Contained semi-field environments for ecological studies on transgenic African malaria vectors: benefits and constraints

Recent successful genetic transformation of disease-transmitting insects has fuelled enthusiasm towards its potential application for disease control in the future. However, advances to date have been confined to laboratory settings and many questions relating to the fitness, behaviour, ecology and phenotypic characteristics of transformed insects remain unanswered. Spread of desired traits, such as refractoriness to Plasmodium infection, will depend on the reproductive fitness and manifestation of life-history behaviours, such as dispersal and mating, by engineered specimens. These should preferably be similar to those displayed by their wild conspecifics but may be compromised by genetic modification and difficult to assess realistically under standard laboratory conditions. Contained semi-field environments that mimic a near-natural environment and are exposed to ambient climatic conditions may serve to verify laboratory findings and yield valuable insights into transgene fixation processes prior to field releases of transgenic specimens into the wild. Here we describe the constraints and benefits of this approach with respect to containment stringency, facility design and operational guidelines for studies involving genetically-engineered malaria vectors. We also report on our initial success with such semi-field systems in West Kenya, using non-transgenic mosquitoes in a variety of behavioural and ecological studies. Successful completion of the Anopheles gambiae life cycle, and thus expression of all major life-history behaviours, occurred in three separate trials. However, our results show that the sustenance of successive and overlapping generations in such systems may be difficult. Considering the frequently expressed and explicit need for contained semi-field trials with engineered insects prior to field releases, this calls for intensified development of improved semifield systems, preferably in field sites earmarked for future release

Development of a Gravid Trap for Collecting Live Malaria Vectors Anopheles gambiae s.l

Background: Effective malaria vector control targeting indoor host-seeking mosquitoes has resulted in fewer vectors entering houses in many areas of sub-Saharan Africa, with the proportion of vectors outdoors becoming more important in the transmission of this disease. This study aimed to develop a gravid trap for the outdoor collection of the malaria vector Anopheles gambiae s.l. based on evaluation and modification of commercially available gravid traps. Methods: Experiments were implemented in an 80 m2 semi-field system where 200 gravid Anopheles gambiae s.s. were released nightly. The efficacy of the Box, CDC and Frommer updraft gravid traps was compared. The Box gravid trap was tested to determine if the presence of the trap over water and the trap’s sound affected catch size. Mosquitoes approaching the treatment were evaluated using electrocuting nets or detergents added to the water in the trap. Based on the results, a new gravid trap (OviART trap) that provided an open, unobstructed oviposition site was developed and evaluated. Results: Box and CDC gravid traps collected similar numbers (relative rate (RR) 0.8, 95% confidence interval (CI) 0.6–1.2; p = 0.284), whereas the Frommer trap caught 70% fewer mosquitoes (RR 0.3, 95% CI 0.2–0.5; p < 0.001). The number of mosquitoes approaching the Box trap was significantly reduced when the trap was positioned over a water-filled basin compared to an open pond (RR 0.7 95% CI 0.6–0.7; p < 0.001). This effect was not due to the sound of the trap. Catch size increased by 60% (RR 1.6, 1.2–2.2; p = 0.001) with the new OviART trap. Conclusion: Gravid An. Gambiae s.s. females were visually deterred by the presence of the trapping device directly over the oviposition medium. Based on these investigations, an effective gravid trap was developed that provides open landing space for egg-laying Anopheles