How can genetically engineered mosquitoes stop malaria?

The first batch of genetically modified mosquitoes is being released in Djibouti in a bid to stop the spread of malaria carrying vectors that bite during the day and thrive in urban areas. How does this work?Also, an overview of South Africa's 'historic' elections.   Who are the main parties and what are the issues? And scientists trace the origins of one of Africa's most iconic trees, the baobab tree, to Madagascar.  Why are they in decline on the Island? Presenter: Richard Kagoe Producers: Charles Gitonga, Frenny Jowi, Rob Wilson and Paul Bakibinga Technical Producer: Daniela Victoria Varela Hernandez Editors: Alice Muthengi and Andre Lombard