Specialist and generalist phytoseiid mites are widely used for biological control of spider mites. Understanding dispersal attributes of these mites is important to implementing more stable, cost-efficient integrated pest management. In this regard, we studied dispersal of phytoseiid mites from a local ambulatory phase of movement within a prey patch to a longer-range phase that includes emigration (aerial take-off and dispersal distance) and immigration to a new plant. Specialist phytoseiids showed higher ambulatory and aerial dispersal than generalist species. Somewhat different dispersal strategies were seen between Neoseiulus fallacis (more specialized predator) and N. calfornicus (more generalized predator): The most important difference was earlier and continuous dispersal of N. californicus from a prey patch. Cues from spider mite infestation suppressed the dispersal rates for specialists, but either increased or did not change the dispersal rates for generalist phytoseiids. Aerodynamic calculations support the hypothesis that Phytoseiulus persimilis may not require a standing take-off behavior to become airborne. However, with less vertical profile, a mite may become airborne more by standing erect (N. fallacis), than a species that does not show standing take-off (N. calfornicus). Jumping behavior by P. persimilis was observed for the first time among Phytoseiidae. Falling speed ranged from 0.4 to 0.73 m/s for 13 phytoseiid species and 0.79 to 0.81 for two-spotted spider mite. These values were quite similar to theoretical estimates for specialist phytoseiids, but less for generalists. From falling speed estimates and other morphological data, it was possible to predict aerial dispersal distance of phytoseiids using analytical models. After landing on bare soil following aerial dispersal, high mortality of N. fallacis was observed in the field during summer. Distance from the landing point to target plants showed negative log linear relationships. Soil surfaces and management actions influenced survival and recovery. Environmental conditions greatly affected survival of the predator. We speculated that phytoseiids that fell on ground were moving to the target plants via both ambulatory and aerial means. / Graduation date: 2001

We identified and evaluated a phytoseiid predator as a biological control agent of multiple spider mites pests that occur in ornamental nurseries. When comparing species, Neoseiulus fallacis (Garman) had a wider prey range than Galendromus occidentalis (Nesbitt), a higher probability of overwintering than Neoseiulus califomicus McGregor and was equally or more effective at suppressing spider mites than either of the other 2 phytoseiids in 4 field tests. To further evaluate N. fallacis we 1) measured prey range when held with 29 ornamental pests or alternative foods under laboratory conditions, 2) tested biological control of spider mites on representative plant species at both small and large spatial scales, 3) developed release and conservation strategies of the predator, and 4) examined the efficacy of the predator in controlling recently introduced pests. Neoseiulus fallacis had greatest survival and reproduction when feeding on spider mites but eriophyid mites, other mites and pollen enhanced survivorship and, in some cases, reproduction. When inoculated into ornamental plants, spider mite suppression was "acceptable" in 81% of small scale tests and-in all large scale tests. Limitations in control occurred in tall, vertical growing plants with little foliar canopy. Inoculation of N. fallacis at low prey densities into apple rootstocks was successful at suppressing Tetranychus urticae Koch and similar to control achieved at moderate prey densities. In small scale banker plant studies, high densities of adult and immature mites of N. fallacis were produced and moved downwind to receiver plants. In field tests with receiver plants placed at greater distances, only N. fallacis adult females readily dispersed to 30 m or more. When comparing overwintering survival of adult females among plant types, N. fallacis survived most on conifers, intermediate on evergreen shrubs and least on herbaceous perennials, deciduous shrubs and shade trees. Covering plants with protective plastic reduced overwintering survival of the predator. Neoseiulus fallacis successfully suppressed the newly introduced pests Panonychus citri (McGregor) and Schizotetranychus celarius (Banks) on Skimmia japonica Thunberg and Sasaella hidaensis (Makino and Uchida), respectively. Initial studies suggest that N. fallacis can be an effective biological control agent of multiple spider mites in low-growing and selected higher-growing ornamental plants. / Graduation date: 2000

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

The two-spotted spider mite (TSM), Tetranychus urticae Koch, is an important pest of many greenhouse and field crops worldwide. The development of resistance in TSM populations to chemical acaricides, allied with public health concerns about pesticide residues, has motivated the search for alternative control measures to suppress the pest. Hyphomycetous fungi are promising agents for mite control and the fungus Beauveria bassiana (Bb) (Balsamo) Vuillemin was investigated in this study as a biocontrol agent. The principal objectives of this study comprised: a) screening Bb strains for their pathogenicity against T. urticae; b) testing the effect of adjuvants on the efficacy of Bb; c) studying the effect of plant type on persistence of Bb and the efficacy of control of Bb against T. urticae; d) evaluating the field efficacy of Bb applications against T. urticae; e) testing the compatibility of Bb with selected fungicides; and f) assessing the synergy between Bb and soluble silicon for T. urticae control. Screening bioassays of sixty-two strains of Bb identified the two most effective strains, PPRI 7315 (R289) and PPRI 7861 (R444), that caused mortality levels of more than 80% of adult mites at 9 d post-inoculation with 2 × 108 conidia ml-1. These strains performed significantly better than the Bb commercial strain PPRI 5339, in laboratory bioassays. The two strains also attacked mite eggs, causing 53.4% and 55.5% reduction in egg hatchability at 2 × 108 conidia ml-1 respectively. However, PPRI 7861 showed relatively higher production of conidia in culture and was, therefore, selected for further trials under greenhouse and field conditions. Greenhouse evaluations of the effects of two adjuvants (Break-thru® and a paraffin oil-based emulsion) on efficacy of Bb demonstrated a higher efficacy of the biocontrol agent (BCA) when it was applied with Break-thru® or the oil solution than with water alone. Moreover, Bb conidia applied in Break-thru® solution resulted in greater control of TSM than conidia applied in the mineral oil. There was also a dose-response effect and the control of TSM by Bb increased when the concentration of conidia was increased. The control of TSM by Bb in beans (Phaseolus vulgaris L), cucumber (Cucumis sativus L.), eggplant (Solanum melongena L.), maize (Zea mays L.) and tomato (Solanum lycopersicum L.) was tested in greenhouse trials. On these crops, the persistence of conidia declined over time. The rate of decline was significantly higher on maize. However, TSM mortality was positively correlated with the amount of conidia deposited on leaves immediately after spraying, rather than their persistence over time. Higher levels of mortality of TSM due to Bb application were observed on beans, cucumber and eggplants, suggesting that the type of crop must be taken into consideration when Bb is applied as a BCA. Field efficacy of Bb against mites was evaluated in two trials on eggplants. Based on assessment of population densities of mites and leaf damage assessments; both trials showed that the strain PPRI 7861 controlled TSM in the field. Two commonly used fungicides, azoxystrobin and flutriafol, were investigated in vitro tests on culture medium and laboratory bioassays on detached bean leaves (Phaseolus vulgaris L.) for their effects on Bb. Azoxystrobin (a strobilurin) was less harmful to Bb while flutriafol was found to be inhibitory. Another important finding of this study was the substantial enhancement of Bb efficacy by soluble silicon. When Bb was combined with soluble Si, the control of TSM was better than when either of the two products was applied alone. Moreover, application of soluble Si as a plant fertilizer in hydroponic water nutrient increased accumulation of peroxidase, polyphenoloxidase and phenylalanine ammonia-lyase enzymes in leaves of plants infested with TSM. Increased activity of these defense enzymes in leaves deters feeding behaviour of mites. We suggested that feeding stress renders them susceptible to Bb infection, which would explain the synergy observed between the two agents. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.