Effects of Resmethrin Spray on
Monarch (Danaus Plexippus)
Butterflies and Larvae
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
www.mlmp.org
By Rosemary Lelich 2004-05
Background: resmethrin
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
www.free.de/WiLa/derik/Resmethrin.gif
• Type 1 pyrethoid
• Synthetic version of natural insecticide
produced by chrysanthemum flowers
• Nerve poison - acts on sodium ion
channels in nerve cell membranes
Background: resmethrin, cont.
• Used to control mosquito populations
• Sprayed in wooded areas and fields where
milkweed can grow
• Recent use has increased in Minnesota due
to spread of West Nile Virus
• No previous studies on effects of resmethrin
on monarchs exist
Background: Larvae
http://www.mbsf.org/news.html
• Monarch larvae (caterpillars) non-target insect for
insecticide sprayings
• Terrestrial
• Only eat milkweed (Asclepias)
Previous study: permethrin
• Similar pyrethoid
• Study done by Sara
Brinda (2003)
• Estimated % mortality
for 1st, 2nd, and 3rd
instars, respectively,
to be 92%, 89%, 71%
QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture.
Photo used with permission of Sara Brinda
Goals and Hypotheses
1. Estimate the percent mortality of monarch larvae and
adult monarchs due to resmethrin exposure
Hypothesis: Resmethrin is lethal to monarchs
2. Determine if there are sub-lethal effects of resmethrin
exposure on monarch larval development time and adult
size
Hypothesis: Sprayed larvae will develop more slowly
and will be smaller adults
Procedure: Round 1
Cage containing milkweed leaves
and monarch larvae
• Kept 8 cages of larvae,
used as controls
• Set out cages of larvae
and cages of mosquitoes
• Resmethrin only reached
stations downwind side of
spray path
Photo by Bruce Leventhal
Resmethrin Sprayer
Photo by Bruce Leventhal
Procedure
• Recorded each time a
larva molted to the
next instar (growth
stage)
• Recorded all mortality
• Continued until all
monarchs emerged
as adults
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
http://asclepias.homestead.com/files/
xmonlarvae.JPG
Results: Round 1 larvae
Significant effect of treatment. More dead larvae in downwind treatment than the control or
upwind treatments. Comparing downwind larvae to control, p = 0.0000.
90
Alive
Dead
Missing
80
Percent in Category
70
60
50
40
30
20
10
0
Control
Upwind
Downwind
Mortality rates for 1st and 3rd Beginning Instars
(Downwind only) p = 0.0273. Assuming missing
larvae died, p = 0.4568.
80
Proportion in Category
70
60
Alive
Dead
Missing
50
40
30
20
10
0
1st
3rd
Mass of emerged adult butterflies that were sprayed as
larvae (with s.d.), p = 0.2862.
0.54
0.53
0.52
0.51
Mass (g)
0.5
0.49
Mass
0.48
0.47
0.46
0.45
0.44
0.43
Control
Control
Upwind
upwind
Downwind
downwind
AOV for total development time for
beginning 3rd instars only, p = 0.3008.
Position
n
(Sample Size)
Upwind
Downwind
Control
15
6
17
Mean
S.E.
(days)
22.4 d 0.3344
23.33 0.5287
22.88 0.3141
Downwind larval mortality rates with respect
to distance, p = 0.7541.
60
Percent Mortality
58
56
54
52
50
48
46
44
1
2
Distance
3
Procedure: Round 2
• Redesigned field set up before spraying
• Added to each station
– Horizontal cages of larvae
– Milkweed plant with larvae on leaves (on ground)
– Milkweed plant with no larvae (on ground)
– Cage of adult butterflies (on ground)
• Wind variable; reached both up and down
wind stations
Dead Larvae: downwind during round 2 spraying
Photos by Brij Basin and Rosemary Lelich
Results: Round 2 Larvae
2 comparing larval mortality rates
Test
p-value
Control vs. Sprayed
0.0151
Upwind vs. Downwind
0.1655
• No downwind/upwind effect -- wind too variable
• Significant mortality rates of sprayed larvae
Larval, adult monarch, and mosquito
mortality rates by station, p = 0.0001.
larvae
adult monarch
mosquitoes
100
Percent Mortality
80
60
40
20
0
1
2
3
4
5
6
7
Station Number
8
9
10
11
12
• Larvae placed directly on milkweed plants
and unsprayed larvae fed sprayed leaves
produced significantly high mortality
• These exposures most closely mimic larvae’s
natural positioning
• This suggests that round 1 underestimates
larval mortality
Percent mortality of sprayed larvae compared to
sprayed mosquitoes
100
90
Percent Dead
80
70
60
50
40
30
20
10
0
Round 1 Larvae
Round 2 Larvae
Mosquitoes
(Rounds 1 and
2)
Discussion
• Accept hypothesis 1: Resmethrin is lethal to
monarch species
• Reject hypothesis 2: Sprayed larvae did not
emerge as significantly smaller adults
• Resmethrin is likely a factor responsible for
decrease in monarch populations
– Very important to understand consequences of
using resmethrin in order to preserve monarch
species
Future Study
• Conduct another round of resmethrin
spraying, again including larvae and
adults.
• Position more larvae downwind, attempt
to retain large sample sizes for more
significant results
Acknowledgements
• Dr. Karen Oberhauser
• Everyone in the lab (especially Ben,
Alma, Reba, Erin, and Jolene)
• Metropolitan Mosquito Control District,
especially Dr. Stephen Manwieler
• Sara Brinda
• Ms. Lois Fruen
• Team Research
Photo courtesy of Lois Fruen
Effects of Resmethrin Spray on
Monarch (Danaus Plexippus)
Butterflies and Larvae
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
www.mlmp.org
By Rosemary Lelich, 2004-05