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