DISTRIBUTION OF FEEDING DAMAGE BY PHYLLOTRETA-CRUCIFERAE (GOEZE) (COLEOPTERA, CHRYSOMELIDAE) ON OILSEED RAPE AND MUSTARD SEEDLINGS IN RELATION TO CROP RESISTANCE

The distribution of feeding damage by adult Phyllotreta cruciferae (Goeze) was examined on the cotyledons, first true leaves, stems, and petioles of four crop species of Brassicaceae (Brassica juncea L. ''Cutlass'', B. napus L. ''Westar'', B. rapa L. ''Tobin'', and Sinapis alba L. ''Ochre''). Previous studies showed that B. napus and B. rapa are susceptible, B. juncea is partially resistant, and S. alba is highly resistant to P. cruciferae. Flea beetles usually fed more on the upper surfaces, bases, and edges of cotyledons and first true leaves, but the feeding patterns were not identical on the four species. Phyllotreta cruciferae had a greater preference for the upper surface of S. alba cotyledons than for the upper surfaces of Brassica species. First true leaves of B. napus had over 90% of the feeding damage along the edge, compared with <70% for the other species. The size of feeding pits did not differ on the upper and lower surfaces of the cotyledons and first hue leaves for the Brassica species, but S. alba had smaller feeding pits on the lower surface. Sinapis alba also had the smallest feeding pits on the upper surface of its cotyledons, and S. alba and B. juncea first true leaves had feeding pits about one-half the size of the feeding pits on the other species. There was no significant difference in the amount of stem damage for the four species, but B. juncea had significantly less petiole damage than S. alba. Although there were differences in the way P. cruciferae exploited the seedling tissues of these Brassicaceae, the differences were not consistent with, or were too small to account for, the different levels of resistance of the four crops.