Susceptibility of potato cultivars to potato tuber moth, Phthorimaea operculella Zell. (Lepidoptera: Gelechiidae)

Abstract

Twelve named potato cultivars and nine coded breeding lines were compared for degree of tuber infestation by potato tuber moth. (Phthorimaea operculella Zell.) in two small-plot trials. Results were consistent with previous published findings, Ham Hardy producing the highest level of infestation and Rua the lowest among the named cultivars. In laboratory tests the named cultivars were compared for oviposition preference using bare and muslin-covered tubers in choice and non-choice tests. All comparisons were made relative to Ilam Hardy. Differences between cultivars varied according to whether or not the tubers were covered with muslin. No differences occurred in non-choice tests. In tests with foliage only cv. Pentland Dell was significantly different from Ilam Hardy (lower). Cultivars were also compared on the basis of numbers of pupae recovered after known numbers of first-instar larvae were seeded on to both intact and pricked tubers. Significant differences occurred between cultivars with both intact and pricked tubers, and increased numbers of pupae were consistently recovered from pricked tubers relative to intact tubers. Pupal weight and adult fecundity varied according to the cultivar on which larvae fed. Differences occurred between cultivars in the mechanical resistance of the skin of tubers to puncture and in the number of eyes per tuber, but the values showed no correlation with percentage pupae recovered. When cultivars were ranked according to oviposition preference, percentage pupation, and fecundity of moths there was close correlation with ranking based on the degree of infestation in the field, suggesting that such factors are largely responsible for the differences in levels of infestation found between cultivars under field conditions.

Keywords:

• Lepidoptera
• Gelechiidae
• Phthorimaea operculella
• potato cultivars
• relative susceptibility