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Entomology 462
Ornamentals Pests:
Intro & Foliage Eaters
David J. Shetlar, Ph.D.
The “BugDoc”
The Ohio State University,
OARDC & OSU Extension
Columbus, OH
© October, 2004, D.J. Shetlar, all rights reserved
Insects and mites that attack
ornamental plants are often grouped
according to three basic plans:
•
By taxonomic group (e.g.,
beetles, caterpillars, etc.).
•
By plant and part of plant
attacked (leaves, stems, roots).
•
By feeding method (e.g.,
chewing, sucking, gall forming,
etc.).
1
Woody Ornamental
Insect and Mite Groups
(by damage)
Chewing Pests - Foliage Feeders
Chewing Pests - Leafminers
Chewing Pests - Borers
Chewing Pests - Root Feeders
Sucking Pests
Gall Making Pests
Nuisance Pests
Woody Ornamental
Insect and Mite Groups
(by plant zone)
Foliage Feeding Pests
chewing, sucking,
leafmining, gall makers
Stem, Branch & Trunk Pests
borers, girdlers,
miners, sucking, gall makers
Root Feeding Pests
chewing, sucking, gall makers
Nuisance Pests
2
We will work through the groups using a hybrid of the “Mode of
Attack” system (for chewing pests) and “Taxonomy” (for sucking
pests). Insects that have chewing mouth parts usually attack in
distinctively different ways or feed in or on different plant zones (e.g.,
foliage feeders, miners, borers, root feeders). While pests with
sucking mouthparts attack similar plant zones, it is easier to group
them according to taxonomic groups, mainly because their life cycles
are similar and control approaches are similar.
For diagnosis, knowing the damage symptoms caused by each pest
group can make identification a simple task. In fact, I have often
stated: “If I know the host plant species, the time of the year that the
damage occurred and the damage symptoms, I can usually identify
the pest! In short, I rarely need an actual specimen of the pest.”
This is why our approach will be to learn the terms used when
describing pest damage.
Woody Ornamental Pest Groups
Chewing Pests - Foliage Feeders
Defoliators and General Feeders
Specialized Feeders
Skeletonizers, Leaf notchers, Hole makers
Nest Makers
Bagworms, Casebearers, Tent caterpillars,
Webworms, Leaftiers, Leafrollers
3
Defoliators and General Feeders are occasionally some of the more
difficult to identify to species because they leave rather non-descriptive
symptoms. The foliage is simply missing or badly chewed up! Many of
these pests, usually caterpillars or sawflies, are what I call “hit artists”!
The adult insect may locate a suitable host, lay dozens to hundreds of
eggs in a single spot, and the young larvae may go undetected for
some time. Once these larvae reach maturity, they “suddenly” strip off
the remaining foliage. They then pupate and disappear “literally over
night”! For many of these pests, they may damage a tree or shrub one
season and be absent the next season.
These pests are difficult to manage unless a regular surveying or
scouting program is adopted.
Even if these pests are missed, their damage is usually not critical to
the long-term health and survival of the tree or shrub. Most plants can
survive a defoliation event every few years. However, repeated
defoliation (as with gypsy moth) may sufficiently weaken a plant that it
dies from infection by diseases or attacks by other pests, such as
borers.
Woody Ornamental Pest Groups
Foliage Feeders General Defoliators
Caterpillars - (moths & butterflies)
2-5 pairs of prolegs
crochets (hooks) on prolegs
Sawflies - (wasp-like insects)
6-9 pairs of prolegs
no crochets on prolegs
4
Spiny elm caterpillar
(mourning cloak butterfly)
Elm looper caterpillar
IO moth caterpillar
Whitemarked tussock moth life stages
cocoon
female
laying eggs
eggs
larva
5
Oak sawfly larva
Darkheaded ash sawfly
Willow sawfly female laying eggs
White pine sawfly pupa
Redheaded pine sawfly
larvae
pupal cases
adult female
6
The next three groups of chewing pests are what I call “Specialized
Feeders” because they produce very characteristic symptoms.
Skeletonizers generally eat the tissues between leaf veins. Even
skeletonization damage can be further characterized. There are crude
skeletonizers, like Japanese beetles, that eat most of the leaf tissues
and only leave behind larger veins. Others are very delicate
skeletonizers, leaving behind all the veins and even the upper or lower
epidermal layer. This is another clue as to the pest identity. Did they
remove the upper leaf tissues or lower tissues? The oak slug
skeletonizes from the lower leaf surface while the poplar leaf beetle
larvae skeletonize from the upper leaf surface.
Woody Ornamental Pest Groups
Foliage Feeders - Skeletonizers
Beetles Leaf Beetles - (elm, poplar)
Scarabs - (Japanese beetle)
Weevils - (yellow poplar weevil)
Caterpillars Sawflies Slug sawflies
7
Japanese beetle adult, a
crude skeletonizer. Note the
old damage in the
background (brown tissues)
compared to recent feeding.
These subtle symptoms can
help the manager determine
if activity is current and
controls would be warranted
and effective.
These hollyhocks have been
nearly completely
skeletonized by the hollyhock
sawfly, not Japanese beetles!
Because the damage is
similar, many people assume
that Japanese beetles caused
the damage.
Poplar leaf beetle larvae skeletonize from the top.
Bristly roseslugs (a sawfly) skeletonize from the bottom.
8
Roseslug sawfly skeletonizing rose leaf
Roseslug adult
Thorn & apple skeletonizer, a caterpillar
Many caterpillars and some sawfly larvae skeletonize the foliage
of their host plants when early instar larvae. As the larvae get
larger, they eventually eat large sections of leaf and finally whole
leaves – defoliators. Many of these defoliators also have similar
larval behavior. They are gregarious as skeletonizers and young
larvae, but as they reach maturity, they often feed separately in
the host foliage.
The first few leaves that are skeletonized often appear white or
yellow and stand out against the background of green foliage.
By learning to watch for this symptom, control can be simply
achieved by removing the clustered larvae that remain on a few
leaves. By disposing by crushing or dropping into soapy water,
extensive insecticide applications can be avoided.
9
Yellowneck caterpillar egg mass
Medium size larvae are
orange & yellow
1st instar larvae skeletonizing leaf
Large larvae are black & yellow
& defoliate host plants
Woody Ornamental Pest Groups
Foliage Feeders - Notchers
Weevil Adults Black vine, rough strawberry root,
& strawberry root weevils
Asiatic weevils
Leafcutter bees -
10
Most notchers in landscapes are weevils, but several caterpillars
and sawfly larvae also occasionally make notches in the margins of
leaves.
The types of plants attacked and size of the notches can often give
clues as to which pest may be present. Black vine weevils produce
relatively large notches, while Asiatic weevils make small and
irregular notches.
Privet leaves severely notched by black vine
weevil, strawberry root weevil and rough
strawberry root weevil adults.
Distinctive notches made by
leafcutter bee collecting leaf
pieces for their nest building.
Black vine weevil adult. Note
notching on taxus needles.
Leafcutter bee adults carry
pollen on their abdomens, not
the legs.
Leafcutter bee brood chambers in
rose cane. Note leaf linings.
11
Woody Ornamental Pest Groups
Foliage Feeders - Hole Makers
Shot Holes - (1-3 mm)
Flea Beetles
Flea Weevils
Yellow Poplar Weevil - (bean shaped)
Shothole Leafminer (a fly)
Larger Holes - (>3mm, irregular)
May/June Beetles
Shothole Leafminer Adults
Flea beetles and flea weevils make small round or oval holes in
the foliage of host plants. Some call their style of feeding “pit
feeding” because the adults usually remove the epidermal layer
and underlying tissues, but the lower epidermal layer is left
intact. If pit feeding is done on young plants, the remaining
epidermis dies and drops out. This results in a larger, usually
teardrop-shaped hole.
The shothole leafminer is a small fly that punctures oak leaves as
they begin to expand. These punctures are made with the
ovipositor but the fly sucks out sap from the damaged areas. As
the leaves expand, the pin-pricks turn into small holes.
Several beetles (especially May/June beetles), small caterpillars
and other insects chew irregular holes in leaves. If these holes
are made when the leaf is small, the holes get larger as the leaf
expands and matures. You can usually tell if damage is old or
recent by seeing if the edge of the holes have healed over and
there will usually be a yellow or brown margin.
12
Flea weevil and typical shotholes
made through pit feeding.
Striped flea beetle feeding
on spinach leaf with other
characteristic holes.
Gypsy moth third instar larva and
characteristic irregular holes.
Larger larvae eventually eat the
entire leaf – defoliation.
Willow flea beetle
and characteristic
shot holes in leaf.
13
Woody Ornamental Pest Groups
Foliage Feeders - Nest Makers
Using Plant Materials Casebearers – caterpillars
Bagworms - caterpillars
Leafrollers - caterpillars & weevils
Leaftiers - caterpillars
Leaffolders - caterpillars
Using Mainly Silk Tent Caterpillars - caterpillars
Webworms - caterpillars & sawflies
Case bearers are usually small insects that use small pieces of leaf to
construct a pouch in which the larva hides, only poking its head out to
feed on foliage. The bagworms actually make single bags or sacs of silk
on which bits and pieces of plant foliage are attached. These insects
increase the bag size as they grow.
Leafrollers, leaffolders and leaftiers make nests by rolling up a single
leaf, folding over the edge of a leaf or tying together two overlapping
leaves. Most of these are caterpillars that skeletonize the foliage within
the protection of their nests. Most are solitary, but several leaftiers live
in small groups.
The tent caterpillars are generally represented by one species, the
eastern tent caterpillar. Tent caterpillars build silk nests in the crotch of
a tree. The caterpillars hide within the nest except when they emerge to
feed on the foliage.
Webworms are caterpillars or sawfly larvae that live in groups which web
over or encase foliage in their silken nests. The larvae feed on this
enclosed foliage and they expand the nests as they grow.
14
Larch casebearer bag on needle.
Adult larch casebearer
(a moth) and needles
damaged by the
larvae.
Elm casebearer adult, a moth.
Elm casebearer larval
bag. Note that the bag is
made from a piece of
elm leaf. The larvae
actually mine small
patches in elm leaves.
15
Bagworm larva extending from bag.
Bagworms on spruce.
Male
bagworm
adult.
Female bagworms remain in the bag as
a pupa that contains the fertilized eggs.
Oak leafroller damage.
Oak leaftier damage.
Pine tube moth.
Oak leaftier larvae and frass.
16
Sweetgum leaftier
Redbud leaffolder damage.
Redbud leaffolder
larva in nest.
17
Eastern tent caterpillar nest in
roadside cherry tree.
Tent caterpillars following web trail.
Mature larva
and cocoon.
Egg mass.
Fall webworm adult male.
Early fall webworm nest.
Purpleleaf plum with dozens of fall
webworm nests in September.
18
Memosa webworn
nest in
honeylocust.
Memosa webworm
adult.
Pine webworm nest.
19