pointers for insect pathologists

Pointers for Insect Pathologists:Lessons from a Bio-based IPM Study

Ayanava MajumdarExtension Entomologist

Gulf Coast Research & Extension Center, Fairhope, AL

Mark A. BoetelAssoc. Prof., Entomology Department

North Dakota State University, Fargo, ND

Stefan T. JaronskiRes. Entomologist, USDA-ARS

Northern Plains Agric. Res. Lab., Sidney, MT

Sugarbeet Research ProjectIntegration of cover crops with Metarhizium anisopliae (Ascomycete) for sustainable management of sugarbeet root maggot (SBRM), Tetanops myopaeformis (Diptera: Ulidiidae)

Damaged root-tipHeavy scarring

Deformed rootAv. Yield loss = 40%

Major insect in 49% sugarbeet acreage in many states. Significant scarring of root surfaces by SBRM feeding

SBRM: healthy & infected

Problem of experimental setupXX

Red river valley of ND & MN

High insect pressure

Moderate insect

pressure

Strain of M. anisopliae: ATCC62176 (MA1200)

Rate of MA: 8 x 1012 viable conidia per ha (2x)

MA applications: modified-in-furrow granules, postemergence spray

Choice of location, design & statistics…do it right the first time! Biomaterials are expensive!

What organism/strain to test?• Choice of fungus and strain is problem, few commercial

formulations• MA persists in disturbed ecosystems:

– Hallsworth & Magan (1999): 41 to 104oF

– Vanninen (1995): <50oF

– Bing & Lewis 1993, Bidochka et al. 1998: persistence in disturbed soil

• Cover crops + conventional i-cides work (Boetel et al. 2000, 2001)

• MA1200 is pathogenic to SBRM (Jonason et al. 2005) – LT50 of 10 d at 2.6 x 106 conidia/ml

• Field testing with three concentrations (Campbell et al. 2006) – linear yield response, 2x rate had good results

• Grower observation: cover crops protect beets from SBRM??• Logical next step…Integration of cover crop + MA

Cover cropping techniqueOats @ 187 & 374 seeds/m2

Rye @ 374 & 187 seeds/m2

1

2

3

Do you see an effect of pathogen?

Results of purely bio-based insect control test can be less encouraging.

Untreated check plot MA granules only MA spray only

Root injury =(0-9 scale)

8-9 5-6 5-6

High insect pressure: MA spray provided similar level of root protection to terbufos (chemical standard)

Consistency of trends: weather, high SBRM insect pressure

Do you see an effect of integration?

Untreated check plot

Root injury =(0-9 scale)

8-9

Oat 374 seeds/m2 + MA spray

3-4

Rye 374 seeds/m2 + MA spray

3-4

Problems with integrated test plots (e.g., cover crop + MA):

• Yields should not be the only parameter (direct assessment is imp.)

• Under high insect pressure, effect of one factor (cover crop) could mask treatment differences

• Under low to moderate insect pressure, root injury data were consistent with rate of cover crop

Delivery method: – 2.5 x 105 conidia/granule

coated on corn grit - required large amount of product

– MIF placement: seed separated from fungus

– 20% Tween solution was binder

MA granules: product application & activity

Bander

MA granules in Noble metering unit

16/20 mesh

• MA granules should be spread around the seed and applied early

• Detection of spores in soil is problematic >>>

• Soil sample at 60 d after treatment indicated delayed sporulation

• Allow time for the fungus to outgrow and sporulate!

MA granules: product delivery & activity

CFUs/g dry soilTreatment 0 DAT 30 DAT 60 DAT

2002Oat186 + MaG 247 1902 Oat233 + MaG 530 905Rye374 + MaG 467 1090 Rye466 + MaG 622 1215 MaG 1185 1875

2003Oat186 + MaG 62 0 NAOat233 + MaG 125 0Rye374 + MaG 92 0Rye466 + MaG 60 30MaG 62 0

2004Oat186 + MaG 122 92 NAOat374 + MaG 122 0Rye186 + MaG 155 62Rye374 + MaG 312 0MaG 92 437

NA = not available

• Conidia activated before or at spray

• Targets were the flies & early instars of SBRM

• Conidia remain in application zone, so placement is critical

• Expect rapid conidial decline

MA spray: product delivery & activityCFUs/g dry soil

Treatment 0 DAT 30 DAT60

DAT2002

Oat186 + MaS 8285 1527 NAOat233 + MaS 10867 1467Rye374 + MaS 11247 872Rye466 + MaS 16430 1527MaS 10310 1652

2003Oat186 + MaS 1580 372 NAOat233 + MaS 4092 247Rye374 + MaS 3182 155Rye466 + MaS 4530 560MaS 2560 217

2004Oat186 + MaS 58800 4465 NAOat374 + MaS 46300 2277Rye186 + MaS 55800 1655Rye374 + MaS 55750 2030MaS 49175 1777

NA = not available

Measuring conidia titers in soil (persistence study)

Techniques commonly used:• Dilution plating: provides reliable

results• Galleria baiting: provides relative

estimates (not recommended for persistence studies) MA colonies on Chase medium

Soil sampling/plating procedure:• Sample using proper equipment (soil core with small diam.)• Sample within application zone• Mark the pit with flag or stick (avoid resample)• Scan plates on flatbed scanner

What do we need to know?

• Soil structure & condition: conidial infectivity low in sandy soil, conidia persist in high water activities (Aw)

• Water removed by vegetation (e.g., cover crops, intercrops, etc.)

• Temperature in bare vs. shaded soil in treated zone (persistence)

• Wind movement inside/outside plant canopy (moderates temperature)

Microsite environment is importantHow to do it?

Soil analysis & cropping history

Soil probes: WatchDogs with moisture & temperature probes

Summary

• Focus on ecological approach to microbial research for soil insects

• Living insecticides should not be assessed as if conventional chemicals

• Product delivery system should be fine-tuned to target insect

• Increasing persistence should be the aim…integrated approach can help!

• Expect wide variances in spore recovery

• Frequent sampling will provide better picture

QUESTIONS?