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Phytoplankton produce allelochemicals; excreted chemical substances that are affecting other microorganisms in their direct environment. In my thesis, I investigated strain specific variability in the expression of allelochemicals of the harmful flagellate Prymnesium parvum, that is euryhaline but mainly bloom forming in brackish water. I found a large variation among strains, but further showed that all strains of P. parvum were more allelopathic in brackish water compared to marine water. In a marine microbial community, allelochemicals can affect prey, competitors and grazers both, directly and indirectly. For instance, in a food web where grazing controls prey abundance, the negative direct effect of allelochemicals on grazers will positive affect their prey. During my thesis, I investigated how marine microbial communities respond to the addition of allelochemicals. I performed field experiments with microbial communities from seawater collected from different places over Europe, and tested how this communities respond to the addition of allelochemicals from the dinoflagellate Alexandrium tamarense. Before I incubated the microbial communities for several days with A. tamarense algal filtrate, I evaluated the allelopathic efficiency of the algal filtrates with an algal monoculture of Rhodomonas spp. This allowed me to compare the effect of A. tamarense filtrate between the different microbial communities. In general, bacteria reached higher abundances when allelochemicals were present. As allelochemicals also inhibited nanoflagellates and ciliates, we concluded, that allelochemicals indirectly benefit bacteria by reducing grazing pressure. In microbial food webs with many heterotrophic grazers, allelochemicals further benefitted other phytoplankton by inhibiting grazers. It was also shown that bioavailable DOM is released from a microbial community when allelochemicals are present. As most DOM was released from the seawater fraction > 60 μm, we concluded, that larger microorganisms are more affected by allelochemicals than smaller microorganisms. The results can be explained by the surface to volume ratio of microorganisms: Larger organisms provide more contact surface for allelochemicals, and therefore, are probably more vulnerable towards allelochemicals. In conclusion, the effect of allelochemicals on a microbial community depends among others on the structure of the microbial food web, the amount of available DOM, the particle density in the seawater and the composition of the phytoplankton community.

The Zabrotes subfasciatus (Boh 1833) (Coleoptera: Bruchidae) is known popularly as weevil of beans being one of the more important pests of stored grains. The pest control is performed basically using efficient chemical insecticides, however, they cause harm to men, fauna and flora, in the surroundings, being non-specific. In the search for alternative and less aggressive control, we study the action of infochemicals in the control of the Zabrotes subfasciatus. The study of reproductive aspects and of the intra- and interespecific communication had been carried out as well as the identification of the chemical constituents of the extracts of males and females of Zabrotes subfasciatus. The sequence of courtship and mating of the Z. subfasciatus had been first observed, which resulted in an etogram. After that the selective behavior of the female in relation to the partner and the differences of the sexual reasons that had influenced in the reduction of the number of mating were analyzed. For studies of the intra and interspecific communication, the study had been conducted through olfatometric and electroanthenographic tests. Using olfatometry, it was confirmed that the females are responsible for the release of the sexual pheromone, which exerted attractiveness only toward the males. The plant hostess did not influence in the production of the pheromone. Extracts prepared with dichloromethane had been more efficient in the attractiveness than hexanic extracts, but were less attractive than the alive females. In the electroantenography tests only the males had answered in a positive way to the treatments that consisted of alive females and extracts of females, females plus beans, using dichloromethane as solvent, in order to strengthen the idea of the female being the releaser of the sexual pheromone. The extracts of males and females had been analyzed through GC-MS, to know their chemical contents. Extracts of females had presented greater amount and variety of chemical compounds than the extracts of the males. In the extracts of females, a homologous series of hydrocarbons, alcohols, carboxylic acids, esters and ethers had been found. Morphology differences between the bristles of males and females of Z. subfasciatus were observed. The females present ramified and voluminous bristles, while the males possess filiform bristles / Fundação de Amparo a Pesquisa do Estado de Alagoas / O Zabrotes subfasciatus (Boh 1833) (Coleoptera: Bruchidae) é conhecido vulgarmente como caruncho do feijão sendo uma das principais pragas de grãos armazenados. O controle dessa praga é feito basicamente utilizando-se inseticidas químicos que são eficientes no controle mas é altamente tóxicos ao homem e ao meio ambiente. Na procura por alternativas de controle menos agressiva, estudamos a ação dos infoquímicos no controle do Zabrotes subfasciatus. O estudo comportamental para esclarecimento de aspectos reprodutivos e da comunicação intra e interespecificas foram realizados assim como a identificação dos constituintes químicos presentes nos extratos de machos e fêmeas dessa praga. Foram observada primeiramente a seqüência de corte e cópula do Z. subfasciatus o qual resultou em um etograma. Em seguida foi analisado o comportamento seletivo da fêmea em relação ao parceiro e as diferenças das proporções sexuais que influíram na diminuição do número de acasalamentos. Para estudos da comunicação intra e interespecífica, foram realizados testes olfatômetricos e eletroantenográficos. Utilizando olfatometria foi confirmado ser as fêmeas as responsáveis pela liberação do feromônio sexual, o qual exerceu atratividade apenas nos machos. A planta hospedeira não influenciou na produção do feromônio. Extratos obtidos em diclorometano foram mais eficientes na atratividade que extratos obtidos em hexano, mas não mais atrativo que as fêmeas vivas. Nos testes eletroantenográficos apenas os machos responderam de maneira positiva aos tratamentos; fêmeas vivas e extratos de fêmeas, fêmeas mais feijão utilizando como o solvente o diclorometano, reforçando a ideia da fêmea ser o sexo liberador do feromônio. Os extratos de machos e fêmeas foram analisados em (CG-EM). Extratos de fêmeas apresentaram maior quantidade e variedade de compostos químicos que os extratos dos machos. Em extratos de fêmeas foram encontrados uma serie homologa de hidrocarbonetos e compostos oxigenados como; álcoois, ácidos carboxílicos , ésteres e éteres. Constatou-se que há diferenças quanto à morfologia das cerdas de machos e fêmeas de Z. subfasciatus. As fêmeas apresentam cerdas mais ramificadas e volumosas enquanto os machos possuem cerdas filiformes