The female melon thrips is approximately 1 mm long, straw- to
dark-yellow in color with little or no banding showing on the
abdominal postocualr setae
of moderate length, shorter than the interocellar
setae. The ocellar color is red. The antennae have seven segments,
with no other outstanding characteristics. The terminal antennae
segments are mostly or entirely dark-brown, which differs from
most of the Frankliniella spp., which have the basal part
of these segments pale.
The prothorax lacks anteromarginal
or anteroangular setae. The presence
of only two pairs of large setae on the posterior edge of the
prothorax readily separates Thrips spp. from Frankliniella
spp. The wings bear black fringe cilia, or hairs (those along
the trailing edge of the fore wing). When these are folded over
the abdomen at rest, they give the appearance of a black line
running the length of the abdomen. This characteristic alone should
not be used to distinguish this species,
as other species, notably the western flower thrips, also have
dark fringe cilia. In specimens on microscope slide, the striations
on the dorsum of the third thoriac
segment can be seen to be convergent along the posterior margin
of the segment. This segment also bears a pair of campaniform sensillae,
which appear as small clear dots on the body surface.
The abdomen bears a complete comb on segment VIII.
The melon thrips infests a wide variety of crops. Vegetables such
as cucurbits, legumes and solanaceous crops are preferred. Although
peppers and eggplants can support massive numbers, populations
do not establish on tomatoes. Strawberries are also not preferred.
Melon thrips will infest many species
of weeds including composites, legumes and nightshades among others.
Economic problems with Thrips palmi seem to be the
greatest during the first few years after the species invades
a new area. They are capable of building up to very high numbers
quickly under favorable conditions. The lack of predators
and parasites in a newly invaded
area increases the potential for such a massive build-up.
Melon thrips tend to utilize more of the host plant than other
species that occur primarily in the blooms. The blooms appear
to be none the less important to the melon thrips, as they appear
to be adversely affect by the presence of competing flower thrips
species (Frantz et al. 1995, Glades Crop Care, unpublished data).
In crops, such as snap beans and most of the vine crops, damage
is caused by the feeding on the foliage. Foliar feeding often
begins inside the tightly rolled leaves at the growing points
of the plant. Larvae and adults soon appear on the undersides
of the expanding leaves. The combined effect of feeding damage
in the growing point and on young leaves can severely stunt and
distort sensitive crops, such as peppers.
In peppers and eggplants, Thrips palmi affects both
fruit and foliage. The greatest damage occurs when thrips become
established in the blooms, and lay eggs around the calyx. Thrips
feeding under the calyx of the expanding fruit cause the characteristic
scars, which may affect a sizable part of the fruit wall.
Careful planning is required in schedules plantings of sensitive
crops. Thrips palmi can move into new parts of a
farm when infested fields are destroyed. This can be critical
in areas with long growing seasons, where new plantings are adjacent
to older fields. The same is true in areas where the foliage of
infested crops, such as snapbeans, is removed during mechanical
harvesting.
Infestation levels in young crops must be monitored carefully.
Awareness of the general level of melon thrips infestation, not
only in your fields, but in neighboring farms as well is especially
important. Crop scouting can be intensified around the time of
critical crop events, allowing early detection and treatment of
immigrants from nearby farms.
In addition to preserving naturally occurring predators
and competing thrips species, judicious
use of suitable insecticides may
be necessary to keep melon thrips from destroying a crop. Recently
registered insecticides, such as imidacloprid and abamectin, can
provide good control, while preserving beneficial
insects. In situations where a
"harder," broad spectrum insecticide may be needed,
the use of carbamates, such as methomyl or oxamyl is preferred.
The use of pyrethroids should be
avoided if possible, as the may cause melon thrips population
explosions (Etienne et al. 1990, Johnson 1986, Seal & Baranowski
1992, South 1991).