Rising from the Litter: The Unusual Happenings of Flea Beetles in 2018

Lesley LubenowExtension Cropping Systems SpecialistLangdon Research Extension Center

SO, WHAT CAUSES HOT SPOTS?

The life of flea beetle….

MAY/JUNE

EggsJUNE/JULY

Larva JULY/AUG

Pupa

JULY/OCT

AdultsSUMMER GENERATION

WINTER IS COMING….

Where do the flea beetles go?

Ulmer and Dosdall (2006) Experiment

Lethbridge, Alberta, Canada

Results

Highest number of flea beetles found in woody

areas, lowest in the grass

Key Message: Prefer to overwinter in leaf litter

Will overwinter in grassy areas

Generally not in the fields

So are hot spots correlated with ideal overwintering locations?

It’s more complicated…

Spring Emergence

WINTER/JUNE

Adults

Temperature matters

Crucifer flea beetles begin to emerge at 50F soil

temps at 2 inch depth.

Striped flea beetles emerge about 3 to 4 weeks

earlier.

Peak Emergence

Commonly during Memorial Day weekend.

Scientifically, 59⁰F soil temps at 2 inch depth.

What happened in 2018?

Unusual happenings

Search for canola begins…..

Want brains! Find host plants!

Jeff Hahn, Univ. of MN

• Seek: isothiocyanates

• Strong fliers

• Prefer young emerging canola

2018 …

early warm air temperatures

When did you notice flea beetles?

“A year that almost broke my insect models” – Dr. Mark Boetel, NDSU Extension/Sugarbeet Insects

2018 2017 2016 2015 2014 2013 2012Predicted Emergence: 14-May 14-May 5-May 1-May 23-May 26-May 10-May

Predicted Peak: 24-May 3-Jun 30-May 26-May 28-May 15-Jun 6-Jun

Modeling dates for expected life events……

Data from Roseau NDAWN station

Flea Beetle Temperature Thresholds:

Emergence at 50⁰FPeak at 59⁰F

2018 2017 2016 2015 2014 2013 2012Predicted Emergence: 14-May 14-May 5-May 1-May 23-May 26-May 10-May

Predicted Peak: 24-May 3-Jun 30-May 26-May 28-May 15-Jun 6-Jun

No. of Days to Peak: 10 20 25 25 5 20 27

Modeling dates for expected life events……

Data from Roseau NDAWN station

Flea Beetle Temperature Thresholds:

Emergence at 50⁰FPeak at 59⁰F

Lessons from 2018

• Did the peak correlate with the temperature data?

• Other models?– Based on March 1st start time

What other research is out there about flea beetle populations?

Will early canola planting impact the next year’s population?

Hypothetical pro: Flea beetle encounter less desirable plants

Answer: No, it will not reduce the next generation

Ulmer and Dosdall 2006

Can spring flea beetle populations be predicted by the

summer generation?

Answer: Yes, sweeping for flea beetles in canola

stubble is predictive. But only in terms of low/high.

Knodel 2005

We need to talk about striped flea beetles…

Tom Murray, bugguide.net

Canadian Shift

In Canada, Prairie Providences have solely striped fb except RR Valley & extreme south have crucifer and striped fb. (J. Soroka via D. Fluery, 2015)

Seeing movement in North Dakota, too.

North Dakota Statewide Canola Survey

• Collected flea beetles using 15-inch sweep net

• 20 sweeps per 5 locations (total of 100 sweeps per field)

• Flea beetles placed in plastic bags and stored in freezer

• Flea beetle species identified and counted for each field site

Slide: Dr. Janet Knodel, NDSU

656 total specimens

1.4% of flea beetles

collected

66% of the fields positive

18 counties out of 22

Slide: Dr. Janet Knodel, NDSU

34.7

5966

84

66

0

10

20

30

40

50

0

20

40

60

80

100

1 2 3 4 5

Striped Flea Beetle (SFB) Populations in Canola from 2014-2018

% of Surveyed Field Positive for SFB Density # SFB per Field

2014 2018201720162015

Slide: Dr. Janet Knodel, NDSU

Striped Flea Beetle Considerations

• May have increased tolerance to neonicotinoid seed

treatments (Tansey et al. 2008)

– New Class 28 product on market

• Cyantraniliprole, Tradename: Lumiderm

• Striped flea beetles emerge in early May

– Found May 1st, 2018 in Langdon

Summary

Flea beetles: Research is ongoing

How do they respond to temperature/rainfall?

Are the populations changing?

Hot spots can’t be predicted. Scout often.