Term of Award

Winter 1985

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

W. Keith Hartberg

Committee Member 2

Richard L. Osburn

Abstract

The seasonal abundance of adult Culicoides spp. on a coastal Georgia barrier island was determined during a 20-month period, September 1983 through May 1985 by CO2-baited CDC miniature light traps and sticky cylinder traps.

A total of 220,670 adult biting midges representing nineteen species and including the first report of C. loughnani Edwards in Georgia was collected. Culicoides furens (Poey), C. hollensis (Melander and Brues), and C. melleus (Coquillett) were the most abundant. Culicoides furens was abundant from early spring to late fall. Culicoides hollensis and C. melleus were bimodal with spring and fall abundance, but C. melleus appeared later in the spring and disappeared sooner in the fall. Adult light trap catches were statistically significant for temperature, but not for rainfall, wind velocity or moon phase.

Culicoides spp. larvae (5717) were recovered from salt marsh substrate and correlated with vegetation type, elevation, soil pH and soil mineral content of calcium, magnesium, phosphorus and potassium. Larvae of C. furens were most abundant in areas dominated by Spartina alterniflora Loisel (<1.2 m) and at an intermediate elevation between the low and high water mark. Larvae of C. hollensis were most abundant in areas dominated by tall S. alterniflora (>1.2 m) at an elevation located near the mean low water mark. Larvae of this species were found to be statistically significant for elevation and phosphorus. Larvae of C. melleus were found mostly in areas characterized by Distichlis spicata L. and at an elevation located near the high water mark. Soil was found to be acidic with a mean value for all species of pH 5.6. Characteristics of larval habitat and adult emergence sites coincided well by species for environmental parameters measured.

Substrate samples from the coastal Georgia salt marsh were also found to provide habitat for other ceratopogonid Diptera, Dasyhelea atlantis Wirth and Williams, D. mutabilis (Coquillett) and Leptoconops linleyi Wirth and Atchley. This is the first report of L. linleyi from the state of Georgia.

Larval head capsule measurements were made and head ratios calculated to determine instar number for the three dominant salt marsh species. Analysis of variance for headlength, headwidth and head ratio values revealed statistically significant differences for inter- and intraspecific instars. Dyar's growth progression factors were 1.34 for C. furens, 1.49 for C. hollensis and 1.25 for C. melleus.

Seasonal incidence of larval instars was compared with adult abundance to predict life cycle and development. Lower larval densities of C. hollensis and C. melleus were present in spring and fall, coinciding with periods of adult abundance. High larval densities in winter and summer may indicate that these species have two generations per year. A majority of third-instar C. furens may indicate both autogenous and anautogenous races in the population.

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