A
sand dilution assay was developed to study how composting affects the nutritional value of stored laying hen
manure for larvae of the house fly, Musca domestica L. Equal numbers of eggs were inoculated into graded amounts of stock
manure and incubated under standardized moisture conditions. Survival and mass per emerging adult diminished with progressively lower supplies of
manure per larva, whether the
manure was diluted into clean, white
sand or placed on top of an equal volume of
sand. Mass of adults per original egg was an increasing linear function of log,
manure supply, with extrapolated lower supply threshold, S(L) = 0.06 g per egg. It is proposed that S(L) is a measure of a substrate's nutritional value--the greater the threshold, the lower its value. Dilution of the same stock
manure in loam or sandy loam reduced the
manure's apparent nutritional value, and
dehydration of the stock
manure to 20% water before
rehydration to 70% also reduced nutritional value. Assays of bulk samples from replicated piles of laying hen
manure mixed with sunflower hulls indicated the mixture was nutritionally equivalent to the stock
manure, but that 3-4 wk of subsequent aerobic, thermophilic composting reduced it to approximately 10% of its initial value. These results suggest that composting may be a useful technique for reducing the fly breeding potential of laying hen
manure and other substrates that must be stored before spreading and incorporation on crop land.