Modeling genetic biocontrol strategies in mosquitoes and other pests

Functional resistance

Our most recent work on gene drives investigates how partially functional resistance modifies overall gene drive dynamics. Resistance to a control strategy, such as pesticides, is often understood in terms of a binary survival outcome: the insect either lives or dies. However, partial resistance occurs when the insect survives but incurs a fitness cost. The same idea applies to gene drives. Resistance is functional if it restores the function of a feature that the gene drive is intended to disrupt (e.g., a process critical for insect survival).

Dispersal

One of the primary issues concerning the wild release of gene drive technology is confinement, or ensuring that the gene drive does not spread to off-target populations. This concern has inspired a class of gene drives that are confined by design, referred to as threshold-dependent gene drives. Threshold-dependent gene drives differ substantially in their design and implementation. We examined their dynamics in a common mathematical framework and use global sensitivity analyses to compare the relative contribution of target organism dispersal and gene drive fitness cost to spatial outcomes. Our work is currently in review at Evolutionary Applications, but you can read the preprint here.

Density dependence

Pest populations are regulated by density-dependent factors. In the yellow fever mosquito, Aedes aegypti, larval survival is affected by intraspecific larval competition. Reducing adult populations of Aedes aegypti can reduce the number of juveniles, thereby relaxing juvenile competition. This can increase individual juvenile survival, and thereby lead to a net increase in the number of adults. Clearly, the interaction between density dependence and population suppression by gene drives is not straightforward. We examine these and other relationships in our work in the Journal of Theoretical Biology, which you can read here.

Modeling gene drive in spotted wing Drosophila

In addition to my mosquito-focused work above, I modeled gene drive performance in spotted wing Drosophila (SWD; Drosophila suzukii)—a severe pest of fruits, especially berries. The Scott Lab at NC State is developing gene drives in SWD, and my modeling assisted with experimental design, projected gene drive performance in cage populations, and simulated the performance of different gene drive constructions. Our work appeared in PNAS, and you can read it here.