Reproduced from the Proceedings of the 71st Annual Meeting of the NJMCA. Please use the following citation when referring to this article:
Romanowski. M., and Candeletti, T. M. 1984. Identification and surveillance of Coquillettidia perturbans breeding habitat, with observations on larviciding techniques, in Ocean County, N.J. Proc. N. J. Mosquito Control Assoc. pp. 54-58.
Michael Romanowski and Thomas M. Candeletti
Ocean County Mosquito Commission, P.O. Box 327, Barnegat, N.J. 08005
INTRODUCTION: During the latter part of the 1983 mosquito season, four horse deaths were reported in Jackson Township, Ocean County. These were confirmed by the State Health Department to be a result of Eastern Equine Encephalitis.
Isolated collections made in the immediate area were tested, yielding EEE virus from samples of Coquillettidia perturbans. Knowing this, there was a need on the part of the Ocean County Mosquito Commission to identify and document Cq. perturbans breeding habitat in the surrounding area. Once the breeding areas were identified, steps could be taken to eliminate the mosquito) problem.
Prior to the horse deaths, this area never had a history of high mosquito populations, and had no recent record of the presence of EEE virus. Relatively few complaints have ever been received from the residents of this part of the county. It has always been a minor problem area when compared to the coastal mosquito problem in the county, and due to the limited time, Cq. perturbans breeding areas could not be sampled or treated effectively. This was due to the difficulty of the sampling technique available at the time. In light of this new vector problem, however, we have been identifying and documenting the breeding areas, and conducting surveillance of the populations Cq, perturbans, in the surrounding area.
IDENTIFICATION OF HABITAT: The first step in identifying the breeding habitat was to determine where to check for breeding. Knowing that Cq. perturbans is always found associated with the roots and stems of emergent vegetation surrounding bogs, ponds, lakes, etc., all possible breeding sites were selected and inspected. These sites were selected with the use of topographic maps and aerial photographs of the area.
Once all possible areas were identified, each of the areas was surveyed, both by ground and air, for the presence of emergent vegetation.
Many areas were overgrown and well drained with little or no emergent vegetation. These areas therefore could not produce large numbers of Cq. perturbans and were not considered to be a problem area. Several areas were found that had the desired habitat. The largest of these areas, with the most emergent vegetation, being the Butterfly Bog group and Jackson Mills Pond.
Both of these are freshwater areas that were altered by man to create a large body of water. Both have a good water flow rate but it is insufficient to create a steady movement of water along the shallow edges of the pond. This allows regions of emergent vegetation to develop.
The Butterfly Bog area is composed of a group of old abandoned cranberry bogs that is now part of a Fish and Wildlife Management area. It has a zone of emergent vegetation ranging from 2 to 20 feet along the banks and a depth up to around 5 feet. The water depth in the emergent vegetation is around 6 inches to 2 feet.
The emergent vegetation consists mostly of Swamp Loosestrife (Decodon verticillatus) with small amounts of Cattail (Typha angustifolia), Arrow Arum (Peltandra virginica), and Buttonbush (Cephalanthus occidentalis).
Jackson Mills Pond is a man-made pond with a depth of 6 to 8 feet. It has a zone of emergent vegetation ranging from 3 feet to 10 feet in some areas. However, the entire north end of the pond is covered with emergent vegetation and several "islands" of emergent vegetation cover the pond. The water depth in the emergent vegetation varies from 10 inches to 3 feet. The vegetation consists mainly of Swamp Loosestrife, but small amounts of Arrowhead are present.
Once the areas were established, the next step was to go in and sample for the presence of Cq. perturbans larvae. Historically, Cq. perturbans larvae are hard to sample for because they attach themselves, by means of a modified air tube, to the roots and stems of emergent vegetation, where they remain throughout development. They do not have to come to the surface like other mosquito larvae and are also very quick to remove themselves from the host plant when disturbed. (Carpenter & LaCasse, 1955).
The larval sampling technique used was very simple and is similar to the method used by McNeel (1931). Clumps of emergent vegetation, with the root mats, were ripped up and quickly placed in a bucket of clear water. The clump was then shaken vigorously to dislodge larvae attached to the root mats and plant stems. After allowing several minutes for the organic debris to settle down, the contents of the bucket were checked by taking dip samples from the bucket and examining thoroughly for larvae. The whitish larvae stood out in the debris and were relatively easy to find. Letting the bucket stand for several minutes forced the larvae, now having nothing on which to attach themselves, to come to the surface. This can make sampling easier, however, it is still best to sample the entire contents of the bucket for accurate results.
In this manner, the relative larval abundance or larval population density was determined based on the number of larvae found per mat of vegetation. This method met with varied success. Counts ranged up to 30 to 35 larvae per mat of vegetation. The drawbacks to this procedure were that it was rather time consuming and also made a muddy disaster of the area being checked. It also destroys habitat, thereby making it difficult to do correct population estimations or to return to the same location to detect population density changes.
Emphasis was placed on identifying the largest areas with the largest amounts of breeding habitat. Also, emphasis was placed on their proximity to the cases of EEE. Based on these criteria, two major areas were identified; the Butterfly Bog area and the Jackson Mills Pond.
A third large area, Bennetts Mills Pond, was identified. But due to its distance from the EEE cases and the low amounts of larvae collected there (around 5 to 7 larvae per vegetation mat) it was not considered a major problem area. However, it will be monitored in the future.
Adult Surveillance: During the latter part of the 1983 season, light traps were placed out at the Butterfly Bog breeding site, and at two of the sites of EEE cases, Frank Applegate Road and Harmony Road. Data from these traps were used to determine the predominance and population levels of Cq. perturbans in the area. Since the light traps were placed out after the first incidence of virus there were no data from the early season to make any comparisons.
Based on our light trap collections, Cq. perturbans made up to 36% of the light trap catch around the time of the occurrence of the EEE cases (Table 1). It was also the most predominant of the ten mosquito species that were collected from the light traps. Later in the season, Cq. perturbans only made up 5% of the catch in the light traps (Table 1). These data indicate that Cq. perturbans was the predominant mosquito at the time of the EEE outbreak and, therefore, a likely candidate for a vector of the disease. It also showed that population levels dropped off quickly towards the end of the season.
Table 1: Mosquito Predominance in Butterfly Bog Light Trap
SPECIES: AUGUST 1983 COLLECTED, SEPTEMBER 1983 COLLECTED
In the future, light traps will be placed out at the beginning of the season so that an adult population curve can be established. Emergence traps, of the kind designed by Dr. Marc Slaff (1983) and his associates of Polk County, Florida, will also be used to determine adult Cq. perturbans produced per area of emergent vegetation.
The two adult surveillances, along with the larval surveillance technique, will provide us with a large data base on the Cq. perturbans populations.
This, in turn, could be used to indicate when adult populations are high and would require an adulticide treatment. It can also be used to indicate when Cq. perturbans larvae are abundant and a larvicide should be attempted, thereby possibly foregoing an adulticide treatment.
Larviciding Techniques: Larval control was tried once in 1983 in the form of an aerial spray of granular Abate.
Control of Cq. perturbans larvae is difficult due to the fact that they are present in the root mats and stems towards the bottom of the pond or bog. It is difficult for enough pesticide to physically reach this area and there is also an abundance of organic material that would cause the rapid breakdown of the pesticide. So you must spray the proper amount of pesticide to reach the bottom .and the larvae before it breaks down.
In our larvicide, Abate 5G was used with our aerial granular application system. Normally, on the salt marsh, we apply this material at a rate of 2 lbs. per acre. However, since Cq. perturbans are in the root mats, we anticipated that a heavier application rate would be needed. This was accomplished by applying at 4 lbs. per acre. Only the areas of emergent vegetation around the bogs were treated. This rate seemed to give good coverage and was still below the maximum rate allowed by the label.
Upon backchecking, using our larval sampling technique, there was a reduction of larvae present per mat of vegetation. In areas where 30 to 35 larvae per mat were collected before the spray, 5 to 10 were found after the spray. This seemed to give us a reduction of up to 60% of the larval population. Also, dead larvae were found in different collections.
CONCLUSIONS: Based on this post-spray collection, there was an indication that the larvicide had some effect. However, because of the variability of sampling (i.e. amounts of vegetation uprooted, how well contents were checked, etc.,) it is only an indication and does not offer any solid evidence on which to base the effectiveness of the spray. In the future, we plan to look for more effective methods of control.
This calls for the use of a better technique to determine the effectiveness of the larvicide spray. Emergence traps should be able to provide us with these data.
These traps, placed out at pre and post spray periods, could provide us with information on the number of adults produced per area. By comparing the two sets of data, along with a control group, a determination, on whether or not a significant change in the number of adult Cq. perturbans being produced, can be made. This, in turn, can give a determination on the effectiveness of the larvicide.
Also, we plan to look at the effectiveness of different application rates of Abate, as well as different agents, such as B.t.i. and Altosid. This can be varied even further by using different formulations such as granular, briquets or pellets, and different carriers, such as sand, celetom or corn cob.
Carpenter. S. J. and W. J. LaCasse. 1955. Mosquitoes of North America University of California Press, Los Angeles. 353 p.
Slaff, M. and J. Haefner, R. Parsons, F. Wilson. 1983. A Modified Pyramidal Emergence Trap for Collecting Mosquitoes. P.O. Box 39, Bartow, Florida. (In Press).
Return to NJ Species List