Forest Health Protection Rocky Mountain Region • 2011
Introduction to Sap-Sucking Insects, Gall Formers, and Mites
Honeydew, spittle masses, growth deformities, or dried out foliage
Sap-sucking insects feed on the sugary sap produced in foliage and transported in the soft phloem tissue beneath the bark. Some insects’ feeding affects plant growth hormones, causing distinctive foliage or shoot deformities called galls. Gall formers feed protected within the gall. They may suck sap, as do gall-forming adelgids, or pierce and scrape the surface, as do some gall-forming midges. Mites (Acarina) are tiny arthropods that are more closely related to spiders and ticks than to insects. The class Acari contains 45,000 described species, but this is possibly only a portion of the total number of species yet to be described. Spider mites puncture individual cell walls on the outside of foliage and suck out the contents. This leads to a characteristic mottling of the foliage.
There are other types of mites that will be seen and noticed in a forested setting, but most are quite inconspicu-ous. One group of mites that may catch the observer’s eye is the mites that are found associated with bark beetles. Opening up a bark beetle gallery or looking at an individual bark beetle may reveal the presence of mites. These bark beetle associates fulfill a wide array of functions, including being predators of bark beetle eggs and larvae, grazers of associated fungi, and even predators of other mites. Because mites are wingless, they must hitchhike to new bark beetle galleries on their bark beetle hosts. This pattern of movement is referred to as phoresy. These mites are an integral part of the bark beetle system.
General Features—
• Hosts and symptoms of sap feeding insects, gall formers, and mites are described in table 1 (see figs. 1-4).
• Sap-sucking insects like aphids and scales feed on foliage, twigs, branches, and, occasionally, on the trunks of trees. These insects often produce large amounts of sweet, sticky honeydew that can sometimes be seen as a fine mist coming from the trees. Honeydew can coat branches and objects below the trees, which can subsequently be covered by black sooty mold.
• The majority of sap-sucking insects belong to the orders Hemiptera (true bugs) and Homoptera (aphids, leafhoppers, scales). Common gall formers belong to the insect orders Homoptera (adelgids), Hymenoptera (cynipid gall wasps), and Diptera (gall midges) and to the mite order Acari, which includes gall-forming mites (eriophyid mites) and spider mites.
Figure 1. The boxelder bug is a seed-feeding insect that may overwinter in and around buildings. Photo: William M. Ciesla, Forest Health Management International, Bugwood.org.
Figure 3. Frothy mass covers spittlebug on juniper. Photo: Whitney Cranshaw, Colorado State University, Bugwood.org.
Figure 2. Pinyon spindle gall. Photo: Brian Howell, USDA Forest Service.
Figure 4. The western conifer seed bug may seek overwintering sites around buildings in the fall. Photo: Whitney Cranshaw, Colorado State University, Bugwood.org.
Forest Health Protection Rocky Mountain Region • 2011
Tabl
e 1. C
ommo
n sap
-suck
ing an
d gall
form
ing in
sects
and m
ites i
n the
Roc
ky M
ounta
in Re
gion.
Inse
ct/m
ite
Host
Sy
mpt
om
Blac
k pine
need
le sc
alea (N
uclas
pis ca
liforn
ica)
Pond
eros
a and
Aus
trian p
ine
Tiny,
black
disc
s on n
eedle
sBo
xelde
r bug
a (fig.
1) (L
epto
coris
trivi
ttatu
s) Se
eds o
f box
elder
and o
ther m
aples
No
table
home
inva
der in
fall
Coole
y spr
uce g
all ad
elgid
(Ade
lges c
ooley
i) Sp
ruce
and D
ougla
s-fir
Galls
on sp
ruce
; woo
lly m
ateria
l on D
ougla
s-fir n
eedle
s and
twigs
Eriop
hyid
mites
(man
y spe
cies)
Aspe
n, oa
k, ma
ples,
and o
thers
Area
s of d
eform
ed fo
liage
, ofte
n red
or pi
nk-co
lored
Euro
pean
elm
scale
(Gos
sypa
ria sp
uria)
El
ms, p
rimar
ily A
meric
an el
m Ho
neyd
ew, b
lack s
ooty
mold,
and s
cales
on br
anch
esGi
ant c
onife
r aph
ids(C
inara
spp.)
Ma
ny co
nifer
s Ho
neyd
ew an
d aph
id co
lonies
Hack
berry
budg
all ps
yllida
Hack
berry
En
large
d, sp
heric
al-sh
aped
kille
d bud
s
(Pac
hyps
ylla
celtid
isgem
ma)
Hack
berry
nipp
legall
mak
era
Hack
berry
Ni
pple-
shap
ed sw
elling
s on l
eave
s
(Pac
hyps
ylla
celtid
ismam
ma)
Oyste
rshell
scale
(Lep
idosa
phes
ulm
i) Ma
ny ha
rdwo
ods
Grey
mod
eling
on ba
rkPe
tiole
gall a
phid
(Pem
phigu
s spp
.) As
pen,
cotto
nwoo
d, an
d othe
r pop
lars
Marb
le-siz
ed ga
lls on
leaf
petio
lePi
ne ne
edle
scale
(Chio
nasp
is pin
ifolia
e)
Pine
s, sp
ruce
, and
occa
siona
lly ot
her c
onife
rs Tin
y, wh
ite, te
ardr
op-sh
aped
scale
s on n
eedle
sPi
nyon
need
le sc
ale (M
atsu
cocc
us a
calyp
tus)
Piny
on pi
ne
Tiny,
black
, bea
n-sh
aped
bump
s on y
ear-o
ld ne
edles
Piny
on sp
indle
gall m
idgea
Piny
on pi
ne
Footb
all-sh
aped
swell
ing jo
ining
need
les w
ith th
e fas
cicle
(P
inyon
ia ed
ulico
la) (fi
g. 2)
Pitch
or R
esin
midg
ea (Cec
idom
yia sp
p.)
Pond
eros
a pine
, prim
arily
Re
sin pi
ts wi
th ma
ny tin
y, br
ight r
ed m
idge l
arva
eSp
ider m
ites (
Oligo
nych
us sp
p.,
Spru
ce, ju
niper
s, an
d othe
rs Dr
ied fo
liage
; dus
ty ap
pear
ance
Tetra
nych
us sp
p. an
d othe
rs)Sp
ittleb
ugsa (A
phro
phor
a spp
.) (fig
. 3)
Prim
arily
junip
ers,
oaks
, and
herb
aceo
us un
derst
ory
Froth
y mas
ses o
n twi
gs an
d foli
age
p
lants;
also
in so
uthwe
stern
dwar
f mist
letoe
Wes
tern c
onife
r see
d bug
a Se
eds o
f pine
s and
Dou
glas-fi
r Da
mage
d see
d; ca
n inv
ade h
omes
in th
e fall
(L
epto
gloss
us o
ccide
ntali
s) (fig
. 4)
a Not
discu
ssed
in th
is gu
ide.
Introduction to Sap-Sucking Insects, Gall Formers, and Mites - page 2
Forest Health Protection Rocky Mountain Region • 2011
• Spider mite injury is usually related to drought conditions.• Spider mites produce very fine webbing that causes a distinctive dirty appearance due to the accumulation of
dust, cast mite skins, and eggs.• There are many natural enemies that help control sap-sucking insects and mites. Insecticide use can some-
times prolong infestations by killing natural enemies of these insects.• There are a number of non-native sap-sucking insects that have been introduced to other parts of the country
that have become serious forest pests. The central Rocky Mountain Region does not have serious problems with non-native sap-sucking insects in its conifer forests, but several non-native species are found in decidu-ous landscape trees.
• Sap-sucking insects such as leafhoppers are known to vector certain plant diseases (e.g., X-disease on chokecherry).
Introduction to Sap-Sucking Insects, Gall Formers, and Mites - page 3