Eave tubes for malaria control in Africa: Videographic observations of mosquito behaviour in Tanzania with a simple and rugged video surveillance system.

BACKGROUND: Eave tubes are novel mosquito control devices that help to protect households against malaria vectors and other mosquitoes. They are installed in the upper walls of human habitations after the eaves have been closed. Mosquitoes trying to enter through these tubes are intercepted by electrostatic netting that can be treated with a variety of insecticides. Using video, mosquito behaviour and duration of contact with netting in eave tubes was recorded and analysed to assess contamination with insecticides under semi-field and field conditions. MATERIALS AND METHODS: Off-the-shelf action cameras were used to observe behaviour of mosquitoes in eave tubes near Ifakara, Tanzania. In an experimental hut in a screen house, we observed Anopheles arabiensis females on electrostatic eave tube netting treated with bendiocarb powder or with Beauveria bassiana spores, both in comparison to untreated netting. In village houses that had been equipped with eave tubes we observed the behaviour of wild mosquitoes towards electrostatic netting treated with bendiocarb. Results were evaluated using a short-contact assay (5 second exposure). RESULTS: In the semi-field setup, the median contact time of An. arabiensis on bendiocarb-powdered eave tube nets was 276.4 sec (n=56), compared to 26.3 sec on the control (n=59). Of all the mosquitoes observed on the treated net, 94.6% had contact times of more than 5 seconds on the bendiocarb-powdered netting. The median time on nets powdered with B. bassiana spores was 34.4 sec (n=26), compared 37.1 sec in the untreated control (n=22). 88.5% of the mosquitoes spent more than 5 seconds on the treated nets. In the field we recorded 106 individual mosquitoes of unknown species inside tubes. They spent a median time of 70.9 sec on the bendiocarb-treated netting, with 90.6% remaining there for more than 5 seconds. CONCLUSIONS: We have found no indication that the behaviour of mosquitoes on electrostatic eave tube netting, treated either with bendiocarb powder or with B. bassiana spores, interferes with successful transfer of lethal doses of these insecticidal actives. The videographic set-up used in this study is simple, sturdy and reliable enough to observe and analyse mosquito behaviour under field conditions.

Eave tubes for malaria control in Africa: an introduction.

In spite of massive progress in the control of African malaria since the turn of the century, there is a clear and recognized need for additional tools beyond long-lasting insecticide-treated bed nets (LLINs) and indoor residual spraying (IRS) of insecticides, to progress towards elimination. Moreover, widespread and intensifying insecticide resistance requires alternative control agents and delivery systems to enable development of effective insecticide resistance management strategies. This series of articles presents a novel concept for malaria vector control, the 'eave tube', which may fulfil these important criteria. From its conceptualization to laboratory and semi-field testing, to demonstration of potential for implementation, the stepwise development of this new vector control approach is described. These studies suggest eave tubes (which comprise a novel way of delivering insecticides plus screening to make the house more 'mosquito proof') could be a viable, cost-effective, and acceptable control tool for endophilic and endophagic anophelines, and possibly other (nuisance) mosquitoes. The approach could be applicable in a wide variety of housing in sub-Saharan Africa, and possibly beyond, for vectors that use the eave as their primary house entry point. The results presented in these articles were generated during an EU-FP7 funded project, the mosquito contamination device (MCD) project, which ran between 2012 and 2015. This was a collaborative project undertaken by vector biologists, product developers, modellers, materials scientists, and entrepreneurs from five different countries.

Size Exclusion High Performance Liquid Chromatography: Re-Discovery of a Rapid and Versatile Method for Clean-Up and Fractionation in Chemical Ecology.

Solvent extraction of bioactive molecules from glands, tissues, or whole organisms is a common first step in chemoecological studies. Co-extraction of a surplus of high boiling materials such as triacylglycerides (TAGs) and other lipids with higher molecular weight might hamper the identification of volatile or medium-volatile semiochemicals by high resolution chromatographic and spectroscopic techniques. Therefore, effective clean-up procedures are needed to separate potential semiochemicals from the accompanying materials. Size exclusion high performance liquid chromatography (SE-HPLC), a technique often disregarded by chemoecologists, has proved to be a rapid and efficient clean-up method for complex crude extracts. We demonstrated that TAGs can be baseline separated from typical semiochemicals within less than 10 min on a porous gel stationary phase based on highly cross-linked polystyrene/divinylbenzene. We applied the method as a rapid one-step clean-up procedure for the analysis of juvenile hormone III in insect hemolymph by gas chromatography-mass spectrometry. We furthermore introduced some recent application examples on insect pheromones to demonstrate that SE-HPLC is not only an effective method for the purification of crude extracts, but can as well be used as a first fractionation step for the bioassay-guided identification of behavior modifying natural products. SE-HPLC can be well operated with low-boiling solvents such as dichloromethane, and results in fraction volumes of typically less than one ml, which decreases the danger of losing volatile analytes during subsequent concentration steps.

Deciphering the signature of cuticular lipids with contact sex pheromone function in a parasitic wasp.

The surface of insects is covered by a complex mixture of cuticular hydrocarbons (CHCs) to prevent desiccation. In many species these lipids also have communicative functions, but often it is unknown which components are crucial for the behavioural response. Furthermore, it is often ignored that polar lipids also occur on the insects' cuticle and might interact with CHCs. In the parasitic wasp Lariophagus distinguendus, CHCs function as a contact sex pheromone eliciting wing-fanning in males. Interestingly, not only females but also newly emerged males have the pheromone, resulting regularly in homosexual courtship. However, males deactivate the pheromone within the first two days after emergence. This deactivation is accompanied by the disappearance of 3-methylheptacosane (3-MeC27) and some minor components from the CHC profile of males. Here we show that 3-MeC27 is a key component of the contact sex pheromone which, however, triggers courtship behaviour only if an olfactory background of other cuticular lipids is present. Males responded to (S)-3-MeC27 enantioselectively when applied to filter paper but on three-dimensional dummies both enantiomers were behaviourally active, suggesting that physical stimuli also play a role in sexual communication of the wasps. Finally, we report that triacylglycerides (TAGs) are also essential components of the pheromone, and present evidence that TAGs actually occur on the cuticle of L. distinguendus. Our data provide novel insights into the semiochemical function of cuticular lipids by showing that the bioactivity of CHCs may be influenced by the stereochemistry and a synergetic interaction with long time ignored TAGs.