MECHANISMS OF RESISTANCE TO THE RED SUNFLOWER SEED WEEVIL IN SUNFLOWER ACCESSIONS

In the northern Great Plains of North America, internal seed feeding by larvae of the red sunflower seed weevil, Smicronyx fulvus LeConte, causes economic damage to sunflower, Helianthus annuus L. Our purpose was to identify sunflower germplasm with resistance to the red sunflower seed weevil and to determine mechanisms of resistance. In 1986, 300 sunflower accessions were evaluated for the percentage of seed damaged by red sunflower seed weevil larvae. In 1987, six accessions selected on the basis of the 1986 results were evaluated for resistance to the red sunflower seed weevil. The selected accessions had flowering dates comparable to the susceptible check. The percentage of seeds with exit holes (emerged and successfully developed larvae), with larvae (unemerged larvae remaining in the seed), with inclusive damage (total percentage of seeds with exit holes or larvae), and with adult feeding or oviposition scars was used to test for larval antibiosis and adult preference. Larval antibiosis was detected in accessions 251465, 175730, 170407 and 170408 which had significantly higher percentages of seeds with larvae than did the susceptible check. The percentages of seeds with larvae and with inclusive damage were positively correlated with adult feeding or oviposition scars. Therefore, in the accessions tested, larval infestations appeared to be at least partially determined by adult red sunflower seed weevil preference.