines in the eastern United States. Dispersal patterns of these species were studied in the summer of 1989 using pitfall traps baited with ethanol and turpentine, and mark-and-recapture techniques. Approximately 17% ofH. palesand 34% ofP. picivoruswere recaptured. Most pales weevils were recaptured in the immediate vicinity of the release point, whereas pitch-eating weevils appeared to disperse farther before responding to the baits. Marked weevils were recaptured up to 8 wk following the release. No gender differences were found in recapture rates. Pronounced temporal differences in recapture rates were observed, with more weevils attracted to baits in spring than in summer. A separate baited trap was developed to monitor weevil flight. Total weevil numbers, and femaleH. palesconsidered singly, were more commonly caught at 81 cm than 160 cm. The role of dispersal and migration in pine root weevil ecology is discussed with respect to the ability of these species to colonize new habitats.

DOI:10.1093/ee/19.6.1829

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

The below-ground effects of weeds (Amaranthus retroflexusL.,Chenopodium albumL.,Ambrosia artemisiifoliaL.,Digitaria sanguinalisL.,Setaria viridisL.,Panicum dichotomiflorumMichx.) and increased soil moisture on damage to peanut pods by southern corn rootworm,Diabrotica undecimpunctata howardiBarber, was investigated in a 2-yr field and greenhouse study. Field experiments demonstrated that weedy areas had less pod damage overall and higher predator numbers than nonweedy areas. However, increased soil moisture, which increased southern corn rootworm oviposition and egg and larval survival, confounded the results. Greenhouse studies showed that three broadleaf species and three grass species were not as good food sources as peanuts for southern corn rootworm larvae. Although the presence of weeds growing with peanuts did not lower larval survival, weeds did significantly (P≤ 0.05) slow larval developmental rate. In greenhouse studies, damage to peanut pods was approximately 66% in peanut-only (control) treatments, 55% in peanut + weed treatments, 32%in peanut predator treatments, and 9%in peanut + weed + predator treatments. The interaction of predators and weeds in lowering the amount of damage caused by southern corn rootworm was significant (P≤ 0.05). Field and greenhouse experiments demonstrated that at least two factors were operating to reduce pest damage in this belowground, multispecies plant association. Predators and the structural complexity of the weed-crop root association may be working synergistically to reduce southern corn rootworm damage to peanuts.

DOI:10.1093/ee/19.6.1837

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

Samples of the air at the tops of cotton plants,Gossypiumspp., treated with long-lasting dispensers containing gossyplure, the sex pheromone of the pink bollworm,Pectinophora gossypiella(Saunders), were pulled through adsorbent cartridges during day and night periods (0600–1800, 1800–0600 hours, respectively) and analyzed by gas chromatography for gossyplure content. The gossyplure was applied (≍1,000 dispensers containing 78 g [AI]/ha) at the pin-square or first flower stage of cotton. Air samples were taken during 3-d periods at approximately 1, 20, 40, and 60 d after treatment. Five Delta traps each baited with 1 mg of gossyplure were used to capture males in each test block. Day and night aerial concentrations of gossyplure in treated cotton fields, with few exceptions, were not significantly different. Average 24-h aerial concentration decreased to 1.4–2.0 ng/m3by day 60, regardless of initial concentration. Catches of male moths in the treated blocks were reduced 99.4–100% compared with controls during 60 d after treatment, indicating that aerial concentrations of ≥1.4 ng/m3of gossyplure generally prevented trap catch. The decreased release of gossyplure from dispensers over time is probably partially compensated for by greater retention of gossyplure in the developing plant canopy.

DOI:10.1093/ee/19.6.1845

出版商:Oxford University Press    

年代:1990

数据来源: OUP