Experience‐ and age‐mediated oviposition behaviour in the yellow fever mosquito Stegomyia aegypti (=Aedes aegypti)

In repeated behaviours such as those of feeding and reproduction, past experiences can inform future behaviour. By altering their behaviour in response to environmental stimuli, insects in highly variable landscapes can tailor their behaviour to their particular environment. In particular, female mosquitoes may benefit from plasticity in their choice of egg‐laying site as these sites are often temporally variable and clustered. The opportunity to adapt egg‐laying behaviour to past experience also exists for mosquito populations as females typically lay eggs multiple times throughout their lives. Whether experience and age affect egg‐laying (or oviposition) behaviour in the mosquito Stegomyia aegypti (=Aedes aegypti) (Diptera: Culicidae) was assessed using a wind tunnel. Initially, gravid mosquitoes were provided with a cup containing either repellent or well water. After ovipositing in these cups, the mosquitoes were blood‐fed and introduced into a wind tunnel. In this wind tunnel, an oviposition cup containing repellent was placed in the immediate vicinity of the gravid mosquitoes. A cup containing well water was placed at the opposite end of the tunnel so that if the females flew across the chamber, they encountered the well water cup, in which they readily laid eggs. Mosquitoes previously exposed to repellent cups became significantly more likely to later lay eggs in repellent cups, suggesting that previous experience with suboptimal oviposition sites informs mosquitoes of the characteristics of nearby oviposition sites. These results provide further evidence that mosquitoes modify behaviour in response to environmental information and are demonstrated in a vector species in which behavioural plasticity may be ecologically and epidemiologically meaningful.     

An in vitro bioassay for the quantitative evaluation of mosquito repellents against Stegomyia aegypti (=Aedes aegypti) mosquitoes using a novel cocktail meal

To assess the efficacy of new insect repellents, an efficient and safe in vitro bioassay system using a multiple‐membrane blood‐feeding device and a cocktail meal was developed. The multiple‐membrane blood‐feeding device facilitates the identification of new insect repellents by the high‐throughput screening of candidate chemicals. A cocktail meal was developed as a replacement for blood for feeding females of Stegomyia aegypti (=Aedes aegypti) (L.) (Diptera: Culicidae). The cocktail meal consisted of a mixture of salt, albumin and dextrose, to which adenosine triphosphate was added to induce engorging. Feeding rates of St. aegypti on the cocktail meal and pig blood, respectively, did not differ significantly, but were significantly higher than the feeding rate on citrate phosphate dextrose‐adenine 1 (CPDA‐1) solutions, which had been used to replace bloodmeals in previous repellent assays. Dose‐dependent biting inhibition rates were analysed using probit analysis. The RD₅₀ (the dose producing 50% repellence of mosquito feeding) values of DEET, citronella, carvacrol, geraniol, eugenol and thymol were 1.62, 14.40, 22.51, 23.29, 23.83 and 68.05 µg/cm², respectively.     

Sustained efficacy of the novel topical repellent TT‐4302 against mosquitoes and ticks

Mosquitoes and ticks are blood‐feeding pests of humans and animals that can vector many important aetiological agents of disease. Previous research demonstrated that TT‐4302 (Guardian^® Wilderness) containing 5% geraniol applied to human subjects gave 5–6 h of repellency against mosquitoes (depending on species) and was repellent to ticks in vitro. This study was conducted to obtain an independent third‐party evaluation of TT‐4302 against Stegomyia aegypti (= Aedes aegypti) (Diptera: Culicidae) mosquitoes and to test the efficacy of the product in the field against ticks. TT‐4302 provided an average of 6.5 h of repellency of ≥ 95% [Weibull mean protection time: 7.4 h, 95% confidence interval (CI) 5.8–11.3 h] for St. aegypti, whereas a 15% DEET formulation provided 4.7 h of repellency (Weibull mean protection time: 5.2 h, 95% CI 3.7–6.9 h). In tick field trials, the efficacy of TT‐4302 did not differ significantly from that of a 25% DEET formulation against Amblyomma americanum (Ixodida: Ixodidae). TT‐4302 was 81.3% repellent at 2.5 h after application, whereas DEET was 77.2% repellent at the same time‐point. Results at 3.5 h after application were 71.4% for TT‐4302 and 72.9% for DEET.     

Lethal and behavioural effects of three synthetic repellents (DEET, IR3535 and KBR 3023) on Aedes aegypti mosquitoes in laboratory assays

The knock-down, mortality and 'irritancy' effects of three synthetic repellents (DEET, IR3535 and KBR 3023) on Aedes aegypti (L) (Diptera: Culicidae) were evaluated in the laboratory in the absence of animal bait. Filter paper tests were carried out to assess the knock-down effect (KDt(50) and KDt(95)) and mortality (LC(50) and LC(95)) induced by each repellent. 'Irritancy' tests were carried out to compare the flight response (time to first take-off, or FT) to increasing concentrations of repellents (2-7%) and at five distances from the treated surface (0-40 mm). DEET had an insecticidal effect (KDt(50) = 9.7 min at 7%; CL(50)= 1165 mg/m(2)), whereas IR3535 and KBR 3023 did not. Relative to an untreated control, IR3535 was an irritant (relative irritancy or RI > 1) at doses of 5% and 7% (RI = 17.7 and 9.9, respectively), whereas DEET was an irritant at lower concentrations (RI = 12.3 at 2% DEET). KBR 3023 was the weakest irritant over the same range of concentrations (RI(max) = 3.6 at 6%). DEET was more of an irritant (RI(20) = 9.4) than IR3535 (RI(20) = 2.9) over a range of distances (0-20 mm), and KBR 3023 was not an irritant unless mosquitoes made contact with the treated surface. All three repellents had a significant effect on mosquitoes, but DEET exhibited a more complex mode of action than the others due to its insecticidal properties. The repellents do not behave as a single class of compounds with a common mode of action, but most probably affect different physiological systems in insects. The physiological and molecular mechanisms of repellents, especially DEET, should be investigated to ensure a better use of these molecules for skin applications and/or for treating materials against mosquitoes.     

Anti‐feeding and insecticidal efficacy of a topical administration of dinotefuran–pyriproxyfen–permethrin spot‐on (Vectra® 3D) on mice against Stegomyia albopicta (= Aedes albopictus)

An ectoparasiticide combining three active ingredients [dinotefuran, permethrin and pyriproxyfen (DPP)] was used in mice in an experiment designed to evaluate its anti‐feeding and insecticidal efficacy against Stegomyia albopicta (= Aedes albopictus) (Diptera: Culicidae) mosquitoes. Twenty‐two adult mice were randomly allocated into two groups consisting of an untreated control group and a DPP‐treated group. Mice were exposed individually for 1 h to a mean ± standard deviation of 27 ± 2 starved female mosquitoes on days 1, 7, 14, 21 and 28 post‐treatment. At the end of the exposure (1 h), mosquitoes were assessed for immediate survival and engorgement status. Additionally, live mosquitoes in both groups were incubated separately and observed for mortality at 24 h after the end of the exposure. The anti‐feeding efficacy of DPP after the 1‐h exposure period was 99.2, 100, 98.0, 89.3 and 87.4% at 1, 7, 14, 21 and 28 days, respectively. Levels of insecticidal efficacy evaluated at 1 h and 24 h after exposure on days 1, 7, 14, 21 and 28 were 36.7, 28.9, 30.8, 23.1 and 11.9%, and 68.4, 45.0, 43.3, 37.9 and 19.9%, respectively. Based on the mouse model, the present study demonstrates that the DPP combination has significant anti‐feeding and insecticidal efficacy against S. albopicta for at least 4 weeks.     

Aedes (Stegomyia) aegypti and Aedes (Howardina) cozumelensis in Yucatán State,México,with a summary of published collection records for Ae. cozumelensis

We collected mosquito immatures from artificial containers during 2010–2011 from 26 communities, ranging in size from small rural communities to large urban centers, located in different parts of Yucatán State in southeastern México. The arbovirus vector Aedes (Stegomyia) aegypti was collected from all 26 examined communities, and nine of the communities also yielded another container‐inhabiting Aedes mosquito: Aedes (Howardina) cozumelensis. The communities from which Ae. cozumelensis were collected were all small rural communities (<6,000 inhabitants) in the north‐central part of Yucatán State. These new collection records for Ae. cozumelensis demonstrate that this mosquito has a far broader geographic range in the Yucatán Peninsula than previously known. Ae. cozumelensis immatures were collected from both residential premises and cemeteries, with specimens recovered from rock holes as well as various artificial containers including metal cans, flower vases, buckets, tires, and a water storage tank. The co‐occurrence with Ae. aegypti in small rural communities poses intriguing questions regarding linkages between these mosquitoes, including the potential for direct competition for larval development sites. Additional studies are needed to determine how commonly Ae. cozumelensis feeds on human blood and whether it is naturally infected with arboviruses or other pathogens of medical or veterinary importance. We also summarize the published records for Ae. cozumelensis, which are restricted to collections from México's Yucatán Peninsula and Belize, and uniformly represent geographic locations where Ae. aegypti can be expected to occur.     

Numerical evaluation of currents induced in a worker by ELF non‐uniform electric fields in high voltage substations and comparison with experimental results

An ungrounded human, such as a substation worker, receives contact currents when touching a grounded object in electric fields. In this article, contact currents and internal electric fields induced in the human when exposed to non‐uniform electric fields at 50 Hz are numerically calculated. This is done using a realistic human model standing at a distance of 0.1–0.5 m from the grounded conductive object. We found that the relationship between the external electric field strength and the contact current obtained by calculation is in good agreement with previous measurements. Calculated results show that the contact currents largely depend on the distance, and that the induced electric fields in the tissues are proportional to the contact current regardless of the non‐uniformity of the external electric field. Therefore, it is concluded that the contact current, rather than the spatial average of the external electric field, is more suitable for evaluating electric field dosimetry of tissues. The maximum induced electric field appears in the spinal cord in the central nervous system tissues, with the induced electric field in the spinal cord approaching the basic restriction (100 mV/m) of the new 2010 International Commission on Non‐Ionizing Radiation Protection guidelines for occupational exposure, if the contact current is 0.5 mA. Bioelectromagnetics 34:61–73, 2013. © 2012 Wiley Periodicals, Inc.