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.

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Título original: Avaliação bioquímica (sangue e urina) e morfohistológica (fígado) de coelhas expostas a acaricida obtido a partir do ácido ricinoléico do óleo de mamona / Orientador: Maria Izabel Souza Camargo / Coorientador: Patricia Rosa de Oliveira / Banca: Rusleyd Maria Magalhães de Abreu / Banca: Matheus Mantuanelli Roberto / Resumo: No presente trabalho verificou-se o efeito dos ésteres do ácido ricinoléico do óleo de mamona, acaricida químico natural pela avaliação dos parâmetros bioquímicos do sangue e da urina e a morfofisiologia do fígado de coelhas, aqui utilizadas como modelo de hospedeiros de carrapatos, alimentadas com ração enriquecida com os referidos ésteres. Os resultados obtidos a partir dos Bioensaios 1 (ração + NaCl) e 2 (ração + ésteres + NaCl) mostraram que os parâmetros clínicos nas análises das enzimas hepáticas fosfatase alcalina (FAT), gama glutamil transferase (GGT) e alanina aminotransferase (ALT) não foram significativamente alterados, exceto para a enzima hepática aspartato aminotransferase (AST) das coelhas do Bioensaio 2, que apresentou maior variância indicando que os ésteres são hepatotóxicos. Os resultados obtidos nas análises das amostras de urina para os parâmetros hemoglobina livre, proteína, bilirrubina e urobilinogênio demonstraram que os índices de referência não foram alterados. Os dados morfohistológicos e histoquímicos do fígado mostraram que as coelhas alimentadas com ração enriquecida tiveram o tecido hepático alterado, o que foi confirmado pela desorganização dos cordões hepáticos, aumento do espaço intercelular, presença de hepatócitos com limites celulares pouco distintos e de núcleos irregulares e picnóticos, geralmente deslocados para a periferia da célula devido a presença de vacúolos. Histoquimicamente detectou-se nas coelhas do Bioensaio 2 redução na prese... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The present study verified the effects of castor oil ricinoleic acid, a natural chemical acaricide, on the clinical blood and urine parameters and on the liver morphophysiology of female rabbits (used as a model of tick hosts) fed with commercial food enriched with castor oil esters. Bioassays 1 (commercial food + NaCl) and 2 (food + esters + NaCl) demonstrated that the clinical parameters of the hepatic enzyme alkaline phosphatase (FAT), gamma glutamyl transferase (GGT) and alanine aminotransferase (ALT) were not significantly altered, except for the hepatic enzyme aspartate aminotransferase (AST) of the rabbits belonging to Bioassay 2, which presented greater variability, indicating that the esters are hepatotoxic. The analyses of the urine samples for the parameters free hemoglobin, protein, bilirubin and urobilinogen demonstrated that the esters were not toxic to the female rabbits. The morphohistological and histochemical data showed that the rabbits fed with enriched food had the hepatic tissue altered, which was confirmed by the disorganization of the hepatic cords, enlargement of the intercellular space, presence of hepatocytes with little evident limits and irregular and pyknotic nuclei, mostly dislocated to the cell periphery due to the presence of vacuoles. Histochemically, the female rabbits of Bioassay 2 presented a decrease in the number of lipids and increased amount of glycogen. In addition, the hepatic cells of these rabbits showed activity of acid phosphatas... (Complete abstract click electronic access below) / Mestre

Spider mites (Acari: Tetranychidae) are an important agricultural pest of many crops and landscape plants. They can reproduce rapidly and quickly develop resistance to many pesticides, making them difficult to manage. Plant water-stress and high temperatures promote spider mite infestations, while spider mite outbreaks can also result from neonicotinoid insecticide applications. Drought is predicted to increase in the Intermountain West due to increases in temperature and reduced frequency of precipitation events in the region, and neonicotinoids are currently one of the most widely used classes of insecticides in field crops. I studied the interactive effect of these two simultaneously occurring abiotic factors on spider mite outbreaks and plant biosynthesis of herbivore-related defense proteins. I also evaluated ways to alleviate spider mite outbreaks with drought-tolerant corn and the exogenous application of plant phytohormones involved in plant resistance toward biotic stressors. I found that plant water-stress increased spider mites and that neonicotinoids exacerbated the effect of water-stress. Although applications of plant hormones did not reduce the effect of water-stress and neonicotinoids, drought tolerant corn showed promise in reducing the effect of water-stress and spider mite outbreaks.

This thesis reports laboratory and field investigations on the aspects of biology of the Stethorus vagans, an Australian ladybird that feeds on all stages of two-spotted mite, Tetranychus urticae. Aspects of the biology of S. vagans were studied in the laboratory at constant and fluctuating temperatures. They regularly fed on all stages of T. urticae and there was no significant difference in male and female longevity at different temperatures. For field studies potted French bean plants infested with T. urticae were exposed in the field. Adult S. vagans was found to consume a range of alternative prey if the primary host was not available, but only one of the alternative hosts had the potential to support reproduction. Time partitioning behaviour and prey consumption rates were assessed, and how S. vagans located their prey was investigated. S. vagans exhibited many of the attributes of an effective biological control agent such as high reproductive level, location of prey at low levels, reproduction at low densities, and ability to feed on alternative hosts. It is concluded that S. vagans has a number of characteristics likely make them useful as a natural enemy of T. urticae / Doctor of Philosophy (PhD)

Blue oat mite species, Penthaleus spp. (Acari: Penthaleidae), and the redlegged earth mite, Halotydeus destructor (Tucker) (Acari: Penthaleidae), are some of the most serious and widespread agricultural pests in southern Australia. Management of these mites has been complicated by the recent discovery of three cryptic species of Penthaleus, whereas prior research had assumed a single species. The species differ markedly in their distribution, plant preferences and response to pesticides. This thesis looks at various aspects of the biology, ecology and molecular analyses of earth mites with particular emphasis on agricultural control. I tested the initiation of diapause egg production in mites using field and shade-house experiments. Halotydeus destructor has a very different diapause response from Penthaleus species. Thus, carefully timed spring sprays are unlikely to be effective against Penthaleus spp., highlighting the importance of correctly distinguishing earth mite species before implementing control strategies. There is also variation in diapause induction among the three Penthaleus spp. that could contribute to their relative distributions and pest status. I examined the effects of different plant hosts on the persistence and reproduction of earth mites. The results are consistent with field observations that mite species differ in their host plants. For all species, pasture is a suitable host and lentils are generally a poor host plant. Canola, ox-tongue, and a mixture of wheat and oats differ in their suitability as long-term hosts for each mite species. This information is important for developing more sustainable management practices, such as weed management and crop rotations. Competitive interactions between earth mites were also investigated in the field and the laboratory over a number of seasons. In order to make valid conclusions with an applied implication, competition was examined on four different plant treatments: pasture, canola, wheat/oats and ox-tongue. I showed that close competition exists between mite species and that competitive interactions differ temporally and on different plant types. Finally, I undertook biochemical analysis of Penthaleus spp. for the development of a rapid and simple field test that could be used by agronomists and farmers to distinguish the different mite species on individual properties. This would allow appropriate control strategies to be devised, as well as reduce the ineffectual application of pesticides. Using mostly immunological techniques, I revealed important information about the complex nature of the Penthaleus group, the similarity between the three species, as well as develop methods for isolating and characterising species-specific proteins. Directions this work may take in future studies are also discussed.

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

The thesis presents research on the life-history polymorphism in the mite Sancassania berlesei. Males of this species are andropolymorphic: there are two distinct male phenotypes. One, the fighter, develops a third thickened leg pair, with which it kills off other fighters and males which do not exhibit a third thickened leg pair, the non-fighters. A review of the life-history of S. berlesei is given, focussing on its general biology, diet, dispersal and mating behaviour. This is followed by a review of the andropolymorphism, and the current understanding of the mechanisms underlying it. The major conclusions from the experimental work presented in this thesis are that fighters primarily develop at low population densities; though the proportion of males becoming fighters at any given density may change over time. This change is likely to be due to condition-dependence. Data is presented to illuminate these matters and a model is developed linking fighter development to the costs of being a fighter (in terms of survival) and the benefits of being a fighter (in terms of fecundity). The sex ratio in S. berlesei is 1:1, and there is no evidence of density or frequency-dependent deviations from this. A delay in food supply at maturation delays the time of maximum fecundity of females for about seven days and lowers their overall egg output. Density-dependent effects reduce the overall daily fecundity of females in higher densities. Female survival is affected by density, food present and rearing conditions. Nearly all eggs laid by S. berlesei hatch regardless of the conditions. Eggs laid in very poor conditions hatched even earlier than the average time of between day three and four. At density two, animals do synchronise their frequency, when isolated together from egg stage. Poor conditions reverse female density-dependence from convex to concave with the lowest life expectancy at intermediate densities. The trade-off between survival and fecundity is the likely cause. Amalgamating the results from the previous experiments, the influence of stochastic population dynamics on male strategy was then modelled. The results indicate that the fighter morph development rule is sensitive to the probability of low population densities arising. When low densities occur, there is a selective advantage to being a fighter. With increasing probability of lower densities, becoming a fighter is more feasible. The ESS rule changes, while in a stable high density environment a density-dependent fighter rule is never selected for. This indicates an influence of stochastic population dynamics on life-history evolution. Modelling demographic stochasticity in the fighter rule shows some buffering effect of this form of stochasticity. The fighter morph determination rule is less sensitive to environmental stochasticity with a high frequency of low densities. Using an agent based model with diploid genetics, I show that under high densities a fighter male is less successful at passing on his genes than a non-fighter. At a density of one male, the fighter gains no advantage to developing the fighter phenotype (as he is not competing with other males). In this case, the advantage may arise through future increases in density (such as through immigration or maturation of offspring). The density-dependent fighter development rule is then switched within the model from density-dependent to frequency-dependent, and the model indicates, that even under the frequency-dependent rule a possible ratio of fighters to non-fighters could exist. The system does not reach this state due to condition-dependence in reality. Following on from the findings discussed above, that morph determination has a condition-dependent component, I develop an argument that relates the observed forms of morph determination (density-dependent and frequency-dependent) in three closely related species of mites via an underlying condition-dependence. It is shown that condition-dependence is likely the linking factor between frequency and density-dependence. This is shown to be possibly a rule for all species displaying polymorphism which includes physical alterations of their bodies.