Comparison of feeding indices and proteolytic activity of Phthorimaea operculella larvae fed on tubers and leaves of ten potato germplasms

Potato tuberworm, Phthorimaea operculella (Zeller) (Lep.: Gelechiidae) is an important pest of potato in field and storage. Waldbauer nutritional indices and midgut proteolytic enzyme activity of P. operculella larvae fed on tubers and leaves of eight potato cultivars including, Agria, Ausonia, Khavaran, Kondor, Morene, Satina, Savalan, Sprit and two Iranian potato selections (PI396124 and PI397082-2) were evaluated. The results of nutritional indices showed that efficiency of conversion of ingested (ECI) and digested food (ECD) in the fourth instar larvae were the highest in larvae fed on tubers (22.30±0.39%, 32.87±0.69%, respectively) and leaves (22.16±0.39%, 33.19±0.89℅, respectively) of Savalan cultivar. The lowest ECI and ECD were recorded in larvae reared on tubers of Morene (15.83±0.35%, 21.99±0.58%, respectively) while the lowest amounts of these two traits were observed in larvae fed on leaves of Khavaran (18.75±0.68%, 25.09±0.76℅, respectively) and Agria (19.35±0.26%, 25.91±0.32%, respectively). Among ten potato germplasms tested in the study, the highest proteolytic activity was on the larvae fed on tubers of Morene (8.204±0.296 U/mg) because of the most tuber flesh firmness and the lowest were recorded in larvae fed on tubers of Savalan (2.740±0.131 U/mg) due to the less tuber flesh firmness. The highest proteolytic enzyme activity was recorded on leaves of Savalan (6.578± 0.068U/mg). Also the lowest protease activity was in larvae fed on leaves of Khavaran (4.339±0.093 U/mg) and Agria (4.407±0.143 U/mg). It can be inferred that Savalan is susceptible and the three potato cultivars Khavaran, Morene and Agria are moderately resistant to P. operculella.

Keywords:

potato tuberworm , cultivar , selection , digestive enzyme , ECI , ECD