SHEEP LICE - CONTROL AND INSECTICIDE RESISTANCE September 2009 Garry Levot
SHEEP LICE ECONOMIC LOSS - $123million PA Lost production: * lousy sheep cut about 10% less wool (up to $12/head for fine wool!) 2mm Bovicola ovis * cotted wool is worth about 10% less decreased tensile strength yellow discolouration d of wool Cockle devalues hides increased susceptibility to flystrike
SHEEP LICE Opportunities to eliminate lice from individual sheep are offshears (0-24h after shearing) OR in short wool (1-42 days after shearing). Treatments applied at other times may reduce lice numbers to the extent that fleece damage is arrested but will not eliminate the infestation.
SHEEP LICE REGISTERED INSECTICIDES: Pyrethroids (cypermethrin, deltamethrin, alphamethrin) (pour-ons ons and spray-on) Organophosphates (temephos( (dip), diazinon (spray under APVMA permit)) Benzoylphenyl urea (IGRs( IGRs) ) (triflumuron( (pour diflubenzuron) (dip and pour-on) on) Ivermectin (jetting fluid) (spray-on, dip (pour-on), on), Magnesium fluorosilicate/sulphur (dip) approved for organics Spinosad (dip and pour-on) on) approved for organics Imidacloprid (pour-on) on) (soon)
SHEEP LICE WHEN THINGS DON T GO AS PLANNED CONTROL FAILURE occurs when a pesticide application does not control a pest as well as expected. This may reflect the unrealistic expectations of the producer, failure to apply the product correctly (dose/head and as per label directions), failure to provide adequate prevention from reinfestation post-treatment, or insecticide resistance.
SHEEP LICE Pyrethroid pour-ons introduced in 1981 Failures reported in 1986
SHEEP LICE pyrethroid resistance Laboratory diagnosis 10 fold difference - enough for pour-ons to fail
SHEEP LICE pyrethroid resistance 640 fold difference 1986 -Low level resistance pour-ons ons failed 1992 - Hartley strain 640+ fold resistance! pour-ons and dips failed! Extreme resistance then became increasingly common and widespread
SHEEP LICE managing pyrethroid resistance HARTLEY Resistance to one pyrethroid conferred resistance to them all No cross-resistance resistance to organophosphates
SHEEP LICE organophosphate resistance only one diazinon-r inon resistant population ( ( Orange ) found for resistance management note the susceptibility of the Orange strain to pyrethroids and the susceptibility of the Hartley strain to diazinon
SHEEP LICE IGR resistance AIM: To develop a laboratory test capable of measuring the susceptibility of lice populations to diflubenzuron with a view to diagnosing resistance if it exists. Normal cuticle Chitin deficient cuticle note the thin band of normal cuticle
SHEEP LICE IGR resistance HYPOTHESIS: That if they exist, IGR-resistant female lice would be capable of laying eggs that would hatch, following treatment with doses of diflubenzuron that prevent hatching of eggs laid by susceptible females. Experiment: 40-50 female lice were treated with 0.2 µl of diflubenzuron solution, provided with wool and adequate food and kept under ideal conditions in the company of males. Egg laying and hatching was monitored over 19 days.
SHEEP LICE Eggs Adult louse Immature lice - nymphs hatch after 10 days @ 37 o C
SHEEP LICE IGR resistance IGR-susceptible Claremont strain (low-range pyrethroid resistance/igr naive) Diflubenzuron dose (µg per louse) Number of adult lice still alive at Day 19 Number of nymphs hatched by Day 19 Control 0.00156 0.0031 0.0063 0.0125 0.025 0.05 58 60 58 59 57 52 66 36 40 26 14 12 0 0
SHEEP LICE IGR resistance IGR-susceptible - Hartley strain (highly pyrethroid resistant/igr naive) Diflubenzuron dose (µg per louse) Control (acetone) 0.00156 0.0031 0.0063 0.0125 0.025 0.05 0.10 Number of adult lice still alive at Day 24 44 30 33 24 35 15 20 18 Number of nymphs hatched by Day 24 19 8 9 4 6 0 0 0
SHEEP LICE IGR resistance IGR Field Failure: Stanthorpe (Qld) strain Diflubenzuron dose (µg per louse) Control (acetone) 0.00156 0.0031 0.0063 0.0125 0.025 0.05 0.10 0.20 Number of adult lice still alive at Day 19 25 18 37 3 15 40 19 43 49 Number of nymphs hatched by Day 19 14 11 26 13 8 18 17 17 22
SHEEP LICE IGR resistance RESISTANCE IS REAL! complaints common no distinctive regional distribution (NSW/Qld/WA/Vic) tell-tale signs are immature lice on treated sheep history of repeated use of IGRs for lice and/or blowflies labels now refer to susceptible strains will become more common if IGRs continued to be used
ACKNOWLEDGEMENTS Funding for this project was provided by Australian wool producers and the Australian Government through Australian Wool Innovation. IGR resistance bioassays - Narelle Sales