Phthorimea opercullella

(potato tuber moth)

• Causal agent

Potato tuber moth (PTM) is a small insect of the order Lepidoptera (Gelechiidae family) which is a major pest in most tropical and subtropical warm regions, especially in the Mediterranean basin.

Adults are small greyish-brown moths (photo 1) with a wingspan of 10-15 mm (photo 2). At rest, the wings are folded in a roof-like habitus, fringed when expanded and covered with silvery fishgrey scales. Adults lay eggs on the underside of leaves, on stems and on tubers, or in the soil near the tubers.

A complete generation lasts 20 to 30 days (at 30°C) and there can be up to 10 to 12 generations a year. On average, the first larval stage (photos 3 to 5) appears one week after laying. Larval development lasts for two weeks in favourable conditions (at 25°C) and larval feeding, i.e. mining, causes direct damage on the foliage and tubers. The full-grown larva may pupate in the tuber (photos 5 and 6) but usually leaves the plant to pupate either in the soil or in the storage facilities. The adult tuber moth may emerge a week later, ready for a new generation.

The potato tuber moth can adapt to the most diverse climatic conditions provided temperatures vary between 10 to 35°C. Preferred hosts are potato and tobacco, but they can also be found on other Solanaceae plants: tomato, eggplant, nightshade, etc.

• Significance

Potato tuber moth (PTM) and other moths can be very damaging pests on Solanaceous plants, but PTM is the most wide-spread in warm areas.