Toxicity and Mortality of Synergized Crude Essential Oil Extracts from Tagetes Minuta (L.) on Periplaneta Americana (Blattidae)
OTENG'O, Antony Otinga
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Cockroaches are insects that belong to the order Blattodea, suborder Blattaria and family Blattidae. The species that is most common and wide spread in the world is Periplaneta americana(L.). They are increasing in number due to their resistance to synthetic insecticides that are in most cases used in their control. This has made them a public health problem due to their close association with human wastes and they are mechanical transmitters of human disease causing pathogens. Therefore there is need of coming up with an alternative insecticide. Although studies have shown that the Tagetes minuta(L.) has insecticidal properties, this property has not been tested on cockroaches. T minuta's insecticidal compounds have never been synergized with oil components of Sesamum indicum(L). In the present study, synergized crude essential oil extracts from T minuta were tested as a potential fumigant and contact toxicant on P. americana. The study took place in Maseno Division where 35 households were interviewed using questionnaires and P. american a collected from their premise. The crude essential oil extracts were obtained from floral and folia parts of the plant by percolating with methanol and rotorvaping, then synergized with oil components (methanol extract) from S. indicum seeds. The mixture of the two oils was tested for toxicity on the P. americana in the laboratory using bio-assay method; where cockroaches were exposed to insecticide. The tersi, tracheal and nervous systems of the P. american a were histologically examined to establish how the affected cells and tissues differ from the unaffected ones. Biopac MP35 unit was used to discern the physiological effect of the crude essential oil extracts from T minuta by doing extracellular multiunit record on the P. americana. Data from questionnaires was converted into frequency counts and percentages using SAS statistical analysis software. Susceptibility of P. americana to T minuta's crude essential oil extracts was analyzed as a four factorial experiment. ANOVA and Duncan's Multiple Range test were used to test for significance of the experiments at P::;0.05, LCso of T .minuta's synergized and non-synergized extracts were determined using probit analysis method. From the questionnaires, 83% of the households admitted to cockroach menace; 54% use insecticides to control them and 91% said that not all cockroaches die after treatment. LCso of synergized extract was 6.31 g/L while that for non-synergized extract was 8.91 g/L. Non-synergized extract had a mortality of 48 (n=60) while synergized extract had mortality of 60 (n=60). 120 g/L of both synergized and non-synergized extract had knockdowns and kills made within 20 and 25 minutes respectively. Oil .components of S. indicum synergized T minuta's crude essential oil extracts thus reduced knockdown and kill times and increased the cockroaches' mortality. T minuta's insecticidal compounds did not cause anatomical changes on the tersi, tracheal and nervous tissue; it worked physiologically via impairing the function of Na+ ion channels of the neurons thus killing P. americana. In conclusion, cockroaches are a menace. to households of Maseno and they are susceptible to synergized and non-synergized extracts from T minuta.