摘要:

We examined the effects of strip-intercropping soybean,Glycine max, and sorghum,Sorghum bicolor, on rates of insect parasitism and fungal disease incidence in larvae of the green cloverworm,Plathypena scabra(F.), a widespread and occasionally serious pest of soybeans, during an endemic year. A completely randomized design with two cropping systems (monocropped soybean and soybean intercropped with sorghum), two sorghum heights (dwarf sorghum ≈1 m in height; tall sorghum ≈2 m in height), and two row patterns (2 rows of sorghum alternating with 10 rows of soybean; 6 rows of sorghum alternating with 6 rows of soybean) was used. Abundance (number per row-meter) ofP. scabralarvae, rates of larval parasitism and incidence of the entomopathogenic fungus,Nomuraea rileyi(Farlow) Sampson did not differ significantly among treatments or their interaction. Soybean yield (grams dry weight of beans per row-meter) did not differ significantly among treatments but sorghum grain yield and biomass (grams dry weight per row-meter) were significantly lower in dwarf sorghum planted in wide rows because of competing weed populations. Results suggest that neither the accrual ofP. scabralarvae in soybean nor the impact of the parasitoid-pathogen complex onP. scabramortality is affected by structural or taxonomic agroecosystem diversification at the scale studied. n

ISSN:1754-5692    

DOI:10.1093/ee/24.2.253

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

We conducted studies to examine distributional patterns of adultBemisia tabaci(Gennadius) strain B (also referred to asBemisia argentifoliiBellows&Perring) in cotton,Gossypium hirsutum L., and to develop and validate a sequential sampling plan for estimating population density. Adults were consistently more abundant on mainstem leaves from the top stratum of cotton plants than on mainstem leaves from the middle and bottom strata. Counts on mainstem leaves from the top of the plant also had the lowest relative variation. Adults on the top stratum of the plant were fairly uniformly distributed over leaves from mainstem nodes 2–7 (terminal = node 1), but numbers of adults were highest and least variable on fifth-node leaves. Patterns of aggregation, as measured by Taylor's power law, did not differ among the top, middle, and bottom strata of cotton plants and were similar among the first six mainstem leaves below the mainstem terminal. Ratios between counts of adults on individual leaves from the top stratum of the plant and whole plant counts were variable and averaged (± SD) 0.075 ± 0.071. Based on fifth mainstem node leaves as the sample unit, we used Kuno's and Green's methods to develop fixed–precision sequential sampling plans. The underlying mean-variance models for these methods and performance of the sequential stop lines were compared and evaluated using a resampling simulation of independent data sets with means ranging from 2 to 50 adults per leaf. Compared with lwao's mean crowding regression, Taylor's power law was a less biased predictor of variance. As a result, Green's plan, on average, achieved the desired precision better than Kuno's plan even though neither plan consistently gave mean estimates with the desired precision. Further simulations provided preliminary adjustments in the stop lines for field implementation.

ISSN:1754-5692    

DOI:10.1093/ee/24.2.261

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

Genetics of host–related Feeding and ovipositional behaviors of the Colorado potato beetle,Leptinotarsa decemlineata(Say), were described, comparing a population from Morelos, Mexico, and a population from Rhode Island, United States. Traits studied were larval feeding acceptance, oviposition ability, and oviposition preference. A preliminary attempt to select for potato intolerance in larval feeding in the Morelos population reduced feeding acceptance of potato after three generations. Host-related difference between the populations in oviposition ability could be explained by inheritance of as few as one gene or two genes with epistasis, suggesting that major genetic change in at least one locus was involved in the original host expansion ofL.decemlineatafrom native hosts to potato. Significant dominance by genome from the Rhode Island population was expressed by hybrids in both feeding acceptance and oviposition preference. Results were used to develop a working hypothesis to explain genetic mechanisms responsible for the original host expansion ofL.decemlineatato potato.

ISSN:1754-5692    

DOI:10.1093/ee/24.2.278

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

Bacillus thuringiensisBerliner val.kurstakiis used extensively in aerial sprays for control of forest defoliators such as gypsy moth,Lymantria dispar(L.), and western spruce budworm,Choristoneura occidentalisFreeman. Although the short half–life ofB. thuringiensisin the field is believed to minimize its impact on nontarget Lepidoptera, there is increasing concern over the immediate and long-term effects of the widespread aerial application of this microbial insecticide. We examined the toxicity and persistence ofB. thuringiensistoward larvae of tree-feeding swallowtail butterflies (papilio glaucus L.andp. canadensisRothschild&Jordan) and the promethea moth,Callosamia promethea(Drury), on seven of their natural host plants.B. thuringiensisapplied to trees at a rate of 40 BIU/ha with a backpack sprayer equipped with a rotary atomizer nozzle (Micronair) was toxic to early and later (fourth) instars, regardless of the host the larvae were feeding on. Long–term persistence ofB. thuringiensison potted tulip trees placed in exposed or below–canopy locations was monitored at 0, 10, 20, 30, and 40 d after the spray. Toxicity toward early–instarp. glaucuspersisted for up to 30 d in 1992 and 1993 field studies. Survival on trees sprayed withB. thuringiensistended to be lower in below–canopy locations, but differences were not always significant. The results of these studies indicate thatB. thuringiensissprays are toxic to some nontarget lepidopterans for at least 30 d after the spray.

ISSN:1754-5692    

DOI:10.1093/ee/24.2.288

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

Paper wasp,Polistes hebraeus(F.), nests appear to serve as reservoirs of fungi. Eighty-nine fungal isolates were obtained from larvae and meconia of this wasp collected on La Réunion Island. Thirty-one fungal genera were recovered and at least 52 species identified. These numerous molds and yeasts survive or grow as saprophytes in excreta; among them two genera were predominant,AspergillusandPenicillium. This mycoflora which is spread in the environment when the nest breaks up contains potentially entomopathogenic and phytopathogenic fungi,Aspergillus flavus, Aspergillus tamarii, Paecilomyces farinosus, Alternaria alternata, remaining viable after passing through wasp intestines.

ISSN:1754-5692    

DOI:10.1093/ee/24.2.298

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

ClonalRhopalosiphum padi(L.) were reared on oats,Avena sativaL., that were either healthy or infected with the PAV strain of barley yellow dwarf Iuteovirus (BYDV). Alate aphids of known posteclosion age were tethered in a wind tunnel and exposed to air speeds of 1 m/s. Flight durations, wingbeat frequencies, and the posteclosion age of maiden flight were recorded. Both viruliferous and nonviruliferousR. padithat begin their maiden flight through the posteclosion age of 40 h appear to exhibit similar tethered flight behavior, including flight duration and the earliest age that maiden flight can commence. Viruliferous aphids older than 40 h had maiden flights of shorter duration than did their younger viruliferous counterparts. Nonviruliferous aphids maintained about the same average length of flight duration for all ages in which flight occurred. The oldest postec1osion age at which an aphid began its maiden flight was 65 and 88.7 h for viruliferous and nonviruliferous aphids, respectively. Wingbeat frequencies ofR. padiwere independent of the age at which maiden flight began and were unaffected by the presence of BYDV. These findings suggest that there is a broader window of opportunity for nonviruliferousR. padito aerially move long distances than their viruliferous counterparts.

ISSN:1754-5692    

DOI:10.1093/ee/24.2.306

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

The specific mechanisms of host plant resistance in alfalfa,Medicago sativaL., to the spotted alfalfa aphid,Therioaphis trifolli f. maculata(Buckton), remain unknown despite three decades of research. Difficulties with Painter's commonly used concept of host plant resistance were avoided when the Salt/Doutt paradigm of host selection by a parasite was used instead. Mechanisms of host plant resistance proposed in the literature were reviewed with respect to this alternative concept. Published results on the effects of host plant resistance are not comparable across different studies because of arbitrary measurements used. This problem is avoided with the use of laboratory age-specific life tables. In this study, four alfalfa cultivars were tested for host plant resistance to the spotted alfalfa aphid at three temperatures, and the statistical tools needed for the analysis are presented. Theintrinsic rate of natural increase(rm) was used as the measure of aphid performance on each cultivar. At the same temperature,rmvalues of the spotted alfalfa aphid on susceptible plants were significantly higher than on resistant cultivars. A developmental threshold of 7.9°C was estimated from the data, and the optimal temperature for growth and reproduction of this aphid was ≈21°C. Life tables of two successive generations of the spotted alfalfa aphid on a resistant cultivar indicated that aphids do not transmit the capacity to overcome resistance in a simple Mendelian fashion. A mechanism involving the random transmission of internal symbionts required by this aphid to overcome alfalfa resistance is hypothesized.

ISSN:1754-5692    

DOI:10.1093/ee/24.2.313

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

Feeding activity, growth, and survival of soybean looper,Pseudoplusia includens(Walker), larvae fed foliage from nonnodulating soybean,Glycine Max(L.) Merrill, plants supplied with different rates of nitrogen (N) fertilizer were examined. Foliage was obtained from the non–nodulating isoline ‘Lee’ soybean beginning at the V8 growth stage (46 d after planting) and continuing through initiation of bloom. Plants were grown in pots fertilized with four sequential applications of five rates of N fertilizer (5.25, 21, 42, 84, and 168 kg N/ha as NH4NO3) and from nonfertilized plants. These six treatments resulted in foliage N concentrations that ranged from 10 to 33 mg/g dry weight and chlorophyll concentrations that ranged from 0.5 to 1.7 mg/g fresh weight (51–50 d after planting) during the feeding bioassay. Foliage from nonfertilized control plants and those fertilized with 5.25 and 21 kg N/ha were low in N(≤12 mg/g) and caused 100% mortality when fed to soybean looper larvae. Foliage from plants fertilized with 42 kg N/ha contained 17 mg N/g dry weight and resulted in moderate levels of mortality (55%), whereas the higher N rates (84 and 168 kg N/ha) resulted in foliage N concentrations of 22 and 33 mg/g dry weight and ≥90% survival. Although the highest three foliage N concentrations were sufficient for survival of soybean looper larvae, differential effects on development of larvae were observed. Greater number of stadia, lengthened duration of the larval development period, and greater foliage consumption were observed with each reduction in foliage N from 33.4, to 22.4, to 16.9 mg/g, but ultimately, similar maximum larval weights were achieved. These three factors appear to be mechanisms tbat allow the soybean looper to compensate for reduced N and may explain how this species maintains itself on such a wide range of hosts (73 plant species in 29 families) including noncultivated species.

ISSN:1754-5692    

DOI:10.1093/ee/24.2.326

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

Winter and spring habitats of the twospotted spider mite,Tetranychus urticaeKoch, were investigated to determine the source of mites infesting seedling cotton crops. The two possibilities were that mites may overwinter in diapause in the soil or litter of cotton fields or they may overwinter on suitable vegetation. Few mites were found in litter or soil collected from fallow cotton fields in winter. Significant numbers of diapause mites were found in litter at only 2 of 15 sites. At one of these sites the abundance of mites in litter declined dramatically following cultivation. The cotton crops at these two sites were late maturing and, therefore, more mites may have been induced to diapause because of cooler temperatures, shorter days, and possibly lower food quality than at other sites where more typical, earlier maturing crops were grown. The contribution of mites that overwinter in the soil or litter of cotton fields to infestations on the subsequent cotton crop is not likely to be significant. Vegetation from within and from the borders of fallow cotton fields and from sites remote from cotton (>1–km distance) were examined for presence of mites in winter and spring. Remote sites were further classified as adjacent to permanent water (wet) or not (dry). Nondiapausing mites, actively feeding and reproducing, were found on a wide range of plant species (37) in the vicinity of cotton fields in winter and spring. Natural senescence of these plants in spring probably forces mites to disperse, often onto young cotton seedlings nearby, resulting in a pronounced edge effect in cotton fields. Mite abundance on weeds was far lower at dry remote than at cotton sites, possibly caused by the lack of a continuous sequence of hosts. Mite abundance at wet remote sites was intermediate between cotton and dry remote sites, probably because they provide a continuity of hosts for mites. Management of the weeds on cotton farms through winter/spring could potentially reduce levels of mite infestation of cotton seedlings in the following season.

ISSN:1754-5692    

DOI:10.1093/ee/24.2.332

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

Heliothis virescens(F.) is a polyphagous pest on cotton, soybean, and tobacco andH.subflexais a monophagous nonpest onPhysalisspp. Oviposition choices of the reciprocal F1hybrids or these two species were compared with those of the parental strains to determine Sex linkage, quantify niche breadth, and rank host preferences. Strains ofH.virescens, H.subflexa, and the reciprocal F1hybrids (SVoand VSo) were each, offered a choice of four plants on which to oviposit (cotton, soybean, tobacco, andPhysalis angulata). Host preferences were ranked based on the proportion of eggs laid on each hostH.virescensoverwhelmingly preferred tobacco,H.subflexapreferredPhysalis, and SVoand VSopreferred tobacco. There were no significant differences among strains in their responses to cottOn and soybean. Because SVoand VSohad similar patterns of preference across hosts, there was no indication or Sex linkage. Niche hreadth, a measure of the degree of specialization, was calculated for each strain. Under greenhouse conditions,H.cirescenshad the narrowest ovipositional niche andH.subflexaand the hybrids had broader niches and were similar to each other. When a novel host (Oenotherasp.) was offered to the strains, there was 110 difference in the responses among strains nor were there changes in preference ranks or diet breadth. The hybrid, despite a major genetic reorganization relative to the parents, did not behave in an unpredictable way.

ISSN:1754-5692    

DOI:10.1093/ee/24.2.341

出版商:Oxford University Press    

年代:1995

数据来源: OUP