ABSTRACT

A nursery pot molded from wood fiber was evaluated as a tool for sampling resting adult mosquitoes. Fiber pots were directly compared to standard plywood resting boxes and to these boxes with collapsible shields attached. One fiber pot yielded equivalent results as one plywood resting box, while addition of collapsible shields increased the catch 6-fold for boxes over fiber pots without shields. Both collection devices (fiber pots and plywood boxes) sampled mainly Culiseta melanura, the enzootic vector of eastern equine encephalitis virus in Massachusetts. An economic comparison of fiber pots and plywood boxes reveals that a mosquito surveillance project using fiber pots spends just 1 % of the resources spent by a project using plywood boxes for sampling adult resting mosquitoes.

INTRODUCTION

A mosquito surveillance project interested in monitoring populations of adult Culiseta melanura mosquitoes may utilize several sampling strategies. A common strategy utilizes the diurnal resting behavior of these mosquitoes, in particular, their affinity for dark, damp enclosed spaces that simulate natural resting locations in underground crypts or underneath overturned root mats. Artificial resting boxes have been used extensively as a reproducible sampling instrument for collection of C. melanura (Carpenter et al. 1946; Burbutis and Jobbins 1958; Gusciora 1961; Moussa et al. 1966; Edman et al. 1968).

Artificial resting boxes are not commercially available. They must be constructed of plywood, painted black or red on the interior surface, and transported to a field site where they are generally placed on the ground in shaded areas. When a collapsible shield is added to the opening, a much larger opening is seen by mosquitoes thereby increasing the yield 5 to 6 times (Edman et al., 1968). Mosquitoes are removed from these resting shelters by aspiration or after application of an anesthetic (chloroform or carbon dioxide). The bulk of the plywood boxes makes their use physically difficult, requiring carpentry skills to build the boxes and then significant effort to transport the boxes, although unlike other trap types, the boxes may be left at a field site throughout the sampling season. Use of collapsible shields, also constructed of

plywood, increase not only the yield of mosquitoes but also the bulk of the device. Agencies interested in using resting boxes must consider the resources required to obtain materials, assemble the boxes, transport boxes to and from field sites, and store the boxes for future use. In an age of ever-shrinking budgets, many agencies may find the resources necessary for a resting box-based mosquito sampling program prohibitive.

In order to facilitate the sampling of resting adult C. melanura, we have identified a commercially-available fiber pot that may make plywood resting boxes obsolete. Below we compare the efficacy of this fiber pot to plywood resting boxes for their attractiveness to resting adult C. melanura. We also compare the resources necessary to use fiber pots versus resting boxes in a mosquito surveillance program.

MATERIALS AND METHODS

Study Site. A wooded location in the Hockomock Swamp Wildlife Management Area in Taunton, MA was chosen as a study site because of its historical infestation with C-. melanura, which breeds nearby. The habitat is forested wetland with American white cedar, red maple and hemlock trees predominating the arboreal stratum.

Mosquito Sampling Devices. Fiber nursery pots (11" x 11") were purchased from Western Pulp Products, Corvallis, OR. Plywood resting boxes (8" x 12" x 15") with interiors painted matte black, and their accompanying collapsible shields, were kindly provided by Dr. John Edman, Dept. of Entomology, University of Massachusetts, Amherst. Sixteen pots and 15 resting boxes were placed at the site such that their openings were oriented in random directions, and such that mosquitoes in the vicinity would likely see only one pot or box opening from any point. A battery-operated hand-held aspirator (BioQuip, Inc., CA) was used to remove resting insects from the sampling devices during daylight hours, usually in the afternoon.

Statistical Analysis. Wilcoxon Rank-Sum Test (Milton, 1992) was utilized to determine statical significance of differences between means of various categories of mosquitoes collected by the two sampling methods of each comparison.

RESULTS AND DISCUSSION

We first compared the mosquito yields from fiber pots and resting boxes with shields extended (Table 1). We then conducted the comparison without the collapsible shields on the resting boxes (Table 2). Finally, we calculated the values of various economic and resource-ise parameters implicated in the operation of these mosquito sampling devices (Table 3).

These comparisons demonstrated that most of the mosquitoes collected by both types of shelters were indeed female C-. melanura. The difference in the collections by the fiber pot and the unshielded plywood box was not significant when analyzed by all mosquitoes collected, all female mosquitoes collected, female C. melanura, or blood-engorged female C. melanura. We conclude, then, that the fiber pot functions as efficaciously as the unshielded resting box for sampling populations of C. melanura. When shields are added to the plywood boxes, the area of the opening of the shelter increases more than 9 times. The yields of mosquitoes in the shielded plywood boxes also increased relative to the fiber pots by more than 6-fold. A similar result was observed by Edman et al. (1968) when shielded boxes were compared to unshielded boxes.

The operation of the fiber pots as a mosquito sampling instrument appear to require many fewer resources than that of plywood resting boxes. If time required for device assembly is translated into dollars at $10 per hour, then fiber pots cost less than a tenth of plywood boxes, and less than a twentieth of plywood boxes with their shields. Cost of accessories was not included in the analysis, but would make the cost difference between fiber pots and plywood boxes even greater. Due to their light weight and nestable form, fiber pots are about five times more transportable than plywood boxes, and ten times more plywood boxes plus shields. Similarly, fiber pots require less than half the storage space of plywood boxes, and more than 5 times less space than plywood boxes with shields. Taking these economic comparisons together, operational resource use of fiber pots is about I % of that for plywood boxes and 0. 1 % of that for plywood boxes plus shields. This analysis is limited to short tenn considerations (within one field season). Fiber pots have not yet been evaluated for duration, and are likely to withstand fewer field seasons than plywood boxes.

A more complete evaluation of fiber pots as mosquito sampling devices, along with a listing of mosquito species that utilize these artificial resting shelters, will be published separately.

ACKNOWLEDGMENTS

The concept of using fiber nursery pots as mosquito collection devices originated with Richard Pollack of Harvard University. Mel Kelsey of Western Pulp Products provided samples of fiber pots of different sizes for an initial evaluation. Special thanks to John Edman (University of Massachusetts) for providing plywood resting boxes. Benjamin Rosenthal (Harvard University) gave statistical advice. Professor Andrew Spielman, as mentor and thesis advisor, provided the opportunity and moral support for this research. Financial support was provided by the Massachusetts Department of Public Health. Nicholas Komar was the recipient of the Daniel M. Jobbins Scholarship of the Northeastern Mosquito Control Association in 1993.

REFERENCES

Burbutis, P.P. and D.M. Jobbins, 1958. Studies on the use of a diurnal resting box for the

collection of Culiseta melanura (Coquillett). Bull. Brooklyn Entomol. Soc. 53:53-58.

Carpenter, S.J., W.W. Middlekauff and R.W. Chamberlain, 1946. The mosquitoes of the

southern U.S. east of Oklahoma and Texas. Proc. N.J. Mosq. Exterm. Assoc. 44:68-78.

Edman, J.D., F.D.S. Evans and J.A. Williams, 1968. Development of a diurnal resting box to collect Culiseta melanura (Coq.). Am. J. Trop. Med.& Hyg. 17:451-456.

Gusciora, W.R., 1961. The resting box technique for the sampling of Culiseta melanura

(Coquillett). Proc. N.J. Mosq. Exterm. Assoc. 48:122-125.

Milton, J. S., 1992. Statistical Methods in the Biological and Health Sciences, 2nd Ed., McGraw-

Hill, Inc., New York. pp. 433-435.

Moussa, M.A., D.J. Gould, M.P. Nolan, Jr. and D.E. Hayes, 1966. Observations on Culiseta melanura (Coquillett) in relation to encephalitis in Southern Maryland. Mosq. News 26:385-393.

Table 1. Comparison of fiber pots to plywood resting boxes with extended shields attached. Sampling occurred between July 18 and August 28, 1994.

Table 2. Comparison of fiber pots to plywood resting boxes without extended shields attached. Sampling occurred between September 1 and September 19, 1994.

Table 3. Resource-use comparison of fiber pots and plywood boxes with and without collapsible shields.