Assessement of different potato varieties to potato tuber moth Phthorimaea operculella (Zeller)(Lepidoptera: Glichiidae) infestation

Two experiments were designed for studying susceptibility of twelve potato varieties to potato tuber moth infestation according to external (epiphylaxis) and internal (endophylaxis) factors. Epiphylaxis factors (external protection agencies) were determined through ovipositional preference tests, while endophylaxies factors (internal protection agencies) were determined through feeding preference tests. The most susceptible varieties, which encouraged PTM female to lay the largest number of eggs, were Bern and Nicola varieties where the average number of laid eggs was 23.8 ± 4.6 and 18.6 ± 2.9 eggs / female, respectively.Bern and Nicola varieties were the most preferred varieties for oviposition by PTM; while CNK-007-021 was the least suitable variety.The highest number of surviving larvae was recorded inside tubers of Bern variety, being 14.4%.The duration of the larval stage inside potato tubers varied from one variety to another. The shortest average of the larval duration was recorded on varieties; Lady Rosetta (19.4 ±0.4 days), Glob (19.2 ± 0.7 days) Sanorata (19.2 ± 0.5 days) and Monaliza (19.2 ± 0.4 days). The susceptibility of the tested twelve potato varieties to PTM larvae was determined by measuring the larval penetrating tunnel length. The shortest average length of tunnel as criteria of variety susceptibility was achieved in case of Monaliza, Charisma and Lady Rosetta tubers with 2.5±0.2, 3.6±0.5 and 3.9±0.6 cm, respectively. On the other hand, the most resistant varieties with longest tunnels were Mirakel (8.9± 0.9), Nicola (8.7± 0.3) and Bern (8.3± 0.9) cm, respectively. The most preferred and attractive varieties for larval feeding were Bern, Nicola and Mirakel. .