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The biochemical systematics of 6 closely related species: Phyllotreta aerea Allard, 1859, P. astrachanica Lopatin, 1977, P. atra (F., 1775), P. consobrina (Curtis, 1837), P. cruciferae (Goeze, 1777) and P. nigripes (F., 1775) were studied. This study is on the genetics and biochemical systematics of these 6 economically harmful species, including several populations of each species. Material from 27 populations divided over 6 species (>3,500 specimens) was used for allozyme electrophoresis. An allozyme-based determination key was constructed. Genetic variability measures for the different populations were calculated; Rogers modified distances and Cavalli-Sforza and Edwards arc distances between each pair of populations are presented. Unweighted pair-group method with arithmetic average and distance Wagner trees based on Rogers and Cavalli-Sforza and Edwards arc distances show slightly different topologies. Two major clusters ( P. aerea / P. consobrina and P. atra / P. cruciferae ) are found in all dendrograms, but the positions of P. astrachanica and P. nigripes leave some room for discussion.

Mustard oil glucosides, principal constituents of the host plants of adult flea beetles, Phyllotreta cruciferae Goeze, stimulated a feeding response on bean leaves, normally unacceptable hosts. Distinct glucoside preferences were found when bean leaves were cultured in 5 different glucosides (0.5% aqueous solutions) and offered in laboratory feeding experiments. When bean leaves were cultured in different sinigrin concentrations, the minimum concentration required to stimulate feeding was 0.01% (153 ppm) sinigrin. The amount of feeding increased with sinigrin concentration up to 3.0% (45,900 ppm) sinigrin but dropped off drastically at 4.0% (61,200 ppm) sinigrin. These findings suggest that mustard oil glucosides play a significant role in host-plant selection by P. cruciferae adults.

Host and parasite life cycles and field incidence are reported for Microctonus vittatae Muesebeck, a parasite on Phyllotreta cruciferae (Goeze) and P. simmermani (Crotch); M. epitricis (Viereck), on Epitrix cucumeris (Harris); M. disonychae Loan, on Disonycha triangularis (Say); M. crepidoderae Loan, on Crepidodera spp.; M. blapstini Loan, on Blapstinus metallicus (F.); and M. muesebecki Loan, on Paria thoracica Melsheimer. Phyllotreta cruciferae , a recent European import destructive to cultivated crucifers, is a new host of M. Vittatae , which is parasitic on the native P. simmermani . Mesochorus phyllotretae Jourdheuil, a secondary ichneumonid new to North America, was reared from Microctonus vittatae .

Insect samples from field plots of plants representing 23 different families indicated that adults of the flea beetle Phyllotreta cruciferae (Goeze) and the striped flea beetle, P. striolata (F.), have a narrow host range, restricted among the plants tested to the families Capparidaceae, Cruciferae, and Tropaeolaceae. This result was confirmed for P. cruciferae adults by laboratory feeding preference tests; of 55 plant species belonging to 31 families, only those plants belonging to the families Capparidaceae, Cruciferae, Tropaeolaceae, and Limnanthaceae were eaten. The coincidence between the preferred plant families and the plant families known to contain mustard oils suggested that these compounds or their glycosides might be acting as chemical attractants for the beetles. Field experiments showed that allyl isothiocyanate is a powerful attractant for adults of both P. cruciferae and P. striolata .