Post on 16-Dec-2015
Biocontrol insect abundance on leafy spurge stems, Cache
Valley, Utah.- By Eric Bingham
Leafy Spurge• Perennial plant whose stems
produce 140 seeds which remain viable for 8 years.
• Rhizomatous roots can reach 18 feet deep and spread 15 feet per year.
• Latex sap is an irritant.• Reduces rangeland by 50-75%.• Causes more than 120 million
dollars of reduced business to the midwest each year.
Leafy spurge biocontrol
• Leafy spurge biocontrol includes:– Apthona flava– Apthona nigriscutis– Apthona lacertosa– Oberea erythrocephala
Cache Valley leafy spurge
• Biocontrol was first released here in the early 1990s
• This meadow has been periodically monitored ever since then.
My research questions
• Are biocontrol insects more abundant on flowering or nonflowering stems?
• Are biocontrol insects more abundant on the hillside or on the meadow?
Methods• Weekly monitoring of 400
randomly selected spurge stems:– 100 meadow flowering plants– 100 meadow nonflowering plants– 100 hillside flowering plants– 100 hillside nonflowering plants
• Measured:– Plant height– Inflorescence diameter– Type of insects present– Type of insect damage (if present)– Presence or absence of seeds
Results – leafy spurge
• Nonflowering stems were more common than flowering stems
Meadow Hillside0%
10%20%30%40%50%60%70%80%90%
100%
Relative Spurge densities
Flowering
Nonflowering
Results – leafy spurge• The spurge was
more dense on the meadow than the hillside
• Flowering stems were taller than nonflowering stems
• Meadow plants were taller than hillside plants
• Meadow plants had larger inflorescence diameter than hillside plants
Meadow HillsideCharacter Mean SD Mean SD
Stem Density (stems per square meter), July 11
1.93 0.35 0.83 0.15
Height of flowering stems (cm), week of June 30
55.48 1.19 50.54 0.88
Height of nonflowering stems (cm), week of June 30
39.33 0.98 34.17 0.81
Inflorescence diameter (cm) on flowering stems
11.38 0.70 7.77 0.48
Results - Oberea• The Oberea were more abundant
on the flowering stems• The Oberea damage was more
abundant on the nonflowering stems
Meadow Hillside0
5
10
15
20
25
Oberea totals for 7/7
FloweringNonflowering
Number of Oberea
present on 400
stems of leafy
spurge
Meadow Hillside0
10203040506070
Oberea damage for 7/7
FloweringNonflowering
% of plants observed
that showed Oberea damage
23-Jun
28-Jun
3-Jul8-Ju
l
13-Jul
18-Jul
23-Jul
28-Jul2-Aug
0
10
20
30
40
50
Oberea totals throughout the summer
Weeks of data collection
Number of
Oberea present on 400
stems of leafy
spurge
Results – A. lacertosa• A. lacertosa were most abundant
on the meadow nonflowering plants.
• A lacertosa damage was most abundant on the hillside flowering plants
June 23rd
June 30th
July 7th
14-Jul
21-Jul
28-Jul
4-Aug
0
100
200
300
400
500
600
A. Lacertosa totals throughout the summer
Weeks of Data collection
Number of lacer-
tosa present on 400
stems of leafy
spurge
Meadow Hillside0
50
100
150
200
250
A. Lacertosa totals for 6/30
FloweringNonflowering
Number of lacer-
tosa present on 400
stems of leafy
spurge
Meadow Hillside0
10
20
30
40
50
60
70
Flea beetle damage for 6/30
FloweringNonflowering
% of plants
observed that
showed flea bee-tle dam-
age
Characteristic being compared Type of ANOVA
F df P
Stem density between meadow and hillside – transformed as natural log [stem density] + 1
1-way 6.95 1,78 0.0101
Plant height 2-way
Effect of habitat (meadow vs. hillside) 18.25 1,396 0.0001
Effect of condition (flowering vs. nonflowering) 227.72 1,396 0.0001
Interaction of habitat and condition 1.43 1,396 0.23
Inflorescence diameter on flowering stems between meadow and hillside
1-way 18.16 1,198 0.0001
Oberea per stem 2-way
Effect of habitat (meadow vs. hillside) 0.26 1,76 0.61
Effect of condition (flowering vs. nonflowering) 9.29 1,76 0.0032
Interaction of habitat and condition 1.61 1,76 0.32
A. lacertosa per stem 2-way
Effect of habitat (meadow vs. hillside) 0.04 1,76 0.84
Effect of condition (flowering vs. nonflowering) 0.29 1,76 0.59 Interaction of habitat and condition 1.01 1,76 0.32
Discussion question
• Why were the Oberea insects significantly more abundant on the flowering stems, but their damage was so much more abundant on the nonflowering stems?
Conclusions
• Negligible difference in biocontrol insects between the meadow and hillside
• Negligible difference for A. lacertosa on flowering versus nonflowering stems
• Oberea occur more abundantly on flowering than nonflowering stems
• Oberea damage occurs more abundantly on nonflowering than on flowering stems
• Knowing occurance and damage trends can influence biocontrol protocols
Acknowledgments
1- Ted Evans2- MSSST program and Holly Godsey3- Committee members:
Dave Chapman, Louisa Stark, Barb Nash4- Emma and Amber Bingham