Thesis (doctoral)--Université d'Aix-Marseille, 1962. / "No. d'ordre: 110." Includes bibliographical references (p. 141-146).

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No description available.

The effects of food availability and the presence of the parasite, Plagiorchis elegans, on the probability of Aedes aegypti preimagos to transform from one immature stage to the next over consecutive 24- or 48-hour periods of time were determined. Under conditions of low food availability, 24- and 48-hr transition probabilities of all larval instars, to the next were reduced. Increases in food availability reversed this process, causing significant decreases in same-stage transition probabilities. However, as transition to successive stages increased among first, second, third and fourth instars, there was concomitant significant increase in first and fourth preimago mortality. Addition of Plagiorchis elegans cercariae caused significant decreases in the 24 and 48-hour same-state probabilities for all pre-imago stages. Successive stage transitions for first, second and third instars were significantly increased while those of fourth instars and pupae were significantly decreased following exposure to the parasites. The mortality of all preimago stages significantly increased with exposure to parasite, but was highest among fourth instars and pupae. There were strong food-by-parasite interaction effects among first, second and third instars. Differences in transition probabilities increased with increasing food levels between controlled and parasite-exposed groups. The opposite was true for fourth instars and pupae. While there was no significant interactive effect between food and the presence of the parasite on pupae regardless of food concentration, this was not true for mortality probabilities among fourth instars. Significantly more fourth instars died in response to parasite exposure and there were significant interactive effects of food and parasites on the probability of fourth instars transformation to pupae over 48 hrs.

The effects of food availability on the population structure of Aedes aegypti in the presence and absence of Plagiorchis elegans cercariae were studied in the laboratory. Under conditions of low food availability and in the absence of the parasite, larval population levels cycled at 40 day intervals. Cycles were initiated by the periodic build-up and decline of fourth instar larvae. These major competitors for food resources appear to be responsible for the release of a cascade of events which allowed the intermittent flow through of larvae from the first to the third instar. Under both optimal and suboptimal conditions of food availability, the introduction of high densities of P. elegans cercariae resulted in a decrease in the production of adult mosquitoes. Although the parasite reduced competition by preferentially removing fourth instar larvae and hastened the development of surviving instars, such survivors were exposed to the effects of the parasite as soon as they reached the fourth instar.

The effects of food availability and selective control of late instar larvae of Aedes aegypti on preimago population structure, mortality, adult abundance, sex ratios, and size of females were examined. Food availability i an important factor in determining preimago population structure and mortality. At optimal food availability more adults emerged, females were larger and in higher proportions than at suboptimal food availability. The effects of selective control on preimago population structure and post treatment larval mortality differed with food availability. At suboptimal food availability the type of control applied had a significant effect. Simulated pathogen-induced mortality resulted in a shift of the population to late instars and temporarily reduced density dependent mortality. The findings suggest that although both pathogens and predators reduce intraspecific competition by directly killing competitors, pathogens also provide an influx of food. Compensatory mortality may result from a reduction of intraspecific competition caused by biocontrol agents.

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No description available.

No description available.

Exposure of fourth instar Aedes aegypti larvae to graded concentrations of the entomopathogenic cercariae of the digenean Plagiorchis elegans, induced fundamental changes in the partitioning of time among a number of major behavioural activities. In the absence of the parasite, swimming, breathing and feeding remained stable over time. Grooming was rarely observed. In the presence of cercariae, larvae increased grooming 26-fold. Concomitantly, feeding was reduced to 33% of control values. Times spent swimming and breathing remained unchanged. The increase in grooming activity was attributable to the attachment of cercariae to the surface of the mosquito larvae, but was independent of infection. Grooming reduced cercarial penetration. Seventy-five percent of cercariae were lost to predation by larvae, but their caloric value was insignificant and failed to compensate for the loss of feeding time due to grooming. The findings are discussed in the context of their impact on larval growth, development and survival.