Biological Control: A Major Component of the Pest Management Program for the Invasive Coconut Scale Insect, Aspidiotus rigidus Reyne, in the Philippines

SIMPLE SUMMARY: Major outbreaks of the coconut scale insect (CSI), Aspidiotus rigidus, occurred in the Philippines, between 2010 and 2016 in the Southern Tagalog region of Luzon Island, and from 2017 to 2020 in the Zamboanga Peninsula, Mindanao Island. Contribution of parasitization by Comperiella calauanica to the management of the outbreaks needed quantification. Our assessments found very high percent parasitization by C. calauanica, which occurred naturally in Southern Tagalog. Findings were similar in the Zamboanga Peninsula, where mass-reared C. calauanica from Southern Tagalog were released for biological control. Significant decreases in the population of CSI were recorded in 1- to 2-year periods, 2014 to 2016 in Southern Tagalog, and 2018 to 2020 in the Zamboanga Peninsula, with parallel findings of recovery by infested coconut palms. Compared to the integrated pest management (IPM) program in Southern Tagalog, that in the Zamboanga Peninsula relied less on chemical control, and no major climatic disturbance was recorded in the region. Our findings strongly suggest that biological control has been a very important factor in the management of A. rigidus. Rearing facilities for C. calauanica as biological control agent should be established and maintained, especially in the different regions, to enable quick response to new areas of CSI invasion in the country. ABSTRACT: The coconut scale insect, Aspidiotus rigidus Reyne, caused a major pest outbreak in coconut plantations and stands in the Southern Tagalog region of Luzon Island in the Philippines between 2010 and 2015. To determine if parasitism by Comperiella calauanica Barrion, Almarinez and Amalin, a native encyrtid, could have been a factor in the eventual management of the outbreak by 2015, we estimated and assessed its parasitization levels on A. rigidus colonies on field-collected samples from selected points in three provinces in the Southern Tagalog Region across three sampling periods. We observed that C. calauanica consistently occurred only in areas where A. rigidus populations occurred, with high parasitization levels in the Southern Tagalog sites from 2014 to 2015. Results of correlation and regression of total scale count against parasitized scale count suggest putative host density-dependent parasitism by C. calauanica in the field. A marked decrease in the abundance of A. rigidus was recorded concurrently with visually observable recovery of coconut trees from the third quarter of 2014 up to the second quarter of 2016. Similar results of significant reduction in A. rigidus populations concurrent with high percent parasitization by mass-reared and released C. calauanica were found in the Zamboanga Peninsula from 2018 to 2020. Our findings and observations altogether suggest that host-specific parasitization by C. calauanica effected biological control, which may have contributed to the eventual management of the A. rigidus outbreak in the Southern Tagalog Region, and also in the Zamboanga Peninsula where similar recovery of coconut trees were observed within a year after inoculative releases of C. calauanica.