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Land disposal of sewage sludge and effluent is becoming a common practice in the United States. The fertilizer content and humus value of such wastes are useful for agricultural purposes, and the recycling of sewage onto the land eliminates many of our stream pollution problems. The potential exists for crops grown in such irrigated soil to be contaminated by viruses that may be present in the sewage. Studies were initiated to determine viral persistence in soil and on crops grown under natural conditions in field plots that had been flooded to a depth of 1 inch (2.54 cm) with poliovirus 1-inoculated sewage wastes. Lettuce and radishes were planted in sludgeor effluent-flooded soil. In one study, the vegetables were planted 1 day before flooding, and in another they were planted 3 days after the plots were flooded. Survival of poliovirus 1 in soil irrigated with inoculated sewage sludge and effluent was determined during two summer growing seasons and one winter period. The longest period of survival was during the winter, when virus was detected after 96 days. During the summer, the longest survival period was 11 days. Poliovirus 1 was recovered from the mature vegetables 23 days after flooding of the plots had ceased. Lettuce and radishes are usually harvested 3 to 4 weeks after planting.

Experiments on competition in house flies reported here extend two previous studies by Sullivan and Sokal (1963) and Sokal and Sullivan (1963). The wild typed OL strain, the autosomal recessive bwb, and the reciprocal crosses bwb x OL (called A for short) and OL x bwb (called B) were reared at seven densities ranging from 40 to 2,560 eggs per 36 g of CSMA larval medium, both in pure and mixed cultures. Three possible mixtures, OL: bwb, A: bwb, and B: bwb, were set up in three proportions, 10:90, 50:50, and 90:10 parts of wild phenotype to mutants, respectively. The nine possible combinations were replicated minimally five times per density. The numbers, dry weights, and times of emergence of adults were recorded by genotype. The responses of the hybrids resembled those established previously for the wild type flies. The reciprocal heterozygotes were not markedly different from each other. In mixed culture the emergence of bwb flies is affected more severely by an increase in density than that of their competitors. Hence the relative fitness of the wild phenotype increases markedly with density. At the highest densities hybrids weigh more in competition than they do in pure culture. Crowding increases the mean and variance of duration of adult emergence. Mutants emerged fastest in pure culture, whereas the wild phenotypes are fastest in mixed culture. Competition reduces the variance of duration of emergence in the wild type, though increasing it in the mutant. When the wild phenotype is present in low proportions in dense mixed culture its survival, weight, and duration of emergence are better than when it is frequent. These findings are Reviewed and discussed from the point of view of genetic factors in competition, genetic facilitation, and gene frequency dependent changes in components of fitness. A brief comparison is made with a related study of the ge strain in the house fly.

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