Niche differentiation by crucifer-feeding flea beetles (Coleoptera: Chrysomelidae)

The coexistence of six closely related crucifer-feeding flea beetles in central New York was due to distinct host-plant and micro-habitat preferences. Extensive sampling from five crucifer species, growing in their natural habitats and cultivated in an open field and shady woodland, revealed obvious differences between the species. Phyllotreta bipustulata, the most specialized species, fed exclusively on Dentaria diphylla in moist woodlands. Phyllotreta cruciferae fed almost exclusively on Brassica nigra in open, sunny fields, and Psylliodes napi fed on Barbarea vulgaris in cool, shady field microhabitats. Phyllotreta striolata was the most generalized herbivore; it fed equally on all five crucifer hosts. Both Phyllotreta zimmermanni and Psylliodes punctulata occurred in small numbers on the host plants in open field habitats and no distinct host-plant preferences were established. Laboratory experiments with four of the flea beetle species confirmed feeding preferences observed in the field. In all three experiments, P. striolata had the broadest host breadth and largest mean host overlap, followed in decreasing order by P. zimmermanni, P. punctulata, P. cruciferae, P. napi and P. bipustulata. Estimates of percentage similarity indicated that competitive interaction between P. striolata and P. cruciferae could be severe, since both species occurred together in high densities. Values for P. bipustulata showed little interaction with other species, further demonstrating its most effective niche isolation.