Effects of insemination and blood-feeding on locomotor activity of Aedes albopictus and Aedes aegypti (Diptera: Culicidae) females under laboratory conditions

Background\ud Dengue is an arbovirus disease transmitted by two Aedes mosquitoes: Ae. aegypti and Ae. albopictus. Virgin females of these two species generally show a bimodal and diurnal pattern of activity, with early morning and late afternoon peaks. Although some studies on the flight activity of virgin, inseminated and blood-fed Ae. aegypti females have been carried out under laboratory conditions, little is known about the effects of such physiological states on the locomotor activity of Ae. albopictus and Ae. aegypti females. The aim of this study was to analyze, under laboratory conditions, the effects of insemination and blood-feeding on the locomotor activity of Ae. albopictus and Ae. aegypti females under LD 12:12, at 25°C.\ud \ud \ud Methods\ud Both Ae. albopictus and Ae. aegypti females were obtained from established laboratory colonies. Control groups were represented by virgin/unfed Ae. albopictus and Ae. aegypti females. Experiments were conducted under laboratory conditions, using an activity monitor that registers individual activity every thirty minutes.\ud \ud \ud Results\ud Virgin/unfed Ae. albopictus and Ae. aegypti females showed a diurnal and bimodal pattern of locomotor activity, with peaks at early morning and late afternoon. Insemination and blood-feeding significantly decreased the locomotor activity of Ae. aegypti females, but inseminated/blood-fed Ae. aegypti and Ae. albopictus females showed a similar significant decrease on the locomotor activity compared to virgin/unfed females.\ud \ud \ud Conclusions\ud This study is the first demonstration of the effects of insemination and blood-feeding on the locomotor activity of Ae. albopictus and Ae. aegypti females under artificial conditions. Data suggest that Ae. albopictus and Ae. aegypti females respond in different ways to physiological status changes and such divergence between these two dengue vectors, associated with several ecological differences, could be related to the greater dengue vectorial capacity of Ae. aegypti in Americas in comparison to Ae. albopictus.HHMIFiocruzFaperjCNP

Dengue Infection Increases the Locomotor Activity of Aedes aegypti Females

BACKGROUND: Aedes aegypti is the main vector of the virus causing Dengue fever, a disease that has increased dramatically in importance in recent decades, affecting many tropical and sub-tropical areas of the globe. It is known that viruses and other parasites can potentially alter vector behavior. We investigated whether infection with Dengue virus modifies the behavior of Aedes aegypti females with respect to their activity level. METHODS/PRINCIPAL FINDINGS: We carried out intrathoracic Dengue 2 virus (DENV-2) infections in Aedes aegypti females and recorded their locomotor activity behavior. We observed an increase of up to ∼50% in the activity of infected mosquitoes compared to the uninfected controls. CONCLUSIONS: Dengue infection alters mosquito locomotor activity behavior. We speculate that the higher levels of activity observed in infected Aedes aegypti females might involve the circadian clock. Further studies are needed to assess whether this behavioral change could have implications for the dynamics of Dengue virus transmission

Assessing the Effects of <i>Aedes aegypti kdr</i> Mutations on Pyrethroid Resistance and Its Fitness Cost

<div><p>Pyrethroids are the most used insecticide class worldwide. They target the voltage gated sodium channel (Na_V), inducing the knockdown effect. In <i>Aedes aegypti</i>, the main dengue vector, the AaNa_V substitutions Val1016Ile and Phe1534Cys are the most important knockdown resistance (<i>kdr</i>) mutations. We evaluated the fitness cost of these <i>kdr</i> mutations related to distinct aspects of development and reproduction, in the absence of any other major resistance mechanism. To accomplish this, we initially set up 68 crosses with mosquitoes from a natural population. Allele-specific PCR revealed that one couple, the one originating the CIT-32 strain, had both parents homozygous for both <i>kdr</i> mutations. However, this pyrethroid resistant strain also presented high levels of detoxifying enzymes, which synergistically account for resistance, as revealed by biological and biochemical assays. Therefore, we carried out backcrosses between CIT-32 and Rockefeller (an insecticide susceptible strain) for eight generations in order to bring the <i>kdr</i> mutation into a susceptible genetic background. This new strain, named Rock-kdr, was highly resistant to pyrethroid and presented reduced alteration of detoxifying activity. Fitness of the Rock-kdr was then evaluated in comparison with Rockefeller. In this strain, larval development took longer, adults had an increased locomotor activity, fewer females laid eggs, and produced a lower number of eggs. Under an inter-strain competition scenario, the Rock-kdr larvae developed even slower. Moreover, when Rockefeller and Rock-kdr were reared together in population cage experiments during 15 generations in absence of insecticide, the mutant allele decreased in frequency. These results strongly suggest that the <i>Ae. aegypti kdr</i> mutations have a high fitness cost. Therefore, enhanced surveillance for resistance should be priority in localities where the <i>kdr</i> mutation is found before new adaptive alleles can be selected for diminishing the <i>kdr</i> deleterious effects.</p> </div

Activity of enzymes related to insecticide metabolic resistance in <i>Aedes aegypti</i> strains.

<p>The cut-offs are (dashed lines) determined by the Rockefeller 99 percentile value of each enzyme (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0060878#pone.0060878-Montella1" target="_blank">[11]</a>). Rockefeller is a reference strain of insecticide susceptibility and vigor. Distributions with less than 15% of individuals beyond the cut-off are considered unaltered. Between 15 and 50% are altered and above 50% are highly altered. CIT-32 is the original <i>kdr</i> strain, derived from a pyrethroid resistant Brazilian <i>Aedes aegypti</i> population. Rock-kdr is the <i>kdr</i> strain, backcrossed for eight generations with Rockefeller in order to reduce the contribution of detoxification enzymes to pyrethroid resistance.</p

Developmental timing of <i>Ae. aegypti</i> Rock and Rock-kdr male adult emergence competing under a stringent condition.

<p>A – Cumulative rate of male emergence up to the 8th day after the beginning of adult emergence when the controls Rock and Rock-kdr were reared separately (‘intra-strain’ conditions). B – Cumulative proportion of Rock or Rock-kdr male emergence from the inter-strain competition. Male strain was daily determined by randomly genotyping 30% of emerging individuals.</p

Oviposition performance of Rockefeller and Rock-kdr <i>Ae. aegypti</i> females.

<p>Oviposition performance of Rockefeller and Rock-kdr <i>Ae. aegypti</i> females.</p

Comparison of larval development time between Rockefeller and Rock-kdr <i>Ae. aegypti</i> strains.

<p>Numbers represent the cumulative daily proportion of Rock and Rock-kdr pupae formation after larvae eclosion under standard laboratory conditions. SEM is indicated. Gray dotted line indicates equal proportion (rate = 1) between strains.</p

Number of eggs laid by females from Rock and Rock-kdr <i>Ae. aegypti</i> strains.

<p>Each dot represents a single female. Only females that laid at least one egg were included. Median value with interquartile range is shown for each distribution. Dotted line points 50 eggs/female, which was herein empirically considered as discriminative of successful insemination. ***Difference between strains was highly significant by <i>t</i> test.</p

Locomotor activity Rock and Rock-kdr <i>Ae. aegypti</i> strains.

<p>Locomotor activity of susceptible (Rockefeller strain – blue line) and pyrethroid resistant (Rock-kdr – red line) <i>Aedes aegypti</i> females exposed two days under LD 12∶12, at 25°C. Dotted lines represent standard errors.</p