Population and community studies dealing with radiation stress have essentially neglected the mites. When references have been made to the responses of mite populations to ionizing radiation, the form of radiation has almost always been gamma. This study reports results of naturally occurring populations of desert mites, at the Nevada Test Site, to ionizing radiation--largely beta. Eighteen species groups were identified from Berlese samples and tested for stress responses with species diversity indices and analyses of variations in predator-prey ratios. General agreement with previous studies showed a decreasing pattern in these two tests within the controls. This was interpreted as the normal seasonal pattern. The increase of these measurements, within the irradiated sites, was due to large fluctuations in the numbers of a few species groups.

Administration of adrenal steroids or blocking agents at optimum doses influenced northern fowl mite development on chickens. Corticosterone at 20 ppm or desoxycorticosterone at 30 ppm in feed were most effective in inhibiting mite infestations. High levels of social stress increased resistance of chickens to mites in a manner similar to but more effective than steroid administration. The mechanism of resistance was a decrease in capillary density at the skin surface. Commercial laying hens caged alone had lower plasma corticosterone levels and supported more mites than hens caged in groups. Stress-induced, steroid initiated, or inbred mite resistance was incompatible with maximum production from chickens. Resistant chickens produced poorer weight gains and testes mass than did susceptible birds. Sex hormones were shown to play a supplementary, and antibody a minor role in mite resistance. Carbaryl was shown to be the compound most toxic to northern fowl mites of those registered in Virginia for application to poultry. Malathien resistance was noted in mites from a commercial poultry house. The synthetic pyrethroid permethrin was effective against these mites. / Ph. D.

Outbreaks of spider mites (Acari: Tetranychidae) in vineyards have been increasing with the expansion of the industry in Virginia. Only three effective acaricides are registered on grapes and as resistance begins to occur, control options are limited. Biological control of spider mites by inoculative or inundative releases of predatory mites has been tried on a wide range of crops including grapes. This project examined the feasibility of using <i>Neoseiulus fallacis</i> (Acari: Phytoseiidae) as a potential large-scale biological control agent in vineyards. Slide dip bioassays were conducted on <i>N. fallacis</i> to determine the toxicity of insecticides, fungicides and herbicides commonly used on grapes in Virginia. In addition to laboratory experiments, commercially obtained <i>N. fallacis</i> were released in vineyards with spider mite infestations. The populations of both mites were then monitored on a regular basis to determine dispersal and distribution patterns. Among the insecticides tested in the laboratory bioassays, carbaryl, azinphos-methyl, phosmet, cyhexatin, and pyridaben all caused significantly higher mortality than the control treatment. Fungicides tested were not toxic to the predator, but three herbicides caused high mortality. Glufosinate caused 100% mortality after 24 hours and both oxyfluorfen and paraquat had adverse effects on <i>N. fallacis</i>. The use of materials that were found to be toxic to the predator would not be compatible with inoculative releases of <i>N. fallacis</i>. Field release results were variable. Three releases were made in 1999 and 2000., Recovery of the predator was low following the releases at two of the sites, probably due to lack of prey. At the third site enough predators were recovered to analyze the spatial distribution of the predator and prey populations. It appears that there is no similar aggregation pattern between the predator and prey at the same point in time although there is an indication of the predator spreading is response to the prey distribution. A more complete season of sampling would give more conclusive evidence of this trend. Although the distribution of the two populations were dissimilar, the predator was present throughout the season and did spread through the entire plot indicating that the predator may be able to colonize the vineyard if it successfully overwinters. / Master of Science

Yes / In this commentary, we focus on allergy as a facilitating factor in the pathogenesis of alopecia areata (AA). From previous studies on AA, it is well known that subsets of patients can have one or more of; seasonal relapse, comorbid atopic rhinitis, asthma and dermatitis, lesion infiltrating eosinophils and plasma cells, high levels of total IgE, specific IgE for house dust mites (HDMs), and/or disrupted skin barrier function by the evaluation of filaggrin. Allergy and AA share a similar genetic background; both contributing to an immune reaction imbalance. Furthermore, adjunctive treatment with antihistamines, or desensitization for HDM, can reduce the severity of alopecia in atopic AA patients. Therefore, allergies may contribute to the onset and relapse of AA. Identification of an allergic or atopic immune component in AA patient subsets may indicate adjunctive treatment intervention measures against allergies should be taken which may improve the success of conventional AA treatment.

Master of Science / Department of Entomology / David C. Margolies / James R. Nechols / Many crops grown in greenhouses are damaged by the twospotted spider mite, Tetranychus urticae. The predatory mite, Phytoseiulus persimilis, is a commercially-available predator that is commonly used to control twospotted spider mites on greenhouse crops; but its efficacy varies among crops, and it is generally ineffective at low prey densities. In general, predator foraging efficiency depends on how well predators find prey patches, the length of stay in prey patches, and consumption of prey while in prey patches. With respect to P. persimilis, I asked how this predator responds to different prey distributions, as might be encountered at different stages of spider mite infestations. I also asked how components of foraging, namely consumption rate and dispersal tendency, affected predator efficiency. To examine the former, I established T. urticae eggs on 6-leafed cucumber plants in two distributions. To examine the latter, I imposed artificial selection on a population of P. persimilis to create a line that exhibited extremely high consumption and one that demonstrated a greater tendency for dispersal. Subsequently, foraging efficiency was assessed by observing predator oviposition and consumption of twospotted mite eggs on individual leaves of 6-leafed cucumber plants. The number of eggs laid by predators corresponded to the number of prey consumed regardless of predator line. In addition, predators from both lines distributed their eggs proportional to where they fed. However, prey consumption differed between selected lines in response to prey distribution. Predators selected for high consumption fed more on the basal leaf where they were released; whereas prey consumption by the high dispersal and control lines were more evenly distributed throughout the plant. These results contribute to a better understanding of how foraging behavior is modified in plant landscapes under different levels of expression of foraging traits. They also indicate that predator release strategies likely would need to modified in accordance with the kind of foraging trait(s) used in artificial selection programs. In general, my research, when combined with future studies at a broader landscape level, will facilitate decisions by biological control practitioners about whether changes in foraging efficiency resulting from artificial selection justify the cost investment of producing selected lines of P. persimilis

Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Within South Africa (SA) parasites have received variable attention with limited research conducted on mites within the family Trombiculidae. They are regarded as temporary parasites with only the larval stage or “chigger” being parasitic. The present study investigated the diversity, ecology and distribution of chiggers associated with small mammal hosts (rodents and insectivores) across SA, with a focus on the Cape Floristic Region (CFR). The study supports the existence of seasonal occurrence of chiggers in a temperate region. Chiggers that occurred on a generalist rodent host were most prevalent during the warm dry months of the year as opposed to wet cold months. Total counts conducted on the bodies of several co-occurring rodent species in the CFR recorded a diverse assemblage of chigger species. The findings support previous studies in that chiggers are host generalist, though there does appear to be a preference for the most abundant host species, Rhabdomys pumilio, in the biotype. Host species were parasitized by multiple chigger species of which Leptotrombidium muridium was the most abundant species. The study recorded and described three new chigger species (Austracarus n. sp., Microtrombicula n. sp. and Schöngastiella n. sp.). Chigger abundances were found to be higher on reproductively active as opposed to non-active hosts. Twelve chigger species were recorded across SA and the individual species showed variation in extent of their geographic range. On-host distribution of chigger species recorded a preference for the tail area of the host, which was shared by the three most abundant chigger species. This pattern may explain the higher co-occurrence of chigger species than expected by chance that was recorded on R. pumilio. It is evident that chiggers of small mammals are a diverse group that vary spatially and temporary across the landscape. / AFRIKAANSE OPSOMMING: Die verskeie parasiet taksa wat in Suid Afrika (SA) voorkom het ongelyke aandag ontvang tydens parasitologie studies tot dusver. Trombiculidae myte is een van die parasiet groepe wat baie min aandag ontvang het. Die groep myte word beskou as tydelike parasiete, weens die feit dat slegs die larf stadium (ook verwys as “chigger”) van die myt parasities is. Die studie het die diversiteit, ekologie en geografiese verspreiding van chiggers bestudeer wat geassosieer word met klein soogdiere binne SA, met ‘n fokus op die Kaapse Floristiese Ryk (KFR). Die studie het bevind dat chiggers ‘n seisoenale voorkoms het, hul was meer volop tydens die warm droë maande in vergelyking met nat en koel winter maande, soortgelyke resultate is aangeteken in ander dele van die wêreld. Die studie het ook gevind dat die myte wat in die KFR nie gasheer spesifiek was nie, maar dat hul wel ‘n voorkeur getoon het vir die gasheer wat die volopste was, Rhabdomys pumilio. Die verskeie gasheer spesies wat ondersoek was was deur verskillende chigger spesies geparasiteer waarvan Leptotrombidium muridium die mees volopste was. Drie nuwe chigger spesies is beskryf tydens die studie (Austracarus n. sp., Microtrombicula n. sp. and Schöngastiella n. sp.). Die resultate van die studie het ook gedui dat gashere wat reproduktief was hoër getalle myte gehad het wat op hul geparasiteer het in vergelyking met gashere wat nog nie reproduktief aktief was nie. Twaalf chigger spesies was tydens die studie aangeteken, hul het verskil in terme van hul geografiese verspreidings. Die verspreiding van die myte op die gasheer se lyf was ook bestudeer en daar was bevind dat die myte ‘n voorkeur toon vir die stert area van die gasheer. Die verskillende chigger spesies het ook saam voorgekom op ‘n spesifieke aanhegtings plek op die muis se lyf en geen uitsluitings-kompetisie was gevind nie. Die gevolgtrekking van die studie is dat chiggers wat klein soogdiere parasiteer in SA ‘n baie diverse groep is wat verskil ten opsigte van hul geografiese verspreiding asook in terme van in hul seisoenale teenwoordigheid binne die landskap.

Um dos fatores que influenciam o crescimento e desenvolvimento das plantas cultivadas é a presença de plantas de ocorrência espontânea, também conhecidas como invasoras, plantas daninhas ou mato. Estas podem afetar negativa ou positivamente diferentes cultivos em que são encontradas. O efeito negativo usualmente se refere à competição com a cultura por água, nutrientes e luz, proliferação de doenças e pragas, e outros. O efeito positivo se refere à proteção do solo contra erosão, reservatório de agentes de controle biológico e outros. O objetivo do presente trabalho foi determinar a composição da acarofauna plantícola de três culturas e das plantas de ocorrência espontânea a estas associadas, assim como estudar a biologia de duas importantes espécies de ácaros encontradas. As culturas consideradas no estudo foram café (Coffea arabica L.), laranja (Citrus sinensis (L.)) e coqueiro (Cocos nucifera L.). Brevipalpus phoenicis (Geijskes) sensu lato (Tenuipalpidae), um dos principais ácaros danosos ao cafeeiro, foi encontrado nesta cultura, assim como em Amaranthus deflexus L., Panicum maximum Jacq, Richardia brasiliensis Gomes e Spermacoce suaveolens (G. Mey.) Kunthze. Polyphagotarsonemus latus (Banks) (Tarsonemidae), também importante em cafeeiro, foi encontrado em cafeeiro e em C. mucunoides Desv.. Brevipalpus phoenicis s.l. foi o único ácaro muito danoso ao citros encontrado sobre esta cultura. Este foi também encontrado em Digitaria insularis (L.) e Chamaesyce hirta L.. Um dos principais ácaros potencialmente danoso ao coqueiro, Raoiella indica Hirst (Tenuipalpidae), foi encontrado nesta cultura e também em 27 espécies de plantas de ocorrência espontânea. Estudos complementares poderão indicar quais das plantas de ocorrência espontânea estavam realmente servindo de hospedeiros aos ácaros sobre elas encontrados. Além dos ácaros fitófagos, várias espécies de ácaros predadores foram encontradas sobre as culturas consideradas e também sobre várias espécies vegetais de ocorrência espontânea, destacando- se Euseius citrifolius Denmark & Muma e Euseius concordis (Chant), ambos Phytoseiidae. Com isto, se observa que muitas das plantas de ocorrência espontânea podem funcionar como reservatório destes e outros predadores. Os resultados sugerem que o uso do termo erva daninha para as plantas de ocorrência espontânea em cultivos de café, laranja e coco não seja apropriado, tendo em vista que estas plantas abrigam diversas espécies de agentes de controle biológico, especialmente ácaros predadores da família Phytoseiidae. Avaliações em laboratório indicaram a capacidade de R. indica de colonizar as seguintes plantas: Amaranthus spinosus L., Ambrosia artemisiifolia L., Bidens pilosa L., Commelina diffusa Burm, Calopogonium mucunoides Desv, e Leonurus sibiricus L. No entanto, a colonização foi tênue, com a manutenção de poucos indivíduos de diferentes estágios na colônia. Estudos de laboratório também mostraram a possibilidade do desenvolvimento e reprodução deste ácaro em Phoenix roebelenii O\'Brien, planta introduzida no Brasil, comumente utilizada como ornamental, podendo ser importante como reservatório de R indica. Mononychelus planki (McGregor) (Tetranychidae) foi encontrado neste trabalho em nove plantas de ocorrência espontânea, dentre as quais, C. mucunoides. O presente estudo confirmou a importância desta planta na manutenção da população de M. planki no campo em condições naturais. O desenvolvimento e a reprodução do ácaro sobre C. mucunoides possibilita sua sobrevivência, sem que sua população atinja níveis que possam comprometer o desenvolvimento da planta, quando comparado ao que se observa na soja, planta cultivada de introdução relativamente recente no país. / One of the factors influencing growth and development of cultivated plants is the presence of plants of spontaneous occurrence, also known as invasives or weeds. These can negatively or positively affect different crops in which they are found associated with. The negative effect usually refers to competition with the crop for water, nutrients and light, proliferation of diseases and pests, and others. The positive effect refers to soil protection against erosion, reservoir of biological control agents and others. The objective of the present work was to determine the composition of the mite fauna of three crops and of plants of spontaneous occurrence associated to them, as well as to study the biology of two impotent mite species. The crops considered in the study were coffee (Coffea arabica L.), orange (Citrus sinensis (L.)) and coconut (Cocos nucifera L.). Brevipalpus phoenicis (Geijskes) sensu lato (Tenuipalpidae), one of the main mites harmful to coffee, was found on the crop as well as in Amaranthus deflexus L., Panicum maximum Jacq, Richardia brasiliensis Gomes and Spermacoce suaveolens (G. Mey.) Kunthze. Polyphagotarsonemus latus (Banks) (Tarsonemidae), also important on coffee, was found in coffee and on Calopogonium mucunoides Desv. Brevipalpus phoenicis s.l. was the only damaging citrus mite found on this crop. One of the main potentially harmful mites to coconut, Raoeilla indica Hirst (Tenuipalpidae), was found on this crop and also on 27 spontaneously growing plant species. Complementary studies may indicate which of the spontaneously occurring plants actually serve as hosts to the mites found on them. In addition to phytophagous mites, several predatory mite species were found on the crops and also on several spontaneously growing plant species, such as Euseius citrifolius Denmark & Muma and Euseius concordis (Chant), both Phytoseiidae. Hence, many of the plants of spontaneous occurrence can function as reservoir of these and other predators. The results suggest that the use of the term weed for plants of spontaneous occurrence in coffee, orange and coconut plantations is not appropriate, considering that these plants harbor several species of biological control agents, especially predatory mites of the family Phytoseiidae. Laboratory evaluations indicated the ability of R. indica to colonize the following plants: Amaranthus spinosus L., Ambrosia artemisiifolia L., Bidens pilosa L., Commelina diffusa Burm, C. mucunoides and Leonurus sibiricus L. However, colonization was tenuous, with the presence of few individuals of different stages in the colony. Laboratory studies have also shown the ability of this mite to develop and reproduce on Phoenix roebelenii O\'Brien, a plant introduced to Brazil, commonly used as ornamental, which may be important as a reservoir of R indica. Mononychelus planki (McGregor) (Tetranychidae) was found on nine plants of spontaneous occurrence, among which, C. mucunoides. The present study confirmed the importance of this plant in the maintenance of the M. planki population in the field under natural conditions. The development and reproduction of the mite on C. mucunoides allows its survival, without reaching population levels that could compromise the development of the plant, when compared to what is observed in soybean, cultivated plant of relatively recent introduction to the country.

Knowledge of how individual organisms behave in their environment can provide a greater understanding of population dynamics. In a predator-prey system, the choices made by predators when foraging for prey are important aspects of behavior. Particularly in the case of a stage-structured prey population, how the predator selects prey stages once a prey patch has been located can have implications for prey population growth, predator development and fecundity, and predator-prey system dynamics. Predaceous mites of the family Phytoseiidae are important biological control agents of Tetranychus spider mites in agricultural settings worldwide. Phytoseiid species range from specialists that require Tetranychus spider mite prey in order to develop and reproduce to generalist omnivores. In studies with 13 phytoseiid species, specialized species tended to prefer T. urticae eggs as prey or have no prey-stage preference while more generalist species tended to have no prey-stage preference or prey more often on mobile immatures. Further testing with a subset of these species suggested variability among species with regard to genetic and environmental influences on prey-stage preference. The specialist Phytoseiulus persimilis also preferred to forage and oviposit in patches containing egg-biased stage distributions rather than in adjacent mobile immature-biased patches. No benefits to offspring developing in either type of patch were found in terms of developmental time or subsequent adult fecundity. However, the results of both manipulative experiments and nonlinear population models indicated potential benefits of egg-biased predation in terms of current adult female fecundity, a less severe impact of predation on the prey population, and an increased number of predator descendents during the predator-prey interaction. Considering both subjective factors and discriminant analyses, prey-stage preference performed well as an indicator for the ecological classification of phytoseiid species. The classifications of four phytoseiid species occurring on apple in central and eastern Oregon, USA, were evaluated accordingly. / Graduation date: 2004

During summer of 1998 and 1999, 34 and 10 vineyard sites, respectively, were sampled to assess spider mite pests and associated biological control by phytoseiid mites. Vineyards studied spanned five major valleys in western Oregon where grape production occurs. Leaf samples were taken from site perimeters and centers. One leaf was taken every ten meters of border length, five meters inward from the border to prevent wind-biased or extreme edge effects, while 20 leaves were taken at regular intervals from centers. Variables recorded at each site were: plant age, grape variety, chemical spray information and local vegetation occurring in proximity to vineyards. Sites were categorized as either agricultural or riparian based on what surrounding vegetation type was in the majority. Several parametric and non-parametric tests were used to analyze data, including multiple linear regressions using a computer-based genetic algorithm in conjunction with the AIC criterion to pre-select a subset of explanatory variables. Typhlodromus pyri was the predominant phytoseiid mite and Tetranychus urticae was the most abundant tetranychid mite sampled. High levels of T. urticae were found when predator densities were very low, and low levels of T. urticae occurred when predator densities were moderate or high. Phytoseiid densities were highest in June and July, while T. urticae densities were highest from August to September. The latter's densities were significantly higher in vineyards surrounded primarily by agriculture, while phytoseiid densities were not significantly different between the two categories. Predatory phytoseiids had significantly higher densities on vineyard edges, while T. urticae densities were higher in vineyard centers. Caneberry, cherry and grape habitats appeared to be sources of predator immigration, while no vegetation type consistently served as a short-range or nearby immigration source for spider mites. Due to insufficient data, pesticide information was not included in multiple linear regression models, although certain chemicals used in vineyards can potentially impact mite populations. Impacts of surrounding vegetation type, grape variety, regional location, plant age, and presence of other mites on phytoseiid and T. urticae densities are discussed. / Graduation date: 2001

Intra- and interplant movement and dispersal of the predator mites Neoseiulus californicus (McGregor) and Neoseiulus fallacis (Garman) were studied on both lima bean (Phaseolus lunatus L.) and apple (Malus pumila Miller) branch plant systems that were seeded with excess numbers of the spider mite Tetranychus urticae Koch. Individuals of either predator were randomly selected from colonies of well-fed, mixed-age adult females and moved to test plants. When tested separately in each plant system, median leaf positions of N. californicus from the point of release were greater than those of N. fallacis at 1-8 d. A fan placed in front of a common source unit (1x3m) containing T. urticae and near equal densities of both predaceous mites, provided continuous air (wind) to 3 isolated receiver units located 2.5, 5, and 7.5 m downwind. Receiver units consisted of continuous bean foliage with excess T. urticae, but no predators. Wind speeds at the source and each receiver unit averaged 2.2, 0.9, 0.4, and 0.03 m/s respectively. As predators eliminated prey, N. fallacis dispersed earlier at higher prey densities and further downwind than N. californicus, but cumulative densities of each predator in all receiver units were alike after 20 d. Results of both plant movement studies supported the hypothesis that N. californicus has dispersal traits more like those of a generalist predator of spider mites than does N. fallacis. Spatial patterns of dispersal and biological control of pest mites are discussed in relation to predation types within the Phytoseiidae. / Graduation date: 1997