Improving Mass-Rearing Techniques for Releases of Floracarus perrepae, a Biological Control Agent for Old World Climbing Fern (Lygodium microphyllum).

Abstract

The United States Department of Agriculture-Invasive Plant Research Laboratory started limited production of a biological control mite, Floracarus perrepae, in 2008 for release against the invasive fern Lygodium microphyllum. Mass-rearing and release of the biological control agent was initiated in 2014 as part of the Comprehensive Everglades Restoration Plan to address the challenge of low establishment rates observed from 2008 to 2010. In late 2021, we critically analyzed our rearing protocols, focusing on aging galls and increasing plant vigor. These adjustments resulted in an exponential increase in colony productivity. We implemented bi-weekly monitoring of mite numbers within galls and identified the gall age class with the highest mite density. Based on this information, we developed a systematic method involving weekly plant readiness criteria and a predefined sequence of stages to select plants for release, ensuring that galls are correctly aged to maximize mite numbers. These changes have resulted in substantial improvements in gall abundance (165.3%), F. perrepae density per gall (86.0%), and estimated F. perrepae per plant (453.2%). The increase in F. perrepae released throughout the landscape improved the rates of establishment, abundance, and impact of the agent throughout the invaded range of L. microphyllum in Florida.