Elucidating the mechanisms of host plant resistance to the banded sunflower moth in selected sunflower accessions

The banded sunflower moth (BSM) Cochylis hospes Walsingham is the most destructive seed-infesting insect pest of sunflowers causing economic losses in northern Great Plains. In an effort to assist the breeding program for developing BSM resistant sunflower hybrids, a three year study was conducted to determine the mechanisms of host plant resistance to BSM in selected sunflower accessions. Five pre-screened resistant sunflower accessions were evaluated for 2-3 years (2005, 2006, and 2008) with Par 1673-2 as susceptible check. Among the tested accessions, PI 494859 appears to be the most preferred for oviposition recording significantly higher number of eggs (49-212) per head than the susceptible check (57-93) in 2 out of 3 years. However, PI 494859 had a significantly lower larval survival (25-68 larvae/head) and percent seed damage (18-35%) compared to Par 1673-2 (66-175 larvae/head and 37-78% seed damage) which indicates either antibiosis or antixenosis (feeding deterrent) as the modes of resistance. The average weights of the larvae feeding on the seeds of PI 494859 were substantially lower further supporting our assumption. Inspite of lack of correlation between egg and larval numbers, the accession PI 170385 appeared to be antixenotic to female BSMs due to low oviposition, which resulted in lower larval numbers and percent seed damage. The accessions PI 291403, 497939, and 251902 exhibited slight antibiosis with moderately low egg and larval numbers and percent seed damage. No strong association was found between resistance to BSM and parasitism.