May 2022 - 10

dr. bugs
BY RAYMOND A. CLOYD
INSECT AND MITE PESTS
Feeding Behaviors and Plant Damage
Question: What are the feeding behaviors of insect and mite pests, and how is feeding
behavior associated with plant damage?
Raymond A. Cloyd
is professor and
Extension specialist
in horticultural
entomology/
plant protection
at Kansas State
University. He
can be reached at
rcloyd@ksu.edu.
Answer: The two major
feeding behaviors of insect and
mite pests of greenhouse-grown
horticultural crops are chewing
and piercing-sucking. Insects
with chewing mouthparts
consume portions of leaves,
flowers, roots, or entire plant
parts by ingesting macerated
plant tissue. The primary insect
pest of greenhouse-grown
horticultural crops with chewing
mouthparts is the larval stage
of fungus gnats, Bradysia spp.,
which feed on plant roots.
Leaf stippling and speckling affiliated with twospotted
spider mite feeding damage.
Honeydew on leaf associated with aphid
feeding. (Photos: Raymond Cloyd, KSU)
However, caterpillars and beetles may also
feed on greenhouse-grown horticultural
crops during the growing season.
Insects with piercing-sucking mouthparts
use a stylet to pierce plant cells and
consume large quantities of plant fluids
in the phloem (food-conducting tissues)
to obtain nutrients. In general, aphids,
mealybugs, leafhoppers, soft scales and
whiteflies use their stylets to cut across
the cuticle, epidermis and mesophyll to
establish feeding sites in the phloem (more
specifically, the phloem sieve tubes).
Insect pests with piercing-sucking
mouthparts cause plant damage; such as,
plant wilting, stunting and leaf distortion.
The amount of plant damage caused
by insect pests with piercing-sucking
mouthparts can vary depending on the
level of an infestation and plant growth
stage. Furthermore, many insect pests
with piercing-sucking mouthparts feeding
in the phloem produce honeydew, a clear,
sticky liquid that serves as a growing
substrate for black sooty mold.
Some insect pests with piercing-sucking
mouthparts feed on other plant tissues.
For example, certain scale insects feed
within the mesophyll parenchyma of
leaves, certain thrips feed within the
epidermal and mesophyll cells of leaves,
and some leafhoppers feed in the xylem
(water-conducting tissues). Although
thrips and spider mites have piercingsucking
mouthparts, they are cell-content
feeders because they lacerate cells
and ingest the exuding contents using
their stylets. Twospotted spider mite,
Tetranychus urticae; western flower thrips,
Frankliniella occidentalis; and leafhoppers
cause similar plant damage, but there are
differences.
Twospotted spider mites use their
stylet-like mouthparts to pierce and feed
on individual plant cells, resulting in
damage to the spongy mesophyll, palisade
parenchyma, and chloroplasts.
Feeding damage symptoms include:
1. leaves that are bleached and/or
stippled with small silvery-gray to
yellow speckles and
2. mottled upper leaf surfaces.
Furthermore, twospotted spider mite
feeding causes bronzing of leaves, which
turn brown, and eventually fall off plants.
10 MAY 2022 GPNMAG.COM
http://www.GPNMAG.COM
May 2022

Table of Contents for the Digital Edition of May 2022
