Diking, or building a wall to contain spoil on dredge 

 islands, was initiated in North Carolina more than a 

 year ago. Dikes are designed to slow the erosion of 

 spoil into waterways. One of the unforeseen effects of 

 diking appears to be an increase in mosquitoes. 



Diking makes headaches 

 for state entomologist 



Diking has created new headaches for state 

 entomologist Don Ashton. Since last year when 

 dredge island diking was begun in North Carolina, 

 he's been in a quandary over how to control the 

 hordes of mosquitoes hatching on the diked spoil 

 islands. 



Conditions perfect for salt marsh mosquito 

 production begin as the spoil dries and cracks, 

 Ashton explained. Mosquitoes deposit eggs on the 

 walls of the cracks. Rain water collects in the 

 cracks, providing moisture needed for the mosquito 

 eggs to hatch, he said. "We've seen literally mil- 

 lions of mosquito larvae on the diked islands," 

 Ashton said. 



"Salt marsh mosquitoes have been known to fly 

 65 miles," he continued. "So you can imagine what 

 happens to people on the beach one-half mile 

 away," he said. 



While Ashton and his co-workers in the state's 

 Division of Health Services Solid Waste and Vec- 

 tor Control Branch have been able to explain the 

 problem's cause, they're pretty much at a loss for 

 its cure. Flooding the islands or covering them 

 with sand to eliminate areas where mosquitoes lay 

 eggs are proposed remedies. Chemical treatment 

 could be another, Ashton explained. But those 

 methods require money and manpower which 

 neither the state nor the counties have, he added. 



"My contention is that it isn't the responsibility 

 of the county or state to rectify the situation," Ash- 

 ton said. He believes instead that permanent steps 

 to eliminate the problem should be taken as the 

 spoil is being dumped. 



"It's just not economically feasible to treat the 

 problem over and over," he said. 



What is needed is research, the state's top in- 

 sect expert said. "We need an entomologist and an 

 engineer to work on this," Ashton said. He cited 

 Dr. R. C. Axtell's research at North Carolina State 

 University as a beginning. "But we need an engi- 

 neer who can communicate with engineers in- 

 volved with dredging," he said. 



Seeking insect controls 



(Continued from page 1) 



Diking, it appears, sets up ideal conditions for 

 the production of some kinds of mosquitoes. As the 

 dredged material dries, permanent cracks form in 

 the spoil. Mosquitoes lay eggs inside the cracks. 

 With the right amount of rain later on, the eggs 

 hatch, producing a horde of mosquitoes. 



While understanding the relationship between 

 diking and insect production poses a significant 

 problem, the real challenge lies ahead in finding 

 ways to control large outbreaks, according to 

 Axtell. 



Flooding the islands or blanketing them with 

 sand — two proposed solutions — would wipe out the 

 mosquito breeding grounds. But in Axtell's view, 

 neither solution is practical because of tremendous 

 expenses involved. 



Chemical insecticides may offer a temporary 

 solution, the scientist said in a February interview. 

 Careful study will be required to find ideal chemi- 

 cals — those that can reduce the mosquito popula- 

 tion without harming the delicate estuarine en- 

 vironment. 



A class of chemical called insect growth regula- 

 tors (IGR), now under study as a possible control 

 method, appears promising, Axtell said. IGR works 

 to interfere with the mosquito's development from 

 one stage to another and appears to affect only 

 mosquitoes, he explained. More research is needed, 

 however, to make sure IGR doesn't interfere with 

 the development of shrimp and other marine Crus- 

 tacea. 



A refined petroleum product, which has proved 

 to be an effective mosquito control, can be safely 

 applied on the islands, Axtell continued. However, 

 application must be closely controlled and timed so 

 that the product, which breaks down, or loses its 

 effectiveness, quickly, hits its target, he said. 



Further research may show ways of handling 

 dredge spoil to reduce the creation of mosquito- 

 breeding areas. This would provide a more long 

 term solution, Axtell said. 



The end of the problem is not foreseeable since 

 dredging is an ongoing activity that each year adds 

 more spoil to the islands, the scientist explained. 

 When the currently-used diked islands are filled in 

 several years, others will take their place and still 

 more potential mosquito breeding grounds will be 

 created. 



— Gayle Morton 



