Thesis (MSc)--Stellenbosch University, 2000. / Full text to be digitised and attached to bibliographic record. / ENGLISH ABSTRACT: The cultivation of citrus in the Vaalharts region is a fairly recent development. With the introduction of this crop, an insect pest complex has also developed in this region. The presence of these pests was studied in eleven orchards, planted with three citrus cultivars and of varying ages, distributed in the 300 square kilometer cultivation area. Each orchard was inspected for the presence of pests by making use of two weekly sampling techniques. Ten of the most important insect pests of citrus in the Vaalharts region are briefly described by refering to their general appearance, life cycles, feeding and pest status and economic threshold. For every pest various control options, including operational systems, crop cultivation, biological and chemical control, are discussed and, where applicable, illustrated by means of graphic presentations. The seasonal presence of the cirtrus pests in the Vaalharts region is tabulated and discussed individually. With these details as background, an insect pest management programme for citrus in the Vaalharts region is compiled. / AFRIKAANSE OPSOMMING: Die verbouing van sitrus in die Vaalhartsgebied is 'n redelik onlangse ontwikkeling. Gepaard met die nuwe gewas het daar ook 'n insekplaagkompleks in die gebied ontstaan. Die voorkoms van die plae is in elt .boorde, beplant met drie sitruskultivars en van verskillende ouderdomme, verspreid in die 300 vierkante kilometer verbouingsareaal, bestudeer. Elk van die boorde is weekliks ondersoek vir die aanwesigheid van plae deur van twee moniteringstegnieke gebruik te maak. Die tien belangrikste insekplae van sitrus in die Vaalhartsgebied word kortliks beskryf deur na hulle algemene voorkoms, lewenssiklus, voeding en plaagstatus en ekonomiese drempelwaardes asook die moniteringsmetodes wat gebruik is, te verwys. Vir elke plaag word beheeropsies, wat operasionele stelsels, gewasverbouing, bloloqlese en chemiese beheer insluit, bespreek wat, waar toepaslik, aan die hand van grafiese voorstellings gemustreer word. Die seisoenale aanwesigheid van die sitrusplae word in 'n tabel aangedui en individueel bespreek. Met die gegewens as agtergrond is 'n insekplaagbestuurprogram vir sitrus in die Vaalhartsgebied opgestel.

published_or_final_version / Botany / Master / Master of Science

published_or_final_version / Ecology and Biodiversity / Doctoral / Doctor of Philosophy

No description available.

No description available.

6 pp.

A three-part study was conducted to characterize and assess the impact of subterranean termite infestation of urban structures in Tucson, Arizona. A termite control questionnaire was administered to all Tucson-based pest control firms offering termite control services, of which 52 percent responded. Twelve study sites were established in and around the city, with toilet paper rolls serving as termite bait at each site. In addition, 5943 active termite control contracts were accessed from Tucson's largest pest control company, and analyzed with accompanying data from various sources including those pertinent to structure location, construction, treatment history, and surrounding soil types. An estimate of over $3 million for gross annual income derived from commercial termite control services performed in Tucson, was calculated from questionnaire responses. Termide (heptachlor + chlordane) was the most frequently used termiticide. Approximately 45 percent of commercial termite control jobs were performed with Termide, the principal termiticide used by 85.7 percent of companies offering termite control services. Gnathamitermes perplexus (Banks) was most prevalent in the toilet paper rolls at bait sites, followed by Heterotermes aureus (Snyder) and Reticulitermes tibialis Banks. G. perplexus infested bait at sites that resembled the surrounding desert while H. aureus and R. tibialis generally infested those which had been significantly altered by irrigation and landscaping. H. aureus and, to a lesser degree, R. tibialis, are by far the most economically important of the 18 termite species inhabiting Tucson and the surrounding area. Significant interrelationships were found between termite contract density, customer affluence, housing density, structure age, and soil permeability, and also between retreatment rate, foundation type, and materials used in wall construction. The percentage of structures under contract requiring retreatment was estimated to be between 17.3 percent and 42.7 percent per year. Analysis utilizing termite control contracts is suggested as a unique and effective approach providing critical insight into factors influencing termite communities and patterns of infestation in the urban environment.

Field studies of population of Geocoris and Nabis indicated that the density of adult Nabis was higher than Geocoris before April, but the reverse was true after April. In general, the abundance of adults and nymphs of each species was caused by alfalfa harvesting, dispersal of adults, discrepancies of sweep-net sampling, differences in mortality of eggs and the differences in the diapause termination of adults. The field cuttings of alfalfa reduced populations of both species, but adults were reduced more than the nymphs. In laboratory studies adults and nymphs of each species fed on each other on alfalfa in small cages, but in larger cages when only adults were caged, interspecific predation of adults did not occur. This suggests that, in the field, interspecific predation of nymphs can be more prevalent than adults of each species since nymphs which are more sedentary than adults are less affected by alfalfa cuttings. A number of predatory insects other than Nabis that were common in the alfalfa, such as Chrysopa carnea Stephens, Orius tristicolor (White), Hippodamia convergens Guerin, and Sinea confusa Caudell, were also found to prey upon Geocoris in the laboratory. Hyalomya aldrichii Townsend was the only parasite reared from Geocoris adults and nymphs from the field. The parasite did not numerically respond to the density of Geocoris and had minor impact on the population of the predator. The host preference of this parasite among the Geocoris spp. and between Geocoris and Nabis was not determined since rearing the parasite in the laboratory failed. Telenomus sp. parasitized groups of Geocoris eggs exposed in alfalfa fields. In the laboratory, it parasitized both G. pallens and G. punctipes eggs. Rearing the parasite at 30(DEGREES)C resulted in poorer emergence of adults than at 20(DEGREES)C and 25(DEGREES)C. Predaceous insects that synchronize with populations of Geocoris, larger in size then Geocoris, especially Nabis and Sinea spp. may be more important than parasites in regulating population of Geocoris in the field.

This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

Reprinted June 1, 1937