Introduction of a non-native lineage is linked to the recent black cocoa ant, Dolichoderus thoracicus (Smith, 1860), outbreaks in Taiwan

Introduction of a non-native lineage is linked to the recent black cocoa ant, Dolichoderus thoracicus (Smith, 1860), outbreaks in Taiwan

The black cocoa ant, Dolichoderus thoracicus (Smith), is widely distributed across the Indomalayan region including Taiwan. Until the recent localized outbreaks in central Taiwan, this ant has never been considered as a pest. The current study tested if an introduction of non-native lineage(s) potentially contributes to the ant’s sudden outbreaks in Taiwan by analyzing phylogenetic relationships of D. thoracicus in Taiwan and Southeast Asia. Our results showed that all ants were grouped into two major mitochondrial clades (Clade I and II) separated by a p-distance of 0.0414. Clade I is widespread in Taiwan and represented by six haplotypes that are genetically similar to the haplotypes from the Philippines, indicating that these ants are likely a result of range expansion of the Philippine lineage(s). In contrast, ants from central Taiwan harbor a single Clade II haplotype that is predominantly found in the samples collected from the Indochina region. Coupled with the low genetic diversity, Clade II D. thoracicus in Taiwan was most likely introduced from the Indochina region. The possibility is further supported by the fact that most D. thoracicus intercepted at the Taiwanese borders had an Indochina origin. Overall, this study suggests that a non-native lineage is responsible for the recent outbreaks of this ant in Taiwan, highlighting a potential research avenue for future research on the association between the“pest”trait and non-native genetic variant in invaded area.