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Developing new treatments for the protection ofStored grain against insect pests

Paul EbertUniversity of Queensland

Plant Biosecurity Cooperative Research Centre

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Phosphine - only general use fumigant available to protect stored grain against insect pests- Resistance is a growing problem

Species (Cryptolestes ferrugineus) Strength (Cryptolestes ferrugineus) Distribution (Western Australia)

Phosphine is under threat

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Distribution of phosphine resistance in C. ferrugineus

High dose and Longer exposure period

1.5 mg L-1 over 10 days

2010

Weak resistance - prevalent

Strong resistance (2008) - East coast Bulk storages

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SF is registered as a grain fumigant in some countries- Single use only due to residues- Expensive

But . . .- No cross-resistance with phosphine- Fast-acting

Excellent break fumigant – when phosphine fails

Sulfuryl fluoride (SF)/Profume

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SF is registered as a grain fumigant in some countries- Single use only due to residues no residues- Expensive cheap- Less effective against eggs effective against all life stages

But . . .- No cross-resistance with phosphine no induced tolerance- Fast-acting slow-acting

SF & Phosphine - complementary strengths

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Combination treatments - adults- PH3 + SF: Additive increase in toxicity - RGB: ½ Phosphine + ½ of SF: 7 days

Sequential treatments- Similar additive increase in toxicity

Effective against all life stagesEffective against all speciesEffective against all resistant strains

Phosphine + SF – combined treatment

Strong-R (RGB) Bioassay: Adults – 48 hr

6.0 mg / L 20.0 mg / L

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Fluoride resistant strains- not resistant to SF

rph2 is cross-resistant to fluoride

New mechanism of SF toxicity

SF toxicity

24h, 25oC

+ F +

Fluorosulfate toxicity

24h, 20oC and 25oC

Fluoride toxicity

48h, 20oC and 25o,C

Control rph2

Control (20°C) Control (25°C) rph2 (20°C) rph2 (25°C)

Control (20°C) Control (25°C) rph2 (20°C) rph2 (25°C)

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DLD

FADS

H2O2

4-HNE

PH3

Phosphine triggers a self-destructive cycle1) DLD begins to generate reactive oxygen (H2O2)2) H2O2 damages membranes 3) Oxidative damage to membranes produces 4-HNE 4) 4-HNE increases H2O2 generation

Mechanism of phosphine toxicity

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• Phosphine is a cholinergic neurotoxin• Similar site of action of several classes of pesticides

• Organophosphorus, carbamate & neonicotinoids

• Nicotine is a potent phosphine synergist• Don’t smoke before fumigation

Phosphine is a neurotoxin

biosecurity built on science

Effect of diet on S. oryzae strains

Fecundity – mild stress x strain

biosecurity built on science

Fecundity – mild stress x strain

low dose phosphineMild temperature stress

Control rph2 Control rph2

biosecurity built on science

Sulfuryl fluoride - Not only a good break fumigant- Good co-fumigant with phosphine- New mechanism of action

Phosphine- Nicotine is synergistic (don’t smoke)- Diet, temperature, residual phosphine

all may affect fitness of resistant strains (+ or -)

Conclusions

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Collaborators

QDAFDr Manoj NayakDr Rajeswaran Jagadeesan

University of QueenslandDr Khadija ShabbiriTirosh ShapiraNisa NathTimothy Puckering

For more information, please email [p.ebert@uq.edu.au]