摘要:

In a 2-yr study, population densities of and damage by second-generation European corn borer,Ostrinia nubilalis(Hübner), larvae were compared among corn plantings containing or lacking different weed communities. Treatments were corn without weeds, corn principally with broadleaves, corn principally with grasses, and corn with a mixture of broadleaves and grasses. In both years, larval density (number of larvae per corn plant) and damage (number of tunnels per corn plant) were significantly lower in treatments with broadleaves than in treatments without broadleaves. Larval density was significantly lower in treatments with grasses than in treatments without grasses in 1989. The broadleaf × grass interaction was significant for larval density in 1989, and significant for damage in both years. Although natural enemies ofO. nubilalismay be more abundant and effective in weedy corn, the presence of weeds, particularly grasses, attracts adult moths to cornfields, which may result in larger infestations of corn and greater damage. In addition, weeds may harbor other pests of corn and compete with corn for nutrients and water, leading to reduced yields.

DOI:10.1093/ee/20.1.276

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Spurgia esulaeGagné (=Bayeria capitigenaBremi of Solinas&Pecora), a multivoltine gall midge recorded onEuphorbia esulain Italy, was selected as a candidate for the biological control of leafy spurge (Euphorbia esulaL. “complex”) in North America. Its potential host range was studied in 1982 at Rome, Italy, and in 1984 at Albany, Calif., using populations associated withEuphorbia esulafrom San Rossore near Pisa, Italy. Of 56 plant species or varieties in 22 families tested at the Rome laboratory, the midge oviposited and completed its life cycle only on plants in the genusEuphorbia(subgenusEsula). In the tests conducted in Rome, complete development occurred on five populations of North American leafy spurge (from Montana, Nebraska, North Dakota, Oregon, and Saskatchewan) and on EuropeanE. peplusL.,E. cyparissiasL.,E. myrsinitesL.,E. characiasL.,E. serrulataThuillier, and onE. lathyrisL. from Chico and Castro Valley, Calif. Of 12 native North AmericanEuphorbiaspecies tested at Albany in 1984, four species in the subgenusEsula(E. incisaEngelmann,E. palmeriEngelmann,E. robusta(Engelmann) Small, andE. spathulataDe Lamarck) supported the complete development ofS. esulae. The restricted host range suggested use of this midge as a biological control agent against leafy spurge in North America. Releases ofS. esulaewere made in Montana in 1985 and in North Dakota in 1986; this species became established in both states.

DOI:10.1093/ee/20.1.282

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Storage of pupae ofAnticarsia gemmatalisHübner in a freezer maintained at −20°C for 150–250 d did not affect the ability of the chalcididBrachymeria ovata(Say) to recognize them as hosts. Odors from live and freezer-stored pupae elicited significant olfactory and behavioral responses byB. ovata. When offered either 10 live pupae or 10 freezer-stored pupae,B. ovataparasitized significantly more (about twice as many) of the live pupae. However, when offered both five live and five freezer-stored pupae together,B. ovataparasitized, on the average, 16 times more of the live pupae. When presented with a choice between a freezer-stored pupa and a live pupa using a Y tube olfactometer,B. ovatashowed a significant olfactory preference for the live pupa. When presented with a choice between a freezer-stored pupa and a blank cell,B. ovatawas attracted to the freezer-stored pupa. Approximately the same length of time was required forB. ovatafemales to locate a live pupa as that required to locate a freezer-stored pupa when each pupal type was offered alone.

DOI:10.1093/ee/20.1.288

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

A field experiment addressed four questions concerning the interaction betweenMicroplitis croceipes(Cresson) andHeliothisspp.: (1) what is the relation between the proportion of hosts parasitized and host density? (2) does this relation depend on the size of the areas (spatial scale) at which it is measured? (3) what is the relation between parasitoid search rate and host density? and (4) what is the relation between parasitoid distribution and host distribution? To answer these questions a cotton field was artificially infested with various densities ofHeliothis virescens(F.).M. croceipeswas released uniformly across the field. At the scale of 30 by 60 m plots, the proportion of hosts parasitized byM. croceipes(adjusted for competition with other parasitoid species) increased from 0.41 ± 0.08 (x± SE) to 0.60 ± 0.06 as host density increased from 6,178 to 16,896 larvae/ha. The calculated search rate (area searched per parasitoid per unit time) ofM. croceipeswas independent of host density, and the density dependence in parasitism byM. croceipescould be explained completely by density dependence in adult female distribution. Natural populations ofCardiochiles nigricepsViereck andCotesia marginiventris(Cresson) parasitized 9 and 7%, respectively, of the hosts collected. At the scale of plots, parasitism byC. nigricepsincreased with host density, but parasitism byC. marginiventriswas independent of host density. At the scale of 1 by 2 m quadrats, parasitism by all species was independent of host density. We discuss the implications of these results for biological control ofHeliothis virescensandHelicoverpa zeaand for theories of parasitoid foraging and population regulation.

DOI:10.1093/ee/20.1.292

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Although considerable study ofChysolina quadrigemina(Suffrian) andC. hyperici(Forster) has occurred in California, Australia, and Canada, these species have not been thoroughly studied in Idaho or the Pacific Northwest. Northern Idaho populations of the two leaf beetles were sampled periodically from four (three grassland and one forest meadow) sites infested with St. Johnswort during 1985 and 1986. The egg was the dominant overwintering stage at most sites and most larval feeding took place in the spring and early summer. Beetle population levels and trends varied from site to site.C. quadrigeminawas the dominant species in the grassland sites;C. hypericidominated in the forested site. The bronze color morph ofC. quadrigeminadominated over the other color morphs at all sites where it was present. Populations ofAgrilus hyperici(Creutzer) (Coleoptera: Buprestidae) also were sampled periodically from the same four St. Johnswort infestations during 1985 and 1986. Adults emerged during late May through July. Eggs were laid during July. The proportion of stems infested with eggs at the four sites ranged from 0 to 92%. However, mean larval numbers were always less than one per plant. Live and dead plants contained live larvae. Nearly one-half of the dead plants at one site had once been infested. Based on the larval infestation levels observed (live larvae and adult exit holes), particularly in dead plants, it appears thatA. hypericihas contributed significantly to St. Johnswort suppression in Idaho. Annual grasses (i.e.,Bromusspp.) and weedy forbs (i.e.,Centaureaspp.) constitute the major replacement vegetation at most of the St. Johnswort infested study sites in northern Idaho.

DOI:10.1093/ee/20.1.303

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

The sunflower moth,Homoeosoma electellum(Hulst), a major pest of commercial sunflower in North America, is susceptible toBacillus thuringiensisBerliner. Besides being used as a biological insecticide, theB. thuringiensisendotoxin gene may be used to create transgenic sunflower (Helianthus annuusL.). Acute and chronic effects and resistance to the pathogen were evaluated in two populations of the sunflower moth. A susceptible sunflower moth population and a laboratory-selected,B. thuringiensis-resistant population did not differ in mortality, developmental periods, pupal weight, female/male ratios, or fecundity whenB. thuringiensiswas not present. However, when larvae were reared on diets treated withB. thuringiensis, the susceptible population had a significantly greater mortality, especially of females, than did the resistant population. Sublethal effects on the susceptible population included reduced pupal weights and lowered fecundity in surviving females. In the resistant population, females were not more likely to die than males, and egg deposition was normal when larvae were treated withB. thuringiensis. Under present cultivation conditions, management ofB. thuringiensisuse in sunflower is not needed to prevent the development of aB. thuringiensis-resistant sunflower moth.

DOI:10.1093/ee/20.1.316

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Behavior of the weevilNeochetina eichhorniaeWarner, a specialist herbivore, varied with leaf age of waterhyacinth (Eichhornia crassipes(Mart.) Solms-Laubach [Pontederiaceae]). In the field, adult feeding decreased as the leaves aged. Accrued feeding damage on 8-d-old leaves was only about 60% of the sum of two respective sets of 4-d-old leaves. Likewise, on 40-d-old leaves the accrued feeding damage was only 21% of that from 10 successive 4-d-old sets. Laboratory studies confirmed a preference for the youngest tissue available and discounted the influence of leaf arrangement. The weevils preferred unfurling bud leaves by a 5-fold margin over open immature leaves. Olfactometer studies showed a 2.4-fold greater attraction to young leaves than to mature leaves. Further, adult feeding exhibited under-dispersed patterns on young leaves but random distributions on old leaves. In contrast, a generalist, the yellow woollybear,Spilosoma virginica(F.), preferred mature waterhyacinth leaves and 14-d-old larvae weighed 85% less when provided young leaves instead of mature leaves. The youngest leaves were higher in N, P, K, and Mg, but low in Ca and Mn compared with older leaves. Total phenolics (compounds reduced by Folin reagent) were also highest in young tissue, but analyses of leaf extracts by thin-layer chromatography and high-performance liquid chromatography showed lowest concentrations of phenolic compounds in the youngest leaves. These data suggest that natural plant products, not necessarily phenolics, attract the weevils to young tissue and stimulate them to feed, especially at sites of previous injury. These constituents also might deter generalists likeS. virginica, forcing them to consume only mature foliage.

DOI:10.1093/ee/20.1.323

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

The efficacy ofBangasternus orientalisCapiomont against its hostCentaurea solstitialisL. was determined at two different sites (low and high elevation) in California over a 2-yr period. Host plant and weevil phenology were delayed at the high elevation site. Consequently, the initiation of secondary flower buds (high elevation site) was extended well into November, long after the ovipositing adult weevil population had expired. More than 50% of the egg-bearing test heads did not become infested with mature pupae because of larval mortality. After seed reduction by the weevil, 70% of the seeds remained in the test heads. Our data suggest thatB. orientalisappears to be ineffective by itself as a biological control agent of yellow starthistle in California.

DOI:10.1093/ee/20.1.335

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

A spore shower technique was used to test four species of aphid-derived entomophthoralean fungi,Pandora neoaphidis(Remaudière&Hennebert) Humber,Zoophthora radicans(Brefeld) Batko,Conidiobolus thromboidesDrechsler, andConidiobolus coronatus(Constantin) Batko, against the cereal aphids,Diuraphis noxia(Mordvilko) andMetopolophium dirhodum(Walker). Six endemic and five foreign isolates of the four fungal species were tested. There was variability in virulence among different isolates and species of the fungi and in susceptibility between the two aphid species. Low LC50's (i.e., high virulence) were produced with twoC. coronatusisolates (2.2–4.0 spores/mm2), threeC. thromboidesisolates (2.3–13.2 spores/mm2), and twoP. neoaphidisisolates (1.4–8.1 spores/mm2). TwoZ. radicansisolates exhibited moderate virulence with LC50's ranging from 25.1 to 46.8 spores/mm2. Two isolates ofC. thromboidesthat had been in long-term storage displayed relatively low virulence. Aphid colonies on leaves were more suitable for bioassays than aphids confined in wire mesh inoculation chambers. The latter were disadvantageous. because the aphid movement within the chamber adversely affected the determination of fungal inoculum exposure rates. These conditions also often induced the production of resting spores instead of primary conidia.

DOI:10.1093/ee/20.1.338

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Survival ofMicroplitis croceipes(Cresson) adults exposed to residues of insecticides applied at recommended rates to cotton was measured in 1989. In unsprayed check treatments, survival was 91.4% after 24 h. The organophosphates profenofos and acephate and the new-generation pyrethroid bifenthrin were highly toxic toM. croceipes. All other compounds tested showed some selectivity, including esfenvalerate, cypermethrin, thiodicarb, oxamyl, dicrotophos, dimethoate, and cyhalothrin in order of decreasing survival. The effectiveness ofM. croceipesas a biocontrol agent of the bollworm and tobacco budworm might be improved through selective use of insecticides to which the parasitoid is tolerant.

DOI:10.1093/ee/20.1.346

出版商:Oxford University Press    

年代:1991

数据来源: OUP