Flea Beetle Movement in a Broccoli Monoculture and Diculture

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Abstract
Colonization of broccoli monocultures and broccoli–white clover dicultures by Phyllotreta cruciferae Goeze (Coleoptera: Chrysomelidae) was observed at Ithaca, N.Y. A simple continuous time model of P. cruciferae movement was developed, and instantaneous immigration and emigration rates were estimated. The movement model fit the observed colonization data extremely well (r2 = 0.971). Immigration was 1.3 times faster into broccoli monocultures than into dicultures, and emigration was about 2 times faster from dicultures than from monocultures. This differential movement in monocultures and dicultures resulted both from differences in host plant quality and presence or absence of white clover. Our results provide strong, direct support for Root's (1973) hypothesis that host plants are harder to find and easier to lose in vegetationally diverse habitats than in monocultures. In addition, after perturbation, population densities rapidly returned to unperturbed levels. This implies that P. cruciferae can rapidly respond to changes in its environment, which might underlie its success as a crop pest.