Potato tuber moth, (Phthorimaea operculella )
Identification
The adult potato tuber moth has a narrow silver-grey body and greyish-brown wings patterned with small, dark specks. The body length is about 10 mm and the wingspan is about 12 mm. The moths are active mainly at dusk, but during the day can be seen flying sporadically within potato crops.
The oval eggs are laid singly on the underside of potato leaves and on exposed tubers. When first laid they are pearly white, changing to yellow on maturity and to black just before hatching.
The larva [caterpillar] on hatching is 1-2 mm long and grows through four instars [stages] to reach a length of 15-20 mm. Young larvae are grey or yellow-white; mature, healthy larvae are tinged with pink or green. All instars have a dark brown head.
Pupae are formed in a silken cocoon covered with soil particles and debris for camouflage. Pupation [change from a larva to a pupa] occurs among dead potato leaves, on the soil, or on stored potato tubers.
Host plants
Potato tuber moth is a major pest of potatoes in New Zealand. The range of hosts is limited to the family Solanaceae. The most commonly attacked plants of economic importance are potato, tobacco, egg plant, and, occasionally, tamarillo leaves. The native weed poroporo may be heavily attacked.
Damage
Both foliage and tubers suffer extensive damage. This is caused by the larvae, which normally spend their entire lives in either one of these food sources; the only exception to this is when infested foliage is destroyed, forcing larvae to abandon it and search for tubers. Foliage-mining larvae create transparent leaf blisters and may also mine the petioles [leaf stalks]. Foliar infestation may be sufficiently severe to destroy the plant. Tuber-mining larvae usually enter through the "eyes" from eggs laid nearby, and make slender, dirty-looking tunnels throughout the tuber. An infested tuber can be identified by mounds of frass [droppings] at the tunnel entrances. High levels of tuber infestation occur in the field during summer, and stored potatoes can suffer severe damage all the year round.
Distribution
Potato tuber moth is cosmopolitan [world-wide in distribution]. In New Zealand it occurs throughout the potato-growing areas of the North and South islands, and thrives best in areas with hot dry summers.
Life cycle
Egg
Larvae
Pupae
Adult
Month
Note: Coloured bars indicate periods of peak activity in each of the life cycle stages
As many as 6-8 generations may occur in the field during summer. As a result generations are not distinct, and between December and April every stage of the life cycle may be present in abundance. In mid summer a complete generation spans 4-5 weeks: eggs hatch in 2-6 days, larvae mature in 16-24 days, pupae hatch after 6-9 days, and adult females begin to lay eggs after 2-4 days. As the temperature drops m autumn the population declines, and the duration of the life cycle gradually lengthens until in winter it spans 20-24 weeks. By August-October the overwintering population consists almost entirely of pupae. These hatch in November with the onset of warm, dry conditions, to begin the next summer population explosion. In stored potatoes the population continues to breed all the year round, the length of the life cycle depending on storage temperature.
Identification
The adult potato tuber moth has a narrow silver-grey body and greyish-brown wings patterned with small, dark specks. The body length is about 10 mm and the wingspan is about 12 mm. The moths are active mainly at dusk, but during the day can be seen flying sporadically within potato crops.
The oval eggs are laid singly on the underside of potato leaves and on exposed tubers. When first laid they are pearly white, changing to yellow on maturity and to black just before hatching.
The larva [caterpillar] on hatching is 1-2 mm long and grows through four instars [stages] to reach a length of 15-20 mm. Young larvae are grey or yellow-white; mature, healthy larvae are tinged with pink or green. All instars have a dark brown head.
Pupae are formed in a silken cocoon covered with soil particles and debris for camouflage. Pupation [change from a larva to a pupa] occurs among dead potato leaves, on the soil, or on stored potato tubers.
Host plants
Potato tuber moth is a major pest of potatoes in New Zealand. The range of hosts is limited to the family Solanaceae. The most commonly attacked plants of economic importance are potato, tobacco, egg plant, and, occasionally, tamarillo leaves. The native weed poroporo may be heavily attacked.
Damage
Both foliage and tubers suffer extensive damage. This is caused by the larvae, which normally spend their entire lives in either one of these food sources; the only exception to this is when infested foliage is destroyed, forcing larvae to abandon it and search for tubers. Foliage-mining larvae create transparent leaf blisters and may also mine the petioles [leaf stalks]. Foliar infestation may be sufficiently severe to destroy the plant. Tuber-mining larvae usually enter through the "eyes" from eggs laid nearby, and make slender, dirty-looking tunnels throughout the tuber. An infested tuber can be identified by mounds of frass [droppings] at the tunnel entrances. High levels of tuber infestation occur in the field during summer, and stored potatoes can suffer severe damage all the year round.
Distribution
Potato tuber moth is cosmopolitan [world-wide in distribution]. In New Zealand it occurs throughout the potato-growing areas of the North and South islands, and thrives best in areas with hot dry summers.
Life cycle
Egg
Larvae
Pupae
Adult
Month
Note: Coloured bars indicate periods of peak activity in each of the life cycle stages
As many as 6-8 generations may occur in the field during summer. As a result generations are not distinct, and between December and April every stage of the life cycle may be present in abundance. In mid summer a complete generation spans 4-5 weeks: eggs hatch in 2-6 days, larvae mature in 16-24 days, pupae hatch after 6-9 days, and adult females begin to lay eggs after 2-4 days. As the temperature drops m autumn the population declines, and the duration of the life cycle gradually lengthens until in winter it spans 20-24 weeks. By August-October the overwintering population consists almost entirely of pupae. These hatch in November with the onset of warm, dry conditions, to begin the next summer population explosion. In stored potatoes the population continues to breed all the year round, the length of the life cycle depending on storage temperature.
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