Among the moths, microlepidoptera of the Gelechiidae family, three species have an economic importance on crops and have Solanaceae as host plants:
Unlike the potato moth, the other two species (which may also have the potato as a host plant) have only recently been described in Europe.
Causal agent(s) and transmission
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.
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.
Symptoms on foliage
Feeding damage on leaves, petioles and stems occurs after larvae have fed on young shoots and leaf axils, this can result in plant wilting and premature plant senescence associated with secondary infection (photo 7).
Symptoms on tubers
More or less superficial galleries and cavities. Cavity walls are often covered with silk threads, blackish frass and larval exuviae (photos 3 to 6 and 8).
Warm climates are favourable to the development of PTM and other moths, as well as practices such as short rotations, superficial planting and presence of inoculum and host plants in the environment.
Recommended measures to control potato tuber moth are:
- thorough disinfection of bags, crates and storage areas;
- destruction of infected tubers, crop residues and leftover potatoes;
- use of uninfested seeds tubers;
- long rotations because the moth needs the potato plant to complete its life cycle;
- deep planting with high and regular hilling to protect newly formed tubers from moth oviposition;
- early harvest because the infestation rate increases during the end of the growing period;
- applying insecticides during the growing season or prior to storage with regular moth monitoring.