Host-Range Studies with the Sweetclover Weevil and the Sweetclover Aphid1

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Abstract
In greenhouse studies the sweetclover weevil, Sitona Cylindricollis Fåhraeus, fed on 18 species of Melilotus, 12 of Trigonella, 1 ofMedicago, but not on Melilotus infesta Cuss.M. infesta did not appear to have any deleterious effect upon the weevil, but did strongly deter its feeding. There seemed to be no relationship between coumarin content and weevil feeding, since some host plants were high while others were low in coumarin. The host range of the sweetclover aphid, Therioaphis riehmi (Börner), was extended to include 9 species of Melilotus and 8 of Trigonella, all previously unreported. Although the sweetclover weevil and the sweetclover aphid share a common group of host species, the factor or factors which determine host suitability appeared to operate independently for the 2 insects.