As a general test of the energetic equivalence rule, we examined macroecological relationships among abundance, density and host body mass in a comparative analysis of the assemblages of trophically transmitted endoparasitic helminths of 131 species of vertebrate hosts. Both the numbers and total volume of parasites per gram of host decreased allometrically with host body mass, with slopes roughly consistent with those expected from the allometric relationship between host basal metabolic rate and body mass. From an evolutionary perspective, large body size may therefore allow hosts to escape from the deleterious effects of parasitism.

The parasite community of animals is generally influenced by host physiology, ecology, and phylogeny. Therefore, sympatric and phylogenetically related hosts with similar ecologies should have similar parasite communities. To test this hypothesis we surveyed the endoparasites of 5 closely related cheilinine fishes (Labridae) from the Great Barrier Reef. They were Cheilinus chlorourus, C. trilobatus, C. fasciatus, Epibulus insidiator and Oxycheilinus diagramma. We examined the relationship between parasitological variables (richness, abundance and diversity) and host characteristics (body weight, diet and phylogeny). The 5 fishes had 31 parasite species with 9-18 parasite species per fish species. Cestode larvae (mostly Tetraphyllidea) were the most abundant and prevalent parasites followed by nematodes and digeneans. Parasites, body size and diet of hosts differed between fish species. In general, body weight, diet and host phylogeny each explained some of the variation in richness and composition of parasites among the fishes. The 2 most closely related species, Cheilinus chlorourus and C. trilobatus, had broadly similar parasites but the other fish species differed significantly in all variables. However, there was no all-encompassing pattern. This may be because different lineages of parasites may react differently to ecological variables. We also argue that adult parasites may respond principally to host diet. In contrast, larval parasite composition may respond both to host diet and predator-prey interactions because this is the path by which many parasites complete their life-cycles. Finally, variation in parasite phylogeny and parasite life-cycles among hosts likely increase the complexity of the system making it difficult to find all-encompassing patterns between host characteristics and parasites, particularly when all the species in rich parasite communities are considered.

Chagas disease caused by infection with Trypanosoma cruzi Chagas (Kinetoplastida: Trypanosomatidae) is widespread in Mexico, transmitted by various triatomine bugs (Hemiptera: Reduviidae). The only domestic vector in Cuernavaca (population 650 000) is Triatoma pallidipennis (Ståhl) with T. cruzi seroprevalence ranging from 1% to 9% in the resident human population. We surveyed possible risk factors for T. pallidipennis infestation at Cuernavaca (altitude 1200-2200 m) on south-western slopes of the Sierra Madre Occidental. This metropolitan area (with five administrative counties) has rapid urbanization, forested environs and proliferation of 'weekend housing' for visitors from Mexico City, 60 km to the north. To assess factors associated with T. pallidipennis infestation, we first stratified Cuernavaca by altitude and by socio-economic status of population catchment units (PCUs). Within each PCU, one to three blocks were chosen for cluster sampling (three houses/block) and information about Chagas disease was distributed. After obtaining signed consent from householders, representative houses were routinely and opportunistically inspected for T. pallidipennis and surveyed for demographic, economic, physical and other potential risk factors. Of the 1129 houses assessed, T. pallidipennis was found in 4.1% (range 3.0-6.8% per county) and the T. cruzi infection rate was approximately 50% in bugs. Rates of house infestation in poor PCUs were double those in higher socio-economic strata (odds ratio 2.12, confidence interval 1.03-4.3), with >4-fold greater crowding index of T. pallidipennis. The bug density index was inversely correlated with PCU altitude and socio-economic category (altitude of homes being associated with prosperity), while the bug colonization index (presence of nymphs indicating breeding) did not vary significantly across the PCU categories, but did vary according to altitude. Multivariate regression analysis showed that the most significant risk factors associated with T. pallidipennis infestation were lower altitude (linked with lower socio-economic status), garden area >80 m(2), dogs at liberty to enter the house, occurrence of squirrels and opossums around the house, presence of pigs in the surrounding area and having at least one of the adjacent lots empty (unconstructed). Householders who had received information about Chagas disease comprised 33% from infested houses (14/42) but only 15% from non-infested houses (148/984). Hence, the awareness of Chagas disease was significantly associated with having a bug-free house (P < 0.01). When shown specimens of T. pallidipennis, the proportions of householders who recognized them were 78% from infested houses but only 29% of those with uninfested houses. Given the low infestation rates and the high capacity of the population to act appropriately once they have received information regarding this disease and its vector, relevant health education is expected to have a significant impact on triatomine control in this metropolitan area.

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cially if manure is surface-applied (Thompson et al., 1987). Conversely, denitrification losses of manure N Repeated N applications to field crops, either as inorganic fertilizers are increased by incorporation or injection (Comfort et or animal manures, can lead to N buildup in soils with potential longterm environmental hazards. The objective of this 3-yr field study al., 1988), and because organic matter in manure serves was to monitor total-and mineral-N levels in soil after repeated as a substrate for denitrifier microorganisms, tend to be fertilizer or single or repeated dairy manure applications, and to comhigher than denitrification losses in fertilized soils pute an N balance for the soil-crop system. Unlabeled and 15 N-enriched (Cates and Keeney, 1987). Immobilization of inorganic dairy manure were used. The experiment was conducted on a Plano N in manure, plus the greater volatilization and denitrificorn silt loam continuously cropped to corn (Zea mays L.) Manure cation losses, cause inorganic N in manure to be less increased total-and NO 3-N levels in soil, especially in the 0-to 30-cm plant-available than equal rates of inorganic fertilizer depth and in plots receiving frequent and recent manure applications. Manure increased NO 3-N in the 0-to 30-cm soil layer more than (Paul and Beauchamp, 1993). Because of its lower N fertilizer N, whereas the opposite was true in the 30-to 60-and 60availability, greater amounts of manure than fertilizer to 90-cm layers. There was a clear NO 3-N buildup with repeated N are applied to crops. This can result in a steady accumanure treatments. Unlabeled N measurements were not accurate mulation of soil N. Long-term soil N accumulation on enough to track trends in soil total N levels, hampering the calculation dairy farms poses a serious environmental risk (Bouldin of an N balance. 15 Nitrogen-labeled manure allowed for direct meaet al., 1984). Heavy and/or repeated manure applications surement and provided more accurate estimates of N recovery in soils and crops. During the 3-yr study period, an average of 18% of applied can lead to NO 3-N buildup in soil and losses through manure 15 N was recovered in corn silage and 46% remained in the leaching (Adriano et al., 1971; Mathers and Stewart, soil. Unaccounted-for 15 N (36%) was assumed to be lost mainly by NH 3 1974; Smith et al., 1980; Cooper et al., 1984). Dairy farms volatilization and denitrification. Most (82%) of the 15 N remaining in in the Midwest are considered significant contributors of soil was present in the top 30 cm, irrespective of frequency of manure N to the hypoxic zone in the Gulf of Mexico (Burkart application. Although costly and time-consuming, the use of 15 Nand James, 1999). labeled manure provided a much better approach to study the fate Excessive soil nutrient accumulation and losses to of manure N within the soil-crop system, compared with unlabeled manure. 1998 63 35 70 224 194 388 57 113 from one cropping season to the next, which were usually 1999 63 38 77 284 250 501 69 137 reflected in ...