Biology and ecology of a mesquite twig girdler, Oncideres rhodosticta, in West Texas


Polk, K.L.; Ueckert, D.N.

Annals of the Entomological Society of America 66(2): 411-417

1973


Oncideres rhodosticta Bates causes severe damage to small branches of mesquite (Prosopis glandulosa) in many rangeland areas of Texas. The adults of the Cerambycid emerge from galleries in girdled branches from late August to the end of November. They feed on the tender bark of mesquite round buds, thorns and small limbs. Each female girdles about one branch and deposits about 8 eggs beneath the bark. Within 10-14 days, 98% of the eggs hatch and the larvae feed on the sapwood, opening the oviposition scar to expel frass after about 3 months. Pupation occurs in late August and early September and is preceded by a prepupal stage. Each larva consumes about 1.44 cm3 mesquite wood during its development. Parasites and predators kill 15-22% of the larvae, while 34-55% die from undetermined causes. Twig girdler larvae may compete for space and food with other Cerambycids and several species of Bostrichids. About 31% of all girdled branches are broken off by wind storms and livestock before the adults emerge, resulting in much mortality of larvae from high temperatures in the branches near the soil surface.

Biology
and
Ecology
of
a
Mesquite
Twig
Girdler,
Oncideres
rhodosticta,'
in
West
Texas
K.
L.
POLK
3
AND
D.
N.
UECKERT
Range
and
Wildlife
Management
Department,
Texas
Tech
University,
Lubbock
79409
ABSTRACT
Oncideres
rhodosticta
Bates
(Coleoptera
:
Cerambyci-
dae)
causes
severe
pruning
of
small
branches
of
mesquite,
Proso/'is
glanduloso
Torr.,
in
many
areas
of
Texas.
Adults
emerge
from
galleries
in
girdled
branches
from
late
August
through
November.
They
feed
on
tender
hark
of
mesquite
around
the
buds,
thorns,
and
small
limbs.
Each
female
girdles
about
one
branch
and
deposits
about
8
elliptically
ovate
eggs
beneath
the
bark
of
the
branch.
Within
10-14
days,
98%
of
the
eggs
hatch
and
the
larvae
feed
upon
the
sapwood,
opening
the
oviposi-
tion
scar
to
expel
frass
after
about
3
months.
Pupation
occurs
in
late
August
and
early
September
and
is
pre-
ceded
by
a
prepupal
stage.
Each
larva
consumes
about
1.44
cc
of
mesquite
wood
during
its
development.
Para-
sites
and
predators
kill
15-22%
of
the
larvae
while
34-
55%
die
from
undetermined
causes.
Larvae
are
attacked
by
parasites
in
the
families
Chalcedectidae,
Pteromalidae,
Eupelmidae,
and
Eurytomidae,
as
well
as
by
predators
in
the
family
Cleridae.
Twig
girdler
larvae
may
compete
for
space
and
food
with
other
cerambycids
and
several
species
of
bostrichids.
About
31%
of
all
girdled
branches
are
broken
off
by
wind
storms
and
livestock
before
adults
emerge,
resulting
in
high
mortality
of
the
larvae
from
high
temperatures
in
the
branches
near
the
soil
surface.
The
twig
girdler
Oncideres
rhodosticta
Bates
at-
tacks
the
crowns
of
mesquite
trees,
Prosopis
glan-
dulosa
var.
glandulosa,
which
infests
ca.
56
million
acres
of
Texas
rangeland
(Smith
and
Rechenthin
1964').
Preliminary
observations
on
the
life
history
and
description
of
this
insect
have
been
presented
(Ueckert
et
al.
1971).
It
chews
through
the
bark
and
living
xylem
layers
of
limbs
0.5-2.0
cm
diam,
killing
the
branch
above
the
girdle.
In
several
areas
of
Texas,
twig
girdlers
have
reduced
the
mesquite
canopy
considerably,
and
the
need
for
detailed
studies
concerning
its
ecology,
life
history,
and
parasite
and
predator
complex
and
its
evaluation
as
a
biological
control
agent
has
been
suggested
(Ueckert
et
al.
1971).
This
study
was
begun
in
1969
to
examine
the
biology
and
ecology
of
0.
rhodosticta.
Bates
described
0.
rhodosticta
in
1885
from
Lerdo,
Mexico
(Linsley
1940).
However,
there
is
much
confusion
in
the
literature
as
a
result
of
misidentifi-
cation
of
this
insect.
Linsley
(1940)
published
the
taxonomy
of
0.
rhodosticta
and
distinguished
it
by
the
presence
of
3
callosities
in
a
transverse
row
on
the
pronotum,
pale
antemedian
fascia
of
the
elytra,
and
yellowish
or
tawny
spots
throughout
the
elytral
pubescenses.
Howard
(1900)
was
the
first
to
report
the
damage
of
0.
rhodosticta
to
mesquite;
however,
he
misiden-
tified
the
beetle
as
0.
putator
Thomson
according
to
Linsley
(1940).
Howard's
report
was
documented
from
specimens
and
information
sent
to
him
by
M.
R.
Wise,
who
speculated
that
the
mesquite
in
Cala-
basas,
Ariz.,
would
ultimately
be
exterminated
from
excessive
pruning
which
eliminated
seed
production.
Linsley
et
al.
(1961)
reported
observations
of
feed-
ing,
girdling,
mating,
and
oviposition
by
0.
rhodo-
sticta
in
Arizona.
Swenson
(1969)
5
reported
that
1
Coleoptera:
Cerambycidae.
2
Texas
Tech
University,
College
of
Agricultural
Sciences
Publication
no.
T-10-109.
Received
Sept.
11,
1972.
3
Present
address:
Thuron
Industries,
Inc.,
12200
Denton
Drive,
Dallas,
Tex.
75234.
4
11.
N.
Smith
and
C.
A.
Rechenthin.
1964.
Grassland
re-
storation
the
Texas
brush
problem.
USDA
Soil
Conserv.
Serv.,
Temple.
Tex.
17
p.
5
W.
If.
Swenson.
1969.
Comparison
of
insects
on
mesquite
in
burned
and
unburned
areas.
M.S.
thesis.
Texas
Tech.
College,
Lubbock.
62
p.
during
autumn
of
1968,
twig
girdlers
killed
ca.
10%
of
the
small
branches
of
mesquite
on
the
Spining
Ranch
in
Garza
Co.,
Tex.
Ueckert
et
al.
(1971)
estimated
that
ca.
90%
of
the
mesquite
trees
in
an
infested
area
in
the
Trans-Pecos
region
of
Texas
had
been
attacked
by
this
insect,
and
that
ca.
40%
of
all
limbs
from
0.5
to
2.0
cm
diam
had
been
girdled.
'METHODS
AND
MATERIALS
We
conducted
field
studies
south
of
Wink
in
Winkler
and
Ward
Co.,
and
northeast
of
Post
in
Garza
Co.,
Tex.,
in
stands
of
mesquite
heavily
in-
fested
by
twig
girdlers.
The
Winkler-Ward
Co.
study
area
is
in
the
Trans-Pecos
region
of
Texas.
The
dominant
vegetation
is
scrubby
mesquite;
black
grama,
Bouteloua
eriopoda;
false
buffalograss,
Mutt-
roa
squarrosa;
and
perennial
broomweed,
Xantho-
cephalutn
sarothrae.
Soils
in
this
area
are
Springer
loamy
fine
sand
or
sandy
loam,
the
topography
is
nearly
level,
and
the
average
annual
precipitation
is
ca.
30
cm.
The
Garza
Co.
study
area
is
in
the
Rolling
Plains
of
Texas
where
the
average
annual
precipitation
is
ca.
47
cm.
Vegetation
consists
of
buffalograss,
Buchloe
dactyloides;
tobosa
grass,
Hil-
aria
inutica;
sideoats
grama,
Bouteloua
curtipendula;
and
scrubby
mesquite;
and
soils
are
Vernon
clay
loam
with
a
3-5%
slope.
Mesquite
in
this
area
is
generally
scrubby,
but
larger
trees
were
predominant
in
low-lying
areas.
The
differential
response
of
male
and
female
gird-
lers
to
artificial
light
was
determined
using
light
traps
in
Garza
and
Winkler
Co.,
on
Oct.
3
and
8,
respec-
tively,
when
the
air
temperature
was
above
21°C.
Light
used
for
these
traps
was
supplied
by
a
100-w
incandescent
bulb
suspended
from
a
1.5-m
tripod,
and
powered
by
a
portable
generator.
Many
twig
girdlers
were
also
collected
by
hand
from
mesquite
branches
in
the
same
areas.
The
sex
of
each
was
determined
by
the
differential
length
of
the
antennae,
and
the
x
2
test
(Snedecor
and
Cochran
1967)
was
used
to
determine
if
the
sex
ratios
were
1:1
using
these
2
collecting
methods.
On
Oct.
14
and
27,
1970,
60
recently
girdled
411
412
ANNALS
OF
THE
ENTOMOLOGICAL
SOCIETY
OF
AMERICA
[Vol.
66,
no.
2
branches
were
collected
at
each
study
area
to
deter-
mine
mean
numbers
of
eggs
per
branch,
incubation
period,
percent
egg
hatch,
and
mean
diameters
of
girdled
branches.
The
incubation
period
was
deter-
mined
by
selecting
branches
in
which
beetles
were
ovipositing
and
dissecting
the
oviposition
sites
from
several
branches
each
day
in
the
laboratory
until
the
eggs
hatched.
Dial
calipers
were
used
to
determine
twig
diameters
immediately
above
the
girdles.
Elytra
and
eggs
of
girdlers
were
measured
with
a
microscope
equipped
with
an
ocular
scale
at
6
and
12X,
respectively.
Elytral
measurements
were
taken
from
45
8
and
45
c'
specimens
to
compare
the
male
:
female
size
ratio.
The
length
and
width
of
60
eggs
from
each
study
area
were
measured.
The
volume
of
wood
consumed
by
girdler
larvae
was
determined
from
girdled
branches,
collected
in
Garza
Co.,
in
mid-November,
from
which
adults
had
emerged.
A
narrow
slit,
ca.
2
mm
wide,
was
cut
the
entire
length
of
the
gallery,
frass
and
exuviae
were
removed,
and
35
individual
galleries
were
filled
with
fine
sand
which
was
weighed
and
converted
to
a
volume
by
applying
a
weight:volume
ratio.
Population
densities
of
adult
girdlers
were
deter-
mined
on
several
dates
at
each
study
area
during
fall
of
1970
from
50
permanently
marked
trees
on
each
of
2
transects.
An
elytron
of
each
beetle
counted
was
marked
with
a
small
dot
of
model
airplane
paint,
using
a
separate
color
on
each
of
the
dates,
to
deter-
mine
the
rate
at
which
the
existing
population
was
replaced
by
new
individuals.
These
2
transects
were
also
used
to
determine
the
percent
of
girdled
branches
broken
off
by
wind
or
grazing
animals.
After
all
girdling
activity
had
ceased
in
late
November,
the
total
numbers
of
branches
girdled
on
each
transect
in
1970
were
counted
and
each
girdled
branch
was
marked
with
paint.
Branches
were
counted
again
in
late
August
1971
to
determine
the
number
still
intact
and
the
number
broken
off.
Field
cages
were
used
to
determine
fecundity,
lon-
gevity,
number
of
branches
girdled
per
female,
and
damage
potential
of
various
population
densities
of
girdlers.
Three
2X2-m
cages,
constructed
of
wood
and
Saran®
screen,
were
placed
over
3
trees
of
about
equal
size.
Population
densities
of
10,
26,
and
50
girdlers/tree
with
equal
sex
ratios
were
confined
in
these
cages.
The
beetles
were
collected
in
Ward
Co.,
immediately
after
emergence
(Sept.
24,
1970)
to
obtain
females
which
had
not
yet
oviposited.
After
girdling
had
ceased
and
the
beetles
were
dead
(Nov.
4,
1970),
the
following
data
were
recorded
for
each
tree:
(1)
percent
of
crown
volume
killed
(visual
estimate)
;
(2)
number
of
branches
girdled;
(3)
mean
diameter
of
girdled
branches
;
and
(4)
mean
number
of
eggs
laid
per
girdled
branch.
The
"t"
test
(Steel
and
Torrie
1960)
was
used
to
deter-
mine
if
population
densities
affected
the
numbers
of
eggs
laid
per
girdled
branch,
and
the
mean
diameters
of
girdled
branches.
The
numerical
relationship
between
twig
girdler
larvae
and
their
parasites
and
predators
was
deter-
mined
by
periodically
dissecting
many
girdled
branches
from
each
study
area.
Each
gallery
was
examined
to
determine
if
the
larvae
had
been
at-
tacked
by
a
parasite
or
predator.
The
number
of
twig
girdler
larvae
and
the
number
of
parasites
and
predators
was
recorded
for
each
branch.
Parasites
and
predators
in
late
larval
or
pupal
stages
were
reared
to
adults
in
the
laboratory
and
were
sent
to
the
former
Entomology
Research
Division,
A.R.S.,
U.S.D.A.,
in
Beltsville,
Md.,
for
identification.
Laboratory
cages
were
used
to
study
relationships
between
twig
girdlers
and
other
insects
inhabiting
girdled
branches.
On
each
of
4
sampling
dates,
200
girdled
branches
were
collected
from
each
study
area.
The
branches
were
placed
in
0.6X
1-m
rearing
cages.
A
1-pint
jar
was
attached
to
the
bottom
corner
of
each
cage
to
collect
positively
phototactic
insects
as
they
emerged
from
the
mesquite
branches.
In-
sects
emerging
from
the
branches
were
periodically
collected
and
preserved
in
70%
ethanol.
The
total
numbers
of
twig
girdlers
reared
from
each
cage
were
compared
with
the
numbers
of
parasites,
predators,
and
competitors
to
determine
their
numerical
rela-
tionship
to
the
twig
girdler
population.
High
(1915),
working
with
0.
putator,
observed
that
when
girdled
huisache
branches
remained
high
in
the
top
of
trees,
the
larvae
died
from
lack
of
mois-
ture,
while
severed
branches
or
those
only
a
few
feet
above
the
ground
apparently
were
under
higher
humidity
conditions
and,
therefore,
produced
more
adult
beetles.
Based
on
High's
observations,
we
designed
a
study
to
determine
the
effect
of
different
environmental
conditions
on
girdler
larvae.
Four
treatments,
each
applied
to
50
girdled
branches
at
each
study
area
in
late
June,
included
:
(1)
placing
girdled
branches
on
the
ground
in
the
shade
of
mes-
quite
trees;
(2)
placing
girdled
branches
on
midgrass
vegetation
(tobosa
or
black
grama)
;
(3)
placing
girdled
branches
on
bare
ground
or
short-grass
vegetation
(buffalograss
and
false
buffalograss)
;
and
(4)
a
control
consisting
of
girdled
branches
left
in-
tact
on
the
trees.
Two
readings
of
daily
maximum
temperatures
were
recorded
in
early
and
late
July
at
positions
corresponding
to
the
5
treatments
to
deter-
mine
if
maximum
temperatures
affected
survival
of
larvae.
In
late
August,
these
branches
were
col-
lected
and
dissected
in
the
laboratory
to
determine
the
mean
numbers
of
larvae
surviving.
The
analysis
of
variance
(Steel
and
Torrie
1960)
was
used
to
determine
if
the
mean
numbers
of
larvae
surviving
under
these
treatments
were
equal
and
Duncan's
new
multiple
range
test
(Steel
and
Torrie
1960)
was
used
to
rank
the
means.
Ninety-five
percent
confidence
intervals
were
calculated
for
all
means.
Significance
of
statistical
analyses
was
determined
at
the
95%
level
of
probability.
RESULTS
AND
DISCUSSION
Life
Cycle
and
Behavior.—Adult
twig
girdlers
be-
gan
emerging
from
galleries
in
late
August
and
early
September,
and
continued
until
late
November.
Branches
dissected
Aug.
28,
1970,
at
the
Garza
Co.,
study
area
contained
2%
adults,
33%
pupae,
and
65%
March
1973]
PoLK
AND
UECKERT
:
BIOLOGY
AND
ECOLOGY
OF
Oncidcres
rhodosticta
413
larvae.
Branches
dissected
at
the
Ward
Co.,
study
area
on
the
same
date
contained
14%
adults,
47%
pupae,
and
37%
larvae.
Thus
adults
probably
emerge
in
Ward
Co.
1-2
weeks
earlier
than
in
Garza
Co.,
which
is
located
ca.
290
km
to
the
north.
In
field
cages,
most
adults
died
in
20-30
days;
however,
a
few
adult
beetles
lived
more
than
45
days.
Only
female
beetles
were
observed
girdling
mes-
quite
branches.
More
males
than
females
were
at-
tracted
to
light
traps
;
ca.
87%
of
the
beetles
at-
tracted
to
lights
were
males
(Table
1).
Males
and
females
behaved
similarly
when
disturbed
;
instead
of
flying,
the
beetles
dropped
from
the
mesquite
tree
to
the
ground
and
remained
motionless.
When
captured
they
stridulated
by
rubbing
the
pronotum
over
the
ridged
mesonotal
plate.
These
behavioral
charac-
teristics
were
presumed
to
have
protective
or
survival
value.
Adult
beetles
fed
on
tender
bark
around
the
buds,
thorns,
and
small
limbs
of
mesquite
for
several
days
prior
to
mating
and
subsequent
girdling.
The
adults
did
little
obvious
damage
to
mesquite
by
this
feeding,
and
only
at
population
densities
of
50/tree
in
field
cages
was
there
any
noticeable
damage.
Diurnal
and
nocturnal
mating
was
observed,
even
while
females
were
involved
in
girdling.
Observations
of
marked
beetles
indicated
that
males
frequently
mated
with
more
than
one
female.
Field
cage
studies
in
September
showed
that
the
number
of
branches
girdled
varied
from
a
low
of
0.96/female
at
a
population
density
of
50
beetles/
tree
to
a
high
of
1.6/female
at
a
population
density
of
10
beetles/tree
(Table
2).
The
mean
numbers
of
eggs
laid
per
branch
for
branches
collected
in
Garza
and
Winkler
counties,
were
8.1±1.1
and
8.2±1.1,
respectively,
with
97
and
98%
egg
hatch,
respectively.
Female
beetles
girdled
branches
before
laying
eggs,
by
chewing
through
the
periderm,
nontranslocating
phloem,
translocating
phloem,
cambium,
and
far
enough
into
the
xylem
to
prevent
the
upward
trans-
location
of
water
and
nutrients,
resulting
in
death
of
the
branches
beyond
the
girdle.
The
leaves
re-
mained
on
these
girdled
branches
for
some
time,
apparently
because
an
abscission
zone
did
not
form.
Girdled
branches
averaged
9±0.05
and
10±0.06
mm
diam
on
the
Winkler
and
Garza
Co.,
study
areas,
respectively
;
branches
of
small
diameter
were
more
abundant
at
the
Winkler-Ward
Co.,
study
area.
Meyer
et
al.
(1971)
stated
that
the
small
stems
of
mesquite
trees
are
important
for
storage
of
carbo-
hydrates
as
starch
granules.
When
these
small
branches
are
killed
by
twig
girdlers,
the
amount
of
stored
carbohydrates
available
to
the
plant
would
cer-
tainly
be
reduced.
The
reduction
of
this
stored
food
by
the
action
of
these
insects
may
make
it
necessary
for
the
plant
to
use
food
reserves
stored
in
the
roots
for
budding
and
leaf
development
the
following
spring,
thus
weakening
the
plant.
After
girdling
a
branch,
the
female
made
an
in-
cision
in
the
bark
with
her
mandibles
while
facing
toward
the
base
of
the
tree.
She
then
turned
around
and
inserted
the
egg
parallel
to
and
beneath
her
abdomen
distal
to
the
incision,
and
then
sealed
the
incision
with
an
amber
secretion.
It
took
ca.
20-30
min
for
the
female
to
lay
each
egg,
while
the
girdling
process
required
as
much
as
2
days.
The
distance
between
the
eggs,
which
hatched
in
10-14
days,
varied
with
the
length
and
diameter
of
the
branch,
but
they
were
usually
ca.
40
mm
apart
on
the
branch.
The
larva
fed
toward
the
oviposition
scar,
opened
it
after
ca.
3
months,
and
used
this
opening
to
expell
frass
from
the
gallery.
Each
larva
fed,
with
its
venter
toward
the
bark,
on
only
one
side
of
the
branch,
severely
weakening
the
branch
at
that
point.
Many
weakened
branches
broke
during
high
winds,
probably
killing
many
larvae
directly
or
indirectly.
A
prepupal
stage
occurred
in
which
the
head
cap-
sule
was
deflexed,
the
mouthparts
became
somewhat
hypognathous,
and
movements
characteristic
of
pupae
were
exhibited.
The
pupa
used
peristaltsis-like
move-
ments
and
dorsal
spines
to
remove
the
larval
exu-
vium
after
it
split
immediately
behind
the
head
cap-
sule.
The
pupal
stage
occurred
in
late
August
and
early
September
and
lasted
for
ca.
14
days.
The
pupa
was
very
mobile,
moving
inside
the
galleries
by
pressing
its
elongated
last
abdominal
segment,
which
was
equipped
with
a
row
of
small
spines
around
its
perimeter,
against
the
walls
of
the
gallery.
Adult
girdlers
were
black,
with
a
grey
band
across
the
elytra.
Each
elytron
was
dotted
with
ca.
35-40
small
patches
of
orange
pubescence
(Fig.
1
A).
The
mean
lengths
of
the
male
and
female
elytra
were
10.1±0.3
and
10.6±0.3
mm,
respectively,
while
the
mean
overall
body
lengths
were
16.3
and
15.1
mm,
respectively.
Average
antennal
length
in
males
was
30.3
mm,
as
compared
with
18.4
mm
in
the
females.
The
distal
segments
of
male
antennae
were
ca.
4
times
as
long
as
those
of
females
;
the
length
of
these
segments
in
the
male
varied
from
3.2
to
6.5
mm
;
in
the
female
Table
1.—A
comparison
of
sex
ratios
of
0.
rhodosticta
collected
by
hand
and
in
light
traps;
Texas.
Autumn
1970.
Beetles
collected
Collection
No.
N
o.
9
No.
Location
Date
collected
method
Winkler
Co.
Oct.
9
Hand
625
300
325
1.0
Winkler
Co.
Oct.
8
Light
trap
239
31
208
131.1"
Garza
Co.
Oct.
3
Light
trap
769
100
669
421.0"
a
Significant
at
the
99%
level
of
probability.
414
ANNALS
OF
THE
ENTOMOLOGICAL
SOCIETY
OF
AMERICA
[Vol.
66,
n0.2
Table
2.-Effects
of
population
density
of
0.
rhodo-
sticta
on
damage
to
mesquite
and
egg
laying
habits
in
cage
studies.
Autumn
1970.
No.
No.
No.
branches
branches
beetles/
girdled/ girdled/
cage
y
tree
Mean
no.
eggs/
branch'
Mean
diam
crown
girdled
volume
branches
killed
(mm)
"
10
1.6
8
4.0
a
10
8.6
a
26
1.15
15
12.6
b
75
9.5
a
50
0.96
24
11.7
b
65
9.1
a
a
1:1
sex
ratio.
b
Means
followed
by
the
same
letter
are
not
significantly
differ-
ent
at
the
95%
level
of
probability.
they
varied
from
0.9
to
1.5
mm.
Males
could
also
be
distinguished
from
females
by
the
shape
of
the
last
ventral
abdominal
segment.
The
posterior
mar-
gin
of
this
segment
in
the
male
was
indented
or
slightly
"V"
shaped
;
in
the
female
it
was
not
"V"
shaped
and
was
broader.
The
eggs
(Fig.
1
B)
were
elliptically
ovate
and
creamy
white,
with
a
mean
length
of
4.3±0.06
and
a
mean
width
of
1.1±0.02
mm.
The
eggs
were
slightly
pointed
on
the
end
away
from
the
oviposition
scar.
Just
before
the
eggs
hatched,
the
yellowish
embryonic
larvae
could
be
seen
through
the
chorion.
The
head
developed
toward
the
oviposition
site,
and
the
dorsum
developed
adjacent
to
the
bark.
The
newly
hatched
larvae,
which
were
yellowish
white,
were
ca.
3.2
mm
long.
The
prothorax
was
ca.
1
mm
wide
and
was
whiter
than
the
rest
of
the
body.
The
head
was
light
brown
;
the
mandibles
were
black.
Just
before
the
larvae
pupated,
they
became
some-
what
scarabaeiform
and
ca.
26
mm
long
(Fig.
1
C).
Each
larva
consumed
a
mean
volume
of
1.44±0.12
cm'
of
wood
during
its
development.
The
pupae
were
ca.
20
mm
long
(Fig.
1
D)
and
were
white
when
they
first
emerged
from
the
last
larval
skin
;
however,
they
gradually
became
darker
until
transformation
to
adults.
The
eyes
darkened
first,
then
the
mandibles,
vertex
of
the
head,
and
prothorax
in
rapid
succession.
Population
Density.-The
highest
population
den-
sity
of
twig
girdlers,
4.7/tree,
occurred
Sept.
24,
1970,
the
1st
sampling
date
(Table
3).
Sampling
may
have
been
begun
too
late
to
determine
peak
population
densities
because
the
numbers
of
twig
girdlers
per
tree
decreased
as
the
season
progressed.
Sampling
probably
should
have
been
started
in
early
September
and
continued
through
early
November.
A
turnover
in
the
population
occurred
within
a
10-
day
period,
thus
the
number
of
beetles
present
on
a
given
day
cannot
be
used
as
a
reliable
estimate
of
the
total
effective
population
for
the
season.
Damage.-Mesquite
twig
girdlers
collected
in
late
September
in
Ward
Co.,
killed
10,
75,
and
65%
of
the
crown
volumes
of
caged
mesquite
trees
at
popula-
tion
densities
of
10,
26,
and
50/tree,
respectively
(Table
2).
The
mean
diameters
of
the
branches
girdled
at
these
population
densities
were
8.6±0.8,
9.5±0.8,
and
9.1±0.7
mm,
respectively.
Thus
these
beetles
would
not
girdle
larger
branches
if
natural
1.-Mesquite
twig
girdler
:
adult,
A
;
egg,
13;
larva,
C;
and
pupa,
D.
population
densities
were
significantly
increased.
Females
laid
more
eggs
in
each
girdled
branch
at
the
2
higher
population
levels
than
at
the
lowest
level.
However,
the
numbers
of
branches
girdled
per
fe-
male
decreased
as
population
densities
increased.
Parasites,
Predators,
and
Competition.-Girdler
lar-
vae
were
attacked
by
both
parasites
and
predators.
No
parasitized
eggs
were
observed,
and
the
pupae
were
attacked
by
predators
on
very
few
occasions.
Dissections
in
late
August
of
girdled
branches
which
Table
3.-Population
densities
of
adults
of
0.
rhodo-
sticta
on
two
50-tree
transects
in
Winkler-Ward
and
Garza
counties,
Tex.
Autumn
1970.
Sampling
dates
Mean
no.
girdlers/tree
Garza
Co.,
transect
no.
Winkler-Ward
Co.,
transect
no.
1
2
1
2
Sept.
24
.
.
4.7
Oct.
7
0
.8
.
.
3.5
2.5
Oct.
14
.5
0
.5
2.8
1.1
Oct.
27
.2
.2
0.6
0.1
Nov.
5
.1
415
March
1973]
POLK
AND
UECKERT
:
BIOLOGY
AND
ECOLOGY
OF
Oncidcrcs
rhodosticta
6-
5
larvae
of
0.
rhodosticta
—parasites
and
predotors
-C
C
-
2-
cr
6,
T
Apr.
May
June
July
Aug.
Sept.
a.
Garza
Co.
Mea
n
num
be
rs
o
f
5-
4-
3-
,
2-
N
N
N
Apr.
May
June
July
Aug.
Sept.
b.
Ward
Co.
FIG.
2.—Trend
in
density
fluctuations
in
interacting
populations
of
larvae
of
0.
rhodosticta
and
their
parasites
and
predators
dissected
from
galleries
in
mesquite
branches
collected
in
1970
in
Garza
Co.,
a,
and
Ward
Co.,
h,
Tex.
remained
intact
on
the
trees
throughout
the
year
in
the
Garza
Co.,
study
area
revealed
that
ca.
34%
of
the
original
8.1
larvae/branch
had
died
of
unknown
causes,
22%
were
killed
by
parasites
or
predators,
and
44%
remained
alive.
The
number
of
live
larvae
per
branch
decreased
as
the
year
progressed
and
there
was
a
corresponding
increase
in
the
number
of
parasites
and
predators
per
branch
(Fig.
2
a).
By
early
November,
20%
of
the
larvae
had
emerged
as
adults,
8%
had
not
pupated,
and
72%
had
died
from
attack
by
parasites
or
predators,
or
unknown
causes.
30
40
50
60
70
508
isimumierieemo
nim
i
N
f
Ai
r
10
20
IL
3
3
wiminmesommilr
A
rL
416
ANNALS
OF
THE
ENTOMOLOGICAL
SOCIETY
OF
AMERICA
[Vol.
66,
no.
2
Dissection
of
girdled
branches
from
the
Winkler-
Ward
Co.
study
area
in
late
August
revealed
that
55%
of
the
original
8.2
larvae/branch
had
died
of
unknown
causes,
15%
were
killed
by
parasites
or
predators,
and
30%
remained
alive.
The
number
of
larvae
per
branch
decreased
and
the
number
of
para-
sites
and
predators
increased
as
the
year
progressed
(Fig.
2
b).
By
mid-December,
24%
of
the
larvae
had
emerged
Ls
adults,
and
76%
had
died
from
at-
tack
by
parasites
or
predators,
or
other
causes.
Numbers
of
Insects
20
40
60
80
100
120
3373
TO"
0.
rhodostict
a
Other
Cerombyc
idoe
Bostrichidoe
C
I
er
idae
Beprestidoe
Other
Coleopt
er
a
lc
h
neureonidoe
C
holcidae
Brac
onidae
Other Hymenoptera
Dipt•r
a
3
IC
4111111
11111.
IngisimulmoimmiOperA
a.
Garza
Co.
Numbers
of Insects
0.
rhodosticta
Other
Cerambycidae
Bostric
hide
e
Cleri
doe
Buprestidoe
Other
Coleoptero
ichneomonidoe
Cha
lc
ida
e
Bra
conidoe
Other
Hymenoptera
Dip
tera
b.
Word
Co.
FIG.
3.—Total
numbers
of
insects
reared
from
mesquite
branches
girdled
by
0.
rhodosticta
in
Garza
Co.,
a,
and
Wa.d
Co.,
b,
Tex.;
800
branches
from
each
county.
March
1973]
POLK
AND
UECKERT
:
BIOLOGY
AND
ECOLOGY
OF
Oncideres
rhodosticta
417
Parasitic
Hymenoptera
dissected
from
larval
gal-
leries
included
Euchrysia
hyalinipennis
Ashmead
(Chalcedectidae)
;
Lampoterma
sp.
(Pteromalidae),
Eupelmus
bruchivorus
(Crawford
1
(
Eupelmidae
)
;
Eurytoma
sp.,
E.
magdalidia
Ashmead,
E.
dorca-
schemae
Ashmead,
Tenuipetiolous
n.
sp.
(Eurytomi-
dae)
;
Odontobracon
nigriceps
Cameron,
/phiau/ax
sp.,
and
Glyptoco/astes
sp.
(Braconidae).
Incidence
of
parasitism
was
about
equal
at
both
areas
and
the
parasites
were
present
in
about
equal
numbers,
ex-
cept
for
Tcnuipctio/ous
n.
sp.
and
braconids,
which
were
less
abundant.
The
date
or
season
that
girdler
larvae
were
attacked
by
parasites
and
predators
could
not
be
determined
by
cage
rearing
trials
;
low
num-
bers
of
adult
girdlers
emerged
from
caged
wood
samples,
probably
because
of
low
temperatures
in
the
cages.
A
clerid,
Enoclerus
sp.,
was
the
only
predator
dissected
from
larval
galleries.
Many
other
insects
were
reared
from
girdled
mes-
quite
branches,
some
were
parasites
and
predators,
while
others
were
believed
to
compete
with
twig
gird-
ler
larvae
for
food
and
space.
The
numerical
rela-
tionship
between
mesquite
twig
girdlers
and
other
insects
occupying
girdled
branches
is
shown
in
Fig.
3
a
and
b
for
branches
collected
in
Garza
and
Ward
Co.,
respectively.
Qualitatively,
the
insects
from
the
2
study
areas
were
very
similar,
but
their
numbers
differed.
All
Coleoptera
inhabiting
girdled
branches,
except
Cleridae,
probably
compete
with
girdler
lar-
vae
for
food
and
space,
with
bostrichids
probably
being
the
most
important
competitors.
The
larvae
of
clerids
were
presumed
to
be
predaceous
on
girdler
larvae
as
well
as
other
insects
within
girdled
branches.
Ichneumonids,
chalcids,
braconids,
other
Hymenoptera
and
Diptera
were
parasites
of
insects
within
girdled
branches
;
however,
no
ichneumonids
were
dissected
from
twig
girdler
galleries.
Numer-
ous
bostrichids
of
the
genera
Xylobiops
and
Amphi-
cerus
were
reared
from
both
areas,
with
Xylobiops
emerging
in
greater
numbers
than
Amphicerus.
Ichneumonids
were
reared
in
the
greatest
numbers
from
branches
collected
in
Garza
Co.
(Fig.
3
a),
while
in
Ward
Co.,
chalcids
were
the
most
numerous
parasites
(Fig.
3
b).
Effect
of
Environment
on
Larvae.—In
Ward
Co.,
survival
of
girdler
larvae
was
significantly
higher
in
girdled
branches
left
intact
(2.3
larvae
per
branch)
and
those
placed
in
shade
on
the
ground
(1.9/
branch),
than
in
branches
placed
on
midgrass
(0.1/
branch)
or
on
bare
ground
(0/branch).
In
Garza
Co.,
larval
survival
was
significantly
higher
in
gird-
led
branches
left
intact
(3.5/branch)
than
in
any
of
the
other
treatments,
while
those
placed
in
the
shade
contained
more
live
larvae
(1.9/branch)
than
those
on
midgrass
(0/branch)
or
those
on
bare
ground
(0/branch).
Maximum
temperatures
recorded
in
mesquite
canopies,
in
shade
on
the
ground,
on
mid-
grass
vegetation,
and
on
bare
ground
or
short-grass
vegetation
were
40,
42,
46,
and
61°C,
respectively.
Thus
it
is
obvious
that
excessively
high
temperatures
were
associated
with
low
survival
of
girdler
larvae.
Our
findings
appear
to
contradict
High's
(1915)
theory
that
more
adult
0.
putator
emerged
from
severed
branches
or
those
near
the
soil
surface.
However,
0.
putator,
which
is
actually
0.
pustulates
LeConte,
girdles
branches
20-40
mm
diam
(Linsley
1940)
as
compared
with
ca.
9
mm
for
0.
rhodosticta;
thus
survival
of
larvae
of
the
2
species
probably
should
not
be
compared.
We
found
that
an
average
of
31%
of
the
branches
girdled
during
fall
of
1970
had
been
broken
off
by
winds
or
livestock
before
fall
of
1971.
Most
of
these
branches
fell
upon
bare
ground
or
short-grass
vegetation,
thus
a
high
percent
of
the
potential
brood
of
girdlers
was
probably
killed
by
excessively
high
temperatures.
REFERENCES
CITED
High,
M.
M.
1915.
The
huisache
girdler.
USDA
Bull.
184.
9
p.
Howard,
L.
0.
1900.
A
troublesome
twig
girdler
of
the
southwest.
USDA
Div.
Entomol.
(n.s.)
Bull.
22:
94-95.
Linsley,
E.
G.
1940.
Notes
on
Oncideres
twig
girdlers.
J.
Econ.
Entomol.
33
:
561-3.
Linsley,
E.
G.,
J.
N.
Knull,
and
M.
Statham.
1961.
A
list
of
Cerambycidae
from
the
Chiricahua
Mountain
area,
Cochise
County,
Arizona
(Coleoptera).
Am.
Mus.
Novit.
2050.
34
p.
Meyer,
R.
E.,
H.
L.
Morton,
R.
H.
Haas,
E.
D.
Robins,
and
T.
E.
Riley.
1971.
Morphology
and
anatomy
of
honey
mesquite.
USDA
Agric.
Res.
Serv.
Bull.
1423.
186
p.
Snedecor,
G.
W.,
and
W.
G.
Cochran.
1967.
Statistical
Methods.
6th
edition.
Iowa
State
University
Press.
593
p.
Steel,
R.
G.
D.,
and
J.
H.
Torrie.
1960.
Principles
and
Procedures
of
Statistics.
McGraw-Hill
Book
Co.,
Inc.,
New
York.
481
p.
Ueckert,
D.
N.,
K.
L.
Polk,
and
C.
R.
Ward.
1971.
Mesquite
twig
girdler
:
a
possible
means
of
mes-
quite
control.
J.
Range
Manage.
24:
116-8.