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
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