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Potato moths

Damages through the potato tuber moth, Phthorimaea opercullella, occur mainly in Solanacaea and are most relevant in potato, tomato, tobacco and eggplant.

In case of potato plants the larvae mine both leaves and tubers, in the field and in storage. This makes pest control rather difficult. Protection of tomatoes under greenhouse conditions is also hard to manage. Larvae create blotch-shaped mines in tobacco leaves, damage photosynthetic tissue by leaving only the upper and lower epidermis, resulting in a ‘window-pane’ appearance. The damaged leaf tissue succumbs and the leafs remain with a split appearance, reducing quality and, consequently, causing economic loss.

The Guatemalan potato moth, Tecia solanivora, has a narrow host range with only potato identified so far. In the field, eggs are laid on the ground or uncovered tubers; also stored tubers are easy targets. In some cases eggs were laid on leaves as well. Damage is similar to that of Phthorimaea operculella. Larvae bore galleries containing residues of food, frass and larval exuviae.

Where does potato moths occur mostly?

Potatoes and tomatoes are the most widely cultivated vegetables in Europe as well as worldwide. Production of several of potato crops is threatened by infestation of Phthorimaea operculella. Potato tuber moth is a damaging pest of stored potatoes and potato crops, mainly in (sub)tropical regions.
Another invasive pest species, Tuta solanivora, was found locally in Canary Islands (Spain). The European and Mediterranean Plant Protection Organization (EPPO) included it in the A2 action list of pests recommended for regulation as a quarantine pest. T. solanivora became the major insect pest of potatoes in Central America and the north of South America.

What are the economic consequences of potato moths?

Potato tuber moth and Guatemalan potato moth are among the most important potato pests in the world. Infestation of tubers both in the field and in storage results in an unmarketable product.
The occurance of potato tuber moth leads to high economic damages in crop production around the world. In regions where temperatures stay above freezing throughout winter, every stage of potato tuber moth can overwinter and re-colonize crop hosts in spring. Phthorimaea operculella is present throughout the world, wherever solanaceous plants are found or cultivated. Even in the EU the pest is present but moderate regions show fewer generations during the year. Global climate change, greenhouse gases and storage conditions may be favourablel for this plant pest.
Ten or more mines of potato tuber moth can develop on an individual tobacco leaf, which can reduce overall harvest weight, causing direct loss for tobacco growers in south-eastern United States. Under favourable conditions in-field damage may reach 100%, with mines in every plant. Tomatoes and eggplants are attacked as well causing reduction of quality or total loss because of mined fruits.

How can the potato moths be controlled?

Infestation of the tuber correlates with infestation of the leaf. In the field potato, leaves are an easier target for protection than the tubers in the soil. Treatment of leaves cannot directly protect the tuber but can help to increase quality of uninfested tubers. Post-harvest protection is needed for potato tubers as well as tobacco. A treatment with chemical insecticides may be possible but it is not the best option in case of food and consumer products. A biological control alternative is therefore essential. Food production in the greenhouse (e.g. tomatoes) also requires efficient biological protection where chemical insecticides are no option within integrated pest management programmes.
Phthorimaea operculella granulovirus (PhopGV) is also known to infect Guatemalan potato moth and is, because of its  high specificity, a good candidate for the development of a higly efficient and selective biocontrol agent.

Use of pesticides

Safety intervals are a problem to deal with in case of pesticides treatments, in particular for food storage conditions. To reduce pesticide residues in food, alternatives for chemical treatments are essential.
Many tomatoes are grown under non-chemical control regimes and in greenhouses where application of chemical insecticides has been abandoned. There is a lack of efficient pest control methods in this economically highly relevant sector.

BIOCOMES biological control agent

The finding that the same entomopathogenic virus is infective for the tomato leaf miner, the Guatemalan potato moth and the potato tuber moth, provides a unique opportunity for a combined control of these three pest insects by a single biological control product. Isolates of the agent will be selected for their virulence to Tuta absoluta, Tecia solanivora and Phthorimaea operculella.

Photo: Potato tuber moth worm. Picture: Merle Shepard, Gerald R. Carner, and P.A.C Ooi, Bugwood.org.

Johannes Jehle
Johannes Jehle
Tomato leaf miner, potato moths
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Biological Control Agents

The isolates will be characterized by biological and molecular means and will be tested in greenhouse and field trials. A product for combined control of pests will be developed on basis of these findings.

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Current stage of the Biological Control Agent

75%

Month 18: Protocol for rearing and bioassaying target insects
Month 24: Report on biological activity of isolates
Month 36: Report on RFLP analysis of all isolates and on the genome sequences of selected isolates
Month 36: Results of field tests1st year
Month 48: Results of field tests2nd year

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