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

Abstract

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 releases