Transcript Effects of Resmethrin Spray on Monarch Butteflies and Larvae

Effects of Resmethrin Spray on
Monarch (Danaus Plexippus)
Butterflies and Larvae
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www.mlmp.org
By Rosemary Lelich 2004-05
Background: resmethrin
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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%
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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
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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
Percent in Category
80
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
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www.mlmp.org
By Rosemary Lelich, 2004-05