摘要:

Induced resistance in soybean was investigated using mechanical injury and herbivory by the soybean looper,Pseudoplusia includens(Walker), as inducing factors. Dual-choice feeding-preference tests with the Mexican bean beetles,Epilachna varivestisMulsant, were used to assess the induced resistance. Comparisons of leaves from plants treated by mechanical injury, soybean looper herbivory, and application of soybean looper larval regurgitate on mechanically wounded leaf surfaces revealed that herbivore-feeding injury was a better inducer than mechanical injury. The regurgitate of soybean looper larvae may contain factors that enhance induction of resistance. Tests using various types of mechanical injury as inducing factors showed that the level of induced resistance depended on the total number of wounded cells in contact with healthy cells and not on the total amount of plant tissue lost. We suggest that there is a positive correlation between the intensity of the inducing factor and the level of resulting resistance in soybean. Interplant transfer of inducing signals was tested, but no evidence was found that such transfer occurred.

DOI:10.1093/ee/19.6.1852

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

Two of four sweet corn plantings, each with a broad spectrum of weed abundance in plots 3 rows by 6 m, showed a positive relationship of ear infestation by European corn borer,Ostrinia nubilalis(Hübner), with total weed biomass sampled 5 wk after corn seedling emergence. The relationship was more apparent with wider row spacing (91 versus 76 cm) and without cultivation. With the dominant weedsDigitaria sanguinalis, Panicum dichotomiflorum, Amaranthus retroflexus, andChenopodium album, linear regression showed an increase from about 20% ear infestation in weedless plots to about 40% infestation in plots with 2,000 kg/ha above-ground dry weight of weeds at week 5 postemergence. The effect may vary with weed species, and the data show a stronger correlation with forb abundance than with grasses. Sweet corn growers would profit economically by avoiding weedy areas of fields when partial harvests are undertaken in infested plantings.

DOI:10.1093/ee/19.6.1858

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

Sesbania punicea(Cav.) Benth. is a perennial legume that has become a weed of major importance in South Africa. Until recently,S. puniceawas colonized by only one insect herbivore of any consequence, an introduced apionid weevil species,Trichapion lativentre(Beguin-Billecocq). The vegetative growth and reproductive capacity ofS. puniceawas shown to be significantly lower on plants at sites colonized byT. lativentrethan on plants at sites without the weevils. However, these initial comparisons did not account for the extraneous effects of intersite differences, and additional analyses have been undertaken to determine the actual effects of the weevils on the weed. Regression models showed that between 77 and 83% of the variance in vegetative growth (leaflets, rachides, and stems) ofS. puniceawas explained by the presence of weevils, by their history of colonization, and to a lesser extent, by the density of the weevils, expressed as cumulative weevil-days. Kruskal-Wallis tests showed that the weevils also almost completely nullified the reproductive capacity of the plants by destroying nearly all of the flower buds. The results confirm that the suppression of plant growth was attributable, almost entirely, to weevil herbivory and that, in moderate to dense infestations of the weed,T. lativentreis equally effective as a biological control agent, regardless of site characteristics such as the spacing, height, or size of the trees.

DOI:10.1093/ee/19.6.1866

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

Two species of European parasites,Agathis pumila(Ratzeburg) andChrysocharis laricinellae(Ratzeburg), have become established in a classical biological control project against the larch casebearer,Coleophora laricella(Hübner), in Oregon. A coarse analysis of population dynamics over 18 yr, including the periods before the population changed and as it changed, is presented for 13 plots. A detailed life table analysis over 9 yr is included for 3 of the plots. In the 10 yr before combined parasitism by introduced parasites exceeded 10%, moth density on the 13 plots averaged 52.6 per 100 buds, and parasitism was the key factor influencing population change on only 1 plot. As introduced parasites increased over the next 8 yr, however, moth density declined to 0.8 per 100 buds.A. pumilawas the key factor on all 3 plots for which a detailed life table analysis was conducted. Mortality byA. pumilaappeared to be delayed density-dependent. In the most advanced plots, mortality of larvae caused byA. pumilaseems to be stabilizing moth numbers at low density. Final evaluation, however, awaits further long-term measurements.

DOI:10.1093/ee/19.6.1873

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

Field surveys and published data revealed that at least 42 species of insects use yellow starthistle as a breeding host in southern Europe. Twelve of these species are newly reported to feed on the plant. A high percentage of these species are in the orders Coleoptera, Lepidoptera, and Diptera and are monophagous endophages associated with the capitulum. The guilds associated with yellow starthistle in southern Europe consist of capitulum-infesting species; endophages in the stems, rosette foliage, and roots; and ectophages on leaves and stems. At least five monophagous species that attack the capitulum in different ways could potentially be used in a biological control program in the United States.

DOI:10.1093/ee/19.6.1882

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

Sixexotic parasites,Trichogramma atopaviriliaOatman&Platner,Allorhogas pyralophagusMarsh,Cotesia flavipesCameron,Macrocentrus prolificusWharton,Digonogastra kimballiKirkland, andPediobius furvus(Gahan), were colonized in commercial corn fields in the Texas High Plains againstDiatraea grandiosellaDyar from 1985 to 1987. Colonization sites were monitored to estimate parasitization, dispersal, and parasite overwintering.D. kimballi, an external parasite of late instars, dispersed farther than other species and was the only parasite to demonstrate a propensity for overwintering. The pupal parasite,P. furvus, was capable of causing seasonal parasitization as high as 50.0% within 10 m of the colonization locus and showed the strongest numerical increase. The egg parasite,T. atopovirilia, caused 33.6% parasitization within 2 m of the colonization locus but was not recovered at greater distances. Parasitization byA. pyralophagus, which attacks medium sized larvae, never exceeded 3.6% in any year of the study. Seasonal parasitization ofC. flavipes, a parasite of late instars, was 0.0–14.5%, but the potential of this parasite as an effective natural enemy ofD. grandiosellais limited by apparent encapsulation in the hosts and inability to overwinter. The polyembryonic larval parasite,M. prolificus, was not recovered during the 3-yr study. An aggregative response to host density was not detected for any of the parasites. The results of this study suggest thatD. kimballimay be able to establish in the Texas High Plains, and thatP. furvusmay have potential as a biological control agent in a seasonal inoculative or inundative approach.

DOI:10.1093/ee/19.6.1889

出版商:Oxford University Press    

年代:1990

数据来源: OUP

DOI:10.1093/ee/19.6.1903

出版商:Oxford University Press    

年代:1990

数据来源: OUP

DOI:10.1093/ee/19.6.1905

出版商:Oxford University Press    

年代:1990

数据来源: OUP

DOI:10.1093/ee/19.6.1906

出版商:Oxford University Press    

年代:1990

数据来源: OUP

DOI:10.1093/ee/19.6.1911

出版商:Oxford University Press    

年代:1990

数据来源: OUP