Thrips - Biology & Control
Thrips have always been a common and difficult to control pest for growers
of greenhouse flowers. The western flower thrips is the most widespread and
troublesome thrips for British Columbia growers, but other species can also
be serious pests. The following species have been encountered in local
flower crops:
Echinothrips americanus
This thrips, which does not have a common name, is easily recognized by
the white band across the thorax at the base of the wings. E. americanus
first appeared in British Columbia in 1994. It has been found on
poinsettias, cucumbers, and peppers. It occurs mainly on foliage, but as
population levels increase the blossoms may be invaded. The pupal stage
occurs on the host plant, unlike other species, that drop to the ground
to pupate.
Frankliniella intonsa (the European flower thrips)
This thrips is found in the blossoms of several commercially grown
greenhouse flower crops. It also occurs in field-grown cut flower crops.
F. intonsa can only be distinguished from Frankliniella occidentalis
by examination with a microscope.
Frankliniella occidentalis (the western flower thrips)
This is a medium sized species (1.0 - 1.2 mm long). It varies in colour
from yellowish to dark brown. This species can only be identified with
certainty under a microscope, but the presence of large numbers of thrips in
blossoms is a strong indicator of F. occidentalis. It feeds on a wide
range of plants, and can spread tomato spotted wilt virus and impatiens
necrotic spot virus to susceptible crops. This thrips can develop resistance
to insecticides relatively quickly.
Thrips fuscipennis (the rose thrips)
T. fuscipennis is very similar in appearance to the onion thrips,
and can only be distinguished with a microscope. It is uncommon in British
Columbia, appearing occasionally on roses and cucumbers. This thrips is easy
to control with insecticides.
Thrips tabaci (the onion thrips)
T. tabaci is a relatively small species, the female being 0.8 -
1.0 mm long. Color variation makes color an unreliable characteristic for
identification. This thrips is found primarily on foliage, seldom invading
blossoms. T. tabaci is usually easily controlled with insecticides.
Other species occasionally found in British Columbia greenhouse flower
crops:
Aelothrips fasciatus
Ceratothrips ericae
Heliothrips haemorrhoidalis
Hercinothrips femoralis
Parthenothrips dracaenae
Thrips atratus
Thrips nigropilosus
Thrips simplex
Thrips trehernei
Thrips vulgatissimus
Thrips Identification
With the exception of the striped E. americanus, it is very
difficult to distinguish between thrips species except under a microscope.
Figure 1, adapted from Kopperts’ “Knowing and Recognizing: The Biology of
Glasshouse Pests and Their Natural Enemies”,
outlines the subtle differences used to identify T. tabaci and F.
occidentalis.
Figure 1.
Thrips tabaci |
Frankliniella
occidentalis |
BODY: |
|
|
|
Colour -
|
yellow to dark-brown; if two-coloured, the thorax
is lighter than the abdomen. |
Colour -
|
light yellow to dark-brown, often darker yellow with irregular brown
spots on thorax and abdomen. |
Length - |
0.8 mm |
Length - |
1.2 mm |
|
|
ANTENNA: |
|
7 Segments |
8 Segments |
HEAD: |
|
|
Setae |
|
- two short hairs between the ocelli
- only short hairs behind the compound eye
|
- two long hairs between the ocelli
- one long and some short hairs behind the compound eye
|
FRONT
WING: |
|
|
|
|
Main Vein |
|
- 6 to 7 hairs at the base, 4 (sometimes 3 to 5) at the tip
|
- covered with hairs over the whole length
|
Secondary Vein |
|
- covered with hairs over the whole length
|
- covered with hairs over the whole length
|
Thrips Life Cycle
Thrips go through six stages: an egg, two larval stages, a prepupal and a
pupal stage, and an adult. One generation takes about a month, but this can
vary somewhat with temperature and the species involved.
|
Eggs are inserted into leaves, flowers and soft parts of the stem.
|
b) Emerging Larvae
Newly emerged larvae feed on early plant tissue. They are very mobile and
often move to other parts of the plant.
c) Prepupae & Pupae: |
|
d) adults:
|
At the end of the second larval stage the thrips
drop to the ground and pupate on or below the surface. In a few
species the prepupal and pupal stages remain on the plant. The
pupal stage is resistant to insecticides. |
|
Adults are the reproductive and winged stage. They
are poor fliers but their feathery wings allow them to be readily
carried by air currents. |
Thrips Management
Producing a thrips-free crop requires a multi-faceted approach. However,
with proper application of the following management practices, growers can
economically keep these pests at non-damaging levels.
- Start clean: An important part of keeping a crop thrips-free
is to make sure the young plants are clean. Examine purchased or
grower-propagated transplants for thrips before placing them in a
greenhouse. Sticky card traps placed among the new plants for a day or
two will quickly indicate the presence of thrips.
- Stay clean: Covering the openings to greenhouses has
been found to reduce pest problems by up to 70%. Screening to
exclude thrips must be very fine. Such screening, known as mircroscreen, has
a maximum hole size of
0.16 mm. This significantly reduces air flow when placed over vents, and
growers must
modify ventilation systems to compensate for this. For some structures this is not practical.
- Eliminate Sources: Thrips feed on a wide variety of plants and can
readily be found in weeds outside a greenhouse. Thrips are not strong fliers
so maintaining a weed-free zone immediately around a greenhouse can reduce the number of thrips entering a greenhouse. Proper
disposal of plant residues is also important. Optimally, plant residues
should be buried or hauled away. At the very least, they should be disposed
of downwind from the structure.
- Monitor: The most reliable way to detect thrips in a greenhouse is with
either yellow or blue sticky traps. By installing traps and checking them
weekly, a grower can discover thrips when they first infest a crop so
immediate action can be taken. On-going monitoring tells growers if a thrips
control program is working. Optimally, there should be one trap for every
100 m2. Be sure to record the number of thrips captured each
week.
- Insecticides: It is difficult to devise a spray program that would be equally effective
for all growers. The effectiveness of insecticides can vary between greenhouses as local populations have developed
resistance. This is especially true for the western flower thrips. Also, thrips
are found deep inside flower buds, which makes them hard to reach with most insecticides.
Insecticides found effective to some degree include DDVP,
Decis, Nicotine, Orthene and Trumpet. The following program (check label for registered crops) has been
effective for many growers:
Apply Trumpet three times at 5-day intervals followed by two sprays of Orthene or Decis at
10- to 14-day intervals. Subsequent sprays should
be applied as needed. Growers should incorporate at least two insecticide
classes (different group numbers)
in their spray program to reduce the possibility of resistance.
- Biological Control: There are a number of commercially available
biological agents to control thrips. Trials have demonstrated that they can
be used successfully on some flower crops. However, there have also been a number of
unsuccessful attempts, usually failing because pesticides had to be applied
to control other pest problems resulting in mortality to the biological
agents. Another factor against the use of biological control in floriculture
is the low tolerance level by customers for thrips or other pests on
flowers. It is difficult to achieve a completely pest free crop using
biological agents. At present, this method of pest control is impractical
for most flower crops.
Thrips Management – Chemical Control
Trade
Name |
Active Ingredient |
Registration* |
Application
|
Carbamate |
Trumpet |
bendiocarb |
greenhouse |
foliar spray / soil drench |
Sevin |
carbaryl |
field |
foliar spray |
Organophosphate |
Cygon/Lagon |
dimethoate |
field |
foliar spray / paint |
D.D.V.P. |
dichlorvos |
greenhouse |
fumigant |
Dursban |
chlorpyrifos |
field |
foliar spray |
Malathion |
malathion |
greenhouse / field |
foliar spray |
Orthene |
acephate |
greenhouse / field |
foliar spray |
Pyrethroid |
Decis |
deltamethrin |
greenhouse |
foliar spray |
Botanical |
Nicotine |
nicotine |
greenhouse |
fumigant |
Other |
Success |
spinosad |
greenhouse |
foliar spray |
*check label for specific crop registrations |
Growers should incorporate
at least two different insecticides from two different classes. If you are
using the product or formulation for the first time, do a test spray to
check for phytotoxicity. Crops with open flowers are more susceptible to
spray damage.
Ministry of Agriculture and Lands
Abbotsford Agriculture Centre
1767 Angus Campbell Road
Abbotsford, BC V3G 2M3
Phone: (604) 556-3001
Revised October 2006
View this page in printable PDF format
Return to Pest Management Home
|