Sunita Pandey , Marc Sporleder , Yubak Dhoj Gharty Chhetry ., Yagya Prasad Giri and Jürgen Kroschel

DOI

ABSTRACT

The potato tuber moth Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae) is major pest of potato (Solanum tuberosum L.) in tropical and subtropical regions of the world causing serious economic damage especially in non-refrigerated potato storerooms. Chemical pesticide use for post-harvest pest management in farmers’ rustic storerooms causes health risks to farmers and consumers, triggered a search for safer pest management alternatives, such as use of entomopathogens. Metarhizium anisopliae (Metsch.) Sorokin culture originally isolated from white grub larvae native from Nepal was grown on artificial media and its biological activity assessed against the potato tuber moth in the laboratory, using potato tuber surface contamination bioassay. A total of 5 bioassays were conducted. In four bioassays fresh fungus stock suspensions were tested while in one bioassay the fungus stock suspension of the first bioassay was reused after 8-month storage period at ambient temperature. All probit lines revealed a common slope of 0.57. The first stock suspension revealed an LC50-value of 6.9×106 conidia/ml while after 8-month storage a significant activity loss of about 90% (7.2 ×107 conidia/ml) was observed. The other three bioassays revealed LC50-values of mean 4.2×105 (2.9 to 6.1×105) conidia/ml without significant differences in their potencies. According to the probit lines (3-5) > 7.5x10^7 conidia/ml would be required to kill >90% PTM. Hence it can be concluded that the M. anisopliae strain showed high biological activity against PTM larvae and has potential as bio-control agent for controlling the pest; however, activity can be significantly reduced if stored inappropriately or for longer periods.