University of Minnesota, Duluth
AgEcon Search - Research in Agricultural & Applied EconomicsNot a member yet
211830 research outputs found
Sort by
Systematics and bionomics of predaceous and phytophagous mites associated with pine foliage in California: II. Population dynamics of mites on three species of pines in the forest falls area of the San Bernardino Mountains
No full textSeasonal and annual changes were determined in species composition and population densities of phytophagous and predaceous mites on three species of native pines (Pinus coulteri, P. lambertiana, and P. ponderosa) in the San Bernardino Mountains. Population trends were recorded for the Phytoseiidae, Tetranychidae, and Tenuipalpidae. Four species of tetranychids of the genus Oligonychus were present, one species of phytoseiid, Metaseiulus validus, and the tenuipalpid, Brevipalpus sp. Mite numbers were generally lowest from January to March. Predaceous mites gave a positive numerical response to increases in tetranychid population
Biological and systematic studies of developmental stages in Aphytis (Hymenoptera: Aphelinidae): III. Meconia as a possible systematic tool in Aphytis
No full textWithin-plant distribution of predators on cotton: Comments on sampling and predator efficiencies
No full textWithin-plant distribution of four predators found in California cotton fields is described. Adult stages of all predators were found in greatest frequency in the terminal portions of the plant, and, within that region, adults tended to be more common on fruiting parts than the same species of larvae. In general, the smaller predators, Geocoris and Orius, were found higher on the plant than the larger predators Cbrysopa (larvae) and Nabis. Their respective areas of activity corresponded to the location of suitably sized (stages) prey. Those predators closest to the plant terminal were more effectively sampled with the standard University of California sweepnet
Ecology of Rhopalomyia californica Felt (Diptera: Cecidomyiidae) and its parasites in an urban environment
No full textThe ecology of an endemic gall midge, Rhopalomyia californica Felt, and its larval parasites was studied over a 3-year period in the city of Davis, California. Six species of parasites were associated with larvae of the midge: Torymus koebelei (Huber), T. baccharidis (Huber), Platygaster california (Ashmead), Zatropis capitis Burks, Mesopolobus sp., and Tetrastichus sp. However, the midge was from four to ten times more abundant in Davis than in the endemic environment. In Davis, neither parasitization by any given species nor by the aggregate of species was a consistent regulating factor. These results suggest that, whereas parasite guilds in urban environments may be structurally similar to their non-urban counterparts, adequate or comparable levels of natural biological control of the host will not necessarily result. Thus, the use of native plants in urban environments may not always minimize attendent pest problems. The data obtained provide some empirical support for multiple-species introductions in classical biological control and illustrate the utility of facultative secondary parasites. A method for assessing competitive interactions among parasites before introduction is described, and the relevance of the theory of r- and K-selection to biological control is assessed
Pink bollworm control in southwestern desert cotton: III. Strategies for control: An economic simulation study
No full textA simulation model for pink bollworm (PBW) and cotton was developed, field validated, and incorporated into an industry sponsored regional PBW management program for southwestern desert cotton. The PBW model differs from earlier versions in its incorporation of stochastic development, the expansion of the concept of physiological time to include nutritional influences of the cotton host on larval development, and its ability to simulate the kinds of data typically collected by pest control advisors when monitoring cotton for pink bollworm
Effect of Pesticide Treatments on Nontarget Organisms in California Rice Paddies: I. Impact of Triphenyltin hydroxide: II. Impact of Diflubenzuron and Triflumuron
No full textAn application of triphenyltin hydroxide at 1.16 kg (AI)/ha to rice fields for stem rot (Sclerotium oryzae Catt.) control resulted in a significant reduction of 57% of the invertebrate taxa and 67% fewer individuals based on two collecting methods that sampled the nekton, neuston, and benthon. Populations of herbivores, carnivores, and filter feeders were sharply reduced after treatment, and most remained so through the 28th day following application. By day 50 many of the winged species recovered in both numbers and diversity. However, recovery of benthic organisms was slower or not at all for most Crustacea. An initial reduction followed by a strong resurgence was noted for the mosquito Culex tarsalis Coq., which was probably due to the significant reduction of five predaceous species
Lumber grade recovery in a circular-saw mill in California
No full textThis report tells small mill operators the grades of lumber they can expect from ponderosa and sugar pine logs of varying size and quality grown in the Sierra pine region
Lumber grade recovery from a second-growth pine operation in California
No full textThe results of this study show that a system of simple log grades based upon surface characteristics may be useful in working with second-growth ponderosa pine grown at medium elevations. Such log grades can provide a basis for improved appraisals of both logs and standing timber by enabling a more accurate prediction of probable lumber grade recovery. In the study area there appeared to be little benefit from grading logs with scaling diameters of less than 14 inches by the particular system used. Above this diameter, however, the differences in lumber grade recovery between log grades increased rapidly
Plant-parasitic nematodes associated with forest trees in California
No full textAs a first step in assessing the importance of plant-parasitic nematodes to California forestry, soil and root samples were taken from 32 kinds of trees in the major forested areas of California. Ninety-seven percent of the 228 samples were from conifers, and 82 percent were from trees important in the lumber industry, mainly ponderosa and Jeffrey pines, coast redwood, Douglas fir, and red fir. In the rhizosphere of these trees, 97 described and 54 undescribed, species of plant-parasitic nematodes in 46 genera were found. Species varied with climate and kind of tree. Most common overall were Criconemella annulata, Xiphinema californicum, Gracilacus epacris, Pratylenchus macrostylus, Rhizonema sequoiae, Sphaeronema californicum, Trichodorus californicus, Tylenchorbyncbus cylindricus, Filenchus vulgaris, Meloidogyne sp., and Ditylenchus anchilisposomus. These nematodes were often present in large numbers and it is likely that parasitism by some species constitutes one of the stresses to California forest trees
