Hosts of Lutzomyia shannoni (Diptera: Psychodidae) in relation to vesicular stomatitis virus on Ossabaw Island, Georgia, U.S.A.

Hosts of Lutzomyia shannoni Dyar, a suspected biological vector of the New Jersey serotype of vesicular stomatitis (VSNJ) virus, were determined using an indirect enzyme-linked immunosorbent assay (ELISA) of 333 blood-fed female sandflies collected from their diurnal resting shelters on Ossabaw Island, Georgia, U.S.A. Sandflies had fed primarily on white-tailed deer (Odocoileus virginianus) (81%) and to a lesser extent on feral swine (Sus scrofa) (16%), two species of host infected annually with VSNJ. Other hosts were raccoons (Procyon lotor) and horses (Equus caballus) or donkeys (E. asinus), with only two (< 1%) mixed bloodmeals from deer/raccoon and deer/swine. A larger proportion of feedings on feral swine was detected in maritime live oak forests than in mixed hardwood forests. These findings are consistent with the hypothesis that L.shannoni is a primary vector of VSNJ virus on Ossabaw Island.

Bionomics of Anopheles quadrimaculatus and Culex erraticus (Diptera: Culicidae) in the Falls Lake basin, North Carolina: seasonal changes in abundance and gonotrophic status, and host-feeding patterns.

Larval and adult Anopheles quadrimaculatus Say (sensu lato) and Culex erraticus (Dyar & Knab) were collected at Falls of the Neuse Lake (Falls Lake) in North Carolina from May 1985 to December 1986. Adult mosquitoes were aspirated weekly from shelters in woodlands adjacent to larval sampling sites. An. quadrimaculatus and Cx. erraticus comprised > 95% of the total number of mosquitoes collected. An. quadrimaculatus adults exhibited vernal and autumnal peaks of abundance during both years. Cx. erraticus adults exhibited several peaks of abundance in summer and early fall of both years. An. quadrimaculatus initiated blood feeding in May and April 1985 and 1986, respectively. Only unfed females were found in late fall and winter. Cx. erraticus initiated blood feeding earlier than An. quadrimaculatus. In 1985, approximately 25% of the females in the first collection in May contained a blood meal, whereas in 1986, approximately 10% of the females in the first collection in April were blood fed. Females of both species ceased blood feeding in late fall. Larvae were sampled on a weekly basis from lake edge, flood plain, and creek edge habitats. Generally, An. quadrimaculatus larvae were most abundant in lake edge and flood plain habitats, whereas Cx. erraticus larvae were most abundant in the creek edge habitat. The population dynamics of An. quadrimaculatus were associated with seasonal changes in the level of Falls Lake. In 1985 and 1986, the level of Falls Lake gradually declined from May to mid-August until heavy rainfall caused a 1-m rise in lake level. Populations of An. quadrimaculatus larvae and adults increased significantly following the rise in the level of Falls Lake. In contrast, the abundance of larval and adult Cx. erraticus decreased with rising lake levels in late August. Water level management should be an effective method for controlling populations of An. quadrimaculatus but not for Cx. erraticus. Blood-fed mosquitoes were tested to identify bloodmeal hosts using both capillary precipitin and enzyme-linked immunosorbent assays. An. quadrimaculatus (n = 941) predominantly (99%) fed on mammals, principally white-tailed deer and horses. Cx. erraticus (n = 348) exhibited an opportunistic host-feeding pattern; blood meals were taken from mammalian (49%), reptile or amphibian (20%), and avian (31%) hosts.

Conspecificity of the ticks Ixodes scapularis and I. dammini (Acari: Ixodidae).

Reciprocal crosses between Ixodes dammini Spielman, Clifford, Piesman & Corwin from Massachusetts and Ixodes scapularis Say from Georgia produced offspring through the F3 generation when the experiment was discontinued. Reciprocal I. dammini x Ixodes pacificus Cooley & Kohls (California) and I. scapularis x I. pacificus crosses produced F1 progeny; however, all progeny were sterile. Assortative mating experiments between I. dammini and I. scapularis indicated that males and females of both species mated with the opposite sex of heterospecific or conspecific ticks when there was a choice. Conventional discriminant analysis of morphometric measurements of ticks from Georgia, North Carolina, Maryland, Massachusetts, and two populations of F1 hybrids indicated that there were recognizable differences. However, size-free (sheared) discriminant analysis indicated that these differences were largely size-dependent, with much overlap of the four eastern and two hybrid populations but no overlap with I. pacificus from California. Analysis of chromosomes (morphology and C band) indicated no differences between the Georgia and Massachusetts populations but showed a difference between them and the California population of I. pacificus. Analysis of isozymes showed that the genetic identity value for the Georgia and Massachusetts populations was within the normal range for conspecific populations, whereas the California population indicated congeneric but not conspecific relatedness to the Georgia and Massachusetts populations. Life cycle data collected under similar laboratory conditions showed no differences in length of feeding and molting periods among Georgia, Massachusetts, and California populations. These data and results of the work of other authors on tick host preferences and vector competence indicate that I. dammini is not a valid species separate from I. scapularis. Because the name Ixodes scapularis Say, 1821, has priority over the name Ixodes dammini Spielman, Clifford, Piesman & Corwin, 1979, I. dammini is relegated to a junior subjective synonym of I. scapularis (based on Article 23 of the International Code of Zoological Nomenclature).

Attempted mechanical transfer of Ehrlichia risticii by tabanids (Diptera: Tabanidae).

The ability of tabanid mouthparts to retain and to transfer mechanically Ehrlichia risticii Holland, Weiss, Burgdorfer, Cole & Kakoma was evaluated by feeding flies on infected and noninfected mice and on capillary tubes containing infected cells and cell-free medium. Flies representing two genera and 29 species were collected at equine boarding stables, farms, and along riding trails in Wake, Johnston, and Duplin counties in North Carolina for the feeding trials. Two species, Tabanus fulvulus Wiedemann and T. pallidescens Philip, fed on mice but failed to transfer the pathogen from infected to susceptible mice. Chrysops vittatus Wiedemann, Tabanus americanus Forster, and T. sulcifrons Macquart transferred E. risticii-infected cells from capillary tubes containing infected cells in medium to tubes containing medium. These studies document that E. risticii-infected cells can be retained on mouthparts and potentially transferred by tabanids.

Spatial and temporal distribution of resting female mosquitoes (Diptera: Culicidae) in the coastal plain of North Carolina.

The spatial and temporal distribution of 28 species of female mosquitoes resting in natural (swamp, woods, and swamp-woods ecotone) and human-made (beneath bridges) habitats in blackwater stream-associated ecosystems in Duplin County, N.C., was determined by sampling with a D-Vac vacuum aspirator during 1984 and 1985. Two types of resting distributions were evident. In type one, species including Aedes atlanticus Dyar & Knab, Ae. canadensis (Theobald), Ae. triseriatus (Say), and Psorophora ferox (von Humboldt) rested predominantly on vegetation and were not collected beneath bridges. In type two, species including Anopheles punctipennis (Say), Culex erraticus (Dyar & Knab), Cx. peccator Dyar & Knab, Cx. pipiens L. and Cx. quinquefasciatus Say and their hybrids, Cx. restuans Theobald, Cx. territans Walker, and Uranotaenia sapphirina (Osten Sacken) rested on vegetation, in natural shelters in swamp habitats, and beneath bridges. Differences in the proportion of gravid mosquitoes among habitats were evident for Ae. canadensis, An. punctipennis, Cx. pipiens and Cx. quinquefasciatus and their hybrids, Cx. restuans, Cx. territans, Ps. ferox, and Ur. sapphirina, indicating that gonotrophic condition may influence resting site selection.

Immunoblot analysis of digestion of human and rodent blood by Aedes aegypti (Diptera: Culicidae).

The digestion of human and rodent blood by Aedes aegypti (L.) was investigated by immunoblot analysis, using polyclonal antisera produced against serum proteins. Rates and patterns of digestion of the principal proteins in serum (albumin and immunoglobulin G) appeared to differ depending on the source of blood. Overall, most intact proteins disappeared 24-48 h after blood ingestion by Ae. aegypti, and albumin and immunoglobulin G appeared to be the most persistent proteins, irrespective of the source of blood.