The lethal ovitrap: a response to the resurgence of dengue and chikungunya.

There has been a global resurgence in dengue fever since the 1960s and now more than one third of the world's population lives in dengue endemic areas. Chikungunya, another mosquito-borne disease, had been limited to sub-Saharan Africa and Southeast Asia, but recently spread to Italy and France, raising concerns that it could spread to many more countries in Europe and the Americas. There are currently no vaccines available to prevent infection with either virus and medical care is limited to symptomatic and supportive treatments. Suppression of the mosquito vector populations reduces disease transmission, however, the tools currently available to control the main vectors of dengue and chikungunya are inadequate. Larval control is very labor intensive and pesticide sprays do not adequately penetrate the microhabitats where adult mosquitoes are sequestered. The lethal ovitrap addresses these shortcomings by luring the potentially viremic female mosquitoes to an egg laying site where they are exposed to a toxic insecticide dose. It is a safe, environmentally sound, economical, and simple means of dengue and chikungunya vector control whose efficacy has been documented in 9 research papers. Management programs using the lethal ovitrap have been shown to halt dengue and chikungunya transmission. Efforts are underway to mass produce the lethal ovitrap under the registered trade name Trap-N-Kill which will ensure its availability to our armed forces deployed in dengue and chikungunya endemic areas.

Using geographic information systems to maximize environmental surveillance efforts and impact.

There has been tremendous advancement in geographic information systems (GIS) software and hardware over the last 2 decades. This article illustrates how these advancements can be used to greatly increase the ease and efficiency of collecting environmental samples and demonstrate how environmental data collected within a GIS is more valuable because of the visualization, analysis, and historical capabilities of GIS. This article reviews 6 actual field surveys conducted using desktop GIS and field GIS by entomologists with the US Army Public Health Command (Provisional). While these examples entail entomological data, the techniques and procedures are applicable to any type of environmental data.

Impact of source reduction on the spatial distribution of larvae and pupae of Aedes albopictus (Diptera: Culicidae) in suburban neighborhoods of a Piedmont community in North Carolina.

Aedes albopictus (Skuse) is a principal nuisance mosquito species and a potential arbovirus vector throughout its geographic range in the United States. This species lays eggs, and progeny complete development in water-filled containers that are discarded in suburban landscapes. Source reduction of containers, achieved through environmental sanitation, was used to experimentally manipulate mosquito production to gain insight into the spatial structure of the population of immature Ae. albopictus. Our studies were conducted in suburban landscapes in Raleigh, NC, during the 2002 and 2003 mosquito seasons. Spatial analyses, using estimates of the mean and total standing crop of pupae and counts of the numbers of mosquito-positive containers, showed that the distribution of mosquito production was not spatially dependent on a neighborhood-wide basis. However, in all neighborhoods, mosquito production was clustered in at least one and often more than one adjacent residence. Point pattern analyses that considered only the presence or absence of pupae showed that pupae-positive residences were dispersed throughout neighborhoods receiving monthly source reduction treatments and clustered throughout control neighborhoods, indicating that source reduction affected the spatial distribution of pupae. Conversely, spatial analyses based on the presence or absence of larvae and pupae showed that mosquito production was randomly distributed among residences in both control and source reduction neighborhoods, showing that Ae. albopictus recolonized containers within several weeks after source reduction was implemented. Knowledge of the spatial distribution of production sites would allow management efforts for Ae. albopictus to be targeted to residences supporting high levels of mosquito production.

Spatial analysis of Aedes albopictus (Diptera: Culicidae) oviposition in suburban neighborhoods of a Piedmont community in North Carolina.

Temporal and spatial distribution of egg-laying by Aedes albopictus (Skuse) (Diptera: Culicidae) was investigated in suburban neighborhoods in Raleigh, NC, by using oviposition traps (ovitraps) at fixed sampling stations during the 2002 and 2003 mosquito seasons. Variations in the phenology of oviposition between the two mosquito seasons resulted from differences in the patterns and amounts of rainfall early in the season. Aerial images of each study neighborhood were digitized, and the proportions of specific types of land cover within buffer zones encompassing ovitraps were estimated. Retrospective analyses showed that in some neighborhoods, oviposition intensity was significantly associated with specific types of land cover. However, in general, it seemed that gravid Ae. albopictus searched throughout the landscape for water-filled containers in which to lay eggs. Peridomestic surveys were carried out concurrently with ovitrap collections to estimate production of Ae. albopictus pupae in discarded water-filled containers and the abundance of females in vegetation that made up the resting habitat. Results of linear regression analyses indicated that the mean standing crop of pupae (total and per container) per residence was not a significant predictor of mean egg densities in ovitraps. However, the mean standing crop of adult females was a significant but weak predictor variable, because the magnitude and sign of regression coefficients varied between neighborhoods. Linear spatial regression analyses revealed that oviposition intensity was not spatially dependent on pupal standing crop or the numbers of pupae-positive containers distributed peridomestically. However, a weak spatial dependence on the standing crop of adult females was found in some neighborhoods. Based on spherical variogram models, kriging was carried out to predict the spatial patterns of oviposition in suburban neighborhoods. Focal areas of high and low oviposition intensity were evident in most neighborhoods; however, the spatial patterns of oviposition changed between mosquito seasons. Kriging predictions were evaluated, using cross-validation, by systematically removing each data point from our data set and predicting the removed point by using the remaining points. The root mean square (standardized) error values of best fitting variogram models approximated 1, and plots of standardized PRESS residuals showed no distinct pattern for most neighborhoods, indicating that predictions of the spatial distribution of oviposition intensity were valid. Spherical variogram models are a satisfactory method for describing the spatial distribution of Ae. albopictus oviposition, and kriging can be a useful technique for predicting oviposition intensity at locations that have not been sampled.

Field evaluation of a lethal ovitrap for the control of Aedes aegypti (Diptera: Culicidae) in Thailand.

In 1999 and 2000 we evaluated a lethal ovitrap (LO) for the control of Aedes aegypti (L.) in three villages in Ratchaburi Province, Thailand. Two blocks of 50 houses (a minimum of 250 m apart) served as treatment and control sites in each village, with each house in the treatment area receiving 10 LOs. Thirty houses in the center of each treatment and control block were selected as sampling sites, with larval and adult mosquito sampling initiated when LOs were placed. Sampling was conducted weekly in 10 of the 30 houses at each site, with each block of 10 houses sampled every third week. Sampling continued for 30 wk. Efficacy of the LO was evaluated by determining number of containers with larvae and/or pupae per house and number of adult mosquitoes collected inside each house. In 1999, the LO had a negligible impact on all measures of Ae. aegypti abundance that were assessed; however, fungal contamination of insecticide-impregnated strips may have been responsible for the low efficacy. In 2000, significant suppression was achieved based on changes in multiple entomologic criteria (containers with larvae, containers with pupae, and number of adult Ae. aegypti); however, control was not absolute and neither immature nor adult Ae. aegypti were ever eliminated completely. We conclude that the LO can reduce adult Ae. aegypti populations in Thailand; however, efficacy of the LO is lower than desired due primarily to the high number of alternative oviposition sites. LO efficacy may be improved when used as part of an integrated control program that places emphasis on reduction of adjacent larval habitats. Further studies are required to assess this issue.

Environmental factors associated with larval habitats of malaria vectors in northern Kyunggi Province, Republic of Korea.

The larval habitats of malaria vectors near the Demilitarized Zone of the Republic of Korea (ROK) were sampled from June through September 2000 to determine larval abundance and to identify environmental factors associated with high larval density. Six primary habitats were identified: rice fields, irrigation ditches, drainage ditches, stream pools, irrigation pools, and marshes. Most habitats harbored similar densities of larvae until August and September, when population densities in rice fields declined and those in irrigation pools increased. The primary vector in the ROK, Anopheles sinensis, occurred in water with a wide range of values for environmental factors, including pH, total dissolved solids, percent of surface covered with floating vegetation, and nitrate and phosphate concentrations. No environmental factor or combination of factors were found that were predictive of high larval densities. This study suggests that larval Anopheles are capable of developing in a wide range of stagnant, freshwater habitats in northern Kyunggi Province, ROK.