University of Cambridge Cambridge, England, United Kingdom
One of the major crops for food security is cassava. Cassava mosaic disease (CMD) is caused by plant infection with cassava mosaic geminiviruses which are vectored by Bemisia tabaci whitefly. CMD has been reported in Africa for more than a century but in recent decades there was an expansion of severe CMD in east and central Africa. Symptom severity resulted in widespread high yield loss in susceptible varieties and was associated with super-abundant populations of the whitefly vector. One suggested cause of super-abundance was a symbiotic relationship between B. tabaci and cassava mosaic virus – mediated through viral manipulation of infected plants leading to increased insect growth. In this talk I will discuss the application of epidemiological modelling to field experiment datasets from the 1990’s which recorded changes in B. tabaci abundance and cassava infection status as a severe CMD expansion arrived. Several scenarios as to the causes of superabundance were analysed using a theory of invasion types that contrasted ‘pushed-’ and ‘pulled-’ invasion waves. Common patterns, constituting evidence that pathogenic manipulation was a dynamic driver in the East African expansion of severe cassava mosaic disease, were found across the datasets studied. Our analyses have adapted a well-established theory of invasion types that is known for its implications for invasion wave-speed. This talk will also briefly consider how wave-speed considerations might be of relevance for novel management techniques.