Artigo Acesso aberto Revisado por pares

Comparative efficacy of three suction traps for collecting phlebotomine sand flies (Diptera: Psychodidae) in open habitats

2009; Wiley; Volume: 34; Issue: 1 Linguagem: Inglês

10.1111/j.1948-7134.2009.00014.x

ISSN

1948-7134

Autores

Roy Faiman, Ruben Cuño, Alon Warburg,

Tópico(s)

Insect Pest Control Strategies

Resumo

The efficacy of three suction traps for trapping phlebotomine sand flies (Diptera: Psychodidae) was compared. Traps were baited with Co2 and used without any light source. CO2-baited CDC traps were evaluated either in their standard downdraft orientation or inverted (iCDC traps). Mosquito Magnet-X (MMX) counterflow geometry traps were tested in the updraft orientation only. Both updraft traps (iCDC and MMX) were deployed with their opening ∼10 cm from the ground while the opening of the downdraft (CDC) trap was ∼40 cm above ground. Comparisons were conducted in two arid locations where different sand fly species prevail. In the Jordan Valley, 3,367 sand flies were caught, 2,370 of which were females. The predominant species was Phlebotomus (Phlebotomus) papatasi, Scopoli 1786 (>99%). The updraft-type traps iCDC and MMX caught an average of 118 and 67.1 sand flies per trap night, respectively. The CDC trap caught 32.9 sand flies on average per night, significantly less than the iCDC traps. In the Judean desert, traps were arranged in a 3×3 Latin square design. A total of 565 sand flies were caught, 345 of which were females. The predominant species was P. (Paraphlebotomus) sergenti Parrot 1917 (87%). The updraft traps iCDC and MMX caught an average of 25.6 and 17.9 sand flies per trap per night, respectively. The CDC trap caught 7.8 sand flies on average per night, significantly less than the iCDC traps. The female to male ratio was 1.7 on average for all trap types. In conclusion, updraft traps deployed with their opening close to the ground are clearly more effective for trapping sand flies than downdraft CDC traps in open habitats. Phlebotomine sand flies are small, fragile, nocturnally active nematoceran insects with weak flight capabilities. Females require blood to mature the eggs and both sexes require plant-derived sugar meals for energy (Alexander 2000, Killick-Kendrick 1999, Schlein and Muller 1995, Schlein and Warburg 1986). Sand flies are endemic to over 85 countries in the tropics and Paleoarctic regions where they transmit leishmaniasis, several arboviral diseases, and bartonellosis (Alexander and Maroli 2003, Killick-Kendrick 1990). Cutaneous leishmaniasis (CL) caused by Leishmania major Yakimoff & Schokhor, 1914 (Kinetoplastida: Trypanosomatidae) is a common affliction in rural areas of the Jordan Valley, the Arava, and the Negev of Israel (Jaffe et al. 2004). The main reservoir host is the fat sand rat Psammomys obesus Cretzschmar, 1828 (Cricetidae: Gerbillinae) and the only proven vector is the sand fly P. papatasi. In the Judean hills east of Jerusalem, foci of CL caused by L. tropica (Wright 1903) have emerged in recent years (Jaffe et al. 2004). The reservoir hosts are probably rock hyraxes (Procavia capensis) and the vector is P. sergenti (Schnur et al. 2004). CDC light traps have become the gold standard for trapping and monitoring mosquitoes and sand flies (Alexander and Maroli 2003). Such traps, baited with dry ice, typically emit CO2 at a rate of 500-1,250 ml/min, equivalent to two to five persons at rest (Service 1976). The Mosquito Magnet-X (MMX) is a counter-flow geometry trap (American Biophysics Corporation, East Greenwich, RI, U.S.A.) and has been used successfully for sampling and mass trapping various mosquito species in the United States (Kline 1999, Kline et al. 2006), and South Africa (Mboera et al. 2000). The updraft airflow lifts attracted insects into a container above the trap, thus discriminating in favor of mosquitoes, sand flies, and other light-weight species and greatly reducing the numbers of non-target species such as moths (Kline 1999, Mutero et al. 1991). Deployment of miniature CDC traps is faster and less labor intensive than most other trapping methods (Davies et al. 1995). On the other hand, MMX traps are large and fragile making them cumbersome to transport and deploy. Here we compare the efficacy of CDC traps (inverted updraft and normal downdraft position) with that of MMX (updraft) in trapping sand flies. Our results showed that inverted CDC (iCDC) traps were as efficient as and even superior than MMX traps for collecting sand flies, and both updraft traps were more efficacious than the standard, downdraft CDC trap. Gilgal, Jordan-Valley: Studies with P. papatasi were conducted in an abandoned ornamental-tree orchard of approximately seven acres belonging to Kibbutz Gilgal, Central Jordan Valley (E 35°26′, N 32°00′, Altitude 260 m). The region is very warm and dry, with summer temperatures exceeding 45° C and an average annual rainfall of 100-150 mm. Agricultural plots cover most of the area, with some open pristine habitats to the east. The phlebotomine sand fly fauna of the region is well-documented comprising almost exclusively P. papatasi (Schlein et al. 1982). Immediately to the south of the study site there was a turkey farm where preliminary trapping with CO2-baited CDC traps yielded on average 60 sand flies per trap/night. Kfar Adumim, Judean Desert: Studies with P. sergenti were conducted on a barren hill near Kfar Adumim (E 35°20′08, N 31°49′34, Altitude 350-300 m), a village located 20 km east of Jerusalem, in the Judean Desert. Annual rainfall averages 150-300 mm, summers are hot, and winters are mild (Goldreich 1998). The traps were set up on a southern slope of the village, where sand flies are abundant throughout the summer months (Orshan et al. 2006). Three trap types were compared: (1) CDC miniature light traps (manufactured by us) were suspended from trees or cane tripods with their openings ∼40 cm above ground (Figure 1A); (2) Inverted CDC miniature light (iCDC) traps were suspended in an updraft position (Sexton et al., 1986), with their openings ∼10 cm above ground (Figure 1C); (3) MMX traps suspended with their openings ∼10 cm above ground (Figure 1B). The three suction traps used in the experiment. A - downdraft CDC, B - updraft MMX, C - updraft iCDC. All traps were baited with CO2 in the form of dry ice (1.5 kg/trap/night) in an insulated 5-liter polystyrene canister. Rubber tubing (1.5 m long, 7 mm internal diameter) was attached to the canister opening. The other end of the tube was secured to the fan guard of the CDC traps or to the designated tube of the MMX traps. The calculated average flow rate of CO2 was 750-1,200 ml/min. Traps were used without any light and the top plates were not used in the CDC or the iCDC traps. In Gilgal (Jordan Valley), trapping was carried out on a weekly basis with traps set out at 17:00 and collected at 06:00 the following morning. Traps were placed at least 20 m apart to reduce the possibility of mutual interference (Gillies and Wilkes 1974). The traps were rotated among the different locations in order to avoid location and/or trap bias. The total number of trap-nights (TNs) was ten for the MMX, 14 for the CDC, and seven for the iCDC. In Kfar Adumim, traps were arranged in a 3×3 Latin square design with traps placed 15 m apart (Fowler et al. 2006). Experiments were conducted for three trapping nights and traps were deployed at 17:00 and collected at 06:00 the following morning. Here too, the traps were rotated among the nine trap locations so that each trap was used in each location in the square on a different night. Representative samples of sand flies from both locations were mounted in Hoyer's medium on microscope slides and identified (Lewis 1982). Sand fly numbers were log-transformed [log(n+1)] to normalize the distribution and control the variance in the case of non-normal distribution, caused chiefly by aggregated distribution. This allowed the application of parameteric tests (Williams 1937, Bidlingmayer 1985, Alexander 2000) and the calculation of the geometric means (Williams means, Mw) (Downing 1976). A univariate analysis of variance (ANOVA) was used to compare the average yields of the trap types. Least significant difference (LSD) post hoc analysis was utilized to ascertain the extent of the difference among the trap types. A Two-way ANOVA was used to test the influence of trap location and trapping night. Gilgal, Jordan-Valley: 3,367 sand flies (2,370 females) were caught during the seven trapping nights, comprised almost entirely P. papatasi (>99%) and some P. sergenti (<1%). Sergentomyia spp., abundant throughout the region, were captured as well but were not included in this study. The female to male ratio was 2.4 for all trap types. The average number of sand flies caught by the updraft traps (iCDC and MMX) was 118.0 and 67.1, respectively. The mean catch of downdraft CDC traps was 32.9, over three-fold less than that of the iCDC traps, and over two-fold less than that of the MMX traps (Table 1, Figure 2). A univariate ANOVA confirmed a significant difference between the trap means (Fdf=2=8.8, P<0.05). Post Hoc (LSD) analysis showed a significant difference between the mean sand fly yields of the CDC and the iCDC traps (P 0.05), nor was there a significant difference found between the updraft iCDC and MMX traps (P>0.05). Mean (Mw ±SE) number of sand flies caught by each of the three trap types: inverted CDC trap (iCDC), Mosquito Magnet X (MMX), and CDC traps. A- Gilgal (>99%P. papatasi). B -Kfar Adumim (87%P. sergenti). Kfar Adumim, Judean Hills: A total of 565 sand flies were caught during three nights, 345 of which were females. The predominant species (87%) was P. sergenti. The female to male ratio was 1.7 for all trap types. The updraft type traps iCDC and MMX caught an average of 25.6 and 17.9 sand flies per trap per night, respectively. The CDC traps caught 7.8 sand flies per trapping night on average, over three-fold less than that of the iCDC traps, and over two-fold less than that of the MMX traps (Table 1). As a part of a long-term sand fly control study, we wanted to optimize our sand fly sampling routines. Use of CDC traps either in the updraft position or placed horizontally on the ground has been previously observed by us and others to increase sand fly yields compared with the downdraft position (Orshan et al. 2006, Y. Schlein, personal communication). MMX traps were reported to be very efficient for sampling mosquitoes in the U.S. (Kline 1999, Kline et al. 2006), and South Africa (Mboera et al. 2000). Therefore, we decided to experiment with CDC trap orientation and MMX traps in order to improve the sand fly yields during routine experimental monitoring. In the initial phases of the study, we compared the efficacy of standard CDC traps with the MMX traps in two locations. After six trapping nights, significant differences between the two trap types were evident. Since the MMX traps are very bulky and cumbersome to work with, we decided to assess whether their superior performance resulted from basic differences in structure and/or function of the MMX traps or from their opposing orientation and the closeness of their suction orifice to the ground. Therefore, we introduced iCDC traps to the experimental set up. Results showed that iCDC traps were at least as efficient as MMX traps, if not more so. Both iCDC and MMX were superior to the standard CDC trap for trapping phlebotomine sand flies. The counter-flow design of the MMX did not appear to give it an advantage in trapping sand flies. The higher numbers of sand flies captured by both updraft traps were probably due to the closeness of their opening to the ground. While the standard CDC was suspended with the opening ∼40 cm above ground, both MMX and iCDC were placed with their opening ∼10 cm above the ground. In open areas lacking any vertical obstacles, sand flies proceed in short flights close to the ground, avoiding wind gusts and following attractant cue gradients such as CO2 plumes (Killick-Kendrick 1999, Yuval et al. 1988). Wind tunnel experiments showed that the CO2 plume from a counter flow updraft trap (MMX) is densest along the ground (CO2 outlet placed 72 cm above ground), with a maximum concentration of the gas closest to the suction orifice of the trap and gradually dissipating along a 2 m gradient. Presumably, similar gas dissipation patterns occur near the iCDC traps. For downdraft type traps similar in setup and function to the CDC trap, CO2 plumes were maximal above ground (CO2 outlet 109 cm above ground) and only reached the ground diffused and scattered almost 2 m away from the trap suction orifice (Cooperband and Cardé 2006). Thus, the combined effect of the focal CO2 plume originating close to the traps and the lower openings of the MMX and iCDC traps probably explains their superior performance in trapping sand flies over the downdraft CDC traps. Another contributing effect may result from the innate tendency of mosquitoes and sand flies to react to threat by flying upwards (Kline 1999, Mutero et al. 1991, Wilton and Fay 1972). This behavior may increase the sand flies' chances of being trapped by updraft suction overhead, as opposed to a downdraft traps pulling them down. Sand fly viability is an additional factor to consider when selecting a trap. For example, a large proportion of the sand flies in CDC traps collected in the morning were already dead, presumably of desiccation, continuous exposure to turbulent air from the fan, and exposure to high levels of CO2. In this respect, MMX traps were clearly superior to CDC traps, yielding a larger proportion of viable flies and mosquitoes (data not shown). Presumably, MMX traps allow trapped sand flies to avoid the airflow passing through it, thus reducing their exhaustion by struggle to escape and dehydration rate. Interestingly, a similar improvement could be achieved using CDC traps (either up- or downdraft) by inserting a crumpled sheet of paper into their collection chamber, in which the trapped sand flies find shelter and avoid the desiccating effect of the wind generated by the fan. In conclusion, both updraft CDC and MMX traps are suitable for collecting and monitoring sand flies in open habitats. However, since CDC traps are considerably smaller, less bulky and require only 3-6V rather than 12V batteries, they are probably the better choice for monitoring purposes. This study 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). Additional funding was provided by grant number SCHO 448/8-1 from the Deutsche Forschungsgemeinschaft (DFG): “Emergence of cutaneous leishmaniasis in the Middle East: an investigation of Leishmania tropica in The Palestinian Authority and Israel” and The Israel Science Foundation (grant No. 135/08). We thank L. Orshan and G. White for suggesting the study and H. Seligman for assistance with the statistical analyses. Karen McKenzie of American Biophysics Corp. supplied the MMX traps. We thank the people of Kibbutz Gilgal and Kfar Adumim for their support and for allowing us to conduct experiments on their property.

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