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).