This study documents dynamic changes in the mean abundance and body size of arthropods in an ephemeral pond over the course of a summer in order to understand the nature of interactions that shape this community, and to assess the risks posed by exposure to cercariae of the entomopathogenic digenean, Plagiorchis elegans, a potential control agent for larval mosquitoes. Chironomids were the most abundant, comprising almost two-thirds of all arthropods collected; they were followed by chaoborids, the most abundant predator. Other arthropods, in decreasing order of abundance, were the ephemerids, isopods, amphipods, odonates, dytiscids, and hemipterans. Infections were found only in chironomids and were extremely rare and of low intensity, conceivably due to predation of chaoborids on cercariae and may have protected the community from exposure to these parasites. Findings are discussed in terms of using entomopathogenic digeneans as agents in the biological control of mosquitoes.

Aedes aegypti pupae were exposed to cercariae of the digenean Plagiorchis noblei in order to assess the effects of infection on the spontaneous flying activity and reproductive success of surviving adults. Infections established primarily in the thorax and abdomen of the insects (mixed infections) or in the abdomen alone. In mixed infections, as few as one or two metacercariae in the thorax reduced the spontaneous flying time of females by almost half. Such infections also reduced total egg production, the number of ovarian cycles, fecundity per cycle, as well as fertility and life span of female hosts. The fertility and life span of males was similarly affected. Purely abdominal infections reduced the life span of males and females as well as the fertility of males, but only at high intensities. Such effects on adult behaviour, reproductive success and life span may augment the known lethal effects of the parasite.

Waters from normal larvae of Aedes aegypti (L.) are highly attractive to ovipositing conspecific females, whereas waters from larvae infected with the entomopathogenic digenean parasite, Plagiorechis elegans Rudolphi, are rendered strongly repellent. The production of the repellent appears to be mediated by the degree of environmentally induced stress experienced by the larvae. Whereas waters from fully fed larvae were highly attractive as an oviposition site, these were rendered progressively less attractive, and eventually strongly repellent as the larvae were deprived of food over a period of 7 days. Crowding of the larvae elicited similar repellent effects as did close contact between larvae and the walls of the container in which they were reared. The site of infection in the tissues of the mosquito larvae also influenced the intensity of repellency. Thus, infections of the head and thorax induced the highest degree of repellency, and infections of the abdomen the lowest. The repellent effect overrode attraction and remained stable for more than one week at 27°C, and even longer at lower temperatures. Stressors which induced repellency all precipitated similar physical and physiological changes in mosquito larvae. They reduced wet and dry weights and the concentration of serum carbohydrates, amino acids, proteins and lipids. Both infection and crowding rendered larvae anorexic. As well, infected larvae appeared to be unable to convert trehalose to glucose, thereby exacerbating the energy deficit. Incubating infected larvae in a dilute glucose solution significantly reduced the repellent effect of their waters. Addition of glucose to already repellent waters had little effect. Larvae of another species, Aedes atropalpus Coquillett, were equally capable of producing repellent effects when infected with P. elegans, and gravid females of Ae. aegypti were equally sensitive to these as to conspecific waters. This sensitivity, however, was not reciprocal. Aedes

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