Sterile Insect Technique in a Metapopulation Model. Impact of Network Structure, Male Annihilation Technique and Entomopathogenic Fungi on the Release Strategies

Abstract

The sterile insect technique (SIT) is a biological control method that reduces insect pest and disease vector populations through the release of sterile insects (in general only males). In this work, spatial aspects are accounted for through an explicit metapopulation model of $n$ interconnected patches. Each patch includes a non-adult stage and adult stages divided into females and males, with distinct dispersal networks for females, wild males, and sterile males. This framework allows to adopt an area-wide integrated pest management perspective. Focusing on the oriental fruit fly, Bactrocera dorsalis, we consider two types of additional control methods, with life stage and sex specificities. These correspond to entomopathogenic fungi soil treatment (EPFST), with a differentiated effect at every life stage; and to the male annihilation technique (MAT), which attracts and kills wild and sterile males. We derive a sufficient condition ensuring elimination of the wild population in all patches, considering either continuous or impulsive periodic release strategies. Under constraints such as the impossibility of releasing sterile males in some patches, we then study an optimisation problem to minimise a weighted sum of the release rates over all release patches to eliminate the wild population. For illustrative purposes, numerical simulations are used to investigate how dispersal network configurations, local conditions, and the simultaneous use of SIT with EPFST or MAT affect optimal release strategies. The main contribution of this work is to identify efficient spatial release strategies for population elimination under practical constraints, in combination with other control methods.