A variety of pathways exist for the introduction of nonindigenous insects, ticks, and mites of veterinary importance into the United States. The most prominent includes the natural migration of mosquitoes and flies by the flight of adults, ectoparasites entering the country on wildlife transport hosts, and accidental introductions on animals legally imported through United States Department of Agriculture (USDA) quarantine facilities. Examples of the establishment and subsequent eradication of exotic pests of livestock are presented to illustrate the critical role of the USDA in protecting American agriculture with particular emphasis on the southern cattle tick, Boophilus microplus (Canestrini), the cattle tick, B. annulatus (Say), and the screwworm, Cochliomyia hominivorax (Coquerel). Priority group rating of nonindigenous arthropod pests and disease vectors are discussed. Although the primary responsibility for preventing the introduction and establishment of arthropods that affect livestock and poultry rests on the shoulders of USDA professionals, insect surveys by extension entomologists along with observations by research specialists and producers are also important in detecting exotic arthropod species. Animal health professionals from all sectors of the livestock and poultry industries may well be the first line of defense from the introduction of nonindigenous arthropods and the diseases they transmit.

During the 1997 season of Ixodes persulcatus Schulze tick activity, 579 specimens were collected by flagging in the vicinity of St. Petersburg (Morskaja, Lisy Nos). Collections were made from April to July, and at each collection time the following measurements were recorded: light intensity (in lux); temperature of soil 1–1.5 cm below leaf litter, at the soil surface, and in the air 1.5 m above the soil surface; and relative humidity. The gradient between soil at a depth of 1–1.5 cm and soil surface temperatures appeared to be the main physical parameter that initiated tick migration out of the leaf litter. At soil temperature intervals of 5–10°C and 21–26°C, ticks were found only when the soil temperature 1–1.5 cm below the soil surface was colder than at its surface. When temperature ranged from 11 to 20°C, 24% of the ticks were collected when the surface temperature was colder than that below the soil surface. Sixty percent of the ticks, especially nymphs, were collected when the soil surface and subsoil temperature difference ranged from 0 to 2.0°C. The gradient between soil temperature and relative humidity appeared to increase the importance of the gradient between the soil and surface temperature at which time the maximum number of ticks were caught. Borrelia burgdorferi sensu lato infected ticks were collected only after 1100 hours. Prior to and just after 1100 h the mean difference between soil temperatures was 4.7°C, whereas the mean difference between soil and surface temperatures was 6.4°C at this time. The most important factors that influenced the appearance of Borrelia-infected ticks were the temperature gradients that existed between the surface and soil temperatures and the soil and air relative humidity. Greater numbers of infected nymphs were collected when temperature intervals ranged from 10 to 14°C and lower numbers were collected between 15 and 20°C. No Borrelia-infected nymphs were captured when the temperature interval ranged from 21 to 26°C. Infected adults appeared to be more tolerant of higher temperatures than Borrelia-infected nymphs. A significant relationship was found between the activity of Borrelia-infected I. persulcatus and the temperature of the air, soil below the surface, at the soil surface, and relative humidity.

Variations in the abundance of larvae and females of Aedes albifasciatus (Macquart) were monitored biweekly during the autumn–winter periods of 1996 and 1997 on the southern edge of the Mar Chiquita Lake in Córdoba Province. The degree of development of the primary ovarian follicles also was determined in host-seeking females. Abundance of the larvae and the females were noticeably different during the 2 yr of the study and matched changes in the pattern of precipitation. Although most females had ovarian follicles in Christophers stages Ib–IIa, 14% and 4% in 1996 and 1997, respectively, were in stages III-V (i.e., exhibited gonotrophic discordance). Females appeared to continue taking blood meals and laying eggs even during the autumn–winter period.

Spatial and temporal changes in the abundance of adult female Aedes (Ochlerotatus) albifasciatus (Macquart) were studied using CDC miniature light traps at 7 sites along an 80-km transect parallel to the southern shore of Mar Chiquita Lake (central Argentina) during the rainy seasons between 1994 and 1997. Abundance was greatest and most variable at sites near larval habitats. Rainfall and an index combining rainfall and temperature predicted adult female abundance near larval habitats 7–15 d in advance. The spatial distribution of population abundance seemed to be influenced strongly by local factors, because temporal change at sampling sites located >10 km apart was asynchronous.

This study establishes the seroprevalence of Hypoderma spp in cattle and the influence of some internal and environmental factors in the distribution of this myiasis in Galicia (northwest of Spain). Humoral antibody levels were measured by means of an indirect enzyme-linked immunosorbet assay, using as the antigen hypodermin C obtained from 1st-instar Hypoderma lineatum (De Villers). The percentage of positive sera in the total sample of 1,473 animals was 78.4%. Considering the different climatic areas in Galicia, the seroprevalence was lower in coastal areas; whereas, in the inland the percentages of positive sera were higher. The study revealed significant differences in seroprevalence between breeds; the autochthonous Rubia Gallega breed was the most prevalent, followed by the crossbreeds Brown Swiss and Friesian. The breeding system was an important factor affecting the occurrence of hypodermosis.

Beakers with aeration were used to rear individual (single) egg batches of Simulium damnosum (Theobald) s.l. to larvae and adults. Chromosomal analysis of the progeny of individual females indicated that multiple mating occurred within the S. damnosum complex and that hybridization occurred between S. damnosum s.s. and S. sirbanum (Vajime & Dunbar) in nature. These results indicate that possibly more extensive hybridization may be taking place in some areas of the Onchocerciasis Control Program than previously reported. Dramatic changes in the rates of hybridization among members of the S. damnosum complex possibly may lead to the formation of new cytotypes.

The allergenic cross-reactivity of both inter- and intraspecies of house dust mites, Dermatophagoides pteronyssinus (Trouessart, 1897) and Dermatophagoides farinae Hughes, 1961, taking into account the allergenic differences that exist throughout the growth curves, was evaluated by means of RAST-inhibition, using sera from patients allergic to these mites. The results demonstrate that extracts obtained from mite cultures during the maximum exponential growth phase are the best source of reagents to better discriminate cross-reactivity studies. The analyses obtained from this work, together with those obtained in previous reports, help to define the ideal conditions related to the allergenic diversity, avidity, and cross-reactivity of specific antibodies for the elaboration of allergenic extracts as a tool for use in diagnosis and specific treatment of IgE-mediated hypersensitivity caused by house dust mites.

Effects of food, density, and heterospecific interactions on temperature-dependent development of Aedes albopictus (Skuse) and Aedes triseriatus (Say) larvae and pupae were described using a degree-day model. Under all conditions, the predicted number of degree-days (DD_T0) to complete larval development was less, and the threshold temperature (T₀) for initiation of larval development was higher for Ae. albopictus than for Ae. triseriatus. The DD_T0 for both species was food and density dependent. However, the per capita food ration appeared to exert a greater influence on the developmental times of Ae. triseriatus immatures, whereas for Ae. albopictus effects of density were not completely eliminated by an increase in the per capita food ration. The presence of heterospecific larvae did not prolong the DD_T0 of either species. At the low food ration, DD_T0 for both species were significantly greater under conspecific conditions. The DD_T0 for Ae. triseriatus increased directly as the proportion of conspecific larvae increased. However, when a higher per capita food ration was provided, conspecific effects on DD_T0 were mitigated. For Ae. albopictus, estimated DD_T0 values for larvae reared in pure culture were significantly higher than when heterospecific larvae were present, regardless of the per capita amount of food provided. Survivorship of immatures was density and food-dependent for both species. Ae. albopictus exhibited higher immature survivorship under all conditions relative to Ae. triseriatus. For both species, survival probabilities were lowest under conditions of high density and low food. Addition of food improved survival for both species. The presence of heterospecific larvae exerted a differential effect on the survivorship response of Ae. albopictus immatures to temperature. Lowest probability of survival for Ae. albopictus was occurred at low temperature when the proportion of heterospecific larvae in containers was the highest. In contrast, at high temperatures, survivorship of immatures improved, but was lowest for pure species cultures. For Ae. triseriatus, survivorship of immatures was consistently lower for pure species cultures regardless of the temperature. Standing crop production of adults of both species was primarily food rather that density-dependent. Under field conditions, Ae. triseriatus were predicted to initiate development sooner and exhibit faster population growth early in the season than Ae. albopictus. However, because of the shorter DD_T0, Ae. albopictus population growth was predicted to surpass that of Ae. triseriatus populations later in the season. Based on optimal DD_T0 values from laboratory experiments, spring emergence dates of Ae. triseriatus females in western North Carolina for 1989 and 1990 were predicted from accumulated degree-days calculated from local air temperature records. Predicted emergence dates were congruent with results of a previous survey for the same locality, indicating that accumulated degree-days can be used to accurately predict the seasonal occurrence of Ae. triseriatus. The utility of the degree-day approach in predicting the phenology of Ae. albopictus remains to be established.

Polymerase chain reaction screening revealed that Armigeres subalbatus (Coquillett), a vector of filariasis, was infected with the intracellular bacteria Wolbachia. Laboratory crosses between infected males and uninfected females resulted in less than half the number of offspring than control crosses between uninfected individuals when young (2- to 3-d-old) males were used in the cross. However, incompatibility was lost when old (14- to 17-d-old) males were used. Field-collected females did not show detectable cytoplasmic incompatibility, and this may be because of the age at which males mate in the field. We used head pigment fluorescence levels to age field males collected from mating swarms, and found that 25–63% of swarming males were older than 13 d. Male age may be one factor influencing the observed low levels of cytoplasmic incompatibility detected in the field.

Aquatic habitats with immature populations of the Culicoides variipennis (Coquillett) complex were sampled across the United States and tested for soil chemistry parameters. Indicators of organic loading, phosphate, percentage of organic matter, and nitrate were high for C. variipennis and C. sonorensis, reflecting the common occurrence of larvae in sediments contaminated with livestock waste; these factors were low in western playa lake habitats with immature C. occidentalis. Levels of salt-forming ions and indicators of salinity, notably sodium, chloride, magnesium, sulfate, boron, and conductivity, were elevated in substrates supporting all 3 species, with values that declined from very high to high across the arid west to moderate east of the Mississippi river, and differed significantly among species. Concentrations of boron differed most strongly among habitats of the respective species, ranging from exceptionally high values in playa lake substrates with C. occidentalis, to high and moderate levels in western and southeastern sites with C. sonorensis, to moderate levels for substrates in the east with C. variipennis. The presence of C. sonorensis in dairy wastewater lagoons and saline springs in geographic regions that are otherwise inhabited by C. variipennis may reflect salinity factors that regulate the distribution of the C. variipennis complex.

We report sympatry among larval populations of the Culicoides variipennis complex in widespread and diverse aquatic habitats throughout the United States. Six sites in California, Nevada, New Mexico, and Texas were co-inhabited by C. v. occidentalis and C. v. sonorensis, whereas 8 sites in Florida, Georgia, Louisiana, Maryland, and Texas were co-occupied by C. v. sonorensis and C. v. variipennis. No intermediate forms were identified either electrophoretically or morphologically in adults reared from field-collected larvae and pupae. The absence of intergrades in zones of sympatry represents sufficient evidence to confirm species status for Culicoides variipennis (Coquillett) and Culicoides occidentalis Wirth & Jones, and to elevate Culicoides sonorensis to species rank (NEW STATUS). Culicoides v. albertensis Wirth & Jones is a synonym of C. sonorensis (NEW SYNONYMY); C. v. australis Wirth & Jones also is confirmed as a synonym of C. sonorensis. We also demonstrated a correlation between population taxonomic status as determined by electrophoresis and adult morphology.

Aspiration collections of adult Aedes aegypti (L.) were made weekly from inside and outside of houses for 3 yr in a rural Thai village (n = 9,637 females and n = 11,988 males) and for 2 yr in a residential section of San Juan, Puerto Rico (n = 5,941 females and n = 6,739 males). In Thailand, temperature and rainfall fell into distinct seasonal categories, but only temperature was correlated with fluctuations in female abundance. Average weekly temperature 6 wk before mosquitoes were collected and minimum weekly temperature during the week of collection provided the highest correlations with female abundance. Accounting for annual variation significantly improved Thai models of temperature and mosquito abundance. In Puerto Rico, temperature, but not rainfall, could be categorized into seasonal patterns. Neither was correlated with changes in female abundance. At both sites the vast majority of females were collected inside houses and most contained a blood meal. Most teneral females were collected outside. Wing length—an indicator of female size—and parity, egg development or engorgement status were not correlated, indicating that feeding success and survival were not influenced by female size. At both sites, females fed almost exclusively on human hosts (≥96%), a pattern that did not change seasonally. In Puerto Rico more nonhuman blood meals were detected in mosquitoes collected outside than inside houses; no such difference was detected in Thailand. Gut contents of dissected females indicated that females in the Thai population had a younger age distribution and fed more frequently on blood than did Ae. aegypti in Puerto Rico. Our results indicated that aspects of this species’ biology can vary significantly from one location to another and 1 yr to the next.

We used a histologic technique to study multiple blood feeding in a single gonotrophic cycle by engorged Aedes aegypti (L.) that were collected weekly for 2 yr from houses in a rural village in Thailand (n = 1,891) and a residential section of San Juan, Puerto Rico (n = 1,675). Overall, mosquitoes from Thailand contained significantly more multiple meals (n = 1,300, 42% double meals, 5% triple meals) than mosquitoes collected in Puerto Rico (n = 1,156, 32% double meals, 2% triple meals). The portion of specimens for which frequency of feeding could not be determined was 31% at both sites. We estimated that on average Ae. aegypti take 0.76 and 0.63 human blood meals per day in Thailand and Puerto Rico, respectively. However, frequency of multiple feeding varied among houses and, in Puerto Rico, the neighborhoods from which mosquitoes were collected. In Thailand 65% of the mosquitoes fed twice on the same day, whereas in Puerto Rico 57% took multiple meals separated by ≥ 1 d. At both sites, the majority of engorged specimens were collected inside houses (Thailand 86%, Puerto Rico 95%). The number of blood meals detected was independent of where mosquitoes were collected (inside versus outside of the house) at both sites and the time of day collections were made in Puerto Rico. Feeding rates were slightly higher for mosquitoes collected in the afternoon in Thailand. Temperatures were significantly higher and mosquitoes significantly smaller in Thailand than in Puerto Rico. At both sites female size was negatively associated with temperature. Rates of multiple feeding were associated positively with temperature and negatively with mosquito size in Thailand, but not in Puerto Rico. Multiple feeding during a single gonotrophic cycle is a regular part of Ae. aegypti biology, can vary geographically and under different climate conditions, and may be associated with variation in patterns of dengue virus transmission.

A method for direct detection of Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner has been developed. Cells are lysed to facilitate release of ribosomal RNA. Lysates are filtered onto nylon membranes that are hybridized with probes specific for sequences in B. burgdorferi 23S rRNA. The technique is rapid and does not require any enzymatic amplification steps. With the use of a cocktail containing five different probes, ≈1,000 organisms could be detected. The assay was successfully applied to direct detection of B. burgdorferi in Ixodes scapularis Say nymphs.

Mosquitoes known to be involved in the transmission of Japanese encephalitis virus (JE) on Taiwan typically develop in rice fields. However, recent serological evidence indicated that JE virus was being transmitted on Liu-Chiu, a rice-free islet. To identify the mosquito vector in this unusual epidemiological situation, 4 mosquito species commonly found in Liu-Chiu were evaluated for their vector competence for a strain of JE (CH1392) virus isolated from central Taiwan. Armigeres subalbatus (Coquillett) was the most susceptible species, indicating its status as a potential vector. In addition, an isolate of JE (T1P1) virus from Ar. subalbatus collected on Liu-Chiu readily infected the salivary glands of orally infected Ar. subalbatus originating from Liu-Chiu. The infection rate reached 79% (11/14) after a 20-d period of extrinsic incubation at 28°C. We conclude that JE likely was transmitted between vertebrate hosts by Ar. subalbatus in this rice-free islet and that this species should be considered as a potential vector in similar ecological conditions.

Larvae of winter ticks, Dermacentor albipictus (Packard), ascend vegetation in autumn and form clumps that attach to passing ungulate hosts. We tested the hypothesis that vegetation height determines the height of clumps. During the vegetation-to-ungulate transmission period (early September to mid-November), larvae were released at the base of simulated vegetation (nylon rods 245 cm tall) in outdoor and laboratory trials and in the absence of host cues. Rod height exceeded the height of the tallest ungulate host, which is the moose, Alces alces (L.). Most larvae stopped climbing and formed clumps 50–190 cm above ground, which coincided with torso heights of moose; elk, Cervus elaphus L.; and deer, Odocoileus spp. Rafinesque. More clumps formed in outdoor trials than in laboratory trials and clump heights tended to increase over the course of the experiment, but clump number, size, and height did not correlate with weather conditions. Winter tick larvae appear to determine their height above ground in the absence of external cues, but this mechanism may be modified by external conditions.

A single application of granular carbaryl approaching the lowest recommended rate to the shrub layer of a forested area in late spring significantly reduced the abundance of Ixodes scapularis Say nymphs throughout their peak activity period, but had little effect on Amblyomma americanum L. nymphs. Factors influencing the efficacy of the application are discussed. The possible explanations for the lack of efficacy of granular carbaryl against A. americanum, including behavior, formulation, and application rate, are discussed.

We report an attempt by an offshore island community to control the vector tick of Lyme disease by providing ivermectin-treated corn to an isolated herd of free-ranging white-tailed deer, 0docoileus virginianus Zimmerman. Medicated corn was supplied in troughs within the island village and from automatic feeders at remote sites during 5 consecutive fall and spring adult tick questing seasons. Acaricide consumption was monitored by assaying its presence in fresh deer pellets and its concentration in deer sera. Its effectiveness was evaluated by recording the number of adult ticks collected from the hides of deer, the number of females becoming sufficiently engorged to oviposit, and the success of subsequent oviposition and eclosion. Entomologic risk was monitored by collecting immature ticks from hosts and adult ticks from vegetation. Estimates based on a subsequent deer reduction program indicated that up to twice as many deer had been present during the project as originally presumed. For this and other reasons related to deer behavior, target levels of serum ivermectin were achieved in a minority of deer. Nevertheless, >90% control of female tick infestation, subsequent oviposition, and larval eclosion was obtained in those 8 of 16 sampled deer with serum ivermectin levels of ≥15 ng/ml. In addition, the ratio of females to males, the numbers of females engorging >10 mg body weight, and the numbers of those eventually hatching, were all significantly less among ticks from island deer in comparison with ticks from untreated deer. No consistent changes in the numbers of ticks found on immature-stage hosts or removed from vegetation were noted within 3 yr of the cessation of treatment.

Development of Leishmania braziliensis (Vianna) and Leishmania amazonensis (Lainson and Shaw) in the sand fly Lutzomyia migonei (França) was compared by studying the parasite microhabitats in the alimentary tract, the sequence of parasite morphological changes leading to the metacyclogenesis process, and the parasite transmission to the vertebrate susceptible host. Although the infections by the 2 Leishmania species were initiated with the same number of amastigotes, Le. amazonensis developed a higher population. Infections with Le. braziliensis were typically peripylarian and those with Le. amazonensis suprapylarian but with an unusual invasion of an organ other than the gut, the Malpighian tubules. The life cycle of the 2 parasites within the sand fly vector included the development of all promastigote forms: procyclics, haptomonads, nectomonads, paramastigotes and infective metacyclics, the last of which are uniquely adapted for transmission to the vertebrate hosts. Appearance of metacyclics coincided with the presence of large number of procyclics and haptomonads, low numbers of nectomonads and the appearance of paramastigotes. In both type of infections, there was a high mortality of the promastigotes inside the bloodmeal during digestion but once infection became established metacyclic forms appeared. Although the numbers of metacyclics that developed in sand flies were low for both parasites they were able to transmit the infection to vertebrates, a key event in the vector competence. We suggest that L. migonei is a true biological host and a possible vector of the 2 Leishmania species, which coexist in extensive geographic areas.

A new juvenile hormone mimic CGA-255′728, developed by Novartis, was tested for its efficacy on different life stages of the cat flea, Ctenocephalides felis (Bouché). The compound was mixed in bovine blood at concentrations of 1, 10, and 100 ppb and fed to adult fleas using an artificial membrane system. Less than 7% of the eggs from fleas fed 10 and 100 ppb hatched, compared with >70% hatch in eggs laid by control fleas or fleas fed 1 ppb. Histological studies demonstrated that ≈50% of the eggs from fleas fed 10 ppb contained unhatched larvae that died after completing embryological development. At 100 ppb, 24% of the fleas died as fully formed larvae within the egg, but at this concentration nearly 20% of fleas also died before embryogenesis was completed. In addition to embryonic and larval mortality, ≈28% of eggs from the 100 ppb-treated group were deposited as empty shells. Evidently these eggs were crushed by the muscular action of the oviduct and yolk was expelled into the oviduct during oviposition. None of the test concentrations showed adulticidal effects over a 10-d period. Fecundity was significantly increased with increased concentrations of CGA-255′728 indicating that the compound mimicked the effect of juvenile hormone.

Evidence of Ross River (RR) virus infection in field-collected mosquitoes and data from laboratory vector competence experiments incriminated a range of mosquito species as important vectors of RR virus in Maroochy Shire, Queensland, Australia. Nine RR and 2 Barmah Forest virus isolates were recovered from 27,529 mosquitoes collected in light traps from Maroochy Shire during 1996. Nine of the 10 most abundant mosquito species collected in light traps were fed on blood containing the B94/20 strain RR isolated from Queensland in 1994. All species except for Culex sitiens Wiedemann were susceptible to experimental infection. Evidence of RR virus transmission to mice was found with Aedes vigilax (Skuse), Aedes funereus (Theobald), Aedes procax (Skuse), Culex annulirostris Skuse, Mansonia uniformis (Theobald) and Culex australicus Dobrotworsky & Drummond. Aedes notoscriptus (Skuse) and Aedes multiplex (Theobald) were susceptible to RR virus infection, although there was no evidence of virus transmission. Based on adult abundance and vector competence results, freshwater species such as Cx. annulirostris, Ae. procax, and Ae. funereus, and saltmarsh Ae. vigilax, appear to be important vectors of RR virus in Maroochy Shire and control programs should be revised to include these species.

In the Cairns area of far north Queensland, Australia, the seasonal abundance of Anopheles farauti Laveran sibling species was studied at 6 locations, representing 3 habitat types, between August 1995 and September 1997. A total of 45,401 An. farauti s.l. was collected using CO₂ octenol baited CDC light traps, and consisted of 29,565 An. farauti No. 2, 14,214 An. farauti No. 3, and 1,622 An. farauti s.s. The relative abundance of all 3 species differed significantly by season and location. An. farauti No.2 was the dominant species except in Cairns, where An. farauti s.s. was most abundant, and at Ninds Creek, where An. farauti No. 3 predominated. The dominant species at each location was present year round, although peaks in seasonal abundance were observed. An. farauti s.s. populations were highest during the wet season (January–April). In lowland freshwater swamp habitats and 1 brackish location, An. farauti No. 2 was more abundant during the wet season. However, at the highland freshwater swamp habitat, populations of An. farauti No. 2 were highest during the late dry season and early wet season (October–December). There was a significant positive correlation of both temperature and rainfall with An. farauti s.s. and An. farauti No. 2 trap collections. There was a negative correlation between An. farauti No. 3 and temperature, indicating that this species may be more abundant during cool weather. Although there were significant relationships among weather variables and An. farauti s.l. collections, correlation values were generally low, indicating that other factors may contribute to variability among An. farauti sibling species trap collections.

Visceral and cutaneous leishmaniasis are major endemic diseases in northeast Brazil. The objective of the current study was to determine the species and geographic distribution of potential sand fly vectors of Leishmania in the state of Rio Grande do Norte. Sand flies were captured using CDC light traps in 30 municipalities distributed throughout the 8 geographic zones of the state. Twelve Lutzomyia species were identified. Lutzomyia longipalpis Lutz & Neiva was the most prevalent and accounted for 85.59% of the sand fly captured. The remaining species were distributed as follows: L. evandroi Costa Lima & Antunes (10.83%), L. oswaldoi Mangabeira (0.99%), L. sallesi Galvão & Coutinho (0.58%), L. intermedia Lutz & Neiva (0.53%), L. lenti Mangabeira (0.53%), L. migonei França (0.49%), L. walkeri Newstead (0.24%), L. goiana Martins, Falcão & Silva (0.15%), L. samueli Deane (0.04%), and L. capixaba Dias, Falcão, Silva & Martins (0.03%), and L. peresi Mangabeira (0.01%). L. longipalpis, which is known to be a vector of Leishmania chagasi Cunha & Chagas (L. donovani chagasi), was captured in 93% of municipalities distributed across all geographical areas of the state and its distribution was independent of obvious climatic and topographic parameters. It was identified in all municipalities where human visceral leishmaniasis had been reported. In contrast, climate and topography appeared to be important for other Lutzomyia species. For example, L. intermedia and L. migonei, which are known to transmit Leishmania braziliensis Viana, were geographically restricted. They were captured in municipalities where cases of cutaneous and mucosal leishmaniasis had been reported. The widespread distribution of L. longipalpis, its adaptation to peridomicillary settings, and its ability to transmit L. (d.) chagasi suggest that a large number of persons may be at risk of acquiring visceral leishmaniasis in the state of Rio Grande do Norte, Brazil.

Head lice are caused by the host-specific, ectoparasitic insect Pediculus humanus capitis De Geer and remain a common human infestation. As a response to increasing resistance of head lice to present insecticidal agents, additional agents must be pursued. Inasmuch as nicotine has been used for controlling poultry lice, an in vitro study assessing its possible usage for human head lice was performed. Nicotine proved not to be an efficient insecticide, although it may facilitate removal of adult lice because it induces muscle twitches that may affect the insect’s normal grip on hair follicles.

The effectiveness of traps baited with (5R,6S)-6-acetoxy-5-hexadecanolide (the synthetic oviposition pheromone) and grass infusions in sampling a population of gravid Culex quinquefasciatus Say was conducted in Muheza, Northeast Tanzania. A counterflow geometry (CFG) trap baited with pheromone and set outdoors, adjacent to a pit latrine building, collected more gravid Cx. quinquefasciatus than a CDC trap baited with pheromone and operated without light. Inside pit latrine buildings, significantly more gravid Cx. quinquefasciatus were collected in a CFG trap-baited with pheromone or grass infusion than in traps baited with tap water. CFG traps baited with either grass infusion or pheromone and set outdoors, away from known breeding sites, caught significantly more gravid Cx. quinquefasciatus than traps baited with tap water. CFG traps baited with pheromone grass infusion caught significantly more gravid Cx. quinquefasciatus than CFG traps baited with either grass infusion or pheromone. In both cases, the proportion of gravid mosquitoes increased as traps were moved away from a natural emergence site. More gravid Cx. quinquefasciatus were collected in a pheromone-baited CFG trap than were egg rafts deposited in a jar with pheromone-treated water. It is concluded that CFG traps baited with oviposition attractants can be used effectively to sample gravid Cx. quinquefasciatus.

A new module for quantitative evaluation of arthropod repellents in human subjects was designed, constructed, and protocols for use of the module were developed. Doses of 3 arthropod repellents, 1-[3-cyclohexen-1-ylcarbonyl] piperidine (AI3-35765), 1-[3-cyclohexen-1-ylcarbonyl]-2-methylpiperidine (AI3-37220), and N, N-diethyl-3-methylbenzamide (deet), were evaluated using the mosquito, Anopheles stephensi Liston. Biting responses to varied doses of the repellents on human skin were quantified, and the effectiveness of the 3 repellents was compared. The new module consists of 6 test cells and permits the simultaneous comparison of up to 5 repellent doses or chemical types and a control using a complete randomized block design with minimal treatment interaction and with ≥6 replicates per human subject.

Optically inactive 1-[3-cyclohexen-1-ylcarbonyl] piperidine and 1-[3-cyclohexen-1-ylcarbonyl]-2-methylpiperidine are repellents against blood-feeding arthropods. Pure stereoisomers of these compounds were synthesized and characterized for use in bioassays. Initial laboratory tests with the malaria vector Anopheles stephensi Liston showed that this species was repelled differentially by the stereoisomers of 1-[3-cyclohexen-1-ylcarbonyl]-2-methylpiperidine. Two stereoisomers were twice as repellent as the other stereoisomers. These results indicate that stereoisomerism influences repellent efficacy in this class of compounds.

The longevity of an Iowa strain of Culex tarsalis Coquillett fed blood meals containing 2 concentrations of western equine encephalomyelitis virus from Iowa (WEE-7738) was compared with that of Cx. tarsalis fed blood without virus. Females exposed to 4.7–5.0 log TCID₅₀ per mosquito of WEE-7738 did not live as long as mosquitoes exposed to 2.7–3.0 log TCID₅₀ per mosquito or controls. Only 1% of mosquitoes fed blood containing the higher virus concentration survived to day 18 after exposure. However, 13% of mosquitoes fed blood with the lower virus titer and 19.5% of the controls were still alive on day 18 after exposure. Flight activity scores of Cx. tarsalis infected with 4.7–5.0 log TCID₅₀ per mosquito of WEE-7738 were 27.5% lower, and there were 26.1% fewer spontaneous flights than noninfected controls from days 6–11 after infection. After day 8 after infection, infected Cx. tarsalis had 37.1% lower activity scores and 40.0% fewer spontaneous flights than noninfected controls. Virus infection did not affect how long a mosquito flew in a 24-h period (the daily flying time) or the duration of individual flights. The spontaneous flight activity pattern (circadian rhythm) of infected mosquitoes was identical to those of controls. Both infected and noninfected mosquitoes began spontaneous flight activity at 2000–2100 hours (CST) and were active throughout the entire dark phase of the 24-h cycle. Although mosquitoes were active throughout the night, there was a burst or peak of activity between 2200 and 2300 hours when the complete dark cycle began. These results indicate that the adverse effect of WEE infection on longevity and spontaneous flight activity of Cx. tarsalis may decrease vectorial capacity of Cx. tarsalis for WEE.

Experiments were designed to evaluate the vector competence of Culex tarsalis Coquillet from an area (Sioux City) where Cx. tarsalis is most abundant in Iowa for western equine encephalomyelitis virus (WEE-7738). WEE-7738 was isolated from Aedes trivittatus (Coquillet) collected in Ames, IA, in 1977. Infection rate, dissemination rate, multiplication efficiency, and transmission rate were determined for this virus in the SC strain of Cx. tarsalis. SC strain of Cx. tarsalis was as susceptible to WEE-7738 as Californian strains of Cx. tarsalis were to BFS1703 strain of WEE; OID₅₀ of SC Cx. tarsalis was 2.63 log TCID₅₀ per mosquito and OID₅₀ of Californian strains of Cx. tarsalis were 2.0–4.1 log PFU per mosquito. However, transmission of WEE-7738 (4.2%) by the SC strain of Cx. tarsalis was lower than those (10–60%) reported in other studies.

The relationship between weights of the nymphal stage and their resultant sexes in Ixodes scapularis Say and Dermacentor variabilis (Say) was examined under laboratory conditions. Nymphs were fed to repletion on laboratory white mice, weighed individually, and held until they molted. Fully engorged I. scapularis nymphs that subsequently molted to females weighed between 3.8 and 6.4 mg (n = 64). Those nymphs that molted to males weighed between 2.0 and 3.2 mg (n = 57). Body weights of engorged nymphs that became females were significantly greater than those of nymphs that became males (P < 0.05). Similarly, the range of body weights of engorged D. variabilis nymphs that subsequently became females was 9.1–15.1 mg (n = 32), whereas those nymphs that molted to males weighed between 3.9 and 13.0 mg (n = 39). Body weights of engorged nymphs that became females were significantly greater than those of nymphs that became males (P < 0.05). This suggests that nymphs of both species that become females presumably imbibe more blood than those that became males.

The relative efficacy of insecticide treated mosquito nets was evaluated under field conditions in Dehra village of Dhaulana PHC, District Ghaziabad, U.P., India, during 1996. Nylon nets were impregnated with deltamethrin, cyfluthrin, lambdacyhalothrin, and etofenprox at 25 mg/m² by standard methods. Repellent, excito-repellency, killing, and airborne actions were monitored from dusk to dawn by hourly collection of mosquitoes that entered and rested in rooms and also females that landed on treated and untreated mosquito nets. Results revealed 15.3–22.9% repellent action, 98.3–99.3% excito-repellency action, and 100% mortality of females that landed on treated fabrics. No significant differences were observed in the efficacy of different synthetic pyrethroids against anophelines. However, against Culex quinquefasciatus Say there was a significant difference between deltamethrin and etofenprox. Control of anophelines was more pronounced than Cx. quinquefasciatus. There was no pronounced airborne action with any insecticide tested. Synthetic pyrethroids with strong airborne action may be more appropriate for impregnation of mosquito nets.