Unraveling the genetic structure of the coconut scale insect pest (Aspidiotus rigidus Reyne) outbreak populations in the Philippines

The Philippines suffered from a devastating outbreak of the coconut scale insect pest, Aspidiotus rigidus Reyne inflicting significant economic losses to the countrys coconut industry. Despite the massive outbreak, little is known about the population and dispersal history of this invasive pest in the Philippines. Here, we examined the genetic diversity, structure and demographic history of A. rigidus sampled from localities with reported outbreaks from 2014 to 2017. We analyzed the genetic structure of seven A. rigidus outbreak populations using mitochondrial COI and nuclear EF-1 markers. Both markers and all methods of population genetic structure analyses indicate clear differentiation among the A. rigidus populations separating the northern (i.e., Luzon provinces) from the southern (i.e., Basilan and Zamboanga Peninsula) regions of the Philippines. Very low or no genetic differentiation was observed within and amongst the populations per geographic region indicating two unrelated outbreak events of the pest originating from two genetically uniform populations isolated in each respective region. Historical data supports the resurgence of an established A. rigidus population in the south which could have been driven by sudden climatic changes or human-induced habitat imbalance. Given no historical information, we disregard the possible resurgence from the northern population and infer that the outbreak could have resulted from a recent introduction of a non-native A. rigidus in the region. Our study provides valuable information on the genetic differentiation of the two A. rigidus groups that would be useful for developing and implementing biological control strategies against this pest in the Philippines.