Combining Natural and Engineered Host Plant Resistance Mechanisms in Potato for Colorado Potato Beetle: Choice and No-choice Field Studies

Colorado potato beetle (Leptinotarsa decemlineata Say) is the leading insect pest of potato (Solanum tuberosum L.) in northern latitudes. Host plant resistance is an important tool in an integrated pest management program for controlling insect pests. Field studies were conducted to compare natural host plant resistance mechanisms (glandular trichomes and Solanum chacoense Bitter-derived resistance), engineered (Bacillus thuringiensis (Bt) Berliner Bt-cry3A), and combined (glandular trichomes + Bt-cry3A and S. chacoense-derived resistance + Bt-cry3A transgenic potato lines) sources of resistance for control of colorado potato beetle. Six different potato clones representing fi ve different host plant resistance mechanisms were evaluated for 2 years in a fi eld situation under natural colorado potato beetle pres- sure in Michigan and New York, and in a no-choice fi eld cage study in Michigan. In the fi eld studies, the S. chacoense- derived resistance line, Bt-cry3A transgenic, and combined resistance lines were effective in controlling defoliation by colorado potato beetle adults and larvae. Effectively no feeding was observed in the Bt-cry3A transgenic lines. The glandular trichome line suffered less defoliation than the susceptible control, but had greater defoliation than the Bt- cry3A transgenic lines and the S. chacoense-derived resistance line. In the no-choice cage study, the Bt-cry3A transgenic lines and the combined resistance lines were effective in controlling feeding by colorado potato beetle adults and larvae with no defoliation observed. The S. chacoense-derived resistance line and the glandular trichome line suffered less defoliation than the susceptible control. Based on the results of the fi eld trials and no-choice fi eld cage studies, these host plant resistance mechanisms could be used to develop potato varieties for use in a resistance management program for control of colorado potato beetle. The colorado potato beetle is the most serious insect pest of potatoes throughout the eastern and north central United States and Canada. Control of the colorado potato beetle has relied almost entirely on pesticides for over 125 years (Casagrande, 1987). Throughout its history, the colorado potato beetle has shown the ability to adapt to every insecticide used for its control (Bishop and Grafi us, 1996). Currently, it has developed resistance to 41 insecticides, including organophosphates, carbamates, organo- chlorines, pyrethroids, hydrogen cyanide, and more recently the neonicotinoids imidacloprid and thiamethoxam (Byrne et al., 2004; Georgiou and Lagunes-Tejeda, 1991; Whalon et al., 2004). Host plant resistance is a central component of a practical long- term solution for controlling the colorado potato beetle in potato. No potato varieties resistant to colorado potato beetle are cur- rently available. Glandular trichomes and leptine glycoalkaloids are two of the most thoroughly investigated natural insect host plant resistance mechanisms available in potato. The glandular tri- chomes of the wild Bolivian potato, Solanum berthaultii Hawkes, confer resistance to at least ten major insect pests, including the colorado potato beetle (Tingey, 1991). The presence of Type A and B trichomes in S. berthaultii leads to entrapment and death of