Pointers For Insect Pathologists

Pointers for Insect Pathologists: Lessons from a Bio-based IPM Study Ayanava Majumdar Extension Entomologist Gulf Coast Research & Extension Center, Fairhope, AL Mark A. Boetel Assoc. Prof., Entomology Department North Dakota State University, Fargo, ND Stefan T. Jaronski Res. Entomologist, USDA-ARS Northern Plains Agric. Res. Lab., Sidney, MT

Sugarbeet Research Project Integration of cover crops with Metarhizium anisopliae (Ascomycete) for sustainable management of sugarbeet root maggot (SBRM), Tetanops myopaeformis (Diptera: Ulidiidae) Damaged root-tip Heavy scarring Deformed root Av. 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 setup Strain of M. anisopliae : ATCC62176 (MA1200) Rate of MA: 8 x 10 12 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! X X Red river valley of ND & MN High insect pressure Moderate insect pressure

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 104 o F
Vanninen (1995): <50 o F
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) – LT 50 of 10 d at 2.6 x 10 6 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 technique Oats @ 187 & 374 seeds/m 2 Rye @ 374 & 187 seeds/m 2 1 2 3

Do you see an effect of pathogen? Results of purely bio-based insect control test can be less encouraging. High insect pressure: MA spray provided similar level of root protection to terbufos (chemical standard) Consistency of trends: weather, high SBRM insect pressure Untreated check plot MA granules only MA spray only Root injury = (0-9 scale) 8-9 5-6 5-6

Do you see an effect of integration?
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
Untreated check plot Root injury = (0-9 scale) 8-9 Oat 374 seeds/m 2 + MA spray 3-4 Rye 374 seeds/m 2 + MA spray 3-4

Delivery method:
2.5 x 10 5 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 NA = not available CFUs/g dry soil Treatment 0 DAT 30 DAT 60 DAT 2002 Oat186 + MaG 247 1902 Oat233 + MaG 530 905 Rye374 + MaG 467 1090 Rye466 + MaG 622 1215 MaG 1185 1875 2003 Oat186 + MaG 62 0 NA Oat233 + MaG 125 0 Rye374 + MaG 92 0 Rye466 + MaG 60 30 MaG 62 0 2004 Oat186 + MaG 122 92 NA Oat374 + MaG 122 0 Rye186 + MaG 155 62 Rye374 + MaG 312 0 MaG 92 437

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 & activity NA = not available CFUs/g dry soil Treatment 0 DAT 30 DAT 60 DAT 2002 Oat186 + MaS 8285 1527 NA Oat233 + MaS 10867 1467 Rye374 + MaS 11247 872 Rye466 + MaS 16430 1527 MaS 10310 1652 2003 Oat186 + MaS 1580 372 NA Oat233 + MaS 4092 247 Rye374 + MaS 3182 155 Rye466 + MaS 4530 560 MaS 2560 217 2004 Oat186 + MaS 58800 4465 NA Oat374 + MaS 46300 2277 Rye186 + MaS 55800 1655 Rye374 + MaS 55750 2030 MaS 49175 1777

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 (A w )
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 important How 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?

Pointers For Insect Pathologists

by Dr. Ayanava Majumdar, Auburn University

Accessibility

Categories

Upload Details

Usage Rights

1 Embed 1

Statistics

Pointers For Insect Pathologists Presentation Transcript