Mosquitoes Associated with Ditch-Plugged and Control Tidal Salt Marshes on the Delmarva Peninsula

Sarah Sandoval-Mohapatra,Paul T Leisnham

doi:10.3390/ijerph8083099

Sarah Sandoval-Mohapatra, Paul T Leisnham

Open Access

https://doi.org/10.3390/ijerph8083099

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Abstract

A study was conducted during the summer of 2009 (from July to September) to characterize mosquito communities among different habitats in five historically ditched tidal salt marshes and three adjacent wooded areas in the E.A. Vaughn Wetland Management Area on the Maryland Delmarva Peninsula, USA. Study marshes are characteristic of Atlantic coastal salt marshes that had undergone grid ditching from the 1930s to 1950s. In the autumn of 2008 (October and November) ditches were plugged near their outlets in two (‘experimental’) marshes with the aim to restore their natural tidal hydrology. The three other marshes were not plugged. Marshes were sampled from July to September in 2009 by using standard dip count method. A total of 2,457 mosquito larvae representing six species were collected on 15.4% (86/557) of all sample occasions and 399 adults representing four mosquito species were collected from landing counts. Aedes sollicitans, Anopheles bradleyi and Culex salinarius were the most common species collected in larval habitats, and Ae. sollicitans was the most common adult collected. Wooded habitats had more total mosquitoes, were also more frequently occupied by mosquitoes and had higher densities of mosquitoes than marsh habitats. Almost all larvae collected from marshes were from one experimental and one control site. The majority of larvae at the control site were Ae. sollicitans in marsh pannes while Cx. salinarius, An. bradleyi, Ae. cantator, and Ae. sollicitans were collected in high numbers from ditches at the experimental site. We found a difference in the proportion of marsh pannes occupied by Ae. sollicitans but not total mosquitoes sampled 4–5 days after spring tide events than on other occasions. Salinity measures of 42 larval habitats showed lower median salinity in mosquito-occupied habitats (11.5 ppt) than unoccupied habitats (20.1 ppt), and in habitats in wooded areas followed by ditches and pannes in marsh areas. The results of this study suggest that wooded areas adjacent to salt marshes may be a substantial source of biting adult mosquitoes usually associated with salt marsh habitats and that ditch plugging may alter the productivity of mosquitoes on some marshes. We recommend future studies consider mosquito productivity from habitats surrounding salt marshes, and if assessments of marsh alterations are a goal, compare multiple experimental and control areas before and after treatments to determine if alterations have a consistent impact on regional mosquito production.

Highlights

Coastal salt marshes are among the most common and productive coastal habitats on Earth and they play an important ecological role in the interface between marine and terrestrial environments [1]
Marsh conservation and mosquito control has usually focused on the effectiveness at controlling mosquito production of open marsh water management (OMWM), which is characterized by the targeted construction of tidal channels, ponds, and shallow radial ditches [10]
Aedes sollicitans was the most frequent species collected overall (45.7%, 1,124/2,457) and in wooded habitats only (57%, 864/1,515), while Anopheles bradleyi was the most frequent species collected in marsh habitats only (34.1%, 321/942)

Summary

Introduction

Coastal salt marshes are among the most common and productive coastal habitats on Earth and they play an important ecological role in the interface between marine and terrestrial environments [1]. There is considerable evidence that grid ditching may negatively impact the ecology of salt marshes by changing the vegetation composition [6], and decreasing habitat quality for semiaquatic invertebrates [1,6], fish [7], and wildlife [8]. With the aim of helping restore the natural ecology of salt marshes and to use more benign mosquito management practices, some conservation efforts have started to plug ditches [9]. Ditch plugging is expected to help marshes hold water in a more natural way during normal tidal flow and restore natural ecological functions [9]. Marsh conservation and mosquito control has usually focused on the effectiveness at controlling mosquito production of open marsh water management (OMWM), which is characterized by the targeted construction of tidal channels, ponds, and shallow radial ditches [10]

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Discussion

Conclusion