Introduction
Potato, one of the most important culinary in Nepalese kitchen, is susceptible to more than 101 arthropod species of pests, according to Simpson, 1977: Potato tuber moth (Phthorimaea opercullela) is one of the most important pest among these which belongs to the order Lepidoptera and family Gelechiidae. It was first appeared in Western South America (Graf, 1917); however, it has been a global pest at the present context. This pest has invaded most parts of Nepal where potato is grown.
Potential hosts of PTM
This pest is a polyphagous pest and attacks egg plant, tobacco, chilli, tomato, wild brinjal, etc. and other members of the Solanaceae family.
Damage and life cycle
The larval stage is the infective stage of this pest which attacks the plant by mining the leaves, penetrating into them and then weakening and breaking the stem. The adult moth lays eggs singly in the eye buds of the potato tubers, the most appropriate place for its oviposition where a slight depression is present enough to accommodate the eggs, causing irregular galleries deep inside the tubers. The number of eggs laid by a female moth at a time ranges from 38-290 and the time taken by those eggs for hatching ranges from 5-34 days. The pupation takes place in the soil and in dead leaves. According to Graf, 1917, the larval and the pupal period of this moth were 13-33 and 12-29 days respectively and he estimated that the progeny of one pair of these moths could be about 60,000,000 at the end of fourth generation.
Management
1. Planting healthy potato tubers at a depth of about 10 cm rather than 6 cm reduced to about 9% from 18% according to Saxena and Raj(1979)
2. Applying sprinkler irrigation method instead of furrow irrigation which reduces the PTM infestation by about 58 times; the first instar larva cannot move through wet soil but can move through water and can penetrate about 12.5 cm of dry soil (Mahajan and Mogal, 1978)
3. Blattisocius keegani, the egg parasitoid of PTM in storage condition can be an effective biocontrol method (Hugh, 1976).
4. Using granulosis virus and baculovirus which are found very effective against the PTM infestation (Reed, 1964) (Raman, 1988).
5. Baculovirus and Bacillus thuringiensis var. Kursataki can be used to protect the tubers for about 60 days (Amonkar et al., 1979).
6. Ageratum conyzoides leaves, Ocimum bacillicum seed extracts, Acorus calamus rhizomes were found toxic to the larvae by Pandey et al. 1982
7. Acetone extracts of Anisomeles malabarica, Lavendula bipinnata, L. gibsoni and Ocimum americanum have been found to deter the oviposition of PTM. Moreover, good ovicidal property has been shown by the extracts of L. gibsoni.
8. By using potato tuber moth resistant varieties.
9. Spraying chlorofenvinphos (0-4 kg a.i./ha), acephate (0-5 kg a.i./ha), quinalphos (0-375 kg a.i./ha), methamidophos (0-9 kg a.i./ha), phosalone (0-525 kg a.i./ha) and monocrotophos (0-6 kg a.i./ha) provided effective control of PTM in field (Raj and Trivedi, 1987 and Raj ef al., 1986).
10. Dusting fields with carbaryl and parathion at 2 kg a.i./ha 60 days after planting was also satisfactory (Awate and Naik, 1979; Awate and Pokharkar, 1976; Awate ef al., 1977).