The tomato
leafminer (Tuta absoluta)
is an emergent pest, intercepted in countries
such as Spain (2006), Italy, the Netherlands,
France and Tunisia.
In April 2009, it was reported for the first
time in Malta. The situation and distribution of
this pest in Malta is being further studied by
the Plant Health Department since this pest was
never intercepted or reported till present.
Host plants
The tomato
leafminer is a harmful leafmining moth with a
strong preference for tomato but it can also
attack potato, pepino and other solanaceous
plants.
Biology
Tuta absoluta can reproduce very rapidly.
One female may lay up to 260 eggs during her
life which are deposited on the aboveground
parts of the plant. The caterpillar lives as a
miner in the leaf, stem or fruit but usually
exits the mine to pupate. Larger caterpillars
can sometimes be found outside the mine or
fruit. Pupation may take place in the soil as
well as on the surface of a leaf, in a curled-up
leaf or in a mine. The moths are active during
the night and hide between the leaves at
daytime.
Identification
The moth has a grey-brown colour, is
approximately 6 mm in size and has a wingspan of
about 10 mm. When maturing, caterpillars turn
yellow-green and a black band developes behind
the head (fig. 1). Fully-grown caterpillars are
about 9 mm in size with a pinkish colour on the
back.
(Source: M.
van der Straten, National Reference Laboratory,
Plant Protection Service, The Netherlands, April
2009)
Damage pattern and detection
All aboveground parts of the plant in each
developmental stage can be infested by Tuta
absoluta. Under greenhouse conditions its
continuous development results in the presence
of all stages of Tuta absoluta throughout
the entire growing season. The caterpillars have
a strong preference for leaves and stems but
they may also be found in or under the crown of
the fruit and in the fruit itself; small heaps
of excrements are often found near the entrance
hole (fig. 2). The most distinctive symptoms of
the presence of the species are the
blotch-shaped mines (blotch mines) in the leaves
in which the caterpillars and dark, granular
excrements (frass) can be found (fig. 3). Damage
to the fruit may give easy access to diseases,
causing decay of the fruit.
(Source: M.
van der Straten, National Reference Laboratory,
Plant Protection Service, The Netherlands, April
2009)
Pathways of
introduction and possible control measures
Host plants
imported for planting, and fruits of tomato are
considered pathways of introduction. Potato
tubers are not normally attacked and therefore
are not considered a likely source of
introduction. Tomato fruits may carry all
stages of the pest.Likewise, plants for planting of tomato
may carry all stages of the pest in leaves and
stems.
Larvae can feed on all parts of tomato plants
and can damage all growth stages. Chemical
control is the main method of control for T.
absoluta, but effective control is
difficult to achieve because the larvae are
internal feeders. Furthermore, control of the
pest has become more difficult due to resistance
to insecticide.
Various active
substances are effective and can be used in
combination with biological control agents.
Concerning chemical control, several treatments
are required per growing season and it must be
noted that a decrease of the efficacy of
products used against T. absoluta has
been observed since the 1980s in tomato crops.
The following active
substances are claimed to be effective against
this pest:
Indoxacarb, Lufenuron,
Spinosad, Thiacloprid and Bacillus
thuringiensis.
The use of pheromone traps in a sufficiently
high density offers a reliable method for timely
detection of the presence of (male) moths of
Tuta absoluta.
Other control
methods include cultural practices such as
rotation with non-solanaceous crops, ploughing,
adequate fertilization and irrigation. The
destruction of infested plants and of
post-harvest plant debris by burning is very
important.
Monitoring surveys are being carried out by the
Plant Health Department to evaluate the spread
of this pest locally. This is essential for
better control of this pest
The Plant Health Department also issued
guidelines on the control of Tuta absoluta,
which guidelines can be accessed from the Plant
Health Department’s website.
A meeting about
this pest is also being organised by the Plant
Health Department and addressed to all those
involved in tomato cultivation. This would
further disseminate information on this pest,
for better control. The meeting is going to be
held next Friday 29th May at 1900 hrs
at FCCS, Ta’ Qali.
The Plant Health
Department encourages the general public
especially those involved in tomato cultivation
to report to the Department the presence of this
pest or its symptoms, which include mines in the
leaves or stem and holes in the fruit. This
information will further help the Plant Health
Department in the assessment of distribution and
situation of this pest. For further
information, one can contact the Plant Health
Department on 23397100, 23397545 or 25904312, or
freephone 80072310. One can also visit the
website
www.planthealth.gov.mt
