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Western Washington
Pheromone-trap Delimiting Survey and Field observations for European
Poplar Shoot Borer,
Gypsonoma aceriana (Duponchel) (Lepidoptera: Torticidae),
an Old World Poplar Pest new to North America. |
 |
Eric H. LaGasa1,
Patrik Hertzog2, Dan Barshis2, Kelley Turner2
and Hannah Smith2
2001 Entomology Project Report - WSDA PUB 034 (N/1/00) 2001 |
Project Results and Discussion |
A total
of 4,245 adult male EPSB were captured in the delimiting survey
traps, with EPSB recorded from every
county surveyed. Catch data is summarized by county in Table
2.
These survey results clearly show that EPSB is well established
across most of Western Washington. However, it should be noted
that direct comparison of summary trap information from one
county to another is difficult, given the variation in trapping
duration (e.g. survey timeframes) due to survey emphasis, travel
distances for field staff, and other variables.
Table 2. 2001 EPSB Survey Trap Results and Averaged Catch Data
County |
EPSB Trap Sites |
Pos. Sites |
% Sites Pos. |
Total EPSB |
Ave. EPSB / Pos.
Site |
Whatcom |
79 |
10 |
12.7 |
43 |
4.3 |
Skagit |
55 |
2 |
3.6 |
3 |
1.5 |
Snohomish |
54 |
3 |
5.6 |
3 |
1.0 |
King |
54 |
14 |
25.9 |
42 |
3.0 |
Pierce |
79 |
64 |
81.0 |
3,249 |
50.8 |
Thurston |
81 |
41 |
50.6 |
252 |
8.1 |
Lewis |
40 |
20 |
50.0 |
274 |
13.7 |
Cowlitz |
40 |
20 |
50.0 |
274 |
13.7 |
Clark |
60 |
15 |
25.0 |
105 |
7.0 |
Totals |
580 |
189 |
32.6 |
4,245 |
12.6 |
The widespread nature of current EPSB establishment in Western
Washington is more clearly demonstrated when positive survey
sites are plotted on a map, as in Figure 3.
(Note: Click
here for a larger format version of the 2001 EPSB Survey Sites
Map, including negative trapping sites.)
Although stastical analysis of the survey data presented in
Table 2 is limited by many variables, an indication of the relative
prevalence of EPSB across the surveyed counties is suggested
by the percentage of traps that caught moths in each county.
In Pierce County, the greater Tacoma area appears to be the
most generally infested area surveyed, with the majority of
traps (81%) catching EPSB. Counties to the south of Pierce had
higher positive-trap percentages than those to the north, and
the average number of moths captured in positive traps is also
higher to the south.
One survey parameter that is likely a noteworthy factor in these
varying results, however, is the survey period timing. In all
counties except Pierce, survey traps were removed around the
end of July, which was fairly early in the adult emergence period
observed in the extended Pierce County trapping. Adult EPSB
emergence would be expected to began later in northern counties
than those to the south (based on previous WSDA surveys for
related defoliator moths), which would potentially result in
lower EPSB catch numbers and fewer positive sites in the northern
counties.
Adult EPSB flight activity for most of the season was recorded
in Pierce County, where trapping continued until September 10
at some sites. For the purposes of examining variation in the
adult EPSB adult catch over time, the number of moths caught
for each positive trap check was divided by the number of interval
days (between checks), to produce a value for the average number
of moths captured per day at each site. These values were added
for all sites in the county and grouped by average date of sequential
trap checks (e.g.; average date for all first positive check,
average date for second, and so forth). The grouping of dates
for each sequential trap check (to calculate an average date)
was necessary, since trap check intervals unavoidably varied
from site to site due to travel and workload limitations, although
the dates for each sequential check generally occurred within
2 or 3 days. The average dates for trap checks and the associated
catch data are presented in Table 3 and the catch total and
average rates of EPSB catch per day for each trap-check interval
are plotted in Figure 4.
Table 3. 2001
Pierce County EPSB Pheromone-trap Catch Summary Statistics
Check Date
(Average - see text) |
Ave. Interval since
last Check (days) |
Total EPSB
Captured |
Sum of Ave. EPSB
per Day |
Overall Average
EPSB per Day |
6-Jul-01 |
52.5 |
140 |
2.82 |
0.00 |
30-Jul-01 |
37.5 |
1,2710 |
44.85 |
0.80 |
13-Aug-01 |
16.4 |
1,247 |
92.70 |
1.63 |
27-Aug-01 |
14.2 |
449 |
31.44 |
0.68 |
10-Sep-01 |
13.9 |
79 |
6.25 |
0.42 |
Figure 4. 2001 Pierce County EPSB Catch Totals and Average
Moth Catch per Day
The Pierce County EPSB catch information shows an extended
flight season for EPSB in 2001. Overall, the first adult EPSB
pheromone-trap capture was recorded June 20, in Thurston County,
and the last captures were the above Pierce County collections
September 10, at which time there were still live adult EPSB
in the traps. The end of EPSB flight activity (including that
in Pierce County) was not recorded in this survey. Although
only a few observation intervals (periodic trap checks) were
possible in this survey, the Pierce County data suggests a single
peak in adult flight activity in late-July or early-August in
2001.
Larval EPSB biology and feeding damage were observed and photographed
at several field sites and during laboratory rearing and examination
of field collected material. Larvae that hatch from eggs laid
on host (poplar) leaves in the late summer and fall feed initially
between leaf layers, creating distinctive “J”-shaped
leaf mines, usually along the leaf mid-rib. Occasionally they
will also bore into the leaf petiole (stalk). Early larval habits
were not observed during the growing season, but both types
of feeding damage were found on fallen leaves in the fall, and
are shown here in Figures 4 and 5. After this leaf- or petiole-mining
stage (and before leaf drop), EPSB larvae leave the leaf mines
to find overwintering shelter in cracks and crevices on twigs
and branches. Overwintering larvae create hibernacula (refuge
chambers) from silk, covering them with frass (larval excrement)
and bits of debris which makes them very cryptic and somewhat
difficult to find. Figures 6 and 7 show a typical hibernacula,
which is opened to show the resident overwintering larva in
Figure 7. In spring, larvae resume activity, boring into and
feeding in green shoots as they develop at branch ends. This
spring shoot-boring deforms the new growth, produces rudimentary
galls which may develop into woody knots in subsequent years,
and may stunt or kill infested tips. Internally feeding larvae
produce tubular silk and frass deposits at the entrances to
feeding galleries, which may persist on infested twigs well
into the fall and winter. A mature EPSB larva and examples of
typical larval feeding sites and the subsequent galling of branch
tips are shown in Figures 8 – 11.
Click any image to enlarge. |
 Figure
4.
Remains of EPSB Larval Leaf-mine. |
 Figure
5.
Remains of EPSB Larval Feeding in Leaf-midrib. |
|
 Figure
6.
EPSB Hibernacula |
 Figure
7.
EPSB Hibernacula (Opened / Larva). |
|
 Figure
8.
Mature EPSB Larva |
 Figure
9.
EPSB Frass / Tip-boring Site |
|
 Figure
10.
Poplar Tip EPSB Damage |
 Figure
11.
Poplar Twig EPSB Damage |
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