Increasing trade and travel has facilitated insect pest invasions in plantation forests globally. Many of these pests now also occur across the world in different environments. Biological control is one of the main ways to deal with these pests, and these are often shared or accidentally moved between countries. This widespread application of biological control agents, however, is highly likely to benefit from the ability to adapt to variable environments and host genotypes. Genetic diversity can influence biotype matching and the capacity to respond to novel or changing conditions. We thus argue that employing strategies that promote or maintain genetic diversity should be explicitly considered in biological control program development and implementation. Here we consider how various stages of the development and deployment of biological control could lead to a loss of genetic diversity and highlight a suite of potential mitigation strategies to counter such loss. We use the biological control program for the Pinus pest, Sirex noctilio, with the nematode Deladenus siricidicola as a case study to explore the role of genetic diversity in biological control of pests in plantations.