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

The life history, temperature, humidity, and feeding requirements of the phytoseiid predator mite, Typhlodromus americanus Chant and Yoshida-Shaul were tested in the laboratory. Occurance of the mite in the field during different times of the year was investigated as well. Effects of temperature and humidity on egg hatch, the feeding requirements of the larvae, the amount consumed by each life stage, the length of each life stage and suitability of different food sources were investigated in the laboratory. The use of the mite as a biological control agent was evaluated by using the information gained from the laboratory experiments. T. americanus was originally discovered in plantation grown Douglas-fir in western Oregon. Since that time the mite has been found on a number of other hosts throughout North America. The mite is active year round in the Christmas tree plantations of the Willamette Valley in Oregon. The adult is found in or near the one year old bud scars and the eggs are typically deposited there also. Life parameters were measured providing a net reproductive rate of 4.23, a mean generation time of 24.45 days, and an intrinsic rate of increase of 0.059 The intrinsic rate of increase was low when compared to other predator mites and numerical response to prey increase would not be possible with such a low rate. The optimal temperature for the shortest eclosion time (54.4 hr.) and the highest survival (96.4%) was 26��C. The regression of temperature vs. time to hatch gave a 90% R�� with both the slope and intercept significantly different from zero. Humidities above 70% had survival rates over 96% and eclosion rates in the range of 50-58 hours. The relative humidity at which 50% of the population died was 58.6%. The mite was found to feed readily on the pest mite Oligonychus ununguis (spruce spider mite), as well as Tetranychus urticae (two spotted spider mite), and corn, oak, and Douglas-fir pollens. The larval form of the predator mite does not require food to molt to the protonymph, but the protonymph does require food to molt. If water is provided the entire time from egg to death, the protonymph can survive about ten days. Females consumed more Tet. urticae than males in both the immature and adult stages. The T. americanus that were fed corn pollen and Tet. urticae (complete diet) lived for over 115 days. Mites raised on oak and corn pollens did not survive as long (only 70-80 days), and those raised on Douglas-fir pollens did not reach adulthood. Egg production was observed on the complete diet, but not on the diets of pollen. The largest number of eggs were laid around the twelfth day after the molt to adult. Control and management of field conditions to improve habitat for T. americanus will be the best approach for its use as a biological control agent. As it does not respond numerically to prey increase, it will be more effective in a regulatory role to prevent these increases while the prey is at low levels. / Graduation date: 1996

Thesis (M. Appl. Sc.) -- Lincoln University, 2000.

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

Pergamasus quisquiliarum Canestini is a polyphagous predatory mite that has been shown to feed on the economically important arthropod, Scutigerella immaculata Newport (Symphyla: Scutigerellidae), Collembola, Diptera larvae, Enchytraeid worms, and miscellaneous other soil organisms. This study examined the feeding behavior of P. quisquiliarum, the effects of cover cropping and tillage practices on P. quisquiliarum populations, the biology and ecology of P. quisquiliarum in agricultural and non-agricultural sites, and the seasonal dynamics of P. quisquiliarum. The interaction of cover crop and tillage treatment was statistically significant for P. quisquiliarum populations (P<0.001). Tillage treatment was the primary factor for P. quisquiliarum populations, as very low densities of P. quisquiliarum were recovered from green manure plots, regardless of the cover crop treatment. Among no-till plots, Monida oats had the greatest densities of P. quisquiliarum, while control (fallow) and white mustard plots had the lowest densities. The two non-agricultural sites had higher densities of P. quisquiliarum than the agricultural site. Among the non-agricultural sites, P. quisquiliarum density was higher in Douglas-fir (Pseudotsuga menziesii (Mirbel) Franco) litter than in Oregon white oak litter (Quercus garryana Dougl.), suggesting that the nature of the chemical and physical micro-environment was more suitable under Douglas-fir trees. In all sites, P. quisquiliarum attained it's greatest density in August, with a second peak in October. Minimum P. quisquiliarum densities were observed in January and February. Seasonal P. quisquiliarum densities were significantly synchronized with seasonal dynamics of it's prey items. / Graduation date: 1998

M.Sc. (Zoology) / This study centres around the findings on mites (Acari: Eriophyidae) (also referred to as "eriophyids") as potential biological control agents of weeds in South Africa. The use of mites in the biological control of weeds is briefly reviewed. Four species of the family Eriophyidae have been used against weeds in other countries. Seventeen eriophyid species, causing symptoms possibly of significance to biological weed control of 12 plant species regarded as weeds in South Africa, are discussed. Methods to rear and study eriophyids in the laboratory have not yet been fully developed and studying these practically invisible arthropods, very closely associated with their host plants, frequently presents difficulties. Reported methods, and those used for the present study, are reviewed and discussed. The eriophyid, Aceria lantanae (Cook), causing flower and leaf galls on Lantana camara L. could not be successfully established in a quarantine laboratory on potted plants propagated from cuttings of L. camara forms from South Africa. The results obtained during this attempt were inconclusive. The failure of establishment on local L. camara forms could be attributed to a variety of factors, of which rearing methods and host incompatibility are the most likely. Convolvulus arvensis is a troublesome agricultural weed and occurs in especially the Orange Free State and the eastern and southern parts of the Cape Province. Biological control may possibly contribute to curbing this weed in South Africa. The eriophyid, Aceria malherbae Nuzzaci, causing deformation and galling on C. arvensis is regarded as one of the most promising candidates for the biological control of this weed. It was imported and successfully established on potted plants in a quarantine laboratory on biotypes of the weed occurring in South Africa. The biology and host specificity of A malherbae are accounted for, by using reported information and data obtained during this study. The biology of A. malherbae broadly conforms to the biology of other eriophyid species. This species has a narrow host range, being restricted to species very closely related to C. arvensis. The symptoms caused by this eriophyid on C. arvensis are described, and seem especially harmful to the reproductive potential of the plant. Two eriophyid species from L. camara from Paraguay, Tegonotus stefneseri and Paraphytoptus magdalenae, are described as new species. An illustrated as well as a dichotomous key to species (Eriophyoidea) described from L. camara, including the two new species, are provided. A key, and a review of known Tegonotus species, incorporated in a compendium based on the original descriptions of 74 species, are included. Shevtchenkella Bagdasarian is considered to be a junior subjective synonym of Tegonotus Nalepa.

Dasineura sp. is a gall forming midge that was introduced into South Africa for the biocontrol of the Australian myrtle, Leptospermum laevigatum. It causes galls on both the vegetative and reproductive buds of the plant. Although Dasineura sp. was initially regarded as a potentially successful agent, galling up to 99 percent of the buds of the host plant, it has been preyed on by native opportunistic mites, which caused a decline in the performance of the midge as a biocontrol agent of L. laevigatum. This raised a concern about whether this fly will be able to perform effectively in the presence of its new natural enemies. Therefore, the objectives of this study were to: 1) ascertain whether mite abundance has seasonal variations; 2) determine if plant density and plant size have an effect on midge predation by the mites; and 3) determine if midge predation varies in different locations. The study was conducted at three sites in the Hermanus area, Western Cape Province. Every three weeks for thirteen months, galls were collected and dissected so as to count and record the numbers of midge larvae, pupae, adults and mites that were found. Data collected showed that predation varied with season, and the mites were scarce during the flowering season. Predation also varied among the study sites and plant density had an effect on midge predation. Midges in smaller plants (saplings) were more vulnerable to predation than those in the bigger plants (plants from isolates and thickets). It was concluded that although mites have an effect on midge populations, they do not prevent their establishment on the plant. Therefore, a survey should be done in two to three years time to check if the midges are still persisting on the plant, vi and recommendations are that a new agent should be released to supplement the midges.

Water hyacinth (Eichhornia crassipes) is an aquatic macrophyte originating from the Amazon basin. Due to its beautiful appearance it has been introduced into numerous countries across the world as an ornamental pond plant. It was introduced into South Africa in the early 1900s and has since reached pest proportions in many of the country’s fresh water bodies, causing significant economic and ecological losses. It is now considered to be the worst aquatic weed in South Africa. Efforts to control the spread of the weed began in the early 1970s and there have been some successes. Biological control has been used widely as an alternative to mechanical and chemical controls because it is cost-effective, self-sustaining and environmentally friendly. To date, six biological control agents have been introduced onto water hyacinth in South Africa. However, due to factors such as cold winter temperatures and interference from chemical control, the agent populations are occasionally knocked-down and thus the impact of biological control on the weed population is variable. In addition, many South African water systems are highly eutrophic, and in these systems the plant growth may be accelerated to such an extent that the negative impact of the agents’ herbivory is mitigated. One of the agents established on the weed is the galumnid mite Orthogalumna terebrantis, which originates from Uruguay. In South Africa, the mite was initially discovered on two water hyacinth infestations in the Mpumalanga Province in 1989 and it is now established at 17 sites across the country. Many biological control researchers believe that the mite is a good biological control agent but, prior to this thesis, little quantitative data existed to confirm the belief. Thus, this thesis is a post-release evaluation of O. terebrantis in which various aspects of the mite-plant relationship were investigated to determine the efficacy of the mite and thus better understand the role of the mite in the biological control programme of water hyacinth in South Africa. From laboratory experiments, in which mite densities were lower than densities occurring in the field, it was found that water hyacinth growth is largely unaffected by mite herbivory, except possibly at very high mite densities. When grown in high nutrient conditions the growth of the plant is so great that any affect the mite has is nullified. Plant growth is thus more affected by nutrients than by mite herbivory. However, mite feeding was also influenced by water nutrient levels and mite herbivory was greatest on plants grown in high nutrient conditions. The presence of the mite had a positive effect on the performance of the mirid Eccritotarsus catarinensis, such that the interactions of the two agents together had a greater negative impact on the plant’s growth than the individual agents had alone. Furthermore, water hyacinth physiological parameters, such as the plant’s photosynthetic ability, were negatively impacted by the mite, even at the very low mite densities used in the study. Plant growth rate is dependent on photosynthetic ability i.e. the rate of photosynthesis, and thus a decrease in the plant’s photosynthetic ability will eventually be translated into decreased plant growth rates which would ultimately result in the overall reduction of water hyacinth populations. In addition, temperature tolerance studies showed that the mite was tolerant of low temperatures. The mite already occurs at some of the coldest sites in South Africa. Therefore, the mite should be able to establish at all of the water hyacinth infestations in the country, but because it is a poor disperser it is unlikely to establish at new sites without human intervention. It is suggested that the mite be used as an additional biological control agent at sites where it does not yet occur, specifically at cold sites where some of the other, less cold-tolerant, agents have failed to establish. Finally, conditions of where, how many and how often the mite should be distributed to water hyacinth infestation in South Africa are discussed.