Abstract:
A method and apparatus are disclosed that can sample a wide variety of mosquitoes attempting to rest. Because all mosquitoes rest daily, biases of typical mosquito traps are avoided, such as targeted collections of host-seeking mosquitoes or gravid female mosquitoes. A particular advantage is the inclusion of blood-engorged mosquitoes in the resting collections. In one embodiment, the apparatus includes an open-sided pot designed to attract mosquitoes seeking a daytime resting location. The mosquitoes that enter a dark space of the pot are aspirated into a screened collection receptacle by means of a battery-powered fan.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from U.S. Provisional Application No. 61/219,684, filed Jun. 23, 2009, which application is incorporated herein by reference in its entirety. 
     FIELD 
     The present invention relates to collecting mosquitoes, and particularly relates to collecting resting mosquitoes. 
     BACKGROUND 
     Interest in mosquito ecology and the use of appropriate sampling methods began early in the 19 th  century with the discovery that mosquitoes could act as vectors of diseases to humans and domestic animals. Resting mosquitoes in houses and animal quarters are typically caught using manual or mechanical aspirators or by knock down spray collections. Historically, the simplest and most widely used aspirator was made of plastic or glass tubing with a piece of mosquito netting taped over one end. Mosquitoes are orally sucked into the aspirator and then gently blown into a suitable storage container. However, the practice of collecting mosquitoes by sucking them into aspirators is no longer permitted due to biosafety concerns. Prolonged inhalation of mosquito scales, dust, and other fine debris may cause or aggravate allergies. 
     Other types of aspirators include small battery-powered devices where suction is produced by high-speed rotation of a plastic or metal fan or gasoline powered aspirators that create a vacuum designed for sucking mosquitoes into a netted container. 
     Although a wide variety of traps have been proposed, most have biases towards certain types of mosquitoes, such as mosquitoes in host-seeking mode, only females, only egg-laying females, etc. The objective of sampling resting mosquitoes eliminates most biases, because all mosquitoes, regardless of physiological stage, must rest each day. However, searches for outdoor resting mosquitoes have frequently proved time-consuming and unrewarding. Thus, it is desirable to have a low-cost device for collecting mosquitoes that samples an unbiased cross-section of physiological stages within the adult mosquito population in such a manner to permit quantitative comparisons among samples. 
     SUMMARY 
     A method and apparatus are disclosed that can sample a true cross-section of a wide variety of mosquito species, particularly  Culex, Anopheles  and  Culiseta  genera. All stages of development are represented in the adult mosquitoes attracted to rest in the apparatus, including the target groups of other popular traps such as host-seeking female mosquitoes (CDC light trap, Mosquito Magnet, BG Sentinel trap) and gravid female mosquitoes (CDC gravid trap, oviposition trap). The apparatus is especially effective relative to other traps for collecting blood-engorged mosquitoes (which are notoriously difficult to collect). The apparatus is adaptable for operation at the ground level or in a vegetation canopy and can be highly portable, durable and inexpensive to operate. 
     In one embodiment, the trap includes an open-ended pot designed to attract mosquitoes seeking a resting location. The mosquitoes that enter the dark space of the pot are aspirated by a battery-powered fan into a collection receptacle. 
     The foregoing and other objects, features, and advantages of the invention will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a suction trap for collecting resting mosquitoes. 
         FIG. 2  is a cross-sectional view of the trap of  FIG. 1 . 
         FIG. 3  is an exploded perspective view of the trap of  FIG. 1 . 
         FIG. 4  is a frontal perspective view of the trap of  FIG. 1 . 
         FIG. 5  is a perspective view of another embodiment for collecting resting mosquitoes. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a trap  10  for collecting resting mosquitoes. The trap  10  includes a pot  12  that attracts mosquitoes seeking a resting place. The pot  12  can be made of a variety of materials, such as natural fibers, wood, or plastic. For example, in one embodiment, a wood-fiber pot can be used. The pot can be stackable with other pots in a nested fashion so that multiple pots can be carried into the field using minimal space. The pot has a large opening at one end and gradually tapers in size towards the opposite end forming a deep cavity, so that even during the day the cavity offers a relatively dark hideaway for mosquitoes. During the collection process, the pot is designed to be immobile and is sized to attract mosquitoes for resting. The pot  12  is coupled to a pipe member  14  having a fan  16  mounted therein. A battery or battery pack  22  is removably coupled to the fan  16  via a wire coupler  24 . A rain guard  26  is mounted to the pipe member  14  at an end opposite the pot  12  using L-shaped brackets  28  that maintain the rain guard  26  in spaced relation to the pipe member  14 . The rain guard  26  is desirably a large disk-shaped member, which can be sized not only for protecting the fan  16  from rain, but also for functioning as a support member or leg to suspend the fan  16  and pipe member  14  a predetermined distance above of the ground. In some embodiments, the rain guard  26  is sized to work in conjunction with the pot  12  to suspend the pipe  14  horizontally. For horizontal placement, the pot  12  acts as one leg and the rain guard  26  acts as an opposing leg to support the trap  10 . The rain guard  26  can further include a hood  30 , which is arcuate-shaped and mounted above the fan  16 , and perpendicular to the disk, to provide the fan with further protection from the elements. In addition to acting like a leg to support the trap  10 , the rain guard  26  can also be used as a mounting disk to secure the trap  10  vertically, such as in a tree with the pot  12  being placed at the lowest position. As shown in  FIG. 1 , the pipe member  14  may be formed of multiple sub-pipes  36 ,  38  that are connected together via a coupler  40 . A bracket  42  is coupled to the pot  12  at a tapered end thereof. The bracket  42  is sized for receiving the pipe member  14  and has a threaded hole for receiving a screw  44  to secure the pipe to the pot  12 . Although the pipe member  14  is shown as having an end that is flush with an inner surface of the pot  12 , the pot can further slid onto the pipe member so that the pipe partially protrudes into the pot. At any desired relative position, the screw  44  can be secured to the pipe. The coupler  40  has a diameter slightly larger than the sub-pipes  36 ,  38  for receiving the sub-pipes with a snug fit. The coupler has threaded holes for receiving screws  46  to secure each sub-pipe  36 ,  38  to the coupler  40 . 
       FIG. 2  is a cross-sectional view of the trap  10 . The bracket  42  can be secured to the pot  12  in a number of ways, such as by glue, screws, etc. The bracket  42  can take a variety of shapes and in the embodiment of  FIG. 2  has a somewhat Z shape with a portion thereof secured to the pot  12  and a portion thereof sized to receive the pipe member  14 . A frustoconical screen  48  can be mounted within the pipe member  14  with the base of thereof mounted adjacent to the pot  12 . A screen  50  can also be mounted at the back end of sub-pipe  36  to form an enclosed collection chamber within the first sub-pipe  36 . Both the frustoconical screen  48  and screen  50  have holes therein to allow the fan  16  to draw air in the direction of arrow  52  through the pipe member  14 . Mosquitoes that are attracted to the resting pot  12  will therefore be aspirated through a hole in the pot  12  into the conical screen  48  and into the collection chamber formed in the sub-pipe  36 . The mosquitoes are thereby trapped between the frustoconical screen  48  and the screen  50 . The frustoconical screen has the advantage of making it easy to aspirate mosquitoes into the collection chamber, while making it difficult for mosquitoes to crawl out. Although the screen  50  is shown at the back end of the sub-pipe  36 , it can also be mounted in the coupler  40  or any other desired location along the pipe member  14 . The benefit of having the screen  50  in the sub-pipe  36  is that the collection chamber formed thereby can be easily removed from the trap  10  and a new collection chamber inserted. Desirably, the collection chamber formed in sub-pipe  36  can have lids (not shown) that can be mounted onto the sub-pipe  36  to maintain the captured mosquitoes therein. The frustoconical screen  48  can be removable in order to extract the mosquitoes from the collection chamber. 
       FIG. 3  shows an exploded view of the different parts used in the trap  10 . The trap can be disconnected so that it can be easily packed for transporting in and out of the field. Although the conical screen  48  and the screen  50  are both shown as removable, either one or both of these screens may be permanently mounted in the pipe member  14  (e.g., such as by using glue or a snap fit), if desired. 
       FIG. 4  is a frontal view of the trap  10  showing that the pot  12  has an enlarged open end  60  and a smaller end  62  with a gradual tapering there between. The smaller end  62  has a hole  64  centrally located through which the mosquitoes are aspirated. The frustoconical screen  48  also has a hole  66  at a tapered end thereof, through which the mosquitoes are aspirated into the collection chamber. The inside of the resting pot  12  can be painted dark colors, such as black, in order to attract the mosquitoes to the dark area. 
       FIG. 5  shows an alternative embodiment of the trap having a resting pot  80  coupled to a pipe or tube  82  and a net  84  secured to the pipe  82  using an elastic band  86 . A battery pack  88  is mounted to the pipe  82  and houses batteries  90  for powering a fan (not shown) mounted within the pipe  82 . Two wooden legs  92  are secured by bolts  94  and have mating holes sized for receiving and mounting the pipe  82  with a snug fit. The legs  92  are used to maintain the trap at a fixed distance from the ground. In this embodiment, the mosquitoes are aspirated through the fan, which can potentially damage the mosquitoes. By contrast, in the embodiment of  FIGS. 1-4 , the mosquitoes are aspirated into a collection chamber without passing through the fan. Although the enclosure is shown as a net  84 , other enclosures can be used, as is well understood in the art. In any event, the enclosure acts as a collection chamber in which the mosquitoes are maintained. 
     In either of the embodiments, the fan may be operated continuously or, alternatively, a timing circuit can be used for intermittent operation in order to conserve power. In any event, the fan creates suction in order to aspirate the mosquitoes. Additionally, although the trap is preferably used for mosquitoes, it may be used for capturing other insects as well. 
     We tested at least one embodiment described herein and found a large improvement in results. We compared the efficiency of the CDC resting trap to wood fiber pots at four study sites in Northern Colorado during August and September, 2008. All fiber pots in the study, including those used as part of the CDC resting traps, were painted flat black on the interior surfaces. Each of the sites was associated with a communal bird roost where we were able to compare how efficiently each trap type collected blood fed mosquitoes. In addition, we collected host-seeking mosquitoes with CO 2 -baited CDC light traps to assess species composition at each site. 
     At each site, thirty to fifty wood fiber pots were set and collections were made using a back pack aspirator (John W. Hock Company, 7409 NW 23 rd  Ave, Gainesville, Fla. 32604) once per day. Four to ten CDC resting traps were deployed at each site concurrently in similar microhabitats and collection nets were picked up daily. Collected mosquitoes were identified and processed using dissecting microscopes on chill tables. Additionally, in a separate comparison evaluating trap placement, an equal number of CDC resting traps were placed in areas either shaded by shrubby vegetation or along buildings and fence lines to simulate two distinct habitat types. 
     To determine the differences in catch rates by trap type, we derived ratios from mixed-effects, Poisson regression model, adjusting for fixed species and random site and date effects. A t-test was used to compare collections derived from two placement strategies for  Culex pipiens  L. and  Cx. tarsalis  independently. 
     Eleven mosquito species were collected with the majority of mosquitoes, principally  Aedes vexans  (Meigen), captured in CDC light traps baited with CO 2 , which are designed to attract host-seeking mosquitoes (Table 1). The wood fiber pots and the CDC resting traps collected mostly  Culex  species, with a greater proportion of engorged mosquitoes than the light traps. The novel CDC resting trap collected 15.1-fold (95% CI 6.0-37.9) more  Culex pipiens  and 5.4-fold (95% CI 3.7-7.8) more adult female  Culex tarsalis  mosquitoes per trap night than did the wood fiber pots when collections from the same location were compared. Placement of the CDC resting traps indicated that fence lines were more effective than shaded vegetation for collecting  Culex  mosquitoes. The traps placed along the fence collected 3.8-fold more  Cx. pipiens  (95% CI 2.3-5.3) and 4.9-fold  Cx. tarsalis  (95% CI 3.1-6.7) mosquitoes per collection (n=9) than those set in vegetation. 
     The objective of this investigation was to improve upon an already effective method of collecting resting female  Culex  mosquitoes. By modifying wood fiber pots we were able to increase our collections by about an order of magnitude for both species of  Culex  targeted. Wood fiber pots and CDC resting traps collected engorged mosquitoes in much greater proportions than CDC light traps, which was expected. However, the percentages of engorged  Cx. tarsalis  and  Cx. pipiens  collected in the pots and resting traps did not differ significantly. 
     Our preliminary observation that trap efficacy increases along fence lines relative to shaded vegetation can be explained by assuming that vegetation successfully competes for resting locations. Collections in homogeneous vegetated habitat were typically lower than collections from individual bushes in habitat with little overall natural vegetation. 
     Resting collections in general are far superior to other types of collections for acquiring blood engorged female mosquitoes. Collecting blooded female mosquitoes is a valuable tool for researchers evaluating host preferences of mosquitoes and pathogen transmission dynamics, and for mosquito control personnel interested in monitoring human biting rates among local mosquito populations. Modern polymerase chain reaction technology can now identify the blood-meal source to the species level among vertebrates, and forensic techniques can be used to determine the individual blood donors for anthropophilic vectors, such as  Aedes aegypti  (L.) (Kent 2009). Elucidating the role of vertebrate host species in zoonotic pathogen transmission ecologies is desirable for effective public health practice. 
     In summary, we present preliminary data demonstrating a more effective trap for collecting resting mosquitoes. We expect this trap to have widespread applicability in research and in public health and veterinary surveillance for certain mosquito populations and their pathogens, including arboviruses (e.g. West Nile virus, etc.) and mosquito-borne parasites, including the agents of filariasis (filarial nematodes) and malaria ( Plasmodium  species). 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Mean number of mosquitoes collected per 
               
               
                 trap-night by trap type (% blood-fed) 
               
             
          
           
               
                   
                 CDC Light 
                 Wood Fiber 
                 CDC Resting 
               
               
                   
                 Trap 
                 Pot 
                 Trap 
               
               
                 Mosquito Species 
                 n = 19 
                 n = 920 
                 n = 115 
               
               
                   
               
             
          
           
               
                   Aedes vexans  (Meigen) 
                 129.1 
                 (2.0) 
                 0.072 
                 (4.5) 
                 0.219 
                 (0.0) 
               
               
                 
                   Culiseta inornata 
                 
                 1.8 
                 (0.0) 
                 0.023 
                 (15.3) 
                 0.057 
                 (28.6) 
               
               
                 (Williston) 
               
               
                   Culex pipiens  L. 
                 2.6 
                 (0.0) 
                 0.037 
                 (47.1) 
                 0.848 
                 (21.0) 
               
               
                   Culex restuans  Theobald 
                 0.1 
                 (0.0) 
                 0.007 
                 (57.1) 
                 0.057 
                 (20.0) 
               
               
                   Culex tarsalis  Coq. 
                 45.5 
                 (0.6) 
                 0.380 
                 (13.3) 
                 2.18 
                 (22.4) 
               
               
                   Aedes dorsalis  (Meigen) 
                 11.1 
                 (0.5) 
                 0.004 
                 (0.0) 
                 0.019 
                 (50.0) 
               
               
                   Aedes melanimon  Dyar 
                 15.2 
                 (0.0) 
                 0.018 
                 (17.6) 
                 0.0 
                 (0.0) 
               
               
                   Aedes trivittatus  (Coq.) 
                 1.3 
                 (0.0) 
                 0.003 
                 (0.0) 
                 0.5 
                 (0.0) 
               
               
                 
                   Aedes hendersoni 
                 
                 0.2 
                 (0.0) 
                 0.03 
                 (0.0) 
                 0.0 
                 (0.0) 
               
               
                 Cockerell 
               
             
          
           
               
                 
                   Culiseta incidens 
                 
                 — 
                 — 
                 0.021 
                 (0.0) 
               
               
                 (Thomson) 
               
               
                   Culex salinarius  Coq. 
                 — 
                 — 
                 0.007 
                 (0.0) 
               
               
                   
               
               
                 n, number of trap-nights 
               
             
          
         
       
     
     In view of the many possible embodiments to which the principles of the disclosed invention may be applied, it should be recognized that the illustrated embodiments are only preferred examples of the invention and should not be taken as limiting the scope of the invention. Rather, the scope of the invention is defined by the following claims. We therefore claim as our invention all that comes within the scope and spirit of these claims.