BackgroundAedes aegypti mosquitoes are the main vectors of dengue viruses to humans. Understanding their biology and interactions with the pathogen are prerequisites for development of dengue transmission control strategies. Mosquito salivary glands are organs involved directly in pathogen transmission to vertebrate hosts. Information on the spatial distribution of gene expression in these organs is expected to assist in the development of novel disease control strategies, including those that entail the release of transgenic mosquitoes with impaired vector competence.ResultsWe report here the hybridization in situ patterns of 30 transcripts expressed in the salivary glands of adult Ae. aegypti females. Distinct spatial accumulation patterns were identified. The products of twelve genes are localized exclusively in the proximal-lateral lobes. Among these, three accumulate preferentially in the most anterior portion of the proximal-lateral lobe. This pattern revealed a salivary gland cell type previously undescribed in Ae. aegypti, which was validated by transmission electron microscopy. Five distinct gene products accumulate in the distal-lateral lobes and another five localize in the medial lobe. Seven transcripts are found in the distal-lateral and medial lobes. The transcriptional product of one gene accumulates in proximal- and distal-lateral lobes. Seven genes analyzed by quantitative PCR are expressed constitutively. The most abundant salivary gland transcripts are those localized within the proximal-lateral lobes, while previous work has shown that the distal-lateral lobes are the most active in protein synthesis. This incongruity suggests a role for translational regulation in mosquito saliva production.ConclusionsTransgenic mosquitoes with reduced vector competence have been proposed as tools for the control of dengue virus transmission. Expression of anti-dengue effector molecules in the distal-lateral lobes of Ae. aegypti salivary glands has been shown to reduce prevalence and mean intensities of viral infection. We anticipate greater efficiency of viral suppression if effector genes are expressed in all lobes of the salivary glands. Based on our data, a minimum of two promoters is necessary to drive the expression of one or more anti-dengue genes in all cells of the female salivary glands.

BackgroundAgrochemicals have been widely used in Pakistan for several years. This exposes mosquito populations, particularly those present around agricultural settings, to an intense selection pressure for insecticide resistance. The aim of the present study was to investigate the toxicity of representative agrochemicals against various populations of Aedes albopictus (Skuse) collected from three different regions from 2008-2010.ResultsFor organophosphates and pyrethroids, the resistance ratios compared with susceptible Lab-PK were in the range of 157-266 fold for chlorpyrifos, 24-52 fold for profenofos, 41-71 fold for triazofos, and 15-26 fold for cypermethrin, 15-53 fold for deltamethrin and 21-58 fold for lambdacyhalothrin. The resistance ratios for carbamates and new insecticides were in the range of 13-22 fold for methomyl, 24-30 fold for thiodicarb, and 41-101 fold for indoxacarb, 14-27 fold for emamectin benzoate and 23-50 fold for spinosad. Pair wise comparisons of the log LC50s of insecticides revealed correlation among several insecticides, suggesting a possible cross resistance mechanism. Moreover, resistance remained stable across 3 years, suggesting field selection for general fitness had also taken place for various populations of Ae. albopictus.ConclusionModerate to high level of resistance to agrochemicals in Pakistani field populations of Ae. albopictus is reported here first time. The geographic extent of resistance is unknown but, if widespread, may lead to problems in future vector control.

House flies, Musca domestica L., are important pests of dairy operations worldwide, with the ability to adapt wide range of environmental conditions. There are a number of insecticides used for their management, but development of resistance is a serious problem. Insecticide mixtures could enhance the toxicity of insecticides in resistant insect pests, thus resulting as a potential resistance management tool. The toxicity of bifenthrin, cypermethrin, deltamethrin, chlorpyrifos, profenofos, emamectin benzoate and fipronil were assessed separately, and in mixtures against house flies. A field-collected population was significantly resistant to all the insecticides under investigation when compared with a laboratory susceptible strain. Most of the insecticide mixtures like one pyrethroid with other compounds evaluated under two conditions (1∶1-“A” and LC50: LC50-“B”) significantly increased the toxicity of pyrethroids in the field population. Under both conditions, the combination indices of pyrethroids with other compounds, in most of the cases, were significantly below 1, suggesting synergism. The enzyme inhibitors, PBO and DEF, when used in combination with insecticides against the resistant population, toxicities of bifenthrin, cypermethrin, deltamethrin and emamectin were significantly increased, suggesting esterase and monooxygenase based resistance mechanism. The toxicities of bifenthrin, cypermethrin and deltamethrin in the resistant population of house flies could be enhanced by the combination with chlorpyrifos, profenofos, emamectin and fipronil. The findings of the present study might have practical significance for resistance management in house flies.

The house fly, Musca domestica L., is one of the major pests in dairy operations that has developed resistance to a number of insecticides with different modes of action. Adult house fly populations from six dairies in Punjab, Pakistan were evaluated for resistance to insecticides with novel modes of action (abamectin, emamectin benzoate, fipronil, imidacloprid, indoxacarb, and spinosad). Significant levels of resistance to most of the insecticides tested were observed in the present study. For avermectins at LC50 level, the resistance ratios were in the range of 38.40 to 94.44-fold for abamectin and 13.16 to 36.30-fold for emamectin benzoate. Fipronil LC50 resistance ratios exceeded 10-fold in three house fly populations, while all the populations had >10-fold resistance ratios for imidacloprid. Indoxacarb and spinosad had the lowest resistance ratios that ranged from 3.02 to 7.12-fold for indoxacarb and 2.91 to 9.0-fold for spinosad. As the resistance to fipronil, indoxacarb, and spinosad are emerging, therefore these chemicals should be used cautiously in management programs to retain the efficacy for longer times.

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The house fly, Musca domestica L. (Diptera: Muscidae) is one of the major pests of confined and pastured livestock worldwide. Livestock manures play an important role in the development and spread of M. domestica. In the present study, we investigated the impact of different livestock manures on the fitness and relative growth rate of M. domestica and intrinsic rate of natural increase. We tested the hypotheses by studying life history parameters including developmental time from egg to adult's eclosion, fecundity, longevity, and survival on manures of buffalo, cow, nursing calf, dog, horse, poultry, sheep, and goat, which revealed significant differences that might be associated with fitness costs. The maggots reared on poultry manure developed faster compared to any other host manure. The total developmental time was the shortest on poultry manure and the longest on horse manure. The fecundity by females reared on poultry, nursing calf, and dog manures was greater than on any other host manures. Similarly, percent survival of immature stages, pupal weight, eggs viability, adults' eclosion, survival and longevity, intrinsic rate of natural increase, and biotic potential were significantly higher on poultry, nursing calf, and dog manures compared to any other livestock manures tested. However, the sex ratio of adult flies remained the same on all types of manures. The low survival on horse, buffalo, cow, sheep, and goat manures suggest unsuitability of these manures, while the higher pupal weight on poultry, nursing calf, and dog manures suggest that these may provide better food quality to M. domestica compared with any other host manures. Our results point to the role of livestock manures in increasing local M. domestica populations. Such results could help to design cultural management strategies which may include sanitation, moisture management, and manure removal.

The house fly, Musca domestica L., is an important hygienic pest of humans and dairy animals with the potential to develop resistance to most chemical classes of insecticides. Six adult house fly strains from dairy farms in Punjab, Pakistan were evaluated for resistance to selected insecticides from organochlorine, organophosphate, carbamate and pyrethroid classes. For a chlorocyclodiene and two organophosphates tested, the resistance ratios (RR) at LC50 were in the range of 5.60-22.02 fold for endosulfan, 7.66-23.24 fold for profenofos and 2.47-7.44 fold for chlorpyrifos. For two pyrethroids and one carbamate, the RR values at LC50 were 30.22-70.02 for cypermethrin, 5.73-18.31 for deltamethrin, and 4.39-15.50 for methomyl. This is the first report of resistance to different classes of insecticides in Pakistani dairy populations of house flies. Regular insecticide resistance monitoring programs on dairy farms are needed to prevent field control failures. Moreover, integrated approaches including the judicious use of insecticides are needed to delay the development of insecticide resistance in house flies.

The diamondback moth, Plutella xylostella, is recognized as a widely distributed destructive insect pest of Brassica worldwide. The management of this pest is a serious issue, and an estimated annual cost of its management has reached approximately US$4 billion. Despite the fact that chemicals are a serious threat to the environment, lots of chemicals are applied for controlling various insect pests especially P. xylostella. An overreliance on chemical control has not only led to the evolution of resistance to insecticides and to a reduction of natural enemies but also has polluted various components of water, air, and soil ecosystem. In the present scenario, there is a need to implement an environmentally friendly integrated pest management (IPM) approach with new management tactics (microbial control, biological control, cultural control, mating disruption, insecticide rotation strategies, and plant resistance) for an alternative to chemical control. The IPM approach is not only economically beneficial but also reduces the environmental and health risks. The present review synthesizes published information on the insecticide resistance against P. xylostella and emphasizes on adopting an alternative environmentally friendly IPM approach for controlling P. xylostella in China.