Response of Phlebotomine Sand Flies to Light Emitting Diode-Modified Light Traps

in Southern Egypt

LCDR David Hoel

NAMRU-3

Cairo, Egypt

U.S. Naval M

edical Research Unit N

o. 3

Cairo, E

gypt

Response of Phlebotomine Sand Flies to

LED-Modified Light Traps in Southern Egypt

• Goals:

– Determine if a preference exists in Phlebotomine sand flies among different colored light produced from light emitting diodes (LEDs) and incandescent light in modified and standard CDC light traps.

– Test prototype LED-modified CDC light trap for ruggedness/reliability in a desert environment.

– U0009_04_N3 - Sand fly Trap Evaluations to Determine the Best Surveillance System for Anthropophilic Sand Flies.

Why research traps? Goals of

trapping… • Develop highly effective light traps that will increase trap

capture and provide more detailed, accurate surveillance in an area.

• Provide environmentally-friendly control of nuisance or vector insects through removal trapping, thus reducing the impact of broadcast insecticide applications on the environment (e.g., thermal fog, ULV). – Trap efficacy may be greatly increased with use of optimal

colors, colored light, trap design, and chemical attractants (Nzi trap and tsetse flies, Mihok 2002, Green 1994; commercial mosquito traps and salt marsh mosquitoes, Xue et al. 2005).

• Delay development of insecticide resistance.

Materials & Methods- Traps

J.W. Hock model 512 light traps were wired with twenty gauge insulated electrical wire routed between a 3-waytoggle switch, LED plug in connectors, and the incandescent light in parallel.

Materials & Methods- Traps

J.W. Hock model 512 light traps were wired with twenty gauge insulated electrical wire routed between a 3-waytoggle switch, LED plug in connectors, and the incandescent light in parallel.

Schematic

Original design LED-modified design

Materials & Methods- Traps

• Four 240 Ω, 1/8 W resistors prevented overdriving the circuit.

• LEDs are easily replaced as needed.

4 LED plug-in sockets were spaced 90o apart around the circumference of traps. Flexible, dual lead LEDs allow for orientation into space (transmitted light) or towards a reflective surface (reflected light).

Materials & Methods- Traps

• LEDs– Sold by Digi-Key Corporation (Thief River Falls, MN). – Color, part number, wavelength and millicandela

(mcd) chosen for testing were:

• blue (P466-ND, 470 nm, 650 mcd)• green (67-1755-ND, 502 nm, 1,500 mcd)• red (67-1611-ND, 660 nm, 1,800 mcd)

– LEDs are 8.6 mm in length by 5.0 mm in diameter with rounded lens and viewing angles of 30o.

Materials & Methods- Traps

• LED Advantages…– Shock resistant– Greatly extended operational life of

LED vs. lamp– Cooler operating temperatures– Greatly reduced power consumption,

80 ma/hr (4 LEDs) vs. 150 ma/hr lamp– Doubles battery life (6V, 12 amp/hr)– Range of colors

Materials & Methods- Location

Bahrif, next to Aswan

Materials & Methods- Location + Design

• Bahrif, Egypt. Farming village on the banks of the Nile River 6 km north of Aswan, 900 km south of Cairo.

• 4 x 4 Latin square design, 3 repetitions.

• Treatment: blue, green, red, and incandescent light.

Materials & Methods- Location

Materials & Methods- Location

Materials & Methods- Location + Design

• All traps baited with ≈ 1 kg dry ice in Igloo containers.

• Traps set with opening 45 cm above the ground (knee level).

• Sand flies removed at sunrise, later IDed using keys of Lane (1986).

Materials & Methods- Analysis

• Trap collections were analyzed for month (trial), position, and treatment (light color) using a 3-way ANOVA (SAS Institute, 2001).

• The Ryan-Einot-Gabriel-Welsh Multiple Range Test was used to delineate significant differences (α = 0.05) between treatments, months, and positions.

• All capture data were transformed with log10 (n + 1) prior to analysis.

Trap sites

Results & Discussion

• 2,298 sand flies were collected over 3 repetitions (12 nights, 48 trap-nights).

• Phlebotomus papatasi was the most abundant species in the field and comprised 94.39% of the entire catch (2,169 of 2,298 adults).

• Other species collected included P. sergenti (1.31%), Sergentomyia schwetzi (4.0%), S. clydei (0.17%), S. tiberiadis (0.09%), and S. antennata (0.04%).

Results & Discussion

• Analysis of data yielded highly significant results (F = 10.62; df = 8, 39, P < 0.0001).

• Sand fly collections differed significantly between...– treatments (F = 17.67; df = 3, 8; P < 0.0001)– collection positions (F = 6.53; df = 3, 8; P = 0.0011)

– trials (F = 6.19; df = 2, 8; P = 0.0046)

P. Papatasi response to colored light

Treatment Trial 1 (May) Trial 2 (June) Trial 3 (July) Total (%)

Red 297 466 467 1230 (56.7)

Control 70 167 237 474 (21.8)

Blue 92 97 51 240 (11.1)

Green 26 128 71 225 (10.4)

Total 485 (61.2) 858 (54.3) 826 (56.5) 2169

P. papatasi response to colored light

1230 (57%)

225 (10%)227 (11%)

474 (22%)

Red

Control

Blue

Green

Species Incan. Blue Red Green P-value

P. papatasi1,2 39.50 ± 11.19b 20.00 ± 3.81bc 102.50 ± 10.01a 18.75 ± 5.27c < 0.0001

P. sergenti 0.58 ± 0.26a 0.58 ± 0.34a 0.83 ± 0.27a 0.5 ± 0.14a 0.96

S. schwetzi1 2.50 ± 0.93a 1.75 ± 0.69a 2.08 ± 0.96a 1.33 ± 0.51a 0.08

S. tiberiadis 0.08 ± 0.08a 0.08 ± 0.08a 0.0 ± 0.0a 0.0 ± 0.0a 0.78

S. clydei 0.17 ± 0.11a 0.0 ± 0.0a 0.08 ± 0.08a 0.08 ± 0.08a 0.63

S. antennata 0.0 ± 0.0a 0.0 ± 0.0a 0.08 ± 0.08a 0.0 ± 0.0a 0.45

1Significant position effect (P < 0.05)2Significant day effect (P < 0.05)

Sand fly species composition (means ± SEM) from light emitting diode-modified CDC light traps (J. W. Hock Co. model 512). Means within each row followed by the same letter are not significantly different (Ryan-Einot-Gabriel-Welsh Multiple Range Test). n = 12 nights.

Sex ratios

• P. papatasi sex ratios were approximately the same, with slightly more females captured than males.

• Sex ratio was consistent over 3 reps.• Males highly attracted to red light as well as females.

142155

250216

269

198

0

50

100

150

200

250

300

1 2 3

papatasi + red light

female

male

Spectral sensitivity

Only one study measured spectral sensitivity to light in Phlebotomine sand flies (Lutzomyia longipalpis) using electroretinograms (Mellor et al. 1996). They found that:

-male and female flies demonstrated greatest sensitivity to light in the UV and a secondary sensitivity to light in the green-yellow spectrum (520 nm ♀, 564 nm ♂).

-typical bimodal response seen in “slow eye”, slow flight insects such as mosquitoes.

-no studies found pertaining to Phlebotomus sand flies and spectral sensitivities.

Luminosity

One possible answer for slow flying P. papatasi to respond strongly to red light (660 nm):

-High luminosity of red LEDs were more attractive than less bright competitors (prior published work with mosquitoes seems to confirm this (Breyev 1963, Barr et al. 1963)).

• Blue (470 nm, 650 mcd)• green (502 nm, 1,500 mcd)• red (660 nm, 1,800 mcd)

Luminosity?

• Blue (470 nm, 650 mcd)• green (502 nm, 1,500 mcd)• red (660 nm, 1,800 mcd)

Note however that…

• green and red mcd ratings are within 17% of each other• green lit-traps collected the fewest number of sand flies• five species of mosquitoes belonging to 3 genera (Culex, Ochlerotatus

and Anopheles) were collected in the following order of success:

Green> incandescent> blue> red lit-traps (~5800 mosq.)

during this test period (this data is largely in agreement with Burkett et al. (1998) concerning collection of mosquitoes with LED-baited traps in Florida).

Luminosity?Using low luminosity glow sticks in the

Sinai, Dr. Szumlas found no preference in P. papatasi for one

color over another, in fact, very little response at all.

Date Color No

7-Jun-05 Yellow 0

7-Jun-05 Control 0

7-Jun-05 Blue 2

7-Jun-05 White 3

7-Jun-05 Red 2

7-Jun-05 Control

7-Jun-05 Orange 1

7-Jun-05 Green 13

9-Jun-05 Blue 3

9-Jun-05 White 1

9-Jun-05 Red 1

9-Jun-05 Control 0

9-Jun-05 Orange 1

9-Jun-05 Green 0

9-Jun-05 Yellow 0

9-Jun-05 Control 0

Luminosity?Low luminosity produced by both radioactive tritium gas lights and chemlites also resulted in few mosquitoes or sand flies captured in trials in the Panama canal zone. Order of success was incandescent light> chemical light> radioactive light (Varva et al. 1974).

Conclusions of study

• Phlebotomus papatasi is very likely more attracted to long-wavelength light (red spectrum) than short wavelength light (UV-blue), however, further field testing is needed in different environments (Riparian vs. Desert).

• High intensity colored light (from LEDs) is better than low intensity colored light (chemlights).

• LED-modified CDC light traps performed very well with no trap or LED failures.

Other work…• Need to run electroretinograms on male and female

P. papatasi, other Phlebotomus sand flies to determine spectral sensitivities.

• Our study used reflected light- how about transmitted light?

• Determine most effective chemical attractants + match with red-LED traps (Dr. Bernier, CMAVE).

• Test LED traps in wet environments for durability.

References

• Barr, A.R., T.A. Smith, M.M. Boreham, K.E. White. 1963. Evaluation of some factors affecting the efficiency of light traps for collecting mosquitoes. Journal of Economic Entomology 56:123-127.

• Breyev, K.A. 1963. The effect of various light sources on the numbers and species of blood-sucking mosquitoes (Diptera: Culicidae) collected in light traps. Entomological Review 42:155-168.

• Burkett, D.A., J.F. Butler, D.L. Kline. 1998. Field evaluation of colored light-emitting diodes as attractants for woodland mosquitoes and other Diptera in north central Florida. Journal of the American Mosquito Control Association 14(2):186-195.

• Green, C.H. 1994. Bait methods for tsetse fly control. Advances in Parasitology 34:229-291.

• Lane, R.P. 1986. The sand flies of Egypt (Diptera: Phlebotominae). Bulletin of the British Museum (Nat. Hist.) Entomol. 52:1-35.

• Mellor, H.E., J.C.G. Hamilton, M. Anderson. 1996. Spectral sensitivity in the eyes of male and female Lutzomyia longipalpis sandflies. Medical and Veterinary Entomology 10:371-374.

References

• Mihok, S. 2002. The development of a multipurpose trap (the Nzi) for tsetse and other biting flies. Bulletin of Entomological Research 92:385-403.

• Vavra, R.W.Jr., R.R. Carestia, R.L. Frommer, E.J. Gerberg. 1974. . News 34(4):382-384 . Mosquito News 34(4):382-384.

• Xue, R., A. Santoro, D.L. Kline, A. Grant. Mosquito magnets as barrier treatments against salt marsh mosquitoes around residential houses in marsh area. Technical Bulletin of the Florida Mosquito Control Association 17 Feb. 2005.