This knowledgebase has evolved from our experience with crops
infested with more than one species
of thrips. In many such cases, insecticide
applications are not called for, since most of the thrips found
on vegetables are species that cause very little damage. Being
able to tell them apart in the field with a 20x hand lens, without
having to go through the process of mounting the insects on microscope
slides, helps a consultant provide accurate recommendations and
advice before leaving the client's field.
Thrips are soft-bodied insects that have three body partsPhysical Structures used in Identification
Accurate field identifications have been provided by Glades Crop
Care's staff. Still, we like to back up field observations with
closer examination of large numbers of insects
using at least a dissecting microscope with 40x magnification.
Even after this process, slide mounted specimens are needed for
closer examination. The characteristics described below will enable
you to separate the common vegetable thrips using a 20x hand lens
and the identification key. There will
always be specimens that are hard to identify, and characteristics
will be included that will help identify them if you have access
to a microscope. Preparing specimens for microscope mounts is
described under Field Activities.
General Morphology
Their unusual mouthparts are not symmetrical since only the left
mandible is fully developed, and
is used to pierce the cuticle of the plant. The paired maxillary
stylets suck out the juices, similar to a stink bug
or an aphid (Childers & Achor
1991a).
Thrips have a fringe of cilia (hairs) along the edges of their
wings. These cilia expand the effective surface area of the wing.
The females families
within the Terebrantia (the suborder which includes the Thripidae),
but this characteristic is not used to separate the species presented
here.
Among the family Phlaeothripidae, there
is no saw-like ovipositor. The terminal abdominal segments
in this family form a tube and females lay their eggs on the substrate
surface, instead of inserting them into plant tissues.
The characteristic used to most easily separate the common vegetable
thrips is the pattern of hairs (setae)
on the head and thorax. Each of these setae will be given a specific
name. Becoming familiar with their names before using the identification
key is important. Other features are used regularly by taxonomic
specialists, and may be mentioned. However, this guide is designed
for non-specialists and the characteristics for identification
will be those most easily observed.
Specific characteristics referred to in the identification key
include the following:
The number of segments in the
antennae separates most species
of the genus Thrips, usually
having seven segments, from species of the genus Frankliniella,
usually having eight segments. The shape of individual segments
is important when identifying specimens mounted on microscope
slides. For example, in Frankliniella bispinosa,
the apex of the second segment bulges over the base of the third
and has two strong spines. Other species discussed here lack these
structures and this segment is referred to as simple. Similarly,
the pedicel or base of the third segment is flanged or annular
in some species, but simple in other.
These are setae located immediately
behind the large compound eyes. These setae vary in length depending
on the species.
These setae arise within or near
the triangle formed by the three small simple eyes (ocelli),
which are found on the top of the head immediately behind the
antennae and between the compound eyes. The position of the interocellar
setae relative to the ocelli can vary between species.
The first thoracic segment, the prothorax,
is the main character used here, and is the only one discussed
in detail. The anteroangular setae (AAS) and the anteromarginal
setae (AMS) are found on the front (anterior) of the prothorax,
along with varying numbers of much shorter species,
these setae are absent. All thrips shown in this knowledgebase
have two well developed pairs of setae along the hind (posterior)
margin of the prothorax. These are called the posteroangular and
posteromarginal setae, arising from the corner and the margin,
just like the AAS and AMS.
In Thrips spp. the pattern of striations or fine ridges
on the upper surface of the thoracic segment is useful in separating
species. This characteristic can only be seen on slide mounted
specimens. The presence or absence of campaniform sensillae, minute
disk-like sensory organs, on this or other segments may also be
used to separate species.
The color of the abdomen varies, and is not very useful. Setation
of the abdomen is useful for microscope identifications. Abdominal
segments VIII has a comb of very fine microsetae along the hind
margin. These are less than a fourth of the length of the major
body setae. A complete comb has
microsetae of uniform size; an interrupted comb has the central
microsetae missing. Some species have no comb.