The Pacific Oak Twig-girdler


Burke, H.E.

Journal of Economic Entomology 13(5): 379-384

1920


The Buprestid, Agrilus angelicus, Horn, causes serious damage to oaks (Quercus agrifolia) in California. It also attacks interior live oak (Q. wislizeni), leather oak (Q. durata), canyon live oak (Q. chrysolepis), mesa oak (Q. engelmanni), California black oak (Q. californica) and tan oak (Q. densiflora.) It is found from a few feet above sea-level to an altitude of 6, 000 ft. The eggs are generally laid singly on the smooth bark of the twig near the end of the last year's growth at the end of June or beginning of July. They hatch in from two to three weeks, and the larvae begin boring under the bark. The complete life-cycle requires about two years. By the middle of the first winter the mine extends down the small twigs for about one to three inches. Some of the larvae may reach the wood, whilst others still remain in the bark. Mining is continued in the following spring and summer, the length of the burrow being increased to from 6 to 12 inches. The winter is passed in the centre of the branch. In the succeeding spring the burrow is lengthened by an inch or two, after which the larva turns and retreats for several inches before entering the wood to form the pupal cell, usually about the middle of May. The adults remain for several days in the pupal cell before emerging in May and June. The natural enemies of this beetle include the following Hymenopterous parasites: - Cryptohelcostizus rufigaster, Cushm., Cryptoideus fasciatus, Ashm., Doryctes muculipennis, Rohw., Callihormius sp., Ptinobius agrili, Rohw., reared from the larvae, Metapelma spectabilis, Westw., which may be a hyperparasite, Tetrastichus anthracinus, Ashm., of which as many as 17 larvae have been found in one larval host, and Dinotus agrili, Rohw. The remedial measures advocated include pruning about April before the beetles emerge. These prunings should be placed in a box or barrel covered with a 16 mesh wire screen to permit the escape of the parasites. Poison and contact sprays exercise a certain amount of check by poisoning the beetles as they feed, but not sufficient to warrant their use against this beetle only.

JOURNAL
OF
ECONOMIC
ENTOMOLOGY
OFFICIAL
ORGAN
AMERICAN
ASSOCIATION
OF
ECONOMIC
ENTOMOLOGISTS
Vol..
13
OCTOBER,
1920
No.
4
Proceedings
of
the
Thirty-Second
Annual
Meeting
of
the
American
Association
of
Economic
Entomologists
(Continued
from
p.
363)
PAPERS
READ
BY
TITLE
THE
PACIFIC
OAK
TWIG-GIRDLER.
,
By
H.
E.
BURKE,
Specialist
in
Forest
Entomology,
Forest
Insect
Investigations,
Bureau
of
Entomology,
U.
S.
Department
of
Agriculture
ECONOMIC
IMPORTANCE
One
of
the
most
important
and
characteristic
native
shade
trees
of
the
coast
valleys
of
California
is
the
California
live
oak
(Quercus
agrifolia
Nee).
As
a
general
rule
this
fine
tree
is
in
a
healthy
and
vigorous
condition,
but
sometimes
it
is
attacked
by
various
insects,
which
give
it
a
ragged
and
unsightly
appearance.
One
of
the
most
important
of
these
insects
is
the
twig-girdler.
Both
small
and
large
trees
sometimes
are
thickly
spotted
with
small
areas
of
fading,
yel-
low,
red
or
brownish
foliage
which
stands
out
strikingly
against
the
normal
green
of
the
healthy
leaves.
In
the
majority
of
cases
the
dead
twig
or
small
branch
bearing
the
coloring
leaves
will
show
at
its
base
the
characteristic
spirally-winding
mine
of
the
twig-girdler.
Some-
times
so
many
twigs
and
small
branches
are
killed
by
the
girdler
that
the
tree
dies.
In
any
case,
the
ragged
appearance
caused
by
numbers
of
dead
and
dying
twigs
seriously
injures
the
tree
for
ornamental
purposes.
HISTORY
AND
IDENTITY
The
species
was
described
by
Dr.
George
H.
Horn
in
1891,
with
host
plant
unknown.
(Trans.
Amer.
Ent.
Soc.,
Vol.
XVIII,
p.
298.)
Agrilus
angelius
Horn,
family
Buprestidm,
order
Coleoptera.
380
JOURNAL
OF
ECONOMIC
ENTOMOLOGY
[Vol.
13
Doane
mentioned
the
work
on
the
live
oak
in
1912
without
naming
the
species.
(Jour.
Econ.
Ent.,
Vol.
5,
p.
347.)
Childs,
in
1914,
gave
a
very
good
account
of
the
insect
and
its
work
under
the
name
of
Agrilus
politus
Say.
(Month.
Bul.
Cal.
State
Corn.
Hort.,
Vol.
III,
pp.
150-5.)
He
also
figured
the
insect
and
its
work
and
recommended
methods
of
control.
Essig,
in
1915,
figured
the
insect
and
gave
a
short
account
of
the
life
history,
work,
distribution,
food
plants,
control
and
natural
enemies
under
the
name
Agrilus
politus.
(Injurious
and
Bene-
ficial
Insects
of
California,
p.
234.)
In
January,
1917,
Burke
figured
the
eggs
as
those
of
Agrilus
angelicus
(U.
S.
Dept.
Agric.,
Bul.
437,
fig.
I,
Pl.
IX)
and
in
June
of
the
same
year
gave
a
short
account
of
the
species
under
the
same
name.
(Jour.
Econ.
Ent.,
Vol.
10,
p.
330.)
Specimens
have
been
sent
to
the
leading
specialists
on
the
genus
Agrilus
and
there
seems
no
doubt
but
that
the
species
is
angelicus
Horn.
It
is
quite
distinct
from
politus
Say.
A
very
similar
species
which
has
been
identified
as
angelicus
by
some
of
the
specialists
lives
in
the
manzanita
(Arctostaphylos
species)
and
the
madrone
(Arbutus
menziesii)
in
the
Sierras
and
coast
valleys
of
Central
California.
There
are
some
differences
in
the
life
history
which
cause
the
writer
to
believe
that
it
is
distinct.
Experiments
are
now
being
carried
on
which
should
settle
this
point.
DISTRIBUTION
AND
FOOD
PLANTS
The
specimens
from
which
the
species
was
named
came
from
near
Los
Angeles
and
from
the
Santa
Cruz
Mountains,
California.
Childs
obtained
his
specimens
at
Palo
Alto
from
the
live
oak.
Essig
says
that
the
insect
is
found
throughout
the
state
of
California,
that
the
favorite
host
is
the
willow,
that
the
live
oak
often
is
severely
damaged
by
its
attacks
and
that
other
food
plants
are
the
buckeye
and
hazel-
nut.
He
undoubtedly
used
the
distribution
and
food
plants
of
A.
politus,
under
which
name
he
accounts
for
the
species.
The
writer
has
reared
specimens
of
the
beetle
from
live
oak
twigs
collected
at
Pasadena
by
Dr.
A.
G.
Smith,
and
at
Palo
Alto,
Los
Gatos,
Laurel
and
near
Saratoga,
Calif.,
by
himself.
Larvae
and
the
charac-
teristic
work
have
been
found
at
Boulder
Creek,
San
Juan,
Monterey,
Carmel,
Woodside,
Niles,
Alum
Rock,
Napa
and
Mt.
St.
Helena,
by
Mr.
R.
Di
Hartman.
Mr.
F.
B.
Herbert
found
the
work
very
common
at
Montecito
near
Santa
Barbara
and
at
South
Pasadena.
During
the
past
summer
heavy
infestations
were
found
in
the
black
oak
and
canyon
live
oak
near
Confidence,
Tuolumne
County,
in
the
middle
Sierras.
The
following
host
plants
have
been
determined:
California
live
oak
(Q.
agrifolia),
interior
live
oak
(Q.
wislizeni),
leather
oak
(Q.
October,
'20]
BURKE:
PACIFIC
OAK
TWIG-GIRDLER
381
durata),
canyon
live
oak
(Q.
chrysolepis),
engelmann
or
mesa
oak
(Q.
engelmanni),
California
black
oak
(Q.
californica)
and
the
tan
oak
(Q.
densiflora).
The
species
range
from
a
few
feet
above
sea
level
to
an
altitude
of
6,000
feet.
CHARACTERISTIC
WORK
The
first
indication
of
an
attack
by
the
twig-girdler
is
scattering
small
patches
of
fading
foliage.
Other
insects
and
diseases cause
somewhat
similar
dying
branches,
but
the
trained
eye
usually
can
detect
the
difference.
Roundheaded
borers
kill
larger
branches
and
their
work
is
not
so
common,
scales
of
the
genus
Kermes
and
some
of
the
gall
wasps
kill
smaller
twigs,
and
a
disease
supposed
to
be
related
to
the
chestnut
blight
kills
large
patches
of
foliage
on
adjoining
branches.
Childs
says
that
the
foliage
that
dies
from
the
girdler
work
is
a
light
straw
color
when
dry,
while
that
killed
by
the
disease
is
a
distinctive
reddish
brown
tinge.
These
color
differences
may
hold
true
in
some
cases,
especially
during
the
first
year,
but
the
girdler
work
of
the
sec-
ond
year
is
apt
to
cause
good
sized
patches
of
reddish
foliage
which
are
difficult
to
distinguish
from
the
disease
work.
A
close
examination
of
the
dying
or
dead
twigs
will
always
show
the
real
cause
of
the
trouble.
If
it
is
the
girdler
there
will
be
a
small
mine
winding
around
under
the
bark
and
down
the
twig.
During
the
first
year
this
only
goes
a
few
inches,
but
during
the
second
it
may
go
for
a
foot
or
more,
sometimes
two
feet,
the
mine
spiralling
the
branch
and
killing
all
of
the
twigs
terminal
to
it.
It
may
go
down
one
fork
and
up
another.
The
foliage
on
the
killed
twigs
will
vary
from
a
fad-
ing
green
to
a
reddish
brown,
depending
on
the
time
of
the
year
each
was
killed.
Usually
most
of
the
mine
is
just
under
the
bark,
but
it
may
go
into
the
wood.
It
usually
spirals
around
the
branch
from
four
to
twelve
times,
but
sometimes
runs
straight
clown
for
a
long
distance.
Just
before
it
is
completed
the
mine
usually
reverses
and
runs
back
up
the
branch
for
an
inch
or
more,
where
it
goes
into
the
wood
and
ter-
minates
in
the
slightly
enlarged
pupal
cell.
After
the
beetle
emerges
the
pupal
cell
opens
on
the
surface
of
the
branch
in
the
oval
emergence
hole.
Most
of
the
branches
killed
by
the
girdler
are
not
over
one
half
an
inch
in
diameter.
The
leaves
fall
before
the
end
of
the
second
year
and
the
work
shows
as
a
leafless
branch,
an
unsightly
blemish
on
a
splendid
object
of
natural
beauty.
THE
TWIG-GIRDLER
The
twig-girdler
is
a
slender,
whitish
flattened
boring
grub
of
the
common
agriloid
type.
It
varies
in
length
from
1
mm.
when
newly
hatched
to
18
mm.
when
full
grown.
The
mouth
parts
and
tail
for-
382
JOURNAL
OF
ECONOMIC
ENTOMOLOGY
[Vol.
13
ceps
are
dark
brown
or
black.
Hatching
from
the
egg
during
June
and
July,
the
girdler
starts
mining
through
the
bottom
of
the
shell
and
under
the
bark.
By
the
middle
of
the
first
winter
it
has
grown
to
be
7
mm.
long
and
has
extended
its
mine
down
the
small
twigs
for
from
one
to
three
inches.
Most
of
the
twigs
have
been
spiralled
and
the
foliage
has
faded
to
yellow.
At
this
time
some
of
the
girdlers
are
under
the
bark
and
some
have
gone
into
the
wood.
Mining
is
continued
during
the
succeeding
spring
and
summer
until
the
second
winter,
when
the
girdler
has
mined
down
the
branch
for
about
6
to
12
inches
and
has
grown
to
about
15
mm.
long.
Most
of
the
foliage
is
reddish
brown
or
rusty'
looking.
The
girdler
now
goes
into
the
wood
and
lies
out-
stretched
in
the
center
of
the
branch
for
most
of
the
winter.
In
the
spring
it
continues
down
the
branch
under
the
bark
for
an
inch
or
more
and
then
turns
and
retreats
back
up
for
several
inches
before
it
again
enters
the
wood
and
forms
the
pupal
cell.
In
the
Santa
Clara
Valley
this
takes
place
about
the
middle
of
May.
The
girdler
is
now
full
grown
and
it
soon
shortens
up
to
about
half
its
former
length
and
gets
ready
to
pupate.
The
pupal
cell
is
usually
formed
at
an
angle
to
the
surface
of
the
branch,
the
mine
entering
the
wood
and
angling
up
to
the
surface
for
the
emergence
of
the
beetle.
THE
PUPA.
The
pupa
when
first
formed
is
a
delicate
whitish
object
with
the
head,
body,
wings
and
legs
faintly
indicated.
It
is
about
7
to
9
mm.
long
and
1
to
2
mm.
broad.
The
eyes
soon
commence
to
darken
and
in
about
two
weeks
all
of
the
head,
thorax
and
under-
side
of
the
body
have
changed
to
a
brownish
bronze.
The
wings
and
elytra,
which
are
folded
on
the
breast
and
the
dorsal
surface
of
the
abdomen,
remain
white.
Upon
the
transformation
of
the
pupa
to
the
beetle
which
now
takes
place
the
wings
and
elytra
change
to
the
back
and
the
elytra
soon
take
on
the
normal
bronze
color
of
maturity.
This
is
done
without
going
through
the
interesting
color
changes
of
some
of
the
other
species
like
politus.
Most
of
the
pupa
were
found
in
the
field
during
the
last
of
May
and
the
first
of
June.
Some
have
been
found
in
April.
THE
BEETLE.
The
beetle
is
a
slender
brownish
bronze
insect
with
a
coppery
or
slightly
golden
thorax.
Its
length
is
from
5
to
7
mm.
and
its
breadth
from
12
to
2
mm.
The
males
have
dark
green
faces
and
the
females
brownish
bronze
ones.
The
claws
are
cleft
in
such
a
manner
that
the
lower
portion
is
turned
inward
and
the
hind
tarsi;
are
stout
and
obviously
shorter
than
the
tibia.
The
newly
formed
beetle
stays
in
the
pupal
cell
for
several
days
before
it
eats
its
way
to
the
outer
world.
After
this
emergence,
which
takes
place
during
May
and
June,
the
beetles
fly
around
in
the
warm
sun,
feed
on
the
edges
of
the
leaves
of
the
oaks
and
mate.
Soon
after
mating
the
female
lays
October,
'201
BURKE:
PACIFIC
OAK
TWIG-GIRDLER
383
her
eggs
and
both
soon
die.
So
far
as
could
be
determined,
most
of
the
beetles
live
about
two
weeks.
THE
EGG.
When
first
laid
the
egg
is
a
dull
white,
flattened
oval
scale-like
object
a
mm.
long
and
4
mm.
broad.
It
soon
becomes
darker
with
age
and
development
and
in
from
4
to
5
days
turns
a
shiny
black.
It
is
covered
with
a
varnish-like
covering
which
catches
the
dust,
etc.,
so
that
in
a
week
or
more
it
looks
like
the
brownish
or
black-
ish
gray
bark
of
the
twigs.
The
egg
is
laid
singly
on
the
bark
of
the
twig,
near
the
end
of
the
last
year's
growth.
It
is
not
tucked
under
a
loose
flake
of
the
bark,
or
in
a
crevice,
but
is
laid
on
the
smooth
bark,
usually
near
the
base
of
a
small
twig
or
a
leaf
scar.
In
the
great
majority
of
cases
only
a
single
egg
is
laid
on
a
twig,
but
in
a
few
cases
two
were
observed
close
together
and
in
one
or
two
instances
three
were
laid
scatteringly
along
the
stem.
In
hatching,
the
young
larva
bores
into
the
bark
through
the
bottom
of
the
shell
and
packs
the
shell
full
of
the
borings.
Most
of
the
eggs
are
laid
during
the
last
of
June
and
the
first
of
July.
All
appear
to
hatch
in
from
two
to
three
weeks
after
they
have
been
laid.
NUMBER
OF
GENERATIONS
The
oak
twig-girdler
is
a
two-year
species.
Eggs
laid
in
June
of
1912,
1914
and
1916
produced
beetles
in
1914,
1916
and
1918.
In
many
localities
there
is
no
brood
of
beetles
during
the
alternate
years.
In
some
there
are
a
few
scattering
individuals
and
in
others
there
is
a
well-defined
brood
each
year;
that
is,
in
June,
beetles
will
be
emerging
from
some
twigs
while
year-old
larva
will
be
found
in
others;
in
Jan-
uary,
eighteen-months
old
larva
will
be
found
in
the
large
twigs
and
six-months
old
larva
in
the
small
ones.
A
most
interesting
occurrence
was
observed
at
Confidence,
Tuolumne
County,
during
August,
1919.
All
of
the
specimens
found
in
the
black
oak
were
small
larva
from
eggs
laid
in
June,
1919,
while
all
of
those
found
in
the
canyon
live
oak
were
year-old
larva
from
eggs
laid
in
June,
1918.
NATURAL
ENEMIES
Natural
enemies
undoubtedly
play
an
important
part
in
the
life
history
of
the
twig-girdler.
Nine
species
of
Hymenopterous
parasites
were
reared
from
the
larval
mines
and
pupal
cells.
One
of
these
was
a
new
species
and
new
genus,
and
three
others
were
new
species.
Messrs.
S.
A.
Rohwer
and
R.
A.
Cushman
identified
the
species
and
named
the
new
ones.
Cryptohelcostizus
rufigaster
Cushman,'
n.
gen.,
n.
sp.,
was
reared
several
times
from
a
single
larva
or
cocoon
found
in
the
pupal
cell
of
the
girdler.
Two
Cryptoideus
fasciatus
Ashm.
were
reared
from
sim-
1
Cushman,
R.
A.,
Proc.,
U.
S.
Nat.
Mus.,
Vol.
55,
pp.
534-35.
384
JOURNAL
OF
ECONOMIC
ENTOMOLOGY
[Vol.
13
ilar
pupal
cells.
Doryctes
maculipennis
Rohwer,
n.
sp.,
was
reared
from
cocoons
found
in
both
the
larval
mines
and
the
pupal
cells.
Another
species
of
Doryctes
was
reared
in
numbers
from
cocoons
found
in
the
same
places.
In
one
locality
near
Palo
Alto
50
per
cent
of
the
girdlers
were
parasitised
by
this
species.
Several
cocoons
occur
packed
in
the
same
cell
or
mine.
Callihormius
sp.
was
reared
from
the
larval
mines
and
possibly
the
pupal
cell.
Ptinobius
agrili,
Rohwer'
n.
sp.,
larva
were
found
to
emerge
from
pre-
pupal
girdler
larvae
in
the
pupal
cells
and
formed
naked
pupa.
Only
a
single
one
was
found
in
each
cell.
Metapelma
spectabilis
Westwood
was
reared
from
the
girdler-infested
twigs.
It
may
be
a
hyperparasite.
Tetrastichus
anthracinus
Ashmead,
a
small
black
tetrastichid,
was
the
commonest
parasite
reared.
It
occurred
in
numbers
in
the
larval
mines
and
pupal
cells
of
the
girdler.
As
many
as
seventeen
larva
were
found
in
one
girdler
larva.
Sometimes
the
girdler
larva
was
killed
before
it
made
the
pupal
cell,
and
sometimes
afterward.
The
Tetrastichus
larva
then
emerged
and
formed
naked
pupa
in
the
mines
or
cells.
Dinotus
agrili
Rohwer,
n.
sp.,
was
reared
several
times
from
girdler-infested
twigs
sent
in
from
Pasadena
by
Dr.
A.
G.
Smith.
METHODS
OF
CONTROL
The
best
method
of
control
developed
at
the
present
time
is
the
pruning
of
the
infested
twigs.
This
should
be
done
in
the
spring
about
April
first
before
the
beetles
emerge.
At
this
time
both
the
twigs
infested
for
one
year
and
for
two
years
are
easily
distin-
guished
and
those
infested
for
the
two
years
must
be
treated
if
the
infesting
insects
are
to
be
killed
before
they
emerge.
As
many
of
the
infesting
girdlers
are
parasitised,
it
is
better
not
to
burn
the
infested
twigs
but
to
cage
them
in
a
box
or
barrel
with
the
side
or
top
made
of
number
16
mesh
wire
screen.
The
beetles
cannot
get
through
this
and
will
soon
die,
while
the
parasites
will
escape
and
attack
the
twig-girdlers
in
the
infested
twigs
overlooked
in
the
pruning.
Poison
sprays
used
against
caterpillars
in
the
spring
kill
some
of
the
beetles
as
they
feed
on
the
foliage
before
mating.
Contact
sprays
used
against
scales
and
other
bark
pests
may
kill
some
of
the
eggs,
but
it
is
doubtful
if
it
will
pay
to
use
either
of
these
if
fighting
only
the
girdler.
FIELD
EXPERIMENTS
FOR
THE
CONTROL
OF
THE
APPLE
MAGGOT
By
GLENN
W.
HERRICK,
Ithaca,
N.
Y.
In
1910
the
writer
urged
Dr.
J.
F.
Illingworth,
then
a
graduate
student
at
Cornell
University,
to
undertake
an
investigation
of
the
1
Rohwer,
S.
A.,
Proc.
Ent.
Soc.
Wash.,
Vol.
21,
pp.
5-8.