Effectiveness of natural and engineered host plant resistance in potato tothe Colorado potato beetle

The Colorado potato beetle, Leptinotarsa decemlineata (Say), is the most se rious insect pest of potatoes throughout the eastern and north central Unit ed States. Host plant resistance to the Colorado potato beetle has been ide ntified in wild Solarium species and Bt-transgenic potato lines. Detached-l eaf bioassays (72 h) were conducted on insecticide-resistant, first instar Colorado potato beetles to study the effectiveness of individual and combin ed host plant resistance traits in potato. Potato lines tested include non- transgenic cultivars ('Russet Burbank', 'Lemhi Russet', and 'Spunta'), a li ne with glandular trichomes (NYL235-4), a line with high foliar leptines (U SDA8380-1), and transgenic lines expressing either codon-modified Bt-cry3A or Bt-cry5 (Bt-cry1Ia1). Bt-cry3A transgenic lines, foliar leptine line, an d foliar leptine lines with Bt-cry5 had reduced feeding compared to non-tra nsgenic cultivars. Glandular trichome lines and glandular trichome lines wi th Bt-cry5 did not reduce feeding in this no-choice feeding study. Some Bt- cry5 transgenic lines, using either the constitutive promoters CaMV35s or ( ocs)(3)mas (Gelvin super promoter), were moderately effective in reducing l arval feeding. Feeding on Bt-cry5 transgenic lines with the tuber-specific patatin promoter was not significantly different than or greater than feedi ng on the susceptible cultivars. Mortality of first instars was highest whe n fed on the Bt-cry3A lines (68% to 70%) and intermediate (38%) on the Bt-c ry5 'Spunta' line SPG3 where the gus reporter gene was not included in the gene construct. Host plant resistance from foliar leptines is a candidate m echanism to pyramid with either Bt-cry3A or Bt-cry5 expression in potato fo liage against Colorado potato beetle. Without multiple sources of host plan t resistance, long-term sustainability is questionable for a highly adaptab le insect like the Colorado potato beetle.