Relationship between Feeding Damage by Beet armyworm, Spodoptera exigua (Lepidoptera: Noctuidae) and Leaf Trichome Density of Potato

The responses (infestation level and feeding preference) of 50 potato cultivars, including seven Korean recommended cultivars to Spodoptera exigua larvae were examined in the field and the laboratory. Based on the number of potato leaves damaged by S. exigua larvae in the field, seven cultivars (Anco, Denali, Bintje, Jidose, Sandra, Shimabara, and Spunta) were found tolerant to the insect attack, whereas Nicola and Dejima cultivars were highly susceptible. In feeding preference tests using leaflets of 10 selected cultivars (Anco, Denali, Bintje, and seven recommended cultivars), no significant differences were seen among the cultivars, indicating no involvement of chemical resistance. In trichome density per mm2 leaf area, underside leaf surface contained higher trichome densities than the upper side, and the number of long trichome were distributed four times more than short trichome on average. Total leaf trichome density was the highest on cv. Dejima of 32.1, followed by cvs. Bintje and Denali, but the lowest on cv. Jopung of 6.9. From correlation analysis, infestation level in the field by S. exigua was correlated with the density of shorter trichome on upper side of leaf surface (r = 0.737* in 1996 and 0.772** in 1997). However, it was not correlated with the density of the longer trichome on underside.