摘要:

We investigated by computer simulations and a field experiment the hypothesis that a species assemblage of generalist predators imposes more mortality on prey populations than a single species does. The simulation tracked the energetics of individual spiders feeding on prey in a patchy and variable habitat. Simulation tests showed that increasing the number of spider species and the variability of prey body sizes contributed Significantly to greater prey limitation and spider survival. Higher variability in spider body sizes had the reverse effect and increasing the number of prey species had mixed effects. Large spiders, although less abundant than smaller ones, cropped disproportion ally more prey biomass by capturing large prey and should have injured, thus reduced the capture rate, of smaller spiders. Simulations also showed that as model habitats were fragmented prey biomass dropped, causing a reduction in spider success variables. Increasing fragmentation enhanced the contribution of built-in negative environmental effects on the growth rate of prey. We showed with a factorial field experiment that lower prey biomass resulted from greater spider species richness, as predicted, higher prey richness increased prey biomass only if spiders were present, and habitat fragmentation only decreased prey biomass in the absence of spiders. At equal spider biomass, larger spiders, which were present only in the highest richness treatment, probably fed more than smaller ones. Only larger spiders could capture the largest prey, which represented a greater fraction of the total biomass. Spider predation seemed indifferent to fragmentation.

ISSN:0046-225X    

DOI:10.1093/ee/23.1.1

出版商:Oxford University Press    

年代:1994

数据来源: OUP

摘要:

This paper models the spread of insect populations using stochastic birth-death-migration processes and presents statistical ethodology for predicting population size. A birth-death-migration model for population growth and a stochastic compartmental model for population dispersal are developed and compared with Skellam's (1951, Biometrika 38: 196–218) classic diffusion model. Statistical inferences are based on approximating gamma distributions. The birth-death-migration models have the advantages of incorporating more biological detail, accommodating releases from multiple sites, containing standard errors for predictions, and yielding inherent spatial correlation structure. A special case of the model is illustrated with data on the population dynamics of the Africanized honey bee,Apis melliferaL. The model is very general and has wide application to the range expansion and migration of other species because of its parameterization with generic birth, death, and migration rates.

ISSN:0046-225X    

DOI:10.1093/ee/23.1.18

出版商:Oxford University Press    

年代:1994

数据来源: OUP

摘要:

The alfalfa weevil,Hypera postica(Gyllenhal), is a univoItine species whose primary period of oviposition is during fall and winter in Oklahoma, with hatching typically occuring in late winter and spring. The objectives of this study were to estimate the total number of eggs laid per generation by the alfalfa weevil, the mortality of eggs through the winter, and reductions in numbers of newly hatched larvae resulting from lethal low temperatures. The study was conducted in alfalfa fields located at Stillwater (northern) and Chickasha (southern), OK, from 1980 to 1990. Population densities of eggs and larvae of the weevil were determined at regular intervals from October to May for each generation. Subsamples of eggs were reared for viability estimates. A summation procedure was used to calculate total eggs laid per generation. Mean total egg production per generation exceeded 900 per 0.1 m2at each location. Mortality of eggs averaged about 30% resulting from low temperatures<−15°C). In most years, hatching began before the last occurrence of temperatures below −6°C. These temperatures killed most alfalfa top growth and most larvae that were present. Combined mortality of eggs and larvae hatching during winter resulted in an average reduction of 38% in the reproductive potential for the weevil.

ISSN:0046-225X    

DOI:10.1093/ee/23.1.35

出版商:Oxford University Press    

年代:1994

数据来源: OUP

摘要:

The potential for combining inherited sterility withArchytas marmoratus(Townsend) (Diptera: Tachinidae) to manage the corn earworm,Helicoverpa zea(Boddie) (Lepidoptera: Noctuidae), was examined in the laboratory and in the field. Larvae from crosses of irradiated males with normal females, irradiated females with normal males, and normal males with normal females were exposed to maggots of A.marmoratusin the laboratory and the field. Emergence of parasitoids from larvae of irradiated female and normal male crosses was significantly less than that of larvae from normal parents and of larvae from irradiated male and normal female crosses, but there were no differences between emergence from larvae from normal crosses and irradiated male by normal female crosses. Mortality of unparasitized larvae was greater when male or female parents were irradiated, than when they were un irradiated. Larvae of irradiated parents developed more slowly than did larvae of normal parents; at the time of collection from the field, larvae resulting from irradiated male by normal female crosses were predominantly fourth and early fifth instars, while larvae resulting from normal male by normal female crosses were predominantly late fifth instars. Among larvae resulting from normal crosses, parasitoid emergence was greater from hosts collected as fifth instars than from hosts collected as fourth and early fifth instars. Combining inherited sterility andA. marmoratusmay be feasible for managing the early season population ofH. zea.

ISSN:0046-225X    

DOI:10.1093/ee/23.1.41

出版商:Oxford University Press    

年代:1994

数据来源: OUP

摘要:

Phytophagous insect faunas ofBaccharis salicinaTorr.&Gray,B. pteronioidesDC, andB. bigeloviiGray were studied in the southwestern United States and northern Mexico. Phytophagous insects representing 61 species, 31 families, and seven orders were collected onB. salicina.About 43% of these species were polyphagous; 13% were oligophagous, apparently restricted to the family Asteraceae; and 15% were monophagous, apparently restricted to the genusBaccharis.Sixteen percent of the insects collected were economically important pests. Phytophagous insects representing 55 species, 26 families, and seven orders fed onB. pteronioides.About 25% of the species were polyphagous, 13% were oligophagous, and 2% were monophagous. Phytophagous insects of 32 species, 22 families, and seven orders fed onB. bigelovii.About 28% were polyphagous, 16% were oligophagous, and 13% were monophagous. Months of the year that immature and adult insects were present on the host plant, relative frequency, and associated plant parts are reported.

ISSN:0046-225X    

DOI:10.1093/ee/23.1.47

出版商:Oxford University Press    

年代:1994

数据来源: OUP

摘要:

Male migrant black cutworms,Agrotis ipsilon(Hufnagel), were sampled by pheromone trapping in several locations in the central and northern Corn Belt of North America in the spring of 1985 and 1990. Moths were also sampled in the southern United States at several locations suspected or known to be sources of migrant black cutworms. Forewing length, forewing width, prothoracic width, and body length were measured; and relative darkness of thoracic pubescence was scored for each moth. By comparing the morphology of northern moths (migrants, by definition) with that of southern moths (presumably containing mixtures of migrants and nonmigrants), we hoped to determine whether migrantA. ipsiloncould be distinguished morphologically from nonmigrants. Principal component analyses extracted two important axes from the raw data. The first was a generalsize axis, and the second was primarily a relative-darkness, or color, axis. All analyses were performed on the factor scores along these axes. There was no difference in mean size of northern and southern moths, nor was there a consistent latitudinal gradient in size between northern locations. There was, however, reduced variation in the migrant populations; i.e., very small and very large moths were underrepresented in the northern compared with the southern populations, Comparisons between northern moths thought to have originated in the Brownsville, Texas, region suggested that migrants tended to have lighter coloration than those in the source population. But light coloration by itself cannot indicate migrant individuals because, in one instance (Columbia, MO 1985), a migrant population was darker than populations from all other locations sampled that year, The data indicate that, at least in the case of males, migrants cannot be distinguished morphologically from nonmigrants. The results are consistent with the hypothesis thatA. ipsilonis an obligate migrant and that there is no distinctive migratory phase induced by environmental cues or conditions.

ISSN:0046-225X    

DOI:10.1093/ee/23.1.58

出版商:Oxford University Press    

年代:1994

数据来源: OUP

摘要:

Pitfall traps located between red clover,Trifolium pratenseL., stands and adjacent pasture and woods were used to monitor seasonal and directional crawling activity by adults of four species of root-feeding insect pests of red clover:Hylastinus obscures(Marsham),Calomycterus setariusRoelofs,Sitona flavescensMarsham, andSitona hispidulus(F.). Trapping was conducted at a site in Monongalia County, West Virginia, from May to November 1990, March to December 1991, and April to June 1992. Peak crawling activity byH. obscurusoccurred in June. PeakC. setariusactivity was from June to September. PeakS. flavescensactivity occurred from April to May and from September to November.S. hispidulushad three periods of peak activity: in the spring (April–May), summer (mid-June–mid-July), and fall (September–mid-November). Few directional trends in movement were apparent forH. obscuresandS. flavescens, indicating that their movement by crawling is limited to short distances within or between red clover stands. MostC. setariuswere caught in traps located between the red clover and adjacent woods. Movement into the red clover was primarily from the direction of the woods. During its period of summer activity,S. hispidulusmovement from the red clover was directed toward adjacent woods. During spring and fall, greater numbers ofS. hispidulusadults moved toward the red clover from adjacent woods than from the red clover toward the woods, and movement from the red clover was toward adjacent pasture.

ISSN:0046-225X    

DOI:10.1093/ee/23.1.68

出版商:Oxford University Press    

年代:1994

数据来源: OUP

摘要:

To understand the damage of the sugi bark borer,Semanotus japonicusLacordaire, to larger Japanese cedars,Cryptomeria japonicaD. Don., we inoculated living cedar trees of different sizes with hatched larvae. We also studied the oviposition preference of adult borers to logs of different sizes. Almost all larvae inoculated into larger trees were killed by resin flow between the outer and inner bark; however, in smaller trees, about half of the larvae survived. In the oviposition preference test, female adults tended to attack logs with larger diameters. This suggests that despite the high mortality of the young larvae in the larger cedar trees, adults prefer large diameter trees because the rougher trunk surface presents more suitable hiding and oviposition sites. Bark roughness was considered to determine the occurrence of damage from the sugi bark borer.

ISSN:0046-225X    

DOI:10.1093/ee/23.1.76

出版商:Oxford University Press    

年代:1994

数据来源: OUP

摘要:

We determined the frequency and duration of flight by tarnished plant bugs,Lygus lineolaris(Palisot de Beauvais), on flight mills. An average maximum speed of 0.45 m/s (≍1.6 km/h) was observed during sustained flights. Bugs of prereproductive (

ISSN:0046-225X    

DOI:10.1093/ee/23.1.80

出版商:Oxford University Press    

年代:1994

数据来源: OUP

摘要:

Host-induced ovipositional behavior byLeptinotarsa decemlineata(Say), from Morelos, Mexico, was studied in greenhouse experiments. MorelosL. decemlineatawere unable to oviposit unless fedSolanum angustifoliumMiller, regardless of their larval feeding history. Neither larval nor preovipositional adult feeding on potato,S. tuberosumL., induced oviposition preference for potato. MorelosL. decemlineatahad much lower oviposition preference for potato than Rhode Island beetles, when given potato andS. angustifoliumsimultaneously, and they ceased oviposition immediately after being confined on potato. Encasement of Mexican pupae with Rhode Island pupal exuviae stimulated the emerging adults to oviposit on potato without feeding onS. angustifolium.

ISSN:0046-225X    

DOI:10.1093/ee/23.1.85

出版商:Oxford University Press    

年代:1994

数据来源: OUP