Term of Award

Summer 1991

Degree Name

Master of Science in Biology

Document Type and Release Option

Thesis (restricted to Georgia Southern)

Committee Chair

Daniel V. Hagan

Committee Member 1

Frank E. French

Committee Member 2

William S. Irby

Abstract

A portable, gasoline-powered suction device was used to collect adult Culicoides spp. from vegetation of the salt marsh and maritime forest of Sea Island in Glynn County, Georgia. Samples were taken for the 15-month period from April 1990 to June 1991. A total of 755 specimens, representing three species, C. furens (Poey), C. hollensis (Melander & Brues) and C. melleus (Coquillett), were aspirated. Samples were aspirated for two minutes from each vegetation type at least once each month. Of the total Culicoides spp. collected, 72% were from Juniperus silicicola. Spartina alterniflora provided 16% of the total specimens; Juncus roemerianus provided 6% of the total and the remaining 6% of the Culicoides spp. were collected from Baccharis halimifolia, Serenoa repens, and Borrichia frutescens.

Wing lengths of female C. furens collected over the 15-month period were 1.09 ± 0.01 mm and 1.0 ± 0.0 mm for males. Female C. hollensis wing lengths were 1.47 ± 0.04 mm and males were 1.44 ± 0.04 mm. Wing lengths for female C. melleus were 1.14 ± 0.11 mm, while males of this species were 1.2 ± 0.0 mm. Mean wing lengths for C. furens remained fairly constant during the summer and fall 1990, but increased in winter and spring 1991. Mean wing lengths of C. hollensis increased steadily starting in September, reaching a peak in February, then declined from February to July. C. malleus only showed a mean wing length decrease from May through August.

Study of the vertical distribution of larval Culicoides spp. in the salt marsh mud, using an 8 cm diameter by 19 cm deep core sampling method, revealed that the first centimeter depth of the salt marsh mud contained most (53%) of the total larvae from the sample. Thirty-three percent of the larvae were found in the second centimeter, 10% in the third and only 4% in the remaining 5 cm.

Laboratory assays of efficacy of four candidate control compounds (temephos, resmethrin, permethrin and dibrom) were tested on biting midge larvae, and non-target organisms collected from our study sites. Larvae were exposed to the four larvicides in water alone and in water with soil substrate. Temephos resulted in control of biting midge larvae and had the least toxicity on the non-target organisms tested (fiddler crabs, shrimp and fish).

Temephos was evaluated as a control agent for larval Culicoidesspp. in field trials by sampling check and treatment plots prior to, and 3, 24, and 48 hours after application of temephos at label rate (1.5 oz/acre) and 2X label rate. Larval populations were significantly reduced (62%) in samples taken 48 hours after application of temephos at label rate. Significant larval reduction occurred in test plots treated with temephos at 2X label rate at 3, 24, and 48 hours after application (76, 78 and 70% reduction, respectively).

All Culicoides spp. larvae (20) collected from a June 1991 transect were found in the region between 2 and 8 m out into the salt marsh. Highest numbers were found 4 m from the edge of the marsh. The vegetation in this zone was composed of a mix of S. alterniflora, D. spicata, Batis maritima, Salicornia virginica and J. roemerianus.

Significantly more C. furens were collected on north Sea Island from CDC light traps baited with both C02 and 1- octen-3-ol (octenol), than were collected from traps baited with octenol alone. Although not statistically significant, most C. furens, C. hollensis and C. melleus were collected from traps baited with both C02 and octenol, fewer from traps baited with C02, and fewest from traps baited with only octenol.

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