Studies on Ecology and Developmental Biology of Ornithodoros Savignyi (Audouin) and Argas (Persicargas) Persicus Oken with Reference to their Water Relations.

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Osman Mansour Osman, Osman
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Distribution of Ornithodoros savignyi in Western Sudan in relation to ecological zones and the livestock density was investigated. It was found to have spread southwards beyond its previously known limits. The factors contributing to its spread were discussed. The species density was studied in some localities in dry and wet seasons and it was found to have a higher density during hot dry months. The species inhabits sandy and alluvial soil areas with high livestock densities. There were more diurnal activities during hot hours around noon. Argas persicus distribution and density in poultry houses in some areas of the country were also investigated. Distribution and infestation rates were not a function of external climatic variation. They were mostly influenced by the type of poultry houses, hygiene and degree of ventilation. It was also observed that there was no seasonal variation of density. The life cycle of O. savignyi and A. persicus was also studied under optimum conditions and the duration of developmental instars was calculated. The effect of humidity on survival and development of O. savignyi and A. persicus was studied. The species were found to have different tolerance to low humidity. In A. (P) persicus, humidity lower than 33% hindered the gonotrophic development and accelerated larval mortality. In O. savignyi females there was an insignificant effect on gonotrophic development and oviposition at humidities lower than that level. The egg hatchability was also affected and the nymphal survival was shortened. The longest survival period of O. savignyi nymphs was obtained at 97% R.H. Nymph 2 and further developmental phases of both species developed at all levels of humidity, but an accelerated developmental rate, high blood meal ratios, and smaller sizes of the resultant instars were observed as the humidity level was decreased. The responses of nymphal stages and females to hydration and dehydration were compared. Nymphal phases were more susceptible to desiccation than females but the desiccated nymphs responded to hydration better than the desiccated females. The weight changes of nymph 1 instar indicated that the equilibrium relative humidity (ERH) of O. savignyi nymph 1 was about 76% R.H. The coxal fluid secretion rate in nymphal and adult stage and Na+ and K+ mEq of the coxal fluid of males, females and nymphs were compared. It was found that only females emitted coxal fluid during feeding. Males and nymphs emitted coxal fluid only after feeding and detachment. This indicates that infectious agents transmissible through the coxal fluid may be transmitted by the female only. The Na+ and K+ mEq were higher in the coxal fluid of males and nymphs than females and it inversely varied with the coxal fluid volume. Longevity and the number of gonotrophic cycles of O. savignyi and A. persicus showed that starvation of females shortened their longevity, reduced the number of cycles and disturbed their rhythm. Females that were not starved had pronounced longevity and up to five cycles of fertile eggs were produced by females of both species. These cycles were regular and the number of eggs was greater. Fertile eggs were produced in all cycles after a single mating before the first meal, but a significant reduction of hatchability was observed in eggs produced in the late cycles
Studies on Bcology and Developmental Biology of Ornithodoros Savignyi (Audouin) and Argas (Persicargas) Persicus Oken with Reference to their Water Relations