Mar_Apr_PCC_2017_Web

CITRUS
Managing Citrus Thrips is Especially
Difficult During Drought Years
Elizabeth E. Grafton-Cardwell
Sara Scott
Joshua Reger
Department of Entomology,
UC Riverside
Citrus thrips is a common pest of
California citrus, attacking leaves
and the calyx end of newly forming
fruit, when the epidermal cells are
quite sensitive. In leaves, this causes
distortion of the leaves and light lines
of scarring (Photo 1). When they infest
fruit, their feeding under the calyx at
the stem end leaves a ring-shaped silvery
scar that is retained when the fruit is
mature (Photo 2).
Biology of Citrus Thrips
Citrus thrips deposit their eggs in
leaves, stems and fruit of citrus trees
and the hatching 1 st and 2 nd instar larvae
(Photo 3) live on leaves and under the
sepals of fruit. Some thrips pupate in the
cracks and crevices of the tree and about
2/3 drop to the soil to pupate. The adults
emerge, mate and begin laying eggs and
the cycle continues. The first generation
of citrus thrips attacks the new leaf flush
and the 2 nd and 3 rd generations attack the
new fruit. They damage the leaves and
fruit when they repeatedly stick their
needle-like mandible into the epidermal
cells and then suck up the fluids that are
released. Citrus thrips are thigmotactic,
that is they like to be in tight places such
as under the calyx of the fruit. The continuous
piercing of cells is what leaves
a scar and as the fruit grows so the ring
scar grow. The 2 nd instar larvae are more
damaging than the first instar larvae
and the adults cause little damage to
fruit. Fruit that is heavily damaged will
be downgraded from fancy to choice or
even to juice grade, reducing returns for
the grower. Fruit is susceptible to this
type of damage from petal fall until it
reaches about 1.5 inches in diameter and
the cells become difficult for the thrips
to pierce. The fruit sensitive period
ranges from 6-10 weeks after petal fall.
Page 6 Progressive Crop Consultant March/April 2017
The next 4-5 generations of thrips feed
on leaf flush and the last generation lays
the eggs that overwinter.
Natural Enemies of Thrips
There are a number of natural enemies
that can attack thrips, but because
the eggs are imbedded in leaves, the
pupae in underground and the larvae
hiding in cracks and crevices, generalist
predators generally don’t reduce
thrips populations quickly enough or
low enough to prevent scarring damage.
One of the best biological control agents
is the predatory mite Euseius tularensis,
which is naturally found on citrus
Photo 1. Distortion of the leaves and
light lines of scarring from citrus thrips.
Photo Credit: Jack Kelly Clark
trees and feeds on the 1 st and 2 nd instar
larvae. However, because the predatory
mite feeds on lots of other type of food
(pollen, leaf sap, red mites) it does not
always control citrus thrips at the level
that growers need, and so often insecticides
are necessary. If growers use insecticides
that allow the predatory mites to
survive, they can assist with citrus thrips
control.
Managing Citrus Thrips in Young
Citrus Trees
While it is tempting to treat flush for
Continued on Page 8
Photo 2. Feeding under the calyx at
the stem end leaves a ring-shaped
silvery scar that is retained when the
fruit is mature.
Photo 3. Citrus thrips deposit their eggs in leaves, stems and fruit of citrus trees
and the hatching 1 st and 2 nd instar larvae live on leaves and under the sepals of fruit.
Photo Credit: Jack Kelly Clark Photo Credit: Elizabeth E. Grafton-Cardwell