Phthorimaea operculella

Phthorimaea operculella (Zeller)

(Formerly placed in the genus Gnorimoschema)

common name: Potato tuber moth.

Taxonomic placing: Insecta, Holometabola, Lepidoptera, Gelechiidae.

Geographical distribution: Cosmopolitan.

Morphology: Body grey, length 8-10 mm. Forewings narrow, with dark spots, hindwings light-grey, with long fringes. Antennae very long. Larva light-brown to pink, head brown, body length up to 15 mm.

Host plants: Many Solanaceae, including crops like potato and tomato, eggplant (Solanum melongena L.), tobacco (Nicotiana tabacum L.) and some ornamental and wild plants.

Life history: Females usually produce 80-120 eggs or more, placing them on potato foliage or on the tubers, usually on the buds (“eyes”). The larvae feed on the foliage or enter the tubers, and their gnawing therein results in extensive galleries. They pupate outside, within silk cocoons, between sacking threads in stores or in the soil. The larvae may also feed on other plants, but P. operculella reproduces only when the larvae had fed on potato, tomato or eggplant. Optimal temperatures are around 25ºC and no development takes place at 5ºC . The adults, which subsist on nectar, live for 1-2 weeks. The pest raises 8-10 annual generations.

Economic importance: Phthorimaea operculella is a devastating pest of potatoes worldwide. It can infest potatoes in the field and thus invade stores, wherein it causes the greatest damage. Within stores the moth may complete more than one generation and then move into other tubers. The wounds in the tuber skin facilitate the entry of rot-causing microorganisms, which spread within the store and infect healthy tubers. More than half, or all, the entire crop may be lost. The greatest damage may occur immediately before harvest, while the crop is left in the field prior to digging, and more damage may occur in storage, if conditions are not well maintained. Potatoes that are left in the field for any length of time can become infested and damage is especially severe in traditional, unrefrigerated storage systems. The larvae also attack tomatoes, being a major pest of processing tomatoes in Israel. .


Monitoring: Pheromone traps that attract males are effective for monitoring pest populations, distribution and the timing of pesticide applications. Checking the traps twice a week is usually recommended in case of high catches (e.g., 15 to 20 moths/trap/night). The soil type affects the number of moths/trap, as in Israel almost twice as many moths were caught in pheromone traps located in sandy soil than in loess fields. Population densities of the pest are characterized by low densities before harvest of nearby potato fields, and the infestations are often first seen at field margins.

Horticultural control: Removal of solanaceous weeds and volunteer plants, which might be the source for later infestations. Deep planting and covering potato seeds with soil more than 5 cm high. Using only healthy tubers for planting. The moths prefer dry soil for oviposition, and because larval survival is inversely related to soil moisture; irrigation will reduce its populations. The crop should be harvested soon after maturity and not be left in the field overnight.

Control in storage: The walls, floor and ceiling of the storage facility should be sanitized and screens installed at entry points. Only new potato sacks, crates or other containers are to be used and the tubers should be stored at 7.2-10°C (the pest does not develop at temperatures below 5°C). Sanitation can be affected by an approved pesticide. In some countries tuber damage can be much reduced by covering the sacks with the foliage of certain plants, like Eucalyptus or Lantana.

Plant resistance: Some potato cultivars are resistant or tolerant to the pest, resulting in low reproduction rates and prolonged development. There is some indication that there are independent resistance mechanisms in the foliage and tubers. Foliage and tubers of transgenic potato plants suffered significantly less moth damage (fewer mines per tuber and number of live larvae) than non-transgenic tubers.

Chemical control: Organophosphates and pyrethroids were often used, the latter applied for seed protection. Other chemicals used include insect growth regulators (IGRs) and compounds based on Bacillus thuringiensis (Bt). Non-chemicals used include the extract of moth frass, and various essential oils, especially of Pithuranthos tortosus (Coss.) and Iphiona scabra DC. ex Decne., which significantly reduced egg hatch.

Biological control: Many natural enemies attack the larvae in different parts of the world. The more important (and at times controlling) parasitoids are the braconids Apanteles subandinus Blanchard, Bracon gelechiae Ashmead_ and Copidosoma koehleri Blanchard. About twice as many larvae on the leaves are attacked (60-70%) as compared to larvae infesting tubers (30%). Species of Trichogramma (Trichogrammatidae) significantly reduced pest numbers in cage experiments. Predators include Anthocoridae, ants, Chrysopidae and Coccinellidae. Predation rates were estimated to be twice as high as parasitism levels (80% vs/ 40%). Applications of the specific granulovirus (PoGV) resulted, within a fortnight, in over 80% pest mortality.

Sound monitoring and sampling, horticultural methods, planting of tolerant and resistant cultivars, applying mild pesticides and the use of natural enemies together, form the basis for integrated potato tuber moth control.


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