Pesticide Misting System Enhances Residual Pesticide Treatment of HESCO Geotextile.

Residual pesticide treatment of US military materials such as camouflage netting and HESCO blast wall geotextile is an effective way to reduce biting pressure within protected perimeters. However, residual treatments eventually wane and require retreatment in situ, which may not be possible or practical in military scenarios. One solution is to install pesticide misting systems on treated perimeters, which may additively enhance residual treatments, and gradually retreat perimeter material as misted pesticide settles. In this investigation we show that pesticide misting can extend efficacy of residual treatments on HESCO geotextile against mosquitoes and sand flies in a hot-arid desert environment by 1-2 wk.

Transfluthrin Spatial Repellent on US Military Materials Reduces Culex tarsalis Incursion in a Desert Environment.

Standard residual pesticides applied to US military materials such as camouflage netting can reduce mosquito biting pressure in the field but may contribute to the evolution of resistance. However, residual applications of a spatial repellent such as transfluthrin could allow mosquitoes the opportunity to escape, only inducing mortality if insects linger, for example after becoming trapped in a treated tent. In this study we investigated the capability of transfluthrin on 2 types of US military material to reduce natural populations of disease vector mosquitoes in a cool-arid desert field environment in southern California. We found that transfluthrin could reduce Culex tarsalis incursion into protected areas by up to 100% upon initial treatment and up to 45% for at least 16 days posttreatment, showing that this compound could be an effective element in the US Department of Defense integrated vector management system appropriate for further study.

Effectiveness of Aquatain® AMF and Cocobear™ Larvicidal Oil Against Culex quinquefasciatus Larvae and Pupae in an Organically Enhanced Aquatic Habitat.

The efficacy of CocoBear™ Larvicidal Oil and Aquatain® AMF Liquid Mosquito Film against larval and pupal Culex quinquefasciatus was compared (at maximum label field application rates) when applied to concrete troughs treated with composted cow manure. At 1 h posttreatment, CocoBear provided significantly greater reduction of mosquito larvae than Aquatain, but both products were equally effective in producing >97% control at 24 h. Each product provided >98% pupal reduction at 1 h posttreatment, with complete elimination of pupae from troughs at 24 h. CocoBear and Aquatain proved to be equally effective against Cx. quinquefasciatus immatures in organically enriched aquatic habitats.

Transfluthrin Spatial Repellent on US Military Camouflage Netting Reduces Tabanids in a Warm-Temperate Environment.

We investigated the capability of transfluthrin on US military camouflage netting to reduce collections of tabanid biting flies in a warm-temperate field environment on the Gulf Coast of Florida. We found that transfluthrin significantly reduced collections of a variety of medically and veterinarily important tabanids inside protected areas by up to 96% upon initial treatment and up to 74% after 20 days posttreatment. These results suggest that transfluthrin could be an effective element in the US Department of Defense integrated pest management system and leveraged in civilian scenarios to protect livestock and humans from potential mechanical transmission of pathogens and disruption of activities caused by painful bites.

Field Evaluation of Indoor Thermal Fog and Ultra-Low Volume Applications For Control of Aedes aegypti in Thailand.

Efficacies of a handheld thermal fogger (Patriot™) and a backpack ultra-low volume (ULV) sprayer (Twister™) with combinations of 2 different adulticides (pyrethrin, deltamethrin) and an insect growth regulator (pyriproxyfen) were field-tested and compared for their impact on reducing indoor Aedes aegypti populations in Thailand. The effectiveness of the indoor space sprays was evaluated by sampling the natural Ae. aegypti population in houses and determining their physiological status, by monitoring mortality of sentinel caged mosquitoes (AFRIMS strain) and by assessing larval mortality in laboratory bioassays using water exposed to the spray. A total of 14,742 Ae. aegypti were collected from Biogents Sentinel traps in this study. The combination of ULD® BP-300 (3% pyrethrin) and NyGuard® (10% pyriproxyfen) sprayed either by the Patriot or Twister significantly reduced some Ae. aegypti populations up to 20 days postspray relative to the control clusters. The addition of pyriproxyfen to the adulticide extended how long household mosquito populations were suppressed. In 2 of the 4 products being compared, the Twister resulted in higher mortality of caged mosquitoes compared with the Patriot. However, neither machine was able to achieve high mortality among Ae. aegypti placed in hidden (protected) cages. The larval bioassay results demonstrated that the Twister ULV provided better adult emergence inhibition than the Patriot (thermal fogger), likely due to larger droplet size.

Permethrin and malathion LD90 values for Culex quinquefasciatus vary with topical application site.

Prior research in multiple insect species has demonstrated that insecticide-induced mortality varies according to the body region exposed on the insect. This variation has been demonstrated in Culex quinquefasciatus Say (Diptera: Culicidae), but has not been quantified using dose-response curves. Applications of technical permethrin or malathion to one of three body regions on Cx. quinquefasciatus resulted in dose-response curves that were not equivalent to one another. The generated LD90 values and curves for each body region were compared with previously reported LD values for analogous sites in several mosquito species, specifically the mesothorax. Based on the present results, the permethrin and malathion LD50 and LD90 concentrations required for droplets impinging on the abdomen and mesothorax of Cx. quinquefasciatus when applied through ground-based spray systems utilized by mosquito control programmes were calculated.

Limited impacts of truck-based ultra-low-volume applications of mosquito adulticides on mortality in honey bees (Apis mellifera).

Adulticides applied against mosquitoes can reduce vector populations during times of high arbovirus transmission. However, impacts of these insecticides on pollinators and other non-target organisms are of concern to mosquito control professionals, beekeepers and others. We evaluated mortality of Culex quinquefasciatus and Apis mellifera when caged insects were exposed to low and high label rates of four common adulticides (Aqua-Pursuit™ [permethrin], Duet® [prallethrin + sumithrin], Fyfanon® [malathion] and Scourge® [resmethrin]) at six distances up to 91.4 m from a truck-mounted ultra-low-volume sprayer. Honey bee mortality was both absolutely low (61 m had limited impacts on honey bee mortality while providing effective mosquito control.

Climate-disease connections: Rift Valley Fever in Kenya.

All known Rift Valley fever(RVF) outbreaks in Kenya from 1950 to 1998 followed periods of abnormally high rainfall. On an interannual scale, periods of above normal rainfall in East Africa are associated with the warm phase of the El Niño/Southern Oscillation (ENSO) phenomenon. Anomalous rainfall floods mosquito-breeding habitats called dambos, which contain transovarially infected mosquito eggs. The eggs hatch Aedes mosquitoes that transmit the RVF virus preferentially to livestock and to humans as well. Analysis of historical data on RVF outbreaks and indicators of ENSO (including Pacific and Indian Ocean sea surface temperatures and the Southern Oscillation Index) indicates that more than three quarters of the RVF outbreaks have occurred during warm ENSO event periods. Mapping of ecological conditions using satellite normalized difference vegetation index (NDVI) data show that areas where outbreaks have occurred during the satellite recording period (1981-1998) show anomalous positive departures in vegetation greenness, an indicator of above-normal precipitation. This is particularly observed in arid areas of East Africa, which are predominantly impacted by this disease. These results indicate a close association between interannual climate variability and RVF outbreaks in Kenya.

Seasonal occurrence of Leptotrombidium deliense (Acari: Trombiculidae) attached to sentinel rodents in an orchard near Bangkok, Thailand.

Leptotrombidium deliense Walch that attached to sentinel laboratory mice and the roof rat, Rattus rattus (L.), placed in an orchard habitat near Bangkok, Thailand, were studied between April 1993 and April 1995. A single L. deliense larva was attached to only 1 of 51 laboratory mice placed in the study area between April and September 1993. Overall, 89/202 (44.1%) R. rattus had 1 or more L. deliense larvae attached, and Orientia tsutsugamushi (Hayashi), the etiologic agent for scrub typhus, was isolated from liver/spleen samples of 2/202 (1.0%) rats placed in an endemic area for a single night. A total of 474 L. deliense attached to sentinel R. rattus, of which 314 larvae successfully fed to repletion and were recovered, and 2 (0.6%) of these were naturally infected with O. tsutsugamushi. The occurrence of L. deliense was influenced by rainfall, with more chiggers attached to rodents in the wetter months of the year. The study showed that the risk of exposure to infection with O. tsutsugamushi is greater during the wetter months of the year, and that only a relatively small number of chigger attachments are needed to infect potential hosts.

Estimates of gene flow among Anopheles maculatus populations in Thailand using microsatellite analysis.

We report an analysis of seven microsatellite loci in eight populations of Anopheles maculatus mosquitoes dispersed over a distance of approximately 1,100 km in Thailand. A wide spectrum of genetic variability, with mean heterozygosities ranging from 0.738 to 0.847 were found. Based on microsatellite analysis, geographic populations of An. maculatus can be grouped into two clusters; one includes upper and lower northern populations that extend from approximately 11 degrees to 16 degrees north latitude, and the other (southern populations) extends south from about 7 degrees to 6 degrees north latitude. Wright's F(ST) and Slatkins's R(ST) for all seven microsatellite loci indicated low estimates of differentiation among all populations (mean values of F(ST) and R(ST) = 0.0406 and 0.051, respectively, corresponding to the Nm values of 5.91 and 4.65, respectively), and suggested that gene flow occurs among populations. However, there is some restriction of gene flow between the northern and southern populations. Geographic barriers could be limiting factors for greater gene flow between populations.

Climate and satellite indicators to forecast Rift Valley fever epidemics in Kenya.

All known Rift Valley fever virus outbreaks in East Africa from 1950 to May 1998, and probably earlier, followed periods of abnormally high rainfall. Analysis of this record and Pacific and Indian Ocean sea surface temperature anomalies, coupled with satellite normalized difference vegetation index data, shows that prediction of Rift Valley fever outbreaks may be made up to 5 months in advance of outbreaks in East Africa. Concurrent near-real-time monitoring with satellite normalized difference vegetation data may identify actual affected areas.

Redescription of Leptotrombidium (Leptotrombidium) imphalum (Acari: Trombiculidae), with observations on bionomics and medical importance in northern Thailand.

Leptotrombidium (Leptotrombidium) imphalum Vercammen-Grandjean & Langston is redescribed and illustrated. Specimens were collected from the rodents Rattus rattus, Rattus losea, and Bandicota indica in Chiangrai Province, northern Thailand. The species was found on hosts collected on dikes at the margins of rice fields and in adjacent fruit plantations and along irrigation canals, especially in areas covered with the grasses Imperata cylindrica (lalang grass) and Saccharum arudinaceum. The etiological agent of scrub typhus, Orientia (formerly Rickettsia) tsutsugamushi has been isolated from L. (L.) imphalum, rodent hosts, and patients who live and work in the same habitats.

Sequence heterogeneity in copia-like retrotransposons in Anopheles (Diptera: Culicidae) in Thailand.

Degenerate primers and the polymerase chain reaction (PCR) detected a conserved region of copia-like reverse transcriptase from Anopheles mosquitoes in Thailand. A total of 43 subclone PCR fragments of the size expected for reverse transcriptase of copia-like elements was isolated from Anopheles dirus (Peyton & Harrison) subspecies A, Anopheles maculatus (Theobald) subspecies E, Anopheles nivipes (Theobald), and Anopheles subpictus Grassi. Sequence analysis of subclones confirmed the identity of these sequences as copia-like reverse transcriptase sequences. The sequences displayed varying degrees of sequence heterogeneity, in contrast to the limited diversity seen in copia-like elements in Drosophila. Phylogenetic analysis of the amino acid sequences of the subclones showed that the majority of the retroelements were clustered together, implying that sequence divergence during vertical transmission of the copia-like retrotransposons has been a major factor in the evolution of copia-like retroelements in Anopheles species. Additionally, there is evidence that horizontal transfer of this transposon group among certain divergent taxa also may have played a role in their evolution.

Systematic review of the genus Acropsylla Rothschild, 1911 (Siphonaptera: Leptopsyllidae), with notes on certain fleas from northern Thailand.

Acropsylla (Leptopsyllidae), a genus of fleas from the Indian Subregion of the Oriental Region, is reviewed to include the seasonal and geographical distribution of the known species. Acropsylla girshami Traub, 1950 is proposed as a junior synonym of Acropsylla episema Rothschild, 1911. Keys are provided for the tribe Meopsyllini and for the species of Acropsylla.

A new ecology for scrub typhus associated with a focus of antibiotic resistance in rice farmers in Thailand.

Following the documentation of chloramphenicol-resistant and doxycycline-resistant strains of Orientia tsutsugamushi (Hyashi) in northern Thailand, we conducted ecological and epidemiological studies near the houses of patients hospitalized with antibiotic-resistant infections. New associations between chiggers, rodents, and O. tsutsugamushi in active rice agriculture areas, an ecological habitat not described previously, are reported. Rattus rattus (L.) was the most common species (representing 85.8% of the 1,433 rodents processed), followed by Rattus losea (Swinhoe) (9.4%), Bandicota indica (Bechstein) (3.6%), and Rattus argentiventer (Robinson and Kloss) (1.3%). O. tsutsugamushi was isolated from 30% of the R. rattus and R. losea, 29% of the B. indica, and 33% of the R. argentiventer collected. Mean minimum infection rates were 0.03 in Leptotrombidium chiangraiensis Tanskul & Linthicum, a new species of chigger, and 0.002 in Leptotrombidium imphalum (Vercammen-Grandjean & Langston), a chigger species not previously associated with scrub typhus transmission. Efficient vertical and horizontal transmission of O. tsutsugamushi by L. chiangraiensis and L. imphalum was demonstrated. During a 19-mo period from October 1993 to April 1995, the overall prevalence of human IgM and IgG antibody to O. tsutsugamushi was 25.5 and 47.3%, respectively. L. chiangraiensis and L. imphalum are incriminated as vectors of O. tsutsugamushi in a rice field habitat associated with a focus of antibiotic resistance.

Immunocytochemical methods to study the distribution of Orientia tsutsugamushi in Leptotrombidium (Acari: Trombiculidae) chiggers.

Immunocytochemical methods were developed and tested for their ability to detect the distribution of Orientia tsutsugamushi in paraffin sections of adult chiggers (Leptotrombidium imphalum Vercammen-Grandjean & Langston). Rickettsial antigen was detected by application of a simple direct or amplified immunocytochemistry procedure and an indirect immunofluorescent procedure. In the direct procedure alkaline phosphatase conjugation to the mouse polyclonal antibody to the Karp strain was followed by the HistoMark Red test system to detect rickettsial antigen. The amplification procedure used a similar method but used an unlabeled primary antibody followed by secondary biotinylated antimouse IgG, streptavidin-alkaline phosphatase, and the HistoMark Red test system. The immunofluorescent procedure included a biotinylated secondary antibody followed by addition of a streptavidin-FITC conjugate. Specific tissue tropisms in infected chiggers were observed in the salivary glands, nervous tissue, and ovaries of adult female mites in all procedures; however, nonspecific fluorescence of the chigger limited definitive identification of tissue tropisms with the indirect immunofluorescent procedure.

Impact of dengue virus infection on feeding behavior of Aedes aegypti.

In addition to heavily infecting the salivary glands of Aedes aegypti (L.) mosquitoes, dengue viruses produce a significant infection of the nervous system, involving the brain, Johnston's organ, compound eye, and thoracic and abdominal ganglion. To determine if dengue infection affects feeding behavior of Ae. aegypti we measured feeding times, counted the number of feeding delays or interruptions, and by in situ immunocytochemistry techniques determined the spatial and temporal distribution of dengue infections in females parenterally infected with dengue 3 virus. The mean of the total time required for feeding by infected mosquitoes was significantly longer than the time required by uninfected mosquitoes. Similarly, the mean of the time spent probing was significantly longer in infected mosquitoes than in uninfected mosquitoes when day after inoculation was considered. Significant increases in the length of feeding activity in infected mosquitoes corresponded to virus infection in organs that are known to control or influence activities associated with blood feeding. Sequential infections of the salivary glands (five days postinoculation [PI]), brain and compound eye (eight days PI), and Johnston's organ and midgut and abdominal ganglion (11 days PI) of most mosquitoes were observed. The increased time required by infected Ae. aegypti mosquitoes to acquire a blood meal may contribute to the efficiency of Ae. aegypti as a vector of dengue virus. Longer feeding periods are more likely to be interrupted by the host, which increases the chance that an infected mosquito will probe or feed on additional hosts.

A new species of Leptotrombidium (Acari:Trombiculidae) collected in active rice fields in northern Thailand.

Leptotrombidium (Leptotrombidium) chiangraiensis Tanskul & Linthicum is described and illustrated as new from specimens collected from the rodents Rattus rattus (L., 1758), Rattus argentiventer (Robinson & Kloss, 1916), Rattus losea (Swinhoe, 1870), and Bandicota indica (Bechstein, 1800) in Chiangrai Province northern Thailand. The new species was collected in active rice fields and adjacent fruit plantation areas. The etiological agent of scrub typhus, Orientia (formerly Rickettsia) tsutsugamushi (Hayashi), has been isolated from patients who live and work in the same habitat where L. chiangraiensis is the predominant Leptotrombidium species.

Microsatellite polymorphism in Anopheles maculatus, a malaria vector in Thailand.

Dinucleotide microsatellites were characterized from Anopheles maculatus, a species of mosquito that transmits malaria. A partial genomic library of An. maculatus, consisting of 3,960 kilobases (kb), was screened with either (GT)12 or (CT)12 probes. Approximately 1.5% of the recombinants contained sequences that hybridized to either (GT)12 or (CT)12 dinucleotide probes, suggesting that microsatellites are abundant in the genome of An. maculatus. Estimation of abundance of the two dinucleotide repeats revealed that (GT)n or (CA)n microsatellites occur on average every 68 kb and (CT)n or (GA)n repeats every 495 kb. Among 23 microsatellite loci sequenced, four loci were selected to synthesize primers to perform polymerase chain reaction scoring for genetic polymorphism in a population of An. maculatus. A high level of polymorphism was observed with all four microsatellite loci analyzed. The number of alleles detected at each locus ranged from eight to 12 and the heterozygosities ranged from 0.25 to 0.54. A total of 42 alleles were found among four microsatellite loci. The large number of alleles and polymorphic nature resolved from microsatellite loci make these markers valuable for the study of population genetic structure and gene flow. Knowledge of gene flow is required to develop vector control strategies using genetic manipulations of malaria vector populations.