摘要:

We explored the action of rain on the translocation of the gypsy moth nuclear polyhedrosis virus (LdNPV) at tree, branch, and leaf level. Artificial rainfall was used to simulate naturally occurring rainfall on leaves contaminated with 1st-instal gypsy moths,Lymantria dispar(L.), which had died of LdNPV. Bioassays using larvae in mesh bags on originally contaminated branches and branches below indicated that rainfall is effective in moving virus from branch to branch. This result was confirmed by an experiment using similar methods and naturally occurring rainfall. To examine this effect at the level of the leaf, we bioassayed leaf disks extracted from leaves with and without cadavers. Mortality of test larvae in leaf disk bioassays was strongly correlated with the presence of a cadaver on a leaf, but not confined to disks with cadavers. Mortality caused by non-LdNPV factors was also associated with consumption of a cadaver.

DOI:10.1093/ee/24.5.1144

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

Male spruce budworm diel trapping periodicity using artificial polyvinyl chloride (PVC) lures, virgin female baited traps, and blank traps was examined from 1988 to 1990 at sites having different population densities. The diel periodicity of female emergence and mating initiation were also determined. Patterns of male trapping periodicity differed substantialy by density and lure type but not by temperature. Virgin female baited traps detected unimodal male periodicity at all densities. PVC traps detected unimodal trapping pattern in the low density sites and bimodal patterns (1 morning and 1 evening peak) in high-density sites. No significant temperature effect on male trapping periodicity was detected. The upper and lower male flight temperature threshold was 11.5 and 27.5°C, respectively. Female emergence was dependent on the thermoperiod and peaked around 1300 hours. The pattern of mating initiation (beginning of copulation) differed significantly with density and coincided with peak PVC trapping periodicity. In low-density populations the majority of matings were initiated by 2100 hours, during the known female calling period; in high-density populations, the majority of matings were initiated by 1300–1900 hours, before the known female calling period. The coincidence of earlier mating and male catches at PVC-baited traps (but not at virgin female baited traps) situated in high-density areas, together with the coincidence of later mating and later catches in PVC and virgin female baited traps in low-density areas cannot be explained by differences in the thermoperiod or differences in the timing of female attractiveness. An appetitive, male mate-searching strategy not requiring calling females is discussed.

DOI:10.1093/ee/24.5.1150

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

Hosts nmging from small larvae to pupae of the Angoumois grain moth,Sitotroga cerealella(Olivier), were exposed to females of the pteromalid parasitoid,Pteromalus cerealellae(Ashmead), to determine the effects of host size on preference, parasitism success, adult size, and progeny sex ratio of the parasitoid. The parasitoid successfully parasitized larvae (>0.43 mm in maximum body width), prepupae (1.55 ± 0.05 mm [mean ± SEM] mm maximum average body width), and a single pupa (1.20 mm maximum body width). All female parasitoid progeny emerged from hosts that had a maximum body width>0.85 mm. Sixtyfour percent of male parasitoid progeny emerged from hosts that had a maximum body width between 0.43 and 0.85 mm. Size ofP. cerealellaeadults was correlated width host size (larger parasitoids developed on larger hosts). The optimal host sizes for producing female parasitoid progeny were larvae with a maximum body width between 1.69 and 2.05 mm and prepupae. The optimal host sizes for producing male parasitoid progeny were larvae with a maximum body width between 0.57 and 0.70 mm. These results are discussed in terms of maximum potential biological control of the Angoumois grain moth by this parasitoid.

DOI:10.1093/ee/24.5.1160

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

Dispersal distance of the male sweetpotato weevil,Cylas formicarius elegantulus(Summers), was estimated in the field. Two experiments were conducted. In experiment 1, release and capture were replicated 3 times from September to October in the same locality consisting mainly of sweet potato fields. Approximately 8,000 marked males were released and ≈30% of released males were captured by pheromone traps each time. Median dispersal distances per 2 d were 325.7 m in September, 119.8 m in early October, and<50 m in late October. The maximum dispersal distance in September was 500 m, whereas it was 200 m in October. In experiment 2, the dispersal distances were compared in the fields with and without sweet potato plants. The dispersal distance in the field without sweet potato plants was longer than that obtained in the sweet potato cultivated area. The maximum dispersal distance in the fields with sweet potatoes was 500 m, whereas it was 1,000 m in the fields without sweet potatoes.

DOI:10.1093/ee/24.5.1167

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

Field experiments were conducted to determine the effect of forest edge, adjacent to clearings, in reducing the rate of transmission of nuclear polyhedrosis virus among forest tent caterpillar,Malacosoma disstriaHübner, larvae. Caterpillars on trees along a southfacing forest edge, picked up far less virus than did caterpillars on trees in the forest interior, and edge caterpillars died at a slower rate. Reduced transmission is presumed to result from the inactivation of virus by high UV radiation at the forest edge. The pattern of reduced transmission of virus at the forest edge may explain, in part, the pattern of prolonged outbreak of forest tent caterpillar in highly fragmented forests.

DOI:10.1093/ee/24.5.1175

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

The sweetpotato whitefly,Bemisia tabaci(Gennadius) biotype B, was reared on ‘DES 119’ and Pima ‘S-6’ cotton at 31 constant temperatures. Development times of eggs, nymphs, and the combined immature stages were recorded and assembled into frequency distributions at each temperature. From these data, median and mean development times and rates were derived for each life stage, as were temperature-independent distributions of normalized development times. Models describing the rate versus temperature and distributional relationships were constructed. The models can be used to predict life-stage development of populations under fluctuating temperatures. Results are compared with those of other biotypes.

DOI:10.1093/ee/24.5.1179

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

Citrus snow scale development was studied under 9 combinations of constant temperature and relative humidity. An effect of temperature and relative humidity on the rate of development was observed. Optimal temperatures for development ranged between 25 and 38°C and developmental thresholds were estimated at 12°e. There were no differences in developmental time between sexes, nor on values of sex ratio between temperatures. Development on grapefruit leaves reported here was faster than that reported previously for development on lemon fruits. A nonlinear model of development was fit to the stage duration data and a gamma distribution model was fit to the mortality data.

DOI:10.1093/ee/24.5.1189

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

Endophytic fungi living within some grasses have been shown to increase resistance of their host plants to insect herbivores. The hypothesis that endophytes also mediate induced resistance by a grass to an insect herbivore was tested. Perennial ryegrass, both infected and uninfected with the fungal endophyteAcremonium loliiLatch, was artificially damaged by clipping 4 wk after germination. Fall armyworm,Spodoptera frugiperda, J. E. Smith), larvae were fed shoot material of damaged and undamaged plants in a 2-factor (infection status and damage) design. The interaction between the main effects of damage and infection status had a significant effect on pupal mass. Pupae reared on damaged, infected plants weighed less than those reared on undamaged, infected plants. The reverse was tme for uninfected plants. Our results suggest that the endophyte may mediate an induced response by its host grass.

DOI:10.1093/ee/24.5.1196

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

A 3-yr study conducted in small apple blocks (≤0.4 ha) examined the effect of synthetic sex pheromone permeation on trap catches of male codling moth,Cydia pomonella(L. l. at different tree heights. Traps (Pherocon 1CP) were placed above upper canopy, at upper canopy edge, in middle canopy, at lower canopy edge, and below lower canopy. Traps were baited with either a 1-mg or 10-mg codlemone-loaded rubber septum lure (Pherocon), a mating disruption dispenser (Isomate-C), or in some casescaged virgin female codling moths. In the blocks receiving commercially recommended insecticide cover sprays and considering all lure types, the upper canopy edge traps always captured the greatest numbers of male moths, significant in 11 of 18 trials. Similarly, in the presence of mating disruption dispensers (at rates of 1,000 and 2,000 dispensers per hectare) and considering all lure types, the upper canopy edge traps nearly always captured the greatest numbers of male moths, significant in 24 of 28 trials. In the insecticide-treated blocks, the 1-mg lure was the most attractive, but in the pheromone-treated blocks, traps loaded with the 10-mg lure captured the most moths.

DOI:10.1093/ee/24.5.1201

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

The hemlock woolly adelgid,Adelges tsugaeAnnand, is maintained at innocuous population levels in Japan on its 2 native hosts,Tsuga diversifoliaMasters andT. sieboldiiCarriere, by host resistance and natural enemies. The most common enemy associated with infestations ofA. tsugaein Japan wasDiapterobates humeralis(Hermann), an arboreal oribatid mite that inhabits coniferous forests throughout the Northern Hemisphere, where it usually feeds on decaying plant tissues, fungi, algae, and lichens. This mite occurred in 12 of 13 prefectures and at 42 of the 76 sites (55%) that were sampled in Honshu, Japan, from 34 to 37° N latitude and between sea level and 2,100 m elevation. This included 17 of 37 forest sites (46%) and 23 of 37 ornamental sites (62%) where adelgids were present, and 2 uninfested ornamental sites. Laboratory cage experiments revealed thatD. humeralisdid not eat adelgid eggs or nymphs, but rather consumed the woolly filaments that enveloped the ovisacs. However, in so doing 20 adult mites dislodged>95% of the eggs contained within 10 ovisacs from hemlock branches in 7 d. This 2:1 ratio of mites to ovisacs is representative of densities in the field. More eggs were dislodged from ovisacs located along the twig (99%) than from those located at the base of terminal buds (95%), the usual oviposition sites when adelgid densities are high and low, respectively. In a field experiment that simulated effects of egg dislodgment by mites, not a single adelgid was found on any of 4 hemlocks beneath which 2,383 eggs had been placed 16 d earlier. Hatching adelgid nymphs were unable to colonize nearby trees and fell victim to desiccation and generalist predators, mainly ants and spiders that inhabited the forest floor. During the same period 96% of 2,262 adelgids placed directly on 4 other hemlocks successfully colonized the trees.D. humeralisdestroyed 86–94% of adelgid egg masses at all 17 infested forest sites and 99–100% of them at 16 of the 23 infested ornamental sites. Included in this latter group were 2 sites where adelgids had been controlled onT. canadensis(L.) Carriere, a highly susceptible North American species. At the other 7 infested ornamental sites where adelgid mortality ranged from 55 to 83%, mites were abundant and were ravaging egg masses ofA. tsugaewhen trees were 1st sampled. At 2 of these latter sites that were revisited 3 wk later, only 2–3% of the ovisacs were viable and adelgid densities had been reduced by 90–93%. AlthoughD. humeraliswas not a predator ofA. tsugae, it was a highly effective control agent by dislodging adelgids from the trees and killing them as it fed on the woolly filaments surrounding the ovisacs. The wide climatic and environmental tolerance of this mite in Japan, its voracity in consuming the woolly ovisacs ofA. tsugae, its propensity to dislodge adelgid eggs from trees, its ability to reduce adelgid populations to innocuous levels onT. canadensisin Japan, and its harmlessness to other organisms in the environment makeD. humeralisan excellent biological control candidate for North America.

DOI:10.1093/ee/24.5.1207

出版商:Oxford University Press    

年代:1995

数据来源: OUP