Potato Tuberworm Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae)

Abstract

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EENY587
Potato Tuberworm Phthorimaea operculella (Zeller)
(Lepidoptera: Gelechiidae)1
Harsimran K. Gill, Gurminder Chahil, Gaurav Goyal, Arshdeep K. Gill, and Jennifer L.
Gillett-Kaufman2
1. This document is EENY587, one of a series of the Entomology and Nematology Department, UF/IFAS Extension. Original publication date February
2014. Visit the EDIS website at http://edis.ifas.u.edu.
2. Harsimran K. Gill, post doctoral research associate, Entomology and Nematology Department; Gurminder Chahil, Dalhousie University, NS, Canada;
Gaurav Goyal, post doctoral research associate, Department of Entomology, Punjab Agricultural University, India; Arshdeep Gill, Department of
Entomology, Punjab Agricultural University, India; and Jennifer L. Gillett-Kaufman, associate extension scientist, Entomology and Nematology
Department, UF/IFAS Extension, Gainesville, FL 32611.
The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services
only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status,
national origin, political opinions or aliations. For more information on obtaining other UF/IFAS Extension publications, contact your county’s UF/IFAS Extension oce.
U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County
Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.
Introduction
e potato tuberworm Phthorimaea operculella (Zeller),
also known as potato tuber moth or tobacco splitworm,
is an oligophagous pest (an insect feeding on a restricted
range of food plants) of crops belonging to the family
Solanaceae (mainly potatoes [Solanum tuberosum L.],
tomatoes [Solanum lycopersicum L.] and tobacco [Nicotiana
tabacum L.]). Phthorimaea operculella has been a minor
pest of tobacco for more than 100 years. However, in
North Carolina, this pest has emerged as a problem in
tobacco plantings over the last ve years. is pest has been
reported in tropical, subtropical and Mediterranean agro-
zones (Westedt et al. 1998, Flanders et al. 1999, Visser 2005,
Golizadeh and Esmaeili 2012).
e potato tuberworm aects production, reduces quality
of the produce and increases the risk of infection by plant
pathogens. e common name potato tuberworm is
given to its damaging larval stage. ere are two species
in dierent genera with similar names: Tecia solanivora
(Povolny) and Symmetrischema tangolias (Gyen). Tecia
solanivora (Povolny), the Guatemalan potato moth, is
found in Central America and northern South America and
attacks potatoes that are still in the eld as well as stored
potatoes. e Andean or South American potato tuber
moth, Symmetrischema tangolias (Gyen), is a pest of stored
potatoes in the Andes.
Distribution
Potato tuberworm is a cosmopolitan pest. In the United
States it has been reported in at least 25 states from the
Atlantic to the Pacic coast. is pest occurs in most areas
where potatoes or other solanaceous plants are grown.
It was rst recorded in California in 1856 (Alvarez et al.
2005). However, it was not a major concern for growers
Figure 1. Damage on a potato inicted by the potato tuberworm,
Phthorimaea operculella
(Zeller).
Credits: Silvia I. Rondon, Hermiston Agricultural Research and
Extension Center, Oregon State University.

2
Potato Tuberworm Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae)
in the Pacic Northwest until 2002, when severe potato
tuberworm damage was documented in a eld near Herm-
iston, Oregon (Rondon et al. 2007). It occurs widely in
Africa (Ethiopia, Egypt, Kenya), Asia (Iran, Syria), Europe,
Americas (Latin America, Andes of Peru and Bolivia) and
Oceania (Australia and New Zealand) (Saour 2004, Vargas
et al. 2004, Davidson et al. 2006, Golizadeh and Esmaeili
2012, Golizadeh and Zalucki 2012, Ahmed et al. 2013,
Kroschel et al. 2013). Potato tuberworm has been reported
in more than 90 countries (Anonymous 2013).
Host Range
Potato tuberworms are mainly associated with potatoes;
however, they have been observed feeding on other plants,
such as tomatoes, eggplants (Solanum melongena L.),
peppers (Capsicum spp.), tobacco and wild solanaceous
plants like Jimson weed or datura (Datura stramonium
L.) (Alvarez et al. 2005). In the Pacic northwest, potato
tuberworms have only been reported infesting potatoes
(Rondon et al. 2007).
Life History
Eggs, larvae and pupae of potato tuberworm can potentially
survive in volunteer potatoes, or in the soil aer harvest.
Potato tuberworm is known to survive in the soil as pupae.
Larval development is interrupted by temperatures below
50°F. Larvae can pupate in the soil, discarded piles of
potatoes, dead leaves, on storage walls, or on eyes of stored
tubers (Raman 1980). ey can also pupate in crevices in
walls, oors and crates.
All instars may occur together in overlapping generations.
ere are two to eight generations per year depending upon
climatic conditions. ere are usually two generations per
year in temperate climates of North America (Alvarez et al.
2005). In the Northern Hemisphere, peak populations of
adults occur from May through June in Israel, from June
through August in Yemen, and from April to October in the
United States. Generation time can vary from two weeks
during summer to seven or eight months if the cycle is
interrupted by winter. Winter populations can be active in
storage facilities where optimum temperature for survival is
maintained. Potato tuber moths can move up to 0.15 miles
between crops to infest plants or tubers. Long distance
movement of potato tuberworms occurs when infested
tubers are accidentally transported (Alvarez et al. 2005).
Eggs
When foliage is not available, potato tuberworm moths can
crawl short distances through cracks in loose soil to nd
a tuber they will use as an oviposition site. In four days,
the adult female can deposit 60 to 200 eggs singly or in
small clusters directly on host plant parts such as the stem,
underside of leaves, or in the eye cracks and indentations
on tubers. Eggs are smooth, oval, and can be pearly white to
yellowish (before hatching) in color. e eggs usually hatch
aer ve days.
Larvae
Larvae are 0.5 to 0.6 inch long, white or yellow with a
brown head andprothorax (midsection of the insect body)
(Raman 1980, Alvarez et al. 2005). e thorax has small
black points and bristles on each segment. e color of
larvae changes from white or yellow to pink or green as
they mature. e larvae feed on their host plants for up to
two weeks before pupation.
Figure 2. Larva of the potato tuberworm,
Phthorimaea operculella
(Zeller).
Credits: Oregon State University Extension.
Figure 3. Leaf mines caused by the potato tuberworm,
Phthorimaea
operculella
(Zeller).
Credits: Silvia I. Rondon, Hermiston Agricultural Research and
Extension Center, Oregon State University.

3
Potato Tuberworm Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae)
Pupa
Pupae are white, narrow and 0.5 inch long. Depending
upon climatic conditions, pupae take 10 to 30 days to fully
develop (Raman 1980, Alvarez et al. 2005). e silken
cocoon spun around pupae can become covered with soil
and debris.
Adults
e moths are narrow bodied, silver grey in color, 0.4 inch
long with a wing span of 0.5 inch. Wings are grayish-brown,
fringed and elongate with small brown or black markings.
Both pairs of wings have fringed edges. At rest, the wings
are held close to the body, giving the moth a slender
appearance. e forewings are yellowish grey with dark
spots (2-3 dots on males and characteristic “X” pattern on
females); the hind wings are grey (Raman 1980, Alvarez et
al. 2005).
e adults are fast iers and like most other moths require
an insect-collecting net for capturing. ese moths live
for one to two weeks, are crepuscular (active at dawn and
dusk), and feed on nectar. Females are slightly larger than
males. Mating begins 24 hours aer emergence.
Damage
Larvae feed on potato leaves, stems, petioles, and, more
importantly, potato tubers in the eld and in storage. e
newly hatched larvae create mines on leaves by feeding on
leaf tissue while leaving the upper and lower epidermis
of the leaf intact. ey prefer feeding on young foliage
(Trivedi and Rajagopal 1992). Typical damage results from
larvae boring tunnels in tubers. Larvae depositing their
excreta make tubers unt for consumption. Potato tuber
eyes become pink due to deposition of silk and excrement
by potato tuberworm infestation. Severe infestations result
in yield and quality losses during storage where previously
infested tubers are stored with healthy potato tubers
(Malakar and Tingey 2006, Rondon 2010). is generally
destroys the entire crop of stored potatoes.
Most economic damage occurs to potato tubers in storage
conditions in developing countries and is caused by larval
feeding. Presence of even one larva is sucient to spoil and
destroy a tuber. Rapidly moving caterpillars penetrate the
tubers, form galleries coated with silken threads and eject
frass outside the tuber. On leaves, caterpillars form galleries
and then penetrate other plant parts. Aer two to three
weeks, caterpillars leave the plant (caterpillars can move
through cracks in soil) and pupate on walls of potato bags
Figure 4. Late larval instars and pupae of the potato tuberworm,
Phthorimaea operculella
(Zeller) on a damaged potato.
Credits: Silvia I. Rondon, Hermiston Agricultural Research and
Extension Center, Oregon State University.
Figure 5. The potato tuberworm,
Phthorimaea operculella (Zeller)
adults. The forewings have 2-3 dark spots on males (right), and a
characteristic “X” pattern on females (left).
Credits: Silvia I. Rondon, Hermiston Agricultural Research and
Extension Center, Oregon State University.
Figure 6. Damage on potato tuber caused by
Phthorimaea operculella
(Zeller).
Credits: Silvia I. Rondon, Hermiston Agricultural Research and
Extension Center, Oregon State University.

4
Potato Tuberworm Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae)
lying in potato elds. Fungi, bacteria and mites can develop
inside the tunnels made by the larvae, which causes the
tubers to rot and emit an unpleasant smell.
Stored crop losses in potatoes ranging from 50% in Yemen
and Peru; 86% in Tunisia, Algeria and Turkey; 90% in
Kenya; and 100% in India and the Philippines have been
reported (Alvarez et al. 2005). In Egypt, potato tuber moth
has caused up to 100% losses to potato plants in elds as
well as in storage (Ahmed et al. 2013). Potato tuber moth
is also a pest of tomatoes where larvae damage the leaves,
stems and unripe fruits.
Monitoring
Monitoring of potato tuber moth is a critical part of its
management. Pheromone traps that attract males have been
eective for monitoring potato tuber moth populations.
Monitoring is one of the most important components of an
integrated pest management (IPM) plan for potato tuber
moth. Monitoring gives an indication of insect presence,
population and distribution and allows for timing of
pesticide applications for its management. Pan-water traps
baited with the pheromone can be used for attracting and
monitoring adult male populations. ese traps are easy to
use and clean between readings. Four traps per quadrant of
a circle, about 50  from the periphery of the circle are sug-
gested for monitoring in eld. No economic threshold level
(ETL) has been determined for crop damage or yield loss
in elds. However, checking traps twice a week is suggested
and pesticide application is recommended in case of high
population (e.g., 15 to 20 moths/trap/night) (Anonymous
2013).
Management
e most common method of control of Phthorimaea
operculella is pesticides (Dillard et al. 1993). e develop-
ment of pesticide resistance, resurgence of pest populations
and potential detrimental eects of synthetic pesticides on
non-target organisms has led to the adoption of integrated
pest management (IPM) strategies. It is important to know
the biology and distribution of a pest for an IPM program
to be successful.
Field Management
CULTURAL CONTROL
Weeds and volunteer plants can act as alternate hosts for
potato tuberworms, and should be eliminated from elds
and surrounding areas. Deep planting and good coverage
of potato seeds with soil more than 2 inches during hilling
helps protect damage by adults and larvae. Discard infested
tuber seeds; only use healthy seed tubers for planting. Vines
should not be used for covering tubers as they wilt aer
some time and larvae and moths can penetrate the cover to
reach underlying tubers.
Harvest soon aer crop maturity. Moth populations are
maintained in plant and tuber debris in the eld in the
absence of main crop. erefore, timely eld cleanliness
is an important preventive measure. Cull piles should be
destroyed to reduce overwintering stages of potato tuber-
worm. Avoid leaving harvested tubers overnight in the eld
as these potatoes could act as egg laying sites for potato
tuber moth (Raman 1980, Alvarez et al. 2005, Rondon et al.
2007, Anonymous 2013).
Figure 7. Exposed tubers are predisposed to tuberworm damage.
Credits: Silvia I. Rondon, Hermiston Agricultural Research and
Extension Center, Oregon State University.
Figure 8. Monitoring male adults of the potato tuberworm,
Phthorimaea operculella
(Zeller) on a pheromone-baited trap.
Credits: Silvia I. Rondon, Hermiston Agricultural Research and
Extension Center, Oregon State University.

5
Potato Tuberworm Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae)
SOIL MANAGEMENT AND IRRIGATION
Irrigation is the most eective preventative method under
dry conditions (Raman 1980). Enough irrigation should be
provided to not allow cracks to develop deeper than two
inches in the soil. It is recommended that elds should be
irrigated aer vine desiccation to avoid cracks in the soil
and that harvest of tubers occurs as soon as the skin sets
(Anonymous 2013).
RESISTANT VARIETIES
Host plant resistance enables plants to avoid, tolerate, or
recover from pest infestations (Tingey 1986, Panda and
Khush 1995). e ecacy of other control methods can be
increased using resistant potato cultivars, thus reducing use
of insecticides (Arnone et al. 1998, Golizadeh and Esmaeili
2012). Rondon et al. (2013) studied potato lines at Oregon,
some of which hold promising results for controlling mines
and number of larvae in potato tubers. An earlier study was
conducted at Oregon by Rondon et al. (2009), and it was
conrmed that tubers of the transgenic clone Spunta G2
were resistant to potato tuberworm damage. e resistance
germplasm to potato tuberworm is an important part of an
IPM program for potato tuberworm.
BIOLOGICAL CONTROL
Natural enemies of potato tuber moth can be used as a part
of an IPM program. e parasitoids, Copidosoma koehleri
and Bracon gelechiae Ashmead (Hymenoptera: Braconidae)
have been used with some success in South America and
Australia, respectively (Symington 2003, Alvarez et al.
2005).
BIO-PESTICIDES AND NATURAL CHEMICALS
Bacillus thuringiensis (Bt) formulations have proved eec-
tive for potato tuber moth control in various parts of world
(Alvarez et al. 2005).
In several South American countries, PhopGV-based
biopesticides (Phthorimaea operculella granulovirus (Phop-
GV), genus: Betabaculovirus of the arthropod-infecting
Baculoviridae) are used to control either Phthorimaea
operculella or Tecia solanivora (Zeddam et al. 2013).
CHEMICAL CONTROL
Chemical control might be necessary when adults or larvae
are present. For chemical recommendations for commercial
growers or home gardens, consult your local county Exten-
sion service and be sure to follow all local laws regarding
pesticide use.
Storage Management
Potato tuberworm is a year-long problem under storage
conditions due to continuous breeding of this pest. e
length of life cycle of potato tuberworm is highly dependent
on temperature. So, storage temperature should always be
kept below 52°F. Monitoring in storage situations relies
on the use of pheromone traps. Under storage conditions,
cultural control options involve elimination of damaged
tubers. Screens should be installed at entry points to
exclude moths.
Sanitation of storage facility walls, oors and ceiling is very
important. Treat facility with an approved pesticide, if this
pest was detected the previous year. Use new or thoroughly
sanitized potato sacks, crates, or other containers. Bt spray
can be used on tubers which are mainly used for human
consumption, and pyrethroids on tubers used for seed
purpose (Anonymous 2013).
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6
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