Combining two parasitoids (Asecodes hispinarum and Tetrastichus brontispae) for biological control of coconut leaf beetle

The coconut leaf beetle (CLB), Brontispa longissima , is a major threat to coconut production worldwide, causing widespread and important losses throughout the tropics. Two eulophid parasitoids, Asecodes hispinarum and Tetrastichus brontispae , are the dominate natural enemies of CLB, but methods for their synergistic use have not previously been developed that would minimize interspecific conflicts and maximize their combined impact. We analyzed the interactions of A. hispinarum and T. brontispae and evaluated possible deployment strategies by determining the outcomes of releases under realistic agricultural conditions. Our laboratory studies showed that the concurrent release of the two parasitoid species did not reduce either species lifespan or reproductive output, and it significantly enhanced the impact on CLB. A 3:1 ratio of A. hispinarum to T. brontispae , a 10:1 parasitoid-to-pest ratio, and a regimen of five consecutive monthly releases proved to be the most efficacious strategy in the laboratory. Field trials over a two-year period consistently demonstrated the advantages of this combined release approach, resulting in significant reductions in pest populations and increases in parasitism rates. This study highlights the potential of integrating multiple parasitoid species to improve biological control impacts, example the context of sustainable pest management strategies.