use of the fluorescent tracer technique (ftt) in the laboratory and field to study rodent-sand fly...
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Use of the Fluorescent Tracer Technique (FTT) In the Laboratory and Field to Study Rodent-Sand Fly Interactions and Identify
Potential Control Methods
T.M. Mascari1, E. Rowton2, J. Clark3, S. Gordon3, L.D. Foil1
1 Louisiana State University Agricultural Center, 404 Life Sciences Building, Baton Rouge, LA2 Walter Reed Army Institute of Research, Silver Spring, MD
3 US Army Medical Research Unit – Kenya Unit 8900, Box 6801, DPO AE
Background
- Phlebotomus papatasi and P. duboscqi are vectors of Leishmania major, agent of zoonotic cutaneous leishmaniasis (ZCL)
- In arid foci, sand fly vectors are associated with rodent reservoirs of L. major
- In Old World ZCL foci, rodent burrows are an immature habitat for P. papatasi
- Sand fly larvae have been observed feeding on rodent feces
-Adult female sand flies feed on blood
-Adults of both sexes feed on sugars
There are many rodent/sand fly interactions
Background
Sand fly marker system developed at LSU
A) Answer important ecological questions- breeding sites for different sand fly populations- dispersal of adult sand flies
B) Identify which insecticide applications would be most effective against a sand fly population- unlikely that all sand flies can be eliminated using a single control method
C) Evaluate sand fly control measures- systemic insecticides- feed-through insecticides- insecticide-treated sugar baits
Fluorescent Tracer Technique (FTT)
Fed rodents diet containing rhodamine B (RhB)
Sand flies took bloodmeals from rodents
Examined sand flies under fluorescence microscopy
Sand flies that fed on RhB-treated rodents were marked
FTT – Systemic insecticides
T M Mascari 2008
Brightfieldmicroscopy
Fluorescencemicroscopy
5000 ppm 0 ppm
FTT – Systemic insecticides
What information could this give us?
- identify extent to which sand flies in different rodent-sand fly interactions take bloodmeals from rodents targeted with baits
- identify rodent-sand fly interactions that could be targeted with systemic insecticides
- allow us to evaluate effects of rodent baits containing systemic insecticides on sand fly populations
- sf infiltration from outside study area- natural pop. decline unrelated to control
FTT – Systemic insecticides
Selection of systemic insecticides
- palatable/non-toxic to target rodents
- have persistent insecticidal effects
Best candidates:
Ivermectin
Spinosad
FTT – Systemic insecticides
Baringo District, Rift Valley Province, Kenya2009
FTT – Systemic insecticides
Results of Sherman trapping by bait type
Bait type Traps set (no.)
Captures (no.)
Capture (%)
Rodents* (genera)
RhB 42 36 85.7 Mastomys, Mus, Tatera, Taterillus RhB + DFB 39 33 84.6 Mastomys, Mus, Tatera, Taterillus * genera in bold are known reservoirs for L. major
FTT – Systemic insecticides
Fed rodents RhB-treated diet
Fed rodent feces to sand fly larvae
Examined emerging sand flies under fluorescence microscopy
Sand flies that fed on feces of RhB-treated rodents were marked
FTT – Feed-through insecticides
Incandescent 1 sec 4 sec
5000 ppm
0 ppm
50 ppm
500 ppm
FTT – Feed-through insecticides
♂
♀
5000 ppm
♂
♀
0 ppm
What information could this give us?
- identify whether sand flies in a certain rodent-sand fly interaction feed on the feces of rodents targeted with baits
- identify what proportion of a sand fly population could be eliminated using feed-through insecticides
- allow us to evaluate effects of rodent baits containing feed-through insecticides on sand fly populations.
FTT – Feed-through insecticides
Feed-through insecticides that
- are palatable/non-toxic to target rodents
- are stable in the environment
(persist in rodent feces once voided)
Best candidates:
Novaluron (persists up to 150 d in feces)
Diflubenzuron
Pyriproxyfen
Ivermectin*
FTT – Feed-through insecticides
A high proportion of sand flies feed on sugar and food dye sprayed on plants
Food dyes don’t persist in sand flies (<20% were marked 3 dat)
Rhodamine B and Uranine O are good alternatives to food dyes- don’t affect sf survival- persist for life of sand fly- can be used in combination (both dyes can be detected within a sand fly)
FTT –Sugar baits
What information could this give us?
- identify sand flies that feed on sugar baits sprayed on vegetation
- information on ecology of sand flies (dispersal, etc.)- identify what proportion of a sand fly population could
be targeted with insecticide-treated sugar baits- our lab currently is evaluating insecticide sugar baits
Use an insecticide with low toxicity against non-target animals – boric acid has been used against mosquitoes
FTT –Sugar baits
Summary
FTT allows us to determine which sand fly populations could be susceptible to feed-through insecticides, systemic insecticides, or insecticide-treated sugar baits
In the event that a treatment doesn’t work, FTT allows us to establish reasons why and to plan future research accordingly
Acknowledgements
This work was supported by a grant from the Deployed War-Fighter Protection (DWFP) Research Program, funded by the U.S. Department of Defense through
the Armed Forces Pest Management Board (AFPMB).