How does residual fertility impact the effectiveness of the sterile insect technique in controlling Ceratitis capitata?

International audienceThe context of this work is the control of the Mediterranean fruit flyCeratitis capitata in orchards in Corsica (France). It aims at optimizing thedeployment of the Sterile Insect Technique (SIT) in an agricultural context.SIT is a biological control technique based on mass-rearing, radiation-basedsterilization, and releases of the pest species targeted for population control.The sterilization process is subject to a trade-off: radiation doses should behigh enough to effectively sterilize the males, but not too high to preservetheir ability to attract females and mate. Among the releases a proportionof the irradiated pupae may therefore lead to non-sterile males.To represent the pest dynamics when sterile males are released, we havebuilt a mathematical model based on differential equations, consisting ofthree compartments: sterile males, wild males and wild females. With thismodel, we compared three cases: perfect male sterilisation, contrasted withtwo situations in which residual fertility is taken into account, associatedeither with or without a fitness cost. We varied the residual fertility leveland the associated fitness cost and studied their influence on the populationdynamics by means of analytical studies (equilibria, stability, bifurcations)illustrated with simulations of the model calibrated for C. capitata.We have shown that when residual fertility is below a threshold value,wild populations can be driven to extinction by flooding the landscape withsterile males, generalizing the results presented in [1]. As expected, too higha level of residual fertility makes SIT less effective and hinders populationcontrol. Finally, the presence of an associated fitness cost, which is verylikely, has a significant impact on control efficiency and generates a higherlevel of acceptable residual fertility.In practice, with the model calibrated to the biological parameters of C.capitata and for a 1% residual fertility rate, value generally obtained, a min-imum of 300 sterile males per day per ha would be required to theoreticallyeradicate the pest population