Embryonic development and egg viability of wMel-infected Aedes aegypti.

BACKGROUND: Aedes aegypti is a major disease vector in urban habitats, involved in the transmission of dengue, chikungunya and Zika. Despite innumerous attempts to contain disease outbreaks, there are neither efficient vaccines nor definite vector control methods nowadays. In recent years, an innovative strategy to control arboviruses, which exploits the endosymbiotic bacterium Wolbachia pipientis, emerged with great expectations. The success of the method depends on many aspects, including Wolbachia's cytoplasmic incompatibility and pathogen interference phenotypes, as well as its effect on host fitness. In this work, we investigated the influence the Wolbachia strain wMel exerts on embryo development and egg viability and speculate on its field release use. METHODS: Wild-type (Br or Rockefeller) and Wolbachia-harboring specimens (wMelBr) were blood-fed and submitted to synchronous egg laying for embryo development assays. Samples were analyzed for morphological markers, developmental endpoint and egg resistance to desiccation (ERD). Quiescent egg viability over time was also assessed. RESULTS: wMelBr samples completed embryogenesis 2-3 hours later than wild-type. This delay was also observed through the onset of both morphological and physiological markers, respectively by the moments of germband extension and ERD acquisition. Following the end of embryonic development, wMelBr eggs were slightly less resistant to desiccation and showed reduced viability levels, which rapidly decayed after 40 days into quiescence, from approximately 75% to virtually 0% in less than a month. CONCLUSIONS: Our data revealed that the wMel strain of Wolbachia slightly delays embryogenesis and also affects egg quality, both through reduced viability and desiccation resistance. These findings suggest that, although embryonic fitness is somehow compromised by wMel infection, an efficient host reproductive manipulation through cytoplasmic incompatibility seems sufficient to overcome these effects in nature and promote bacterial invasion, as shown by successful ongoing field implementation.

The Impact of Selection with Diflubenzuron, a Chitin Synthesis Inhibitor, on the Fitness of Two Brazilian Aedes aegypti Field Populations.

Several Aedes aegypti field populations are resistant to neurotoxic insecticides, mainly organophoshates and pyrethroids, which are extensively used as larvicides and adulticides, respectively. Diflubenzuron (DFB), a chitin synthesis inhibitor (CSI), was recently approved for use in drinking water, and is presently employed in Brazil for Ae. aegypti control, against populations resistant to the organophosphate temephos. However, tests of DFB efficacy against field Ae. aegypti populations are lacking. In addition, information regarding the dynamics of CSI resistance, and characterization of any potential fitness effects that may arise in conjunction with resistance are essential for new Ae. aegypti control strategies. Here, the efficacy of DFB was evaluated for two Brazilian Ae. aegypti populations known to be resistant to both temephos and the pyrethroid deltamethrin. Laboratory selection for DFB resistance was then performed over six or seven generations, using a fixed dose of insecticide that inhibited 80% of adult emergence in the first generation. The selection process was stopped when adult emergence in the diflubenzuron-treated groups was equivalent to that of the control groups, kept without insecticide. Diflubenzuron was effective against the two Ae. aegypti field populations evaluated, regardless of their resistance level to neurotoxic insecticides. However, only a few generations of DFB selection were sufficient to change the susceptible status of both populations to this compound. Several aspects of mosquito biology were affected in both selected populations, indicating that diflubenzuron resistance acquisition is associated with a fitness cost. We believe that these results can significantly contribute to the design of control strategies involving the use of insect growth regulators.

Effect of triflumuron, a chitin synthesis inhibitor, on Aedes aegypti, Aedes albopictus and Culex quinquefasciatus under laboratory conditions.

BACKGROUND: Resistance to traditional insecticides represents a threat to the control of disease vectors. The insect growth regulators (IGR) are a potential alternative to control mosquitoes, including resistant populations. The chitin synthesis inhibitors (CSI) are IGRs, which interfere with the insect molting process and represent one major class of compounds against Aedes aegypti populations resistant to the larvicide organophosphate temephos. In the present study, we evaluated the efficacy of the CSI triflumuron on Culex quinquefasciatus, Aedes albopictus and against several Ae. aegypti field populations. METHODS: The efficacy of triflumuron, against Cx. quinquefasciatus and Ae. albopictus was evaluated with laboratory strains through dose-response assays. Additionaly, this CSI was tested against seven Ae. aegypti field populations exhibiting distinct resistance levels to both temephos and the pyrethroid deltamethrin. Aedes aegypti populations were exposed to both a dose that inhibits 99% of the adult emergence of mosquitoes from the susceptible reference strain, Rockefeller, (EI99 = 3.95 µg/L) and the diagnostic dose (DD), corresponding to twice the EI99. RESULTS: Our results indicate that triflumuron was effective in emergence inhibition (EI) of Cx. quinquefasciatus (EI50 = 5.28 µg/L; EI90= 12.47 µg/L) and Ae. albopictus (EI50 = 1.59 µg/L; EI90= 2.63 µg/L). Triflumuron was also effective against seven Ae. aegypti Brazilian populations resistant to both temephos and deltamethrin. Exposure of all the Ae. aegypti populations to the triflumuron EI99 of the susceptible reference strain, Rockefeller, resulted in complete inhibition of adult emergence, suggesting no cross-resistance among traditional insecticides and this CSI. However, a positive correlation between temephos resistance and tolerance to triflumuron was observed. CONCLUSION: The results suggest that triflumuron represents a potential tool for the control of disease vectors in public health. Nevertheless, they point to the need of constant monitoring of the susceptibility status of vector populations to CSIs.

Fitness evaluation of two Brazilian Aedes aegypti field populations with distinct levels of resistance to the organophosphate temephos.

In Brazil, decades of dengue vector control using organophosphates and pyrethroids have led to dissemination of resistance. Although these insecticides have been employed for decades against Aedes aegypti in the country, knowledge of the impact of temephos resistance on vector viability is limited. We evaluated several fitness parameters in two Brazilian Ae. aegypti populations, both classified as deltamethrin resistant but with distinct resistant ratios (RR) for temephos. The insecticide-susceptible Rockefeller strain was used as an experimental control. The population presenting the higher temephos resistance level, Aparecida de Goiânia, state of Goiás (RR(95) of 19.2), exhibited deficiency in the following four parameters: blood meal acceptance, amount of ingested blood, number of eggs and frequency of inseminated females. Mosquitoes from Boa Vista, state of Roraima, the population with lower temephos resistance level (RR(95) of 7.4), presented impairment in only two parameters, blood meal acceptance and frequency of inseminated females. These results indicate that the overall fitness handicap was proportional to temephos resistance levels. However, it is unlikely that these disabilities can be attributed solely to temephos resistance, since both populations are also resistant to deltamethrin and harbour the kdr allele, which indicates resistance to pyrethroids. The effects of reduced fitness in resistant populations are discussed.

Fitness evaluation of two Brazilian Aedes aegypti field populations with distinct levels of resistance to the organophosphate temephos

In Brazil, decades of dengue vector control using organophosphates and pyrethroids have led to dissemination of resistance. Although these insecticides have been employed for decades against Aedes aegypti in the country, knowledge of the impact of temephos resistance on vector viability is limited. We evaluated several fitness parameters in two Brazilian Ae. aegypti populations, both classified as deltamethrin resistant but with distinct resistant ratios (RR) for temephos. The insecticide-susceptible Rockefeller strain was used as an experimental control. The population presenting the higher temephos resistance level, Aparecida de Goiânia, state of Goiás (RR95 of 19.2), exhibited deficiency in the following four parameters: blood meal acceptance, amount of ingested blood, number of eggs and frequency of inseminated females. Mosquitoes from Boa Vista, state of Roraima, the population with lower temephos resistance level (RR95 of 7.4), presented impairment in only two parameters, blood meal acceptance and frequency of inseminated females. These results indicate that the overall fitness handicap was proportional to temephos resistance levels. However, it is unlikely that these disabilities can be attributed solely to temephos resistance, since both populations are also resistant to deltamethrin and harbour the kdr allele, which indicates resistance to pyrethroids. The effects of reduced fitness in resistant populations are discussed.

Effect of the chitin synthesis inhibitor triflumuron on the development, viability and reproduction of Aedes aegypti.

The control of Aedes aegypti is impaired due to the development of resistance to chemical insecticides. Insect Growth Regulators (IGR) exhibit distinct mechanisms of action and are considered potential vector control alternatives. Studies regarding the effects of sublethal IGR doses on the viability of resulting adults will contribute to eval-uating their impact in the field. We analyzed several aspects of Ae. aegypti adults surviving exposure to a partially lethal dose of triflumuron, a chitin synthesis inhibitor. A highly significant difference in the proportion of males and females was noted in the triflumuron-exposed group (65.0% males) compared to the controls (50.2% males). Triflumuron affected adult longevity, particularly for females; after 16 days, only 29.2% of males and 13.8% of females were alive, in contrast with 94% survival of the control mosquitoes. The locomotor activity was reduced and the blood-feeding ability of the treated females was also affected (90.4% and 48.4% of the control and triflumuron-exposed females, respectively, successfully ingested blood). Triflumuron-surviving females ingested roughly 30% less blood and laid 25% fewer eggs than the control females. The treated males and females exhibited a diminished ability to copulate, resulting in less viable eggs.

Effect of the chitin synthesis inhibitor triflumuron on the development, viability and reproduction of Aedes aegypti

The control of Aedes aegypti is impaired due to the development of resistance to chemical insecticides. Insect Growth Regulators (IGR) exhibit distinct mechanisms of action and are considered potential vector control alternatives. Studies regarding the effects of sublethal IGR doses on the viability of resulting adults will contribute to eval-uating their impact in the field. We analyzed several aspects of Ae. aegypti adults surviving exposure to a partially lethal dose of triflumuron, a chitin synthesis inhibitor. A highly significant difference in the proportion of males and females was noted in the triflumuron-exposed group (65.0 percent males) compared to the controls (50.2 percent males). Triflumuron affected adult longevity, particularly for females; after 16 days, only 29.2 percent of males and 13.8 percent of females were alive, in contrast with 94 percent survival of the control mosquitoes. The locomotor activity was reduced and the blood-feeding ability of the treated females was also affected (90.4 percent and 48.4 percent of the control and triflumuron-exposed females, respectively, successfully ingested blood). Triflumuron-surviving females ingested roughly 30 percent less blood and laid 25 percent fewer eggs than the control females. The treated males and females exhibited a diminished ability to copulate, resulting in less viable eggs.

Chitin synthesis inhibitor effect on Aedes aegypti populations susceptible and resistant to organophosphate temephos.

BACKGROUND: In Brazil, dengue vector control is hampered by the resistance of Aedes aegypti L. populations to organophosphates (OPs). Insect growth regulators (IGRs) are a promising alternative, as their mechanisms of action are different from those of conventional insecticides. The authors analysed the effect of the IGR triflumuron, a chitin synthesis inhibitor, on the Ae. aegypti insecticide-susceptible strain Rockefeller, as well as on field populations both susceptible (TemS) and resistant (TemR) to the OP temephos. RESULTS: Triflumuron arrested development and inhibited adult emergence of the Rockefeller strain in a dose-dependent way (EI(50) and EI(90) of 0.8 and 1.8 microg L(-1) respectively). A direct relationship between triflumuron concentration and the precocity of its effects was evident. TemS and TemR temephos resistance ratios (RR(90)) were 4.5 and 13.8, triflumuron RR(90) being 1.0 and 1.3 respectively. CONCLUSION: The IGR triflumuron exhibited a dose-dependent effect against the reference Ae. aegypti Rockefeller strain. It was also effective against two field populations, regardless of their OP resistance status. The present results are discussed in the context of utilization of chitin synthesis inhibitors as potential alternatives in the control of Ae. aegypti in Brazil.

Efeito de triflumuron- um inibidor da síntese de quitina - sobre o desenvolvimento e a reprodução de culicídeos vetores de doenças / Effect of triflumuron- an inhibitor of the synthesis of quitina - on the development and the reproduction of culicidae disease vectors

Aedes aegypti, Aedes albopictus e Culex quinquefasciatus são 3 espécies de mosquito difundidas principalmente nas regiões tropicais e subtropicais do globo. No Brasil, estão relacionadas com a transmissão de doenças como a dengue e a filariose linfática e há grande preocupação com sua potencial participação na transmissão de outras arboviroses, como o vírus do oeste do Nilo e o da febre amarela. Atualmente, a principal forma de combate a vetores de doenças é realizada através do uso de inseticidas químicos, cujo sítio de ação é o sistema nervoso central do inseto. Como conseqüência do uso maciço destes produtos, a freqüência de indivíduos resistentes em populações de várias espécies de insetos vetores tem aumentado. Os reguladores do desenvolvimento de insetos aparecem como uma nova alternativa de controle de mosquitos vetores. Neste grupo, encontram-se os inibidores da síntese de quitina (CSI), substâncias que prejudicam o processo de muda, acarretando deficiências principalmente na cutícula dos insetos. No presente trabalho, verificou-se que o CSI triflumuron foi eficaz contra estas 3 espécies de culicídeos vetores, em concentrações na ordem de (miu)g/L. Além disso, foi investigado o efeito da aplicação, em larvas, de dose parcialmente letal de triflumuron sobre vários aspectos da biologia de Ae. aegypti. De modo geral, a longevidade, aceitação do repasto sangüíneo, volume de sangue ingerido, reprodução e postura são afetados negativamente nos adultos sobreviventes ao tratamento na fase imatura. Triflumuron foi eficaz contra diversas populações de campo de Ae. aegypti, com diferentes níveis de susceptibilidade ao organofosforado temephos e ao piretróide deltametrina: não houve emergência de adultos viáveis quando as larvas foram expostas à IE99 de triflumuron para a cepa-referência Rockefeller. Embora não tenha sido detectada resistência cruzada entre aqueles inseticidas químicos e o CSI, a mortalidade de populações resistentes ao temephos, mas não à deltam...