摘要:

Patterns of relative densities of a dominant leafmining species,Camerariasp. (agrifoliellaBraun group), on eight trees ofQuercus emoryiTorrey were documented over five growing seasons. Relative abundances tended to remain constant among trees throughout the five growing seasons, and densities were consistently greater in the shaded regions of trees than in the sunny regions. To test the hypothesis that variation in leaf size affects colonization, dispersion, and survival ofCamerariasp., equal numbers of leafminers were introduced into field enclosures and allowed to colonize branches varying in mean leaf size. Densities of leafminers were lower and dispersion was more aggregated on small-leaved branches than on large-leaved ones. Mortality of larval leafminers was either inversely density-dependent or density-independent at the spatial scale of the branch. However, log linear analysis showed that survival of leafminers was a negative function of clumping of leafminers among and within leaves. Small-leaved branches and trees appear to be less susceptible to leafminer attack because adult females deposit fewer eggs overall, and eggs are more frequently laid singly on leaves of inadequate size for development or are more frequently clumped on leaves with competing conspecifics. It is suggested that variation in leaf size, coupled with variation in other morphological and phenological traits, acts as a ceiling on densities ofCamerariasp. on Emory oak at the study site by altering dispersion such that interference and exploitative competition increase.

DOI:10.1093/ee/20.1.196

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Food source had a significant effect on development time ofGlischrochilus quadrisignatus(Say) from neonate larva to adult, with the shortest mean developmental time of 41.2 d on multiple-species rearing diet (MSRD)and longest mean of 63.4 d on sap beetle diet (SBD). Pupae that developed on MSRD were heaviest, followed by those on SBD, apple (Malus domesticaBorkh), and tomato (Lycopersicon esculentumMill.). Percentage survival from neonate larva to adult differed significantly among food sources. Survival to adult was highest on MSRD. Females fed on MSRD, SBD, and apple produced significantly more eggs than on tomato. Beetles survived significantly longer on MSRD and apple than on SBD. Highest mortality occurred on tomato. The adult sex ratio on both artificial diets conformed to a 1:1 ratio. However, on natural foods, males were significantly more abundant than females.G. quadrisignatusreared on any food resulted in population increases of from 20.0- to 71.3-fold after each generation. MSRD proved to be the most suitable food for rearingG. quadrisignatus.

DOI:10.1093/ee/20.1.205

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Soils from 351 sites representing ecologically diverse habitats from six Hawaiian Islands (sea level to 4,200 m) were assessed for entomopathogenic nematodes using theGalleriabaiting technique. Twenty-four sites (6.8%)were positive for entomopathogenic nematodes. Twenty-two sites (6.3%) were positive for aHeterorhabditissp. from the islands of Kauai (6), Oahu (5), Maui (4), Molokai (1), and Hawaii (6), and two sites were positive for aSteinernemasp. from Maui. No entomopathogenic nematodes were recovered from soils on the island of Lanai. Heterorhabditids were highly correlated with ocean beaches within 100 m of seashore (0 m elevation). These positive sites had soils containing sand grains from coral and shells with moderately alkaline pH (8.0) and low organic content (12%). The steinernematid isolates came from inland areas in silty clay and silt loam soils with higher organic content (15–35%).

DOI:10.1093/ee/20.1.211

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Since its invasion of eastern Ontario during the late 1960s, damaging outbreaks of the alfalfa weevil,Hypera postica(Gyllenhal), have recurred at frequent intervals. The most recent of these surfaced in 1985, when larval populations in the Bay of Quinte dairy belt increased to 5.9 per stem. Details of population change during the 5-yr period (1983–1987) that spanned the rise and fall of the outbreak were recorded in life tables. Origins of the outbreak were attributed to weather conditions in the spring of 1982, when heavier than normal precipitation provided highly optimal conditions for conidiation inZoophthora phytonomi(Arthur), the principal regulator of weevil populations. This led to severe epizootics, causing numbers of the weevil to plunge to record low densities in the following year. These densities were too low to support efficient mobilization and spread of disease inocula, and dry weather in two successive springs (1983 and 1984) inhibited conidiation. These factors triggered a sharp rebound in weevil survival rates and evoked two step-wise population increases to outbreak levels. The outbreak lasted for 2 yr but lost momentum when abundant spring rainfalls in 1985 and 1986 set the stage for epizootics to recur. Because of lag effects in their response to change in host numbers, adult parasitoids played only a secondary role in terminating the outbreak.

DOI:10.1093/ee/20.1.217

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

The biology ofGalendromus helveolus(Chant) (Acari: Phytoseiidae) was, studied usingEotetranychus sexmaculatus(Riley) (Acari: Tetranychidae) as the food source. Larvae developed to protonymphs without feeding. The total developmental times ofG. helveoluswere 12.36, 9.66, 5.63, 4.61, and 4.84 d at 18, 20, 25, 30, and 32°C, respectively, at 76% RH. A higher percentage of eggs (32%) did not hatch and higher larval mortality (37%) occurred at 32°C. The intrinsic rates of natural increase (rm) at 16, 20, 25, 30, and 32°C were 0.100, 0.153, 0.286, 0.327, and 0.144, respectively. The optimal temperature range forG. helveoluswas considered to be between 25 and 3O°C. The sex ratio ofG. helveoluswas strongly female biased (females/total = 0.82).G. helveoluswas able to survive and reproduce onPanonychus citri(McGregor),Eutetranychus banksi(McGregor), andTetranychus urticaeKoch (Acari: Tetranychidae) with a daily rate of oviposition of 2.21, 1.96, and 2.25, respectively, compared with 2.37 when fed onlyEotetranychus sexmaculatus. Females ofG. helveoluswere observed to feed and survive for 10 d onPhyllocoptruta oleivora(Ashmead) (Acari: Eriophyidae), but no eggs were laid. In addition,G. helvelousprotonymphs and deutonymphs were observed feeding onP. oleivora. A low percentage of the predator eggs (8%)was able to develop to the adult stage onP. oleivoracompared with 82% when providedEotetranychus sexmaculatusand 70–80% when providedPanonychus citri, Eutetranychus banksi, orT. urticae.

DOI:10.1093/ee/20.1.224

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Canopy and bidirectional Malaise traps were used to estimate the flight activity of northern corn rootworms,Diabrotica barberiSmith&Lawrence, and western corn rootworms,D. virgifera virgiferaLeConte, above the plant canopy and at the lateral boundaries of cornfields. Capture of beetles in both types of traps was greatest during pre- and post-flowering intervals, particularly for northern corn rootworms, indicating increased flight activity in response to changes in habitat quality. Based on comparison of ratios of northern/western corn rootworms in the field with those ratios in traps, northern corn rootworm beetles were generally more active at field boundaries than western corn rootworm. There were marked differences in flight activity between males and females and between reproductively immature and mature females of both species. In general, Malaise traps captured a greater number of males and canopy traps a greater number of females in relation to their abundances in source fields. In comparison with source field populations, a greater number of western, but not northern, corn rootworm females captured in canopy traps had immature ovaries, suggesting that vertical movement may represent the initiation of migratory flight. Bidirectional trap results suggest that northern corn rootworm females move from cornfields when silks and pollen become unavailable and later return to fields for oviposition. Comparison of field data with computer simulations for both species suggested that there was substantial emigration from the early-planted field and that most of the beetles in the late-planted field were immigrants. Seasonal trends in flight activity tend to reflect these patterns; however, data from bidirectional Malaise traps-failed to provide strong evidence of greater emigration over immigration in the early-planted field or an opposite trend in the late-planted field. Overall, flight activity measured in passive traps at field boundaries may be a poor index of site-specific patterns of beetle movement, especially for western corn rootworms.

DOI:10.1093/ee/20.1.230

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Movement patterns of japanese beetle,Popillia japonicaNewman, and European chafer,Rhizotrogus (Amphimallon) majalis(Razoumowsky), grubs as influenced by gravity, host plant position, and external disturbances were studied in laboratory soil–turfgrass microcosms. Second through third instars just before pupation were monitored using radiographic techniques. Neonates were monitored using destructive sampling. Results demonstrate significantly different movement patterns between species and among age groups. The development stage of the grub had a large effect on Japanese beetle grub behavior and a measurable, but lesser effect, on European chafers. All larval stages of European chafers and all larval stages of Japanese beetle, except neonates and postoverwintering third instars, displayed a downward movement in response to disturbance. Neonate Japanese beetles showed little movement while postoverwintering. Japanese beetles moved upward when disturbed. European chafer grubs of all age classes displayed random vertical movement with some arrestment in or near sod. Preoverwintering and postoverwintering third-instar chafers showed less dramatic arrestment behavior than other instars tested. Second-instar Japanese beetles behaved similarly to European chafers; however, third instars behaved very differently. All third instars except those tested in late winter and early spring showed some innate downward movement in the soil microcosms. Japanese beetles tested in late winter displayed random movement with some arrestment in sod, whereas those tested in early spring exhibited upward movement and arrestment in sod.

DOI:10.1093/ee/20.1.241

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

A simulation model was developed to increase understanding of how varietal resistance and predation may affect sugarcane borer,Diatraea saccharalis(F.), populations on an areawide basis. The model includes the processes of immature development, oviposition, host-dependent mortality, and mortality due to arthropod predation. Varietal parameters in the model were obtained from replicated small-plot evaluation trials. Percentages of bored internodes were used to compare survival of sugarcane borers from the egg stage until establishment in the stalk among sugarcane cultivars with and without predator suppression. A relative survival index was used to estimate survival among cultivars, from establishment in the stalk until pupation. Simulations showed that differences in moth emergence and total emergence would be greatest in the absence of adult exchange among varieties. These studies indicated that the impact of susceptible varieties on sugarcane borer populations might be mitigated if these varieties are dispersed among varieties with greater resistance. Varietal differences observed in small-plot varietal evaluations were substantially magnified during simulations when the amount of adult redistribution among varieties was reduced. Based on this research, data obtained from small-plot varietal resistance studies alone may not adequately address the potential impact that such varieties, when grown on larger acreages, might have on pest populations.

DOI:10.1093/ee/20.1.252

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Studies in a hemlock plantation and in four hemlock forests in Connecticut revealed that hemlock woolly adelgid,Adelges tsugaeAnnand, severely reduced the growth and survival ofTsuga canadensis(L.) Carriere, which had a major impact on the subsequent performance and population dynamics of this insect. The presence of adelgids at all but relatively low densities (93% of the adelgids produced in each of the subsequent 3 yr became sexuparae; in the fourth year only sexuparae were produced. Density-dependent production of the unsuccessful sexuparae played a major role in the decline ofA. tsugaepopulations on their deteriorating host.

DOI:10.1093/ee/20.1.258

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

The spatial and temporal foraging dynamics of western harvester ant colonies,Pogonomyrmex occidentalis(Cresson), in a shrub–steppe ecosystem in southwestern Wyoming were studied. Ant foraging was spatially organized by permanent trunk trails that were formed by workers traveling in corridors between shrubs. An exponential decline was observed in forager flows with distance along trails, a pattern which changed when foragers were recruited to experimental seed patches. Trails also differed in seasonal forager activity and the seed species returned by ants. Soil surface temperature was a significant contributor to variation in forager departure rates in 70% of the 48 samples taken across months and colonies during the 2-yr study. Densities of soil seeds in the foraging areas ofP. occidentaliscolonies were significantly correlated with seasonal ant activity levels. The composition of forage returned by ants differed seasonally and according to daily changes in surface temperature.

DOI:10.1093/ee/20.1.265

出版商:Oxford University Press    

年代:1991

数据来源: OUP