We studied the distribution of Forcipomyia taiwana (Shiraki) in Taiwan, and found this species almost island-wide. Midge seasonality was studied for 4 yr at 3 sites in Nantou, central Taiwan, to identify the extent and causes of midge population outbreaks. The midge population in 1995 was significantly lower than in 3 other years because several typhoons inundated breeding sites. Maximum populations of F. taiwana occurred in June, July, and August. There was a highly significant correlation between the monthly abundance of F. taiwana and temperature and rainfall. A step-up multiple regression indicated that temperature was the most important factor leading to the outbreaks of F. taiwana. Temperature increases from 15°C to near 30°C will increase the midge abundance.

An experimental survey was carried out in western Spain to investigate both the chronobiology of Hypoderma spp. and the immunoresponse of their bovine hosts. This study was initiated with a new system of obtaining Hypoderma spp. larvae directly from their host, including the eclosion of adults from their pupae, infestation under natural but controlled conditions, and confirmation of the resulting infection. This survey was carried out over 2 cattle grub seasons; it was possible to infest and reinfest the experimental animals and to monitor them by both parasitological methods and by an enzyme-linked immunosorbent assay. This method permitted the evaluation of the development of anti-Hypoderma antibodies during the experiment. The experimental design also enabled us to establish the period of detectable H. lineatum infection to be from December until the end of April with the largest number of warbles observed during March and April. After a pupal period of <30 d, adults were seen in April and May. Hypoderma bovis (de Geer) showed a delay of 2 mo relative to H. lineatum (de Villiers). This study reports a completed biological life cycle of Hypoderma spp. under controlled conditions in both natural and experimental environments.

Phlebotomine sand fly species composition and diversity were studied in Acosta, an area of Costa Rica endemic for cutaneous leishmaniasis. Two CDC miniature light traps per house were set overnight in 72 houses distributed in 6 localities, once a month, during the rainy seasons of 1994 and 1995. Of the 22 species collected, the most common were Lutzomyia serrana (Damasceno & Arouck), L. youngi Feliciangelli & Murillo, L. ylephiletor (Fairchild & Hertig), L. shannoni (Dyar), L. cruciata (Coquillett), L. gomezi (Nitzulescu), L. sanguinaria (Fairchild & Hertig), and Warileya rotundipennis (Fairchild & Hertig). The Czekanowsky index and the Sorensen index as modified by Bray and Curtis to consider abundance were used to compare species composition and β-diversity. Comparisons were made among localities within years, between years, and localities each year. The data strongly indicated that phlebotomine species composition is more stable than diversity or abundance.

An artificial membrane, blood-feeding method was used to assess the repellent and antifeedant effects of derivatives of salicylic acid on the biting midge Culicoides impunctatus Goetghebeur. Trans-2-hydroxycyclohexanecarboxylic acid, 6-methylsalicylic acid, 2,6-dihyrodxy-4-methylbenzoic acid, and salicyluric acid caused highly significant inhibition of feeding, with salicyluric acid performing significantly greater than the other compounds. Investigating the effects of alkyl substitution of salicylic acid, o-thymotic and o-cresotic acids were also effective. A pilot clinical trial using salicyluric acid indicated that it provided a protective effect and it was hypothesized that this may have resulted primarily from contact, because no significant repellent effects were shown for this compound in a microscope slide test, designed to demonstrate repellency with volatile compounds.

The hypothesis that dermally applied imidacloprid may transfer from treated cats, Felis catus L., to their immediate environment in quantities sufficient to have a significant effect on developing immature cat fleas, Ctenocephalides felis (Bouché), was tested in a controlled experiment. Flea eggs harvested from untreated donor cats were incubated on replicated samples from blankets used by treated or untreated cats under standardized conditions. As compared with controls, the percentage of adult flea emergence on blankets used by treated animals was reduced by 100% in the 1st wk after treatment and by 84, 60, and 74% in subsequent weeks (P < 0.001).

Spatial and temporal abundance patterns of anopheline larvae and their relationships with wetland conditions were studied in an endemic malaria area in northeastern Venezuela, where Anopheles aquasalis Curry is the main vector. Larvae were sampled over a 2-yr period in 7 wetland types (brackish and freshwater herbaceous swamps, mangrove swamps, freshwater ponds, clear-cut marsh forests, small irrigation canals, and swamp forests), covering 3 environmental gradients (salinity, aquatic vegetation, and habitat permanence). Twelve variables were quantified to describe each habitat. Two species of anophelines were collected. An. aquasalis was the species with the widest distribution, and its highest abundance was in the seasonal brackish mangrove habitat during the rainy season. An. oswaldoi Peryassu was rarely encountered, but was mainly associated with the dry season and with the permanent freshwater wetlands (such as ponds). Principal components and correlation analyses revealed that the physicochemical (salinity, dissolved oxygen) variables of the wetland were associated most strongly with the spatial distribution of both species. Variations in salinity were strongly associated with the abundance of An. aquasalis. Both the occurrence and abundance of An. oswaldoi were most closely correlated with dissolved oxygen. Changes in seasonal abundance of both species were associated with rainfall. The relevance of these results to vector control in northern Venezuela is discussed.

The phenology of intrapuparial development in Oestrus ovis L. is described, based on 302 specimens collected from the head cavities of goats and reared in the laboratory at a photoperiod of 12:12 (L:D) h and 32 and 16°C. Dissection and histology of puparia at pupariation and at 3, 6, 9, 12, 15, 18, 21, 24, 30, 36, 42, 48, 66, and 72 h after pupariation and every day of the intra-puparial period showed that pupariation was achieved in ≈12 h in heavily pigmented larvae (range, 2–46 h in postfeeding period). Larval-pupal apolysis began immediately after pupariation and was completed by 18–36 h after pupariation (prepupal period). The cryptocephalic pupa was found from this time to the 5th d, when head eversion occurred. Pupal-adult apolysis was initiated before head eversion and completed by day 7. The pharate adult presented progressive coloration in compound eyes (transparent, white, yellow, orange, red, brown, silver) while integumental pigmentation and sclerotization were in progress. Adult emergence occurred at 22 and 23 d in males and females, respectively. Changes in the weekly puparial weight of specimens reared under both field and laboratory conditions was described. It was concluded that although the intra-puparial development of O. ovis displayed some unique characteristics, it was essentially similar to other cyclorraphous flies. The actual pupal period of O. ovis lasted from the 2–7 d postpupariation, whereas approximately two-thirds of the intrapuparial period was used for the maturation of the pharate adult.

A protocol was developed for significantly reducing resident midgut bacteria in newly emerged anopheline mosquitoes using a combination of antibiotics. Pupa harvested from colony-reared Anopheles gambiae s.l. Giles and Anopheles stephensi (Liston) were placed in cages wiped previously with 70% alcohol and kept under UV light for 24 h. Emerging adult mosquitoes were fed for 3 consecutive days on antibiotic solution, consisting of 0.4% gentamicin sulfate and 1% penicillin-streptomycin solution in a 10% sterile sucrose solution. Bacterial suspensions of Escherichia coli, Klebsiella pneumoniae (Schroeter, 1886), and Pseudomonas stutzeri (Lehmann & Neumann, 1896) isolated from wild-caught anophelines were fed to antibiotic-treated mosquitoes starved for 24 h via either sugar or membrane-feeding. Mosquitoes dissected 1 and 24 h after blood-feeding or sugar-feeding, and plated on trypticase soy agar plates, yielded the same type of bacteria fed originally without evidence of contaminants. There was no residual effect of the antibiotics on introduced single bacteria strains as judged by the presence of bacteria in antibiotic-treated mosquitoes. This experimental reduction of resident midgut bacteria and their replacement with single strains in newly emerged anopheline mosquitoes should facilitate further investigations of the interactions between malaria parasites and bacteria found in the midguts of mosquitoes.

The effects of method of infection and virus dose on the viremia and antibody responses of 1-wk-old chicks and after-hatching-year house finches to infection with western equine encephalomyelitis (WEE) and St. Louis encephalitis (SLE) viruses were studied under laboratory conditions. Using a capillary tube technique, females from 2 strains of Culex tarsalis Coquillett mosquitoes were estimated to expectorate from 1.0 to 1.7 log₁₀ plaque forming units (PFU) of WEE and from 1.9 to 2.2 log₁₀ PFU of SLE. Based on the proportion of parenterally infected females that transmitted and the number that blood fed during each experiment, virus doses per bird were estimated to be 1.0–1.9 log₁₀ PFU for WEE and 1.4–2.3 log₁₀ PFU for SLE. When infected with comparable doses of WEE by subcutaneous inoculation, there was no significant difference in the duration or magnitude of the viremia response between birds infected by mosquito bite or syringe; few birds developed a viremia response after infection with SLE, precluding analysis. In chickens, increasing the syringe dose of WEE from 0.3 to 1.7 log₁₀ PFU/0.1 ml shortened the time when viremia first appeared from 3 to 1 d postinfection and increased the duration of the viremia period from 1 to 3 d, but did not alter the maximum viremia titer. In house finches, increasing the syringe dose of WEE from 2.6 to 3.3 log₁₀ PFU/0.1 ml did not alter markedly the viremia response. Most birds developed antibody detected by enzyme immunoassay (EIA) or plaque reduction neutralization test (PRNT). In chickens, WEE EIA levels and PRNT titers were higher for birds infected by syringe than by mosquito bite, whereas in house finches the pattern was reversed. For birds infected with SLE, there was overlap among groups infected by mosquito bite or syringe. These results indicate that subcutaneous syringe inoculation provides a biologically sound mode of infection that did not alter viremia and antibody responses when compared with infection by mosquito bite.

Adult house finches from Kern County were inoculated subcutaneously with recent sympatric and allopatric isolates of western equine encephalomyelitis and St. Louis encephalitis (SLE) viruses made from Culex tarsalis Coquillett collected in Kern County and Coachella Valley, CA, respectively. Virulence, as measured by the amplitude of the viremia response during days 1 and 2 postinfection, varied significantly among strains, but independently of geographic origin. The intensity of the immune response, as measured by an enzyme immunoassay and a plaque reduction neutralization test, seemed to be independent of virulence, especially for SLE where some strains failed to produce a detectable viremia but elicited a strong antibody response. Our preliminary data indicated that strain virulence may be associated with the level of enzootic activity during the year of isolation.

When Borrelia burgdorferi B31 low passage strain spirochetes were directly injected into the hemocoel of Dermacentor variabilis (Say) females, the bacteria were cleared from the hemocoel within <24 h. Viable spirochetes were not found in hemolymph, salivary gland, or ovary tissues by subculturing or by IFA. The hemocyte population increased ≈6 times within the first 6 h after inoculation compared with the uninoculated controls. In contrast, the soluble total hemolymph protein content decreased inversely with the increase in hemocytes. Borreliacidal activity was demonstrated with cell-free hemolymph from D. variabilis. In vitro antimicrobial assays using hemolymph from borrelia-challenged and nonchallenged ticks resulted in 72% spirochete reductions compared with only 11.5%, respectively, within 1 h. Additional evidence of induced antimicrobial hemolymph protein activity was demonstrated by SDS-PAGE, which revealed upregulation of a lysozyme-like peptide (≈15 kDa) (22% increase) and the induction of a ≈5.8 kDa peptide in the B. burgdorferi-challenged ticks. In contrast with the nonvector borne Bacillus subtilis, D. variabilis presented a rapid and robust response to challenge with cultured B. burgdorferi spirochetes and lead to their early elimination. The role of the tick immune system, including possible differences between vector and nonvector ticks, in determining the success of invasive bacteria is discussed.

Feces from Triatoma infestans (Klug) infected with TrV showed a large number of well-preserved viral particles when examined by electron microscopy. No viral particles were observed in suspensions of feces from uninfected insects. Fecal suspensions inoculated parenterally into uninfected triatomines killed the insects within 36 h, showing that infective TrV is present in the feces of infected insects. It also is demonstrated that T. infestans becomes infected with TrV while feeding on contaminated chickens, and all the chickens used to feed a colony of triatomines infected with TrV showed high anti-TrV titer in their sera, although no TrV replication could be demonstrated in chickens. Oral infection of T. infestans by contaminated feces probably contributes to virus dispersal in nature. This observation provides the rationale for the potential use of TrV as a biological control agent.

Human monocytic ehrlichiosis is an emerging zoonosis caused by infection with Ehrlichia chaffeensis Anderson, Dawson, Jones & Wilson, which is transmitted to mammals by ixodid ticks. Prevalence of infected ticks and distribution of infection foci indicate relative risk of human exposure to ehrlichiosis and may be influenced by factors such as geographic isolation, human disturbance, and the availability of suitable mammalian reservoir hosts. To test this, individual and pooled lone star ticks, Amblyomma americanum (L.), were collected from three populations from the Georgia coast (1 mainland site and two barrier islands) and screened for E. chaffeensis. A species-specific, nested polymerase chain reaction (PCR) assay was used to amplify a 572 bp fragment of the E. chaffeensis 16S rRNA gene from infected ticks. PCR product specificity was confirmed by nucleotide sequencing. Our results showed the prevalence of infected ticks to be 0.0% (n = 151), 0.9% (n = 111), and 9.3% (n = 129) for Sapelo Island, St. Catherine’s Island, and Fort McAllister, respectively.

Laboratory bioassays and field trials were carried out to study the effect of metallic copper on the development of Aedes albopictus (Skuse). Multiwire electric cable was used as a source of metallic copper. Three different doses were used in laboratory tests (5, 10, and 20 g/liter) and two in field tests (20 and 40 g/liter). In the laboratory, 10 g/liter induced high mortality and a lack of development in Ae. albopictus larvae and doses of 20 g/liter completely inhibited development. Larval mortality was higher in earlier instars than in third through fourth instars and pupae. No effects were reported on egg hatching. Copper ion concentration in water increased up to 574 ppb for 5 g/liter dose, 710 ppb for 10 g/liter dose, and 1,210 ppb for 20 g/liter dose, within week 6. The increasing concentration of copper in water was correlated positively with the decreasing production of adults. Copper ions concentration <500 ppb did not or only slightly affected larval development and mortality of Ae. albopictus in laboratory tests. Copper concentrations between 500 and 1,000 ppb delayed larval development and caused high mortality. Copper concentrations >1,000 ppb inhibited larval development completely killing all the larvae. This last result has been achieved by the use of a 20 g/liter dose of metallic copper in water. Copper also affected adult weight. In field trials, 20 g/liter reduced the number of larvae in treated pots by 90%, and 40 g/liter completely prevented oviposition. Moreover, the persistence of the toxic action of metallic copper in the field lasted for several months.

Field tests showed that Anopheles gambiae s.l. from 4 villages in Gokwe District, Midlands Province, Zimbabwe, were susceptible to 4% DDT, 0.025% deltamethrin, 0,025% alphacypermethrin, and 0.1% lambdacyhalothrin. In the laboratory, F₁ progeny of field-caught females that were identified as Anopheles arabiensis Patton were completly susceptibile to deltamethrin, alphacypermethrin, lambdacyhathrin, and DDT. The use of insecticides in Gokwe district has not yet induced detectable resistance in An gambiae s.l.

Phlebotomus simici Theodor and P. brevis Artemiev & Dergacheva are closely related species in the subgenus Adlerius that only may be identified by the male terminalia. Females only may be differentiated by collecting them in copula. Because females of P. simici may be involved in Leishmania transmission, their identity should be verified. Our study separated individuals from 2 sympatric populations in Lebanon by means of agarose enzyme electrophoresis. Differential patterns were found at the PGM and HK loci. Results were confirmed by morphological reexamination of female spermathecae and pharyngeal armature.

Two species of mosquitoes reared to adults from field-collected larvae or egg rafts in or near Los Angeles County, CA, were exposed to dogs with known levels of Dirofilaria immitis (Leidy) microfilariae per 20 cubic millimeters of blood. Aedes taeniorhynchus (Wiedemann) readily blood fed on an infected dog ingested microfilariae but did not become infected. Culiseta incidens (Thomson) also fed on an infected dog became infected, and 10% of the microfilariae developed to the L₃ stage. Cs. incidens is a peridomestic species broadly distributed in Los Angeles County and abundant from February through December. The wide distribution of this species as well as its long annual period of reproductive activity in Los Angeles County may contribute to its potential as a vector of D. immitis.