The Promise of Biological Control of Insect Pests with Rhizobacteria

Henry Fadamiro Simon Zebelo and Esther Ngumbi

Introduction • 1 million insect species discovered (<1% are crop pests) • Insect pests cause considerable losses in crop production

o Defoliators, sappers, root feeders, fruit feeders, stored products pests, etc. o Direct vs. indirect pests

Hein Bijlmakers Ency New Zealand

• Producers typically rely on chemical insecticides to protect their crops against herbivorous insects

o 1-2 million tons applied annually

• Negative impacts of intensive use of insecticides

oToxicity to humans oEnvironmental pollution oEffect on non-target species oDevelopment of pest resistance

Insecticide use

• Increasing demand from consumers oTo reduce the use of chemical insecticides in crop production

By Freepik Popular Resistances

Backlash to negative impacts of insecticides

• Biological control and biopesticides – promising alternatives to chemical insecticides

o Biocontrol with predaceous and parasitic insects o Microbial pesticides

• Advantages of biopesticides

o Unique mode of action o Specificity o Reduced toxicity

Biological control of insect pests

Biopesticide formulations • Formulations of entomopathogenic microbes o Fungi

(e.g., Beauveria spp. and Metarhizium spp.)

o Nematodes (e.g., Steinernema spp. and Heterorhabditis spp.)

o Bacteria (e.g., Pseudomonas spp. and Bacillus spp.)

PGPR as biopesticides?

Plant growth promoting rhizobacteria (PGPR)

• Increased rates of plant growth • Suppress soil pathogens • Induce systemic resistance(ISR) against

plant diseases

• PGPR effect on insect herbivores ▫ Indirect - ISR ▫ Direct – entomopathogenic

• PGPR are specific strains of root-colonizing bacteria which can elicit:

PGPR elicit ISR against insect herbivores

Recent work at Auburn University

• Have increased VOC emissions • Not good hosts for cotton and maize herbivores • Attractive to parasitoids • Higher gossypol, wax and lignin levels • Higher expression of defense-related genes

PGPR-treated plants

PGPR-3

PGPR-2

PGPR-1

Control

• Volatiles trapped from PGPR-treated and untreated plants

PGPR treatment elicit increased VOC emissions

GCMS

PGPR-treated plants are not good hosts for some herbivores

No-choice oviposition test test

PGPR-2 PGPR-3 PGPR-1 Untreated

PGPR-treated plants are attractive to parasitic wasps Four-choice olfactometer

PGPR

-2

Blank

PGPR

-1

Untreated

PGPR-2 PGPR-3 Untreated Blank

Model proposed

Entomopathogen

• PGPR strains show direct insect pathogenicity

• Not all PGPR strains are created equal

• Formulation is a key challenge

PGPR strains as entomopathogens (direct activity)

Kupferschmied et al., 2013

Summary - Benefits of PGPR • Enhance plant growth • Suppression of soil pathogents

• ISR against plant diseases • Direct pathogenic activity against insect pests • Indirectly repel insect herbivores and attract natural enemies • Fringe benefits:

o No requirement of vector o Always present in the rhizosphere o Highly persistent in agricultural fields

PGPR strains may be exploited for novel approaches to insect control!

Acknowledgements

• Dr. Joseph Kloepper and lab

• Fadamiro lab

• Auburn University/AAES • Industry funding