Attraction of Parasitic Wasps of the Invasive Emerald Ash Borer
to Different Colored Pan Traps
Edna Bailey Sussman Foundation Final Report
December 2015
Stephen Pecylak
Introduction:
Emerald ash borer (Agrilus planipennis, EAB) is a destructive wood-boring beetle first
detected in Michigan in 2002 (2). EAB has spread to 25 states and has killed millions of ash
trees already (5). Scientists traveled to EAB’s native range in Asia and discovered four species
of parasitic wasps, which hunt down and kill EAB. Each has been approved for release in the
United States after extensive testing to make sure they were EAB specific (1,6,8) . Monitoring
establishment of these parasitic wasps after their release is important to ensure they are surviving
long enough to control EAB populations. Pan traps are the most commonly used monitoring
method, but we may be able to improve this method by determining the most attractive color for
each parasitic wasp. Yellow pan traps are currently being used, due to the known attraction of
Hymenoptera (bees and wasps) to the color yellow (3,7), but this color has not yet been
determined to be the most attractive for all of the EAB parasitic wasps, with the exception of the
EAB parasitic wasp S. agrili (4). The goal of this research is to help USDA-APHIS in
determining the most attractive color for EAB parasitic wasps to help with monitoring efforts.
Work Completed:
Specific objectives include:

compare catch rates of the four EAB parasitic wasps (Spathius agrili, Spathius galinae,
Tetrastichus planipennisi, and Oobius agrili) to four different pan trap colors (red, white, blue,
and yellow) under controlled and field conditions.

contrast the controlled conditions with the field releases for differences between the two.

test if yellow pan traps really are the most efficient trap for monitoring EAB parasitic wasps.
Methods:
Medium Scale Experiment: A wind tunnel was set up in a controlled setting and used as a
medium scale arena (Fig. 1). On each side of the interior of the medium scale arena, pan traps of
all four colors were placed on top of ash bolts on tables (Fig. 1). All four species of parasitic
wasps were released into the wind tunnel using ash bolts with parasitized EAB larvae and plastic
containers with parasitized EAB eggs. There were two replicates and parasitic wasps were given
6 weeks to emerge and choose a pan trap color. Parasitic wasps were collected from the pan
traps every two weeks.
Figure 1: Controlled experimental setup (left), showing release devices for all four parasitic wasp species and pan
traps inside arena (right).
Field Release: Two field sites were chosen to test the color choice of EAB parasitic wasps in
the field, one in Rochester NY and one in Syracuse NY (Fig. 2). Ooobius, and Tetrastichus were
released in the summer of 2014 in the Rochester site. S. agrili (as well as Oobius and
Tetrastichus) were also released at a nearby study site in 2012-2013. Pan traps of all four colors
were attached to eight black ash trees. Oobius, Tetrastichus, and S. galinae were released in the
summer of 2015 in the Syracuse release sites. Pan traps of all four colors were attached to 15
green and white ash trees, with five trees for each of the three release points (Fig. 2). Parasitic
wasps were collected from pan traps weekly from 14-Jul to 29-Sept for the Rochester site and
from 20-Jul to 12-Oct for the Syracuse site.
Syracuse
Rochester
Figure 2: Locations of both release sites in upstate New York (left) and pan trap setup on a tested ash tree (right).
Current Results:
Medium Scale Arena: None of the parasitic wasps were attracted to any particular color
(considering only the first two replicates) under controlled conditions (Fig. 3). Twenty out of 74
S. agrili recovered were in pan traps, the rest were recovered inside the arena but not in pan traps
(Table 1). Seven out of 72 S. galinae recovered were in pan traps, the rest were recovered inside
the arena but not in pan traps (Table 1). Six out of 24 Tetrastichus were recovered in pan traps,
the rest were recovered inside the arena but not in pan traps (Table 1). Seven out of 21 Oobius
recovered were in pan traps, the rest were recovered inside the arena but not in pan traps (Table
1). This was a lower recovery rate than anticipated.
25
Red
White
Blue
Yellow
Number of Wasps
20
15
10
5
0
Tetrastichus
Oobius
S. agrili
S. galinae
Parasitic Wasp Species
Figure 3: Mean (±SE) number of recovered parasitic wasps from medium scale arena (n = 2).
Table 1: Medium scale arena release and recovery numbers separated by parasitic wasp species and color.
Species
Total
Released
Total
Recovered
(% Released)
Red
(% Recovered)
White
(% Recovered)
Blue
(% Recovered)
Yellow
(% Recovered)
S. agrili
74
20 (27%)
0
0
0
20 (100%)
S. galinae
72
7 (10%)
0
2 (29%)
0
5 (71%)
Tetrastichus
24
6 (25%)
0
0
0
6 (100%)
Oobius
21
7 (33%)
0
4 (57%)
0
3 (43%)
Field Release:
As with the medium scale arena, none of the parasitic wasps were significantly attracted
to any particular color under field conditions (Fig. 4). Three S. agrili were recovered from pan
traps in Rochester and no S. galinae were recovered from pan traps in Syracuse. There were 100
Tetrastichus recovered and three Oobius recovered from pan traps between both sites. For the
Syracuse site, 98 Tetrastichus and two Oobius were recovered (Table 2). Of the 98 Tetrastichus,
50 of them came from a single tree, which a high catch rate compared to all the other trees. This
reinforces the idea that pan traps are not an efficient method for monitoring EAB parasitic wasps
(Table 1), with the exception of Tetrastichus (Table 2). Color attraction for Tetrastichus because
one tree produced half of the data points, and color attraction for the other parasitic wasps is hard
to distinguish due to low recovery.
3.5
Red
Number of Wasps
3
White
Blue
Yellow
2.5
2
1.5
1
0.5
0
Tetrastichus
Oobius
S. agrili
S. galinae
Parasitic Wasp Species
Figure 4: Mean (±SE) number of recovered parasitic wasps from field sites (n = 23).
Table 2: Syracuse recovery of EAB parasitic wasps separated by color and species
Species
Total
Released
Total
Recovered
(% Released)
Red
(% Recovered)
White
(% Recovered)
Blue
(% Recovered)
Yellow
(% Recovered)
S. galinae
29
0
0
0
0
0
Tetrastichus
1359
98 (7%)
18 (18%)
12 (12%)
17 (17%)
51 (52%)
Oobius
1295
2 (<1%)
0
1 (50%)
1 (50%)
0
Future Directions
Currently, the remaining pan trap’s contents are being sorted through to determine if the
above results for the field releases still hold. More replicates of the medium scale assay will also
be performed for a more robust comparison.
Future research will include a more targeted approach to color attraction by using an
electroretinogram (ERG), which shines light of a specific wavelength into the eyes of parasitic
wasps and measures increases in sensitivity. If the ERG test shows sensitivity to some
wavelengths, the actual attractiveness of these wavelengths will be tested by releasing parasitic
wasps into a netted cage with colored sticky traps of the specific wavelengths. Preliminary work
for S. agrili and S. galinae with the ERG has already been done. If the additional research shows
there is no most attractive color for any of these parasitic wasps, it would be interesting to
explore why color does not seem to matter for all EAB parasitic wasps, but does for other bees
and wasps (4,7).
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