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The number of mite species using cricetid rodents in North America is related to the host distributional areas. The age and latitude of the distributional areas have unimportant effects on the number of mite species using a rodent species. The relation between species and areas is analogous to species equilibrium numbers of island faunas.

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SUMMARYInsect herbivores colonizing cyanogenic and acyanogenic white clover plants were investigated. With the exception of aphids, the herbivores studied were infrequent visitors and failed to discriminate between the two phenotypes. Aphids, however, were two to three times more abundant on acyanogenic than cyanogenic plants. Evidence of visible insect feeding damage was identical for both phenotypes. The evidence suggests that the trait of cyanogenesis confers protection against herbivory by aphids and, possibly, other insects. Such protection would be most important at the seedling stage, but feeding of the insects studied would not lead directly to seedling mortality of either phenotype. Instead, mortality of weakened seedlings may result from other causes later in the season.

The response of carabid beetles to differences in tillage and chemical use was studied using four matched pairs of sites. Abundance and species richness were significantly different between treatments, but four commonly used measures of diversity were relatively insensitive indicators of change. It is suggested that the use of diversity indices in impact assessment is redundant or, when used with ground beetles, misleading.

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