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The synergistic effect of nitric oxide toward dephosphorylation reactions involving phosphate esters was the subject of investigation in this research. Sodium nitroprusside under UV irradiations at 254nm, 365nm and white light was utilized as nitric oxide donor in solutions. The effects of cobalt trimethylenediamine and nitroprusside towards dephosphorylation of nitrophenylphosphate and pyrophosphate which were modeled as organophosphate ester substrates were also investigated. The activated substrate models showed more rate enhancement than the unactivated models in all cases. The direct interaction of nitric oxide with the phosphorus centre is presumed to be the reason for enhanced hydrolysis. This study demonstrates the possible role of nitric oxide in decontamination reactions of poorly biodegradable phosphate esters in the biosphere. / Chemistry / M. Sc. (Chemistry)

Thesis (PhD (Botany and Zoology))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The use of organophosphate pesticides is still an integral part of commercial farming activities and these substances have been implicated as a major source of environmental contamination in South Africa. Evidence exists that many non target animals in and around agricultural areas are at risk of being affected due to the mobile nature of pesticides and the intermittent nature of pesticide application. The extent to which non-target animals are affected by exposure to two organophosphates (azinphos-methyl and chlorpyrifos) was investigated through monitoring selected biomarker responses and life cycle effects under laboratory conditions in two selected test species. A representative species from both the aquatic and terrestrial environment was used as these two compartments of the environment are inevitably linked due to the mobility of pesticides from the area of application to surrounding areas. The earthworm Eisenia fetida was used as test organism in the terrestrial environment while the fish Oreochromis mossambicus served as representative of the aquatic environment. Juvenile life stages of both species were subjected to standard acute toxicity tests which showed that for both species, juvenile life stages were more sensitive to both pesticides than adults. It was also illustrated that azinphos-methyl is more toxic than chlorpyrifos to both species. Both test species were also subjected to an intermittent exposure regime in order to assess the effects of repeated pesticide application on biomarker, life-cycle and behaviour responses. The results indicated that for similar exposure regimes, azinphos-methyl was more toxic to E. fetida than chlorpyrifos and detrimentally affected all endpoints investigated. The present study suggests that exposure concentration may have a more pronounced effect in inducing a toxic response than exposure interval, irrespective of the pesticide used. In addition to this, E. fetida was unable to avoid the presence of these pesticides in soil, even at concentrations as high as 50% of the LC50 value, indicating that the presence of pesticides in the soil pose a realistic threat to earthworms and other soil dwelling organisms. Biomarker responses, morphological effects and feeding behaviour was assessed for O. mossambicus and similar to the terrestrial toxicity experiments, there was evidence to suggest that in the case of an intermittent exposure scenario, azinphos-methyl was more hazardous than chlorpyrifos to this species. For the majority of endpoints that were investigated, it appeared that exposure interval played a more important role in inducing an effect than exposure concentration. At a shorter exposure interval, the majority of endpoints showed no difference between higher and lower exposure concentrations, while at a longer exposure interval the effects of exposure concentration became evident. In addition, feeding behaviour was affected by pesticide exposure in a dose-dependent manner. The present study yielded important results that improve the understanding of biological impacts of pesticide pollution on the environment. This can aid in optimising farming practices such as pesticide application not only in terms of eradicating the pest organisms, but also in terms of mitigating the environmental effects associated with large-scale pesticide use, thereby ensuring sustained biodiversity in these areas. / AFRIKAANSE OPSOMMING: Die gebruik van organofosfaat plaagdoders is ‘n integrale deel van kommersiële landbou aktiwiteite maar hierdie middels is ook ‘n prominente bron van omgewingsbesoedeling in Suid-Afrika. Daar is bewys dat verskeie nie-teiken diere in en om landbouareas geaffekteer word weens die nie-statiese aard van plaagdoders in die omgewing, sowel as die herhalende aard van plaagdodertoediening. Die graad waartoe nie-teiken diere geaffekteer word deur die plaagdoders azinphos-metiel en chlorpyrifos is ondersoek deur die monitering van verskeie biomerkerresponse en lewenssiklus-effekte in geselekteerde toetsspesies binne ‘n beheerde laboratoriumomgewing. ‘n Verteenwoordigende spesie van beide die akwatiese en die terrestriële omgewing is gebruik aangesien hierdie twee dele van die omgewing onlosmaaklik verbind is weens die beweging van plaagdoders vanaf die area van toediening na omringende areas. Die erdwurm Eisenia fetida is gekies as toetsorganisme vir die terrestriële omgewing en die varswatervis Oreochromis mossambicus het gedien as verteenwoordigende spesie vir die akwatiese omgewing. Onvolwasse diere van beide spesies is onderwerp aan standaard akute toksisiteitstoetse en daar is gevind dat, vir beide spesies, onvolwasse diere meer sensitief vir die betrokke plaagdoders is as volwasse diere. Dit is ook gevind dat azinphosmetiel giftiger is as chlorpyrifos vir beide spesies. Beide toetsspesies is ook onderwerp aan ‘n chroniese blootstellingsregime om die effek van herhaalde plaagdodertoediening op biomerker-, lewenssiklus- en gedragsresponse te ondersoek. Die resultate van die herhaalde blootstelling het aangedui dat vir soortgelyke blootstellingsregimes, azinphos-metiel giftiger is as chlorpyrifos vir E. fetida en dat beide middels alle eindpunte wat ondersoek is, nadelig affekteer. Die huidige studie toon ook bewyse dat blootstellingskonsentrasie ‘n meer prominente effek as blootstellingsinterval kan hê in die teweegbringing van ‘n toksiese respons. Verder was E. fetida nie in staat om die teenwoordigheid van die plaagdoders in grond te vermy nie, self nie by konsentrasies so hoog as 50% van die LC50 waarde nie. Laasgenoemde resultaat dui dus aan dat die aanwesigheid van plaagdoders in die grondomgewing ‘n realisitese bedreiging inhou vir erdwurms en ander grondorganismes. Soortgelyk aan die terrestriële toksisiteitseksperimente, was daar getuienis vir die verhoogde toksisiteit van azinphos-metiel relatief tot chlorpyrifos vir O. mossambicus. Dit blyk dat blootstellingsinterval ‘n meer prominente rol as blootstellingskonsentrasie speel in die teweegbringing van effekte vir die meerderheid van die eindpunte wat ondersoek is. In die geval van ‘n korter blootstellingsinterval het die meerderheid van eindpunte wat ondersoek is geen verskille getoon tussen ‘n hoër en ‘n laer konsentrasie nie, terwyl met ‘n langer blootstellingsinterval daar ‘n aanduiding was dat blootstellingskonsentrasie ‘n meer prominente rol gespeel het. Verder is gevind dat voedingsgedrag in O. mossambicus geaffekteer is op ‘n konsentrasie verwante manier. Die huidige studie toon resultate wat ‘n belangrike bydrae kan lewer tot die begrip van die biologiese impakte van organofosfaat plaagdoders op die omgewing. Die resultate kan gebruik word vir die optimisering van boerderypraktyke soos plaagdodertoediening, sodat laasgenoemde effektief is vir die beheer van pes-organismes, maar ook die impakte van grootskaalse plaagdodertoediening kan minimaliseer en sodoende die biodiversiteit binne hierdie areas sal beskerm.

The purpose of this research was to develop and standardize a novel feeding bioassay with Macrobrachium rosenbergii for use in the laboratory and allowing it to be easily deployed under field conditions. Standardization of the test aimed to minimize feeding rate variations and to ensure that subsequent statistical analyses have sufficient power to consistently detect changes in feeding rates. These were accomplished through the development of a post-exposure feeding toxicity test under laboratory, microcosm and in situ/field conditions. This procedure was proven to be repeatable and economical. M. rosenbergii as test animals were available in terms of quantity and uniformity in sizes. The standard guidelines and procedures for M. rosenbergii bioassay developed from this study include the size of test animals (9-10 mm), density in exposure containers (10 animals in 500 mL of medium in the laboratory, 10 animals in field chambers with 98.6 mL volume), exposure time (24 hours), feeding period for post-exposure feeding (4 hours) and number of replicates for the feeding test (10 replicates for individual measurements). The tiered approach used in the preliminary risk assessment of pesticide using TOXSWA was capable of screening the risk level of pesticide in the study area, identifying profenofos and dimethoate as test chemicals for the lethal and sub-lethal experiments. This model was beneficial in the preliminary risk assessment of pesticides in the tropics, since it was not necessary to set up laboratory work. This method could also provide preliminary data to support the environmental planner and decision/policy maker. This is an alternative way to develop a cost efficient model to inform and warn the risk of pesticide use. The effects of pH, temperature and hardness on control post-exposure feeding rates of M. rosenbergii were assessed and indicated that M. rosenbergii was very sensitive to acidic and basic conditions. The use of post-exposure feeding inhibition as the endpoint under laboratory conditions revealed that prawns were sensitive to pesticides (chlorpyrifos, dimethoate and profenofos) and a heavy metal (zinc). Post-exposure feeding rate inhibition could be used as a sublethal endpoint as the EC50 values obtained for chlorpyrifos and zinc were lower than their lethal levels. Mortality of prawn was also another endpoint used to define the toxicity of pesticides such as carbendazim, in which mortality occurred during exposure, but post-exposure feeding rate of the surviving animals did not decrease. The microcosm experiments were able to link the laboratory toxicity tests and the effects observed in the field. Microcosm studies provided another dimension to studies looking at pesticide effects on aquatic systems. In this research, carbendazim affected feeding and survival rates in the microcosm set-up but in the laboratory only mortality showed a significant difference (P < 0.05). In situ bioassays were able to show the effects of pesticides on post-exposure feeding rates using the methods developed. Post-exposure feeding rates were significantly lower than control in farms using pesticides while in uncontaminated sites (pesticide-free), the post-exposure feeding rates did not decrease. However, mortality was observed even in the uncontaminated sites which could be attributed to other factors such as low dissolved oxygen and presence of some other unidentified chemical substances. The degree of mortality and the effect on feeding rates depends not only on the type and concentration of the known pesticide but also on water quality parameters. The basic methods developed for in situ bioassay from this research is a simple, easy and fast way to determine the effect of pesticides because the results can be seen in the field. The procedures developed and results obtained from this study can be used as a basis for further toxicity studies on M. rosenbergii and other potential tropical species.

Global consumption of organophosphate esters (OPs), which are used as flame retardants and plasticizers, is rapidly increasing. Their use as additives in diverse applications poses a risk as they may be emitted from the products they are added to and be further transported in the environment. Therefore, the levels, distribution, and possible sources of 15 OPs, some of which are reported to be toxic, were investigated in indoor and outdoor environments. An exposure assessment was performed, and the exposure to OPs via inhalation was examined for five occupational groups. In addition, based on the findings of the studies, the total flow of OPs in Sweden was estimated. In indoor environments, the OPs detected in air and dust varied between the sites, but generally reflected the building materials, furniture etc. used in the premises. A majority of the analysed OPs were detected in all samples, and public buildings tended to have higher levels than domestic buildings. The chlorinated OPs dominated in indoor air and wipe samples from vehicles. They were also abundant in the dust samples. Some occupational groups were significantly more exposed to OPs than others. Aircraft technicians, for example, were exposed to about 500 times more tributyl phosphate than day care centre personnel. Upon domestic and industrial cleaning, OPs are discharged with the wastewater via the sewage system to sewage treatment plants (STPs). Irrespective of the size of the STPs investigated, they had similar levels of OPs in their influents, indicating that products containing OPs are widely used by the communities they serve. In some cases, it was possible to trace elevated levels of individual OPs to specific sources. The OPs were poorly removed from the wastewater, and the chlorinated OPs especially tended to pass through the STPs without being removed or degraded. Thus, levels of OPs in their effluents were also similar, as were the levels in their sludge. Of the total amounts of OPs entering the STPs, 50% was emitted to the recipients via the effluent. Hence, there is room for significant improvement in the treatment processes. Carps living in a pond, receiving STP effluent were found to contain relatively high levels of OPs compared to perch collected in lakes from background locations. Air and road traffic were also identified as sources of OPs: the concentration of total OPs in snow samples decreased with increasing distance from a major road intersection, and OPs were detected in aircraft lubricants and hydraulic fluids and in waste oil from cars and lorries. OPs are emitted from both diffuse and direct sources to the environment and may then be spread by long-range air transport, rivers and streams. This probably explains why OPs were also detected in air and fish from background locations. Finally, OPs are ubiquitous substances in both indoor and outdoor environments. The possibility that prolonged exposure to OPs at the levels found may cause adverse effects, for instance in aqueous organisms, cannot be excluded. For example, the OP levels in snow were of the same magnitude as reported effect concentrations. Similarly, in some premises, indoor exposure to OPs was close to the suggested guideline value. However, since these studies include only a limited number of samples, and data regarding the health and environmental effects of OPs are sparse, no definitive conclusions regarding their possible environmental effects can be drawn. / Den globala konsumtionen av organiska fosfatestrar (OP) för användning som flamskyddsmedel och mjukgörare har ökat kraftigt på senare tid. Det breda användningsområdet för dessa additiv medför en risk att de kan avges från de produkter de är satta till och transporteras vidare ut i miljön. Följaktligen undersöktes källor till, halter av, och fördelning i inom- och utomhusmiljöer av 15 OP, varav en del har toxiska effekter. Vidare har exponering för OP i bl.a bostäder och offentliga byggnader beräknats. Utöver detta undersöktes exponeringen för OP via inandning hos 5 yrkesgrupper. Slutligen användes resultaten för att uppskatta det totala flödet av OP i Sverige. I de olika inomhusmiljöerna uppmättes ett flertal OP i varierande halter i damm och luft, men generellt speglade halterna byggnadsmaterial, möbler etc. som fanns i lokalerna. De offentliga lokalerna tenderade att uppvisa högre halter än privata hus, förmodligen beroende på högre brandskyddskrav. Klorerade OP dominerade i inomhusluft samt i avstrykningsprov från fordon och förekom även i höga halter i damm. Vissa yrkesgrupper var exponerade för betydligt högre halter OP än andra, t.ex. exponerades flygtekniker för upp till 500 ggr högre lufthalter av tributylfosfat jämfört med förskollärare. I samband med våtskurning i inomhusmiljöer (hushåll, industrilokaler, osv.) släpps avsevärda mängder OP ut i avloppet och når till sist reningsverk. Oberoende av storlek på reningsverken var halterna av OP relativt lika, i vardera ingående vatten och slam, vilket indikerar en bred användning av OP i samhället. I vissa fall kunde specifika källor till OP i avloppsvattnet spåras. Exempelvis hade två av reningsverken högre halter av en klorerad OP jämfört med övriga reningsverk. Dessa behandlade vatten från en skumplastfabrik, respektive en fabrik som tillverkar flamskyddad färg. Avskiljningsgraden av OP från avloppsvatten visade sig generellt vara dålig, i synnerhet klorerade OP tenderade att passera genom reningsverken utan att degraderas eller avskiljas från vattnet. Av den mängd OP som nådde reningsverken släpptes 50 % ut till miljön via utflödet. Som ett resultat av detta uppvisade karpar från en damm påverkad av utflödet från ett reningsverk höga halter OP jämfört med abborrar från referenssjöar. Det finns därför anledning att förbättra tekniken på reningsverken. Flyg- och vägtrafik kunde också identifieras som källor till OP i miljön. OP uppmättes i hydrauloljor och smörjmedel för flygplan samt i spillolja från bilar och lastbilar. Vidare minskade totalhalten OP i snöprov med ökat avstånd från en större vägkorsning. OP släpps således ut från både diffusa och direkta källor och kan sedan spridas vidare via luft och vattendrag. Därmed var det inte förvånande att OP även påträffades i luft och fisk från bakgrundslokaler. Avslutningsvis förekommer OP i varierande halter i såväl inom- som utomhusmiljöer. Det kan inte uteslutas att långvarig exponering för de halter av OP som uppmätts skulle kunna orsaka negativa effekter hos t.ex vatten- eller jordlevande organismer. I smälta snöprov från en flygplats uppmättes exempelvis halter av OP i samma storleksordning som rapporterade effektkoncentrationer. Dessutom visade sig den beräknade exponeringen av OP, i några av de provtagna inomhuslokalerna, uppgå till halter nära det föreslagna riktvärdet för OP i Tyskland. Dessa studier inkluderar dock ett begränsat antal prov och provtyper och kunskapen om dessa föreningars miljö- och hälsoeffekter är bristfällig. Därför bedöms underlaget som för litet för att några definitiva slutsatser ska kunna dras angående OPs eventuella effekter på miljön.

O metamidofós é um inseticida organofosforado altamente tóxico por ser um forte inibidor da acetilcolinesterase, sendo utilizado em diversas culturas para o controle de pragas. Há poucas informações sobre a biodegradação deste composto disponíveis na literatura. Foram isoladas e caracterizadas 12 bactérias a partir de amostras de solo e água de uma área contaminada com metamidofós, as quais mostraram inicialmente capacidade de degradar o pesticida, utilizando-o como fonte de enxofre/nitrogênio e fósforo/enxofre. Estes isolados foram identificados por métodos de biologia molecular e pela caracterização do perfil lipídico da célula como pertencentes aos gêneros, Serratia, Pseudomonas, Stenotrophomonas e Curtobacterium. Ensaios preliminares da cinética de degradação do metamidofós por GC/MS evidenciaram o consumo do pesticida pelas bactérias isoladas. A retomada destes ensaios após alguns meses de armazenamento em glicerol a -80ºC resultou na perda da capacidade de biodegradação do composto-alvo por causas não-identificadas. Fatores que podem ter contribuído para este resultado negativo incluem eventual perda de plasmídeos com partes das vias de biodegradação ou interferentes utilizados na estabilização do metamidofós. / Methamidophos is a strong acetylcholinesterase inhibitor and, therefore, a very toxic organophosphorus insecticide. This product has been widely employed for pest control in a variety of cultures, but little information is available about its biodegradation. 12 bacteria were isolated and characterized, from water and soil samples obtained from a site contaminated with methamidophos, which in preliminary tests showed the ability to degrade methamidophos, using it as a combined source of sulfur/nitrogen and/or phosphorus/sulfur. These isolates were identified by molecular biology methods and by characterization of its fatty acids profile as members of the genus Serratia, Pseudomonas, Stenotrophomonas and Curtobacterium. The ability to biodegrade the compound was lost after prolonged storage at -80ºC for unknown reasons. It was hypothesized that this negative result may have occurred due to loss of plasmids or by interference of products used in the stabilization of commercial methamidophos formulations.

O processo Humifert é uma alternativa para produção de compostos fertilizantes fosfatados, com solubilização mais lenta do que os fertilizantes tradicionais, resultando em um tempo de nutrição da planta maior. No processo, utilizam-se rochas fosfáticas com algum tipo de limitação para o aproveitamento normal, seja pelos teores menores, seja por dificuldades de tratamento industrial dos minérios, além de materiais orgânicos. O objetivo deste trabalho foi melhorar o equipamento existente no Instituto de Geociências, para tornar possível condições de produção de NOx, no Processo Humifert, capaz de produzir um teor de fósforo disponibilizado em condições controladas de processo. Empregando-se planejamento estatístico de experimentos foi possível selecionar as variáveis de entrada mais importantes ao processo (agitação da mistura de rocha fosfática, matéria orgânica e umidade, A codificada; temperatura de oxidação da amônia, B codificada; umidade da mistura, C codificada; porosidade da placa difusora, D codificada; vazão do ar auxiliar, E codificada). A análise estatística, também, permitiu construir modelos de regressão nos quais as influências das variáveis de processo foram sentidas na solubilidade do fósforo nos extratores: ácido cítrico, solução 2% (Pácido cítrico); água, (Págua); citrato neutro de amônio mais água, (PCNA+água). Estas últimas variáveis aqui denominadas de variáveis de saída ou de resposta. A manipulação dos referidos modelos permite obter o fertilizante de acordo com as necessidades da cultura e do solo. O estudo, também, permitiu concluir que a maior quantidade de fósforo disponível nos compostos organofosfatados foi o solúvel em ácido cítrico, portanto, a maior quantidade de compostos gerados encontra-se na melhor condição de disponibilidade pela planta. / Humiphert process is an alternative used for producing phosphated compound fertilizers with a slower solubilization when compared to other traditional fertilizers, resulting in a longer period of plant nutrition. During the process, phosphatic rocks are used along with some sort of limitation according to the normal development, both by their lower content percentage and by treatment of difficulties of industrial ores, besides organic materials. This work aim to improve an equipment existing at the Instituto de Geociências in order to find out the best process condition to produce NOX in Humifert process. This way, the process is able to produce an available phosphorus content under process conditions controlled. The process variables were select by using of experimental design. These variables were: agitation of phosphatic rock mixture (rock, organic material and humidity), A coded; ammonia oxidation temperature, B coded; humidity of mixture, C coded; porosity of the diffusing board, D coded; auxiliary air, E coded. Statistical analysis also allowed to build regression models in which the influences of process variables were felt in the solubility of phosphorus in the extractors: 2% solution of citric acid (Pacid Citric), water (Pwater); ammonium neutral citrate plus water (PCNA + water). These last variables here called output variable or response. The manipulation of these models allows to obtain the fertilizer according to the needs of the crop and soil. The study still conclude that the greater amount of available phosphorus in compound was soluble in citric acid, therefore, a greater amount of compounds generated is in the best condition of availability for the plant. The study still conclude that the greater amount of available phosphorus in the organophosphated compounds were soluble in citric acid. Therefore, the greater amount of compounds generated is in the best condition of availability for the plant.

O processo Humifert é uma alternativa para produção de compostos fertilizantes fosfatados, com solubilização mais lenta do que os fertilizantes tradicionais, resultando em um tempo de nutrição da planta maior. No processo, utilizam-se rochas fosfáticas com algum tipo de limitação para o aproveitamento normal, seja pelos teores menores, seja por dificuldades de tratamento industrial dos minérios, além de materiais orgânicos. O objetivo deste trabalho foi melhorar o equipamento existente no Instituto de Geociências, para tornar possível condições de produção de NOx, no Processo Humifert, capaz de produzir um teor de fósforo disponibilizado em condições controladas de processo. Empregando-se planejamento estatístico de experimentos foi possível selecionar as variáveis de entrada mais importantes ao processo (agitação da mistura de rocha fosfática, matéria orgânica e umidade, A codificada; temperatura de oxidação da amônia, B codificada; umidade da mistura, C codificada; porosidade da placa difusora, D codificada; vazão do ar auxiliar, E codificada). A análise estatística, também, permitiu construir modelos de regressão nos quais as influências das variáveis de processo foram sentidas na solubilidade do fósforo nos extratores: ácido cítrico, solução 2% (Pácido cítrico); água, (Págua); citrato neutro de amônio mais água, (PCNA+água). Estas últimas variáveis aqui denominadas de variáveis de saída ou de resposta. A manipulação dos referidos modelos permite obter o fertilizante de acordo com as necessidades da cultura e do solo. O estudo, também, permitiu concluir que a maior quantidade de fósforo disponível nos compostos organofosfatados foi o solúvel em ácido cítrico, portanto, a maior quantidade de compostos gerados encontra-se na melhor condição de disponibilidade pela planta. / Humiphert process is an alternative used for producing phosphated compound fertilizers with a slower solubilization when compared to other traditional fertilizers, resulting in a longer period of plant nutrition. During the process, phosphatic rocks are used along with some sort of limitation according to the normal development, both by their lower content percentage and by treatment of difficulties of industrial ores, besides organic materials. This work aim to improve an equipment existing at the Instituto de Geociências in order to find out the best process condition to produce NOX in Humifert process. This way, the process is able to produce an available phosphorus content under process conditions controlled. The process variables were select by using of experimental design. These variables were: agitation of phosphatic rock mixture (rock, organic material and humidity), A coded; ammonia oxidation temperature, B coded; humidity of mixture, C coded; porosity of the diffusing board, D coded; auxiliary air, E coded. Statistical analysis also allowed to build regression models in which the influences of process variables were felt in the solubility of phosphorus in the extractors: 2% solution of citric acid (Pacid Citric), water (Pwater); ammonium neutral citrate plus water (PCNA + water). These last variables here called output variable or response. The manipulation of these models allows to obtain the fertilizer according to the needs of the crop and soil. The study still conclude that the greater amount of available phosphorus in compound was soluble in citric acid, therefore, a greater amount of compounds generated is in the best condition of availability for the plant. The study still conclude that the greater amount of available phosphorus in the organophosphated compounds were soluble in citric acid. Therefore, the greater amount of compounds generated is in the best condition of availability for the plant.

Made available in DSpace on 2015-03-26T13:30:55Z (GMT). No. of bitstreams: 1 texto completo.pdf: 425912 bytes, checksum: f916df0f0bb071da87434b28d89e5189 (MD5) Previous issue date: 2007-07-16 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Sitophilus zeamais Motsch. (Coleoptera: Curculionidae) is an important pest of stored maize because of the losses caused. This insect has been studied for responding to selection pressure for insecticide resistance, which impairs its control. In the present study, we carried out a survey of physiological and behavioral resistance to two organophosphate insecticides in 15 populations of S. zeamais collected in Brazil and Paraguay and investigated if differences in population growth, body size and metabolic rate were associated with the resistance. The insects were maintained in the laboratory, and concentration-mortality bioassays were conducted to determine lethal concentrations with 48 hours of exposure. Behavioral resistance was studied by recording the walking behavior on insecticide-treated and untreated surfaces and determining the distance walked, speed, resting time, and proportion of time spent on the treated surface. The instantaneous rate of population growth (ri) was determined, and so was the maize consumption for 90 days, body mass, and production of CO2 as indicative of the metabolic rate of the insects. Results of the concentration-mortality bioassays indicated variations in susceptibility to methyl clorpiriphos (≤ 6,06x) and fenitrothion (≤ 7,71x) relative to the standard susceptible population (Sete Lagoas), but these resistance levels are low and should not cause control failures in the field. The walking behavior on treated surfaces also varied among the populations, but no clear evidence of repellency was detected and no significant correlation was observed between physiological and behavioral resistance. The instantaneous rate of population increase and the respiratory rate were similar among the populations although there were differences in food consumption and body mass of the insects. Importantly, none of these four traits correlated with organophosphate resistance in the populations studied, suggesting absence of detectable fitness costs. We can conclude that the levels of resistance to methyl clorpiriphos and fenitrothion are low, and the physiological resistance in these populations is independent of the behavioral resistance. Furthermore, and even due to the low levels of organophosphate resistance detected, no fitness costs associated with insecticide resistance seems to occur. / Sitophilus zeamais Motsch. (Coleoptera: Curculionidade) é reconhecidamente importante pelos danos causados a grãos de milho armazenados. Essa espécie tem sido bastante estudada por responder à pressão de seleção para resistência a inseticidas, dificultando seu controle. Neste trabalho foi realizado um levantamento da resistência fisiológica e comportamental a dois inseticidas organofosforados em 15 populações de S. zeamais coletadas em vários estados do Brasil e no Paraguai e investigado se características corporais, metabólicas e demográficas estão associadas à resistência. Os insetos foram mantidos em laboratório e testados mediante bioensaios de concentração-mortalidade para determinação de doses letais com 48 horas de exposição. Insetos de cada população foram também submetidos a ensaios de caminhamento em superfície tratada e não-tratada com inseticida para detecção de resistência comportamental, onde foi avaliada a distância caminhada, a velocidade de caminhamento, o tempo em repouso e a proporção de tempo em que os insetos permaneceram sobre a superfície tratada. Foram também determinados a taxa instantânea de crescimento populacional (ri), e o consumo alimentar de milho por 90 dias, além da massa corporal dos indivíduos de cada população estudada. Determinou-se ainda a produção de CO2 como indicativo da taxa metabólica dos insetos. Os resultados dos bioensaios de concentração-mortalidade indicaram variação de suscetibilidade a clorpirifós-metílico (≤ 6,06x) e fenitrotiom (≤ 7,71x) em relação à população padrão de suscetibilidade (Sete Lagoas). Entretanto, este baixo nível de resistência não deve ser alarmante a ponto de levar a falhas de controle no campo e nem parece haver um padrão de distribuição espacial da mesma. As características comportamentais de caminhamento na área tratada variaram entre as populações, embora não pareça haver repelência pelos inseticidas. Não se detectou diferença significativa na taxa instantânea de crescimento populacional e nem na taxa respiratória dos insetos, apesar de haver diferenças de consumo alimentar e massa corporal dos insetos das diferentes populações. É importante salientar que nenhuma dessas quatro características esteve associada com a resistência a inseticidas apresentada pelas populações, indicando que a incipiente resistência aos fosforados das populações estudadas parece não estar associada a custos adaptativos. Pode-se concluir que os níveis de resistência a clorpirifós-metílico e fenitrotiom detectados neste estudo são baixos e a presença de resistência fisiológica nas populações é independente da resistência comportamental. Além disto, e até em função dos baixos níveis de resistência observados, não há indícios de custos adaptativos associados à resistência.