Agriculture Reference
In-Depth Information
the source of the CO
2
attractant. Due to all the
variables associated with wireworm sampling,
Horton (2006) reported that it remained chal-
lenging to predict damage, and hence to make
management recommendations based on wire-
worm baiting.
Adult wireworm can be sampled using
pheromone traps or pitfall traps, but in most
situations, adult sampling will just alert one to
the presence of wireworm in a general area and
not specifically address the risk of damage to the
potato crop by wireworm larvae.
black prior to emergence in the adult stage.
Depending on location, the potato tuber moth
can produce anywhere from four to ten gener-
ations per year, with the range due largely to
temperatures in the different regions. Devel-
opment from egg to adult also ranges with
temperature, but at 26°C, it takes approxi-
mately 23 days, and adult longevity ranges
from
6
to 15 days (Broodryk, 1970).
Distribution
The potato tuber moth is believed to have ori-
ginated in the tropical mountains of South
America, near the origin of the potato (Graf,
1917), and is currently found in over
90
coun-
tries across the globe. Adults are weak fliers,
and the cosmopolitan distribution and range
expansion of potato tuber moth is probably
due largely to movement of larvae-infested
seed. The potato tuber moth is a pest of potato
from temperate to tropical regions, but tends
to be less damaging in regions with cold win-
ters that reduce survivorship and the number
of generations per growing season. The lower
developmental threshold for the potato tuber
moth has been estimated as low as 4.25°C,
possibly accounting for expansion and estab-
lishment in cool temperate regions.
The Guatemalan potato tuber moth is a pest
of potato in Central and South America, and
Guatemala is believed to be the place of origin
(Povolny, 1973). The Andean potato tuber moth
is believed to have originated in Peru and Bolivia,
and can now be found in South America, Aus-
tralia, and Indonesia.
Potato tuber moths (Gelechiidae)
Recognition
Three species of Gelechiidae make up the potato
tuber moth complex that attacks potato crops.
The three species are the potato tuber moth,
Phthorimaea operculella
(Zeller), the Guatemalan
potato tuber moth,
Tecia solanivora
( Povolny),
and the Andean potato tuber moth,
Sym-
metrischema tangolias
(Gyen).
The potato tuber moth is cosmopolitan in
distribution and will therefore be the main
focus of this discussion. Adult potato tuber
moths are light brown in color, 8 mm in
length, and when fully extended, the wings
span 15 mm. The forewings have two to three
dark bands along the rear edge, and the rears
of the forewing, as well as the entire hind-
wing, are fringed. The long antennae resemble
strands of thick hair, and there are three lon-
gitudinal dark stripes on the thorax. Eggs are
white when newly laid, but turn yellow as
they approach maturing to neonate larvae.
The eggs are oblong (0.5 × 0.35 mm) and de-
posited singly, or in strings, on plant tissue.
Each female can produce
100-300
eggs over
her lifetime, depending on food resources and
temperature (Broodryk, 1971). Larvae when
newly hatched are 1 mm long and grow to
nearly 13 mm in the fourth instar, just prior to
pupation. Larvae feeding on leaf tissue will be
purple to green in color, while those feeding
on tubers will be white to purple. Larvae have
a dark head capsule, obvious segmentation,
six legs, and five pairs of prolegs on the rear
abdominal segments. Pupae are 8 mm long
and begin brown in color but darken to nearly
Damage
The potato tuber moth, like many other Gel-
echiidae larvae, typically feeds as leafminers,
which in potato rarely causes economically im-
portant damage. Potato tuber moths tend to
reach higher levels of infestation during warm
and dry weather, in crops that are not irrigated
with sprinklers and in places where potato is
grown throughout the year. Conversely, they
tend to be lower in numbers during wet weather
and in crops grown with sprinkler irrigation.
When foliage senesces or is killed with desic-
cants prior to harvest, larvae will drop to the
soil and feed on potato tubers, which is where
