Physiological resistance and behavioral responses of mosquito vectors to insecticides are critical aspects of the chemical-based disease control equation. The complex interaction between lethal, sub-lethal and excitation/repellent ('excito-repellent’) properties of chemicals is typically overlooked in vector management and control programs. The development of “physiological” resistance, metabolic and/or target site modifications, to insecticides has been well documented in many insect groups and disease vectors around the world. In Thailand, resistance in many mosquito populations has developed to all three classes of insecticidal active ingredients currently used for vector control with a majority being synthetic-derived pyrethroids. Evidence of low-grade insecticide resistance requires immediate countermeasures to mitigate further intensification and spread of the genetic mechanisms responsible for resistance. This can take the form of rotation of a different class of chemical, addition of a synergist, mixtures of chemicals or concurrent mosaic application of different classes of chemicals. From the gathered evidence, the distribution and degree of physiological resistance has been restricted in specific areas of Thailand in spite of long-term use of chemicals to control insect pests and disease vectors throughout the country. Most surprisingly, there have been no reported cases of pyrethroid resistance in anopheline populations in the country from 2000 to 2011. The precise reasons for this are unclear but we assume that behavioral avoidance to insecticides may play a significant role in reducing the selection pressure and thus occurrence and spread of insecticide resistance. The review herein provides information regarding the status of physiological resistance and behavioral avoidance of the primary mosquito vectors of human diseases to insecticides in Thailand from 2000 to 2011.

The blow fly, Chrysomya megacephala (Fabricius), and house fly, Musca domestica L., are medically and forensically important flies. The population dynamic of these flies is essential for both control and forensical aspects. The aim of this study was to investigate the climatic and physical factors affecting the population trend of both species in Chiang Mai province, northern Thailand, using the Geographic Information System (GIS). Based on systematic random sampling, 18 study sites were selected in three districts (Mueang Chiang Mai, Mae Rim, and Hang Dong). Six land use types were involved in the study sites, i.e., disturbed mixed deciduous, mixed deciduous forest, mixed orchard, lowland village, city, and paddy field. Adult flies were sampled every 2 weeks using an in-house prototype reconstructable funnel trap. Two types of bait were used--one with fresh beef viscera for luring M. domestica and the other with 1-day tainted beef viscera for luring C. megacephala. Collections were conducted from May 2009 to May 2010, and analysis of climatic factors (temperature, relative humidity, and light intensity) was carried out. Correlation bivariate analysis was performed initially to determine the relationship between climatic factors and the number of flies. Consequently, an ordinary co-kriging approach, in ArcGIS 9.2, was performed to predict the spatial distribution of flies with land use and climatic factors as co-variables. A total of 63,158 flies were captured, with C. megacephala being the most common species collected (68.37%), while only 1.3% were M. domestica, thus proving that C. megacephala was the most abundant species in several land use types. A significantly higher number of females than males was found in both species. Fly populations can be collected throughout most of the year with a peak in late summer, which shows a positive relation to temperature but negative correlation with relative humidity. C. megacephala was predicted to be abundant in every land use type, from lowland to forested areas, while the density of house fly was association with altitude and land use types.

No abstract

Background, aim and scope Street sediment samples were collected at 50 locations in a mixed land use area of Hamilton, Ontario, Canada, and metal levels were analyzed using a sequential extraction procedure for different particle size classes to provide an estimate of potential toxicity as well as the potential for treatment through best management practices (BMPs). Methodology The street sediment samples were dry sieved into four different particle size categories and a sequential extraction procedure was done on each size category following the methodology proposed by Tessier et al. 1979 using a Hitachi 180-80 Polarized Zeeman Atomic Absorption Spectrophotometer. Results and discussion Analysis of variance, post hoc leastsignificant difference tests, and kriging analysis showed that spatially Mn and Fe levels were associated with a well-defined heavy industrial area that includes large iron-and steelmaking operations; Cu and Pb were associated with both the industrial and high-volume traffic areas, while Zn tended to be more associated with high-volume traffic areas. The potential bioavailability of the metals, based on the sum of chemical fractions 1 (exchangeable) and 2 (carbonate-bound), decreased in order: Zn > Cd > Mn > Pb > Cu > Fe. Based on aquatic sediment quality guidelines, there is some concern regarding the potential impact of the street sediment when runoff reaches receiving waters. Conclusions It is possible that a combination of BMPs, including street sweeping and constructed wetlands, could help to reduce street sediment impact on environmental quality in the Hamilton region. The data presented here would be important in developing and optimizing the design of these BMPs.

Lucilia cuprina and Hemipyrellia ligurriens are forensically important blow flies in many countries. The immature stage, in particular the third instar, of both species are generally similar in morphological appearance. In this study, the use of three main characteristics, the posterior spiracle, the dorsal spines between the first and second thoracic segments, and the cephalopharyngeal skeleton, allows for identification of both fly species, with the number of papillae on anterior spiracle being a supportive characteristic in some cases. Comparison of these characteristics is illustrated in detail.