Determining the native region of an invasive insect, through host parasitoid relations, and taxonomic, molecular, and ethnobotanical approaches, to facilitate its biological control

Background/Question/Methods

The invasive lobate lac scale insect attacks more than 350 woody plants in Florida and the Bahamas, including 2/3 of the native woody plants. The insect, which experiences little parasitism, potentially threatens numerous economic and native plants throughout the West Indies. First discovered in southern Florida in 1999, it was identified as Paratachardina lobata, a species native to India and Sri Lanka. Surveys in India sought and located P. lobata and its parasitoids, which were evaluated as potential control agents. Quarantine lab testing determined that several of these parasitoid wasps could oviposit in the invasive lobate lac scales, but almost all the parasitoid eggs where encapsulated and killed by the scale’s immune system cells. This suggested a mismatch between parasitoids of P. lobata and the invasive lobate lac scale. New taxonomic and molecular analyses of the invasive lobate lac scales from Florida, the Bahamas, and Christmas Island, where it is also invasive, found them to represent an undescribed species of no known origin, subsequently named P. pseudolobata. Determining the native home of the invasive lobate lac scale was important if its co-evolved specialist parasitoids were to be found and evaluated as potential biological control agents of the pest. P. pseudolobata almost certainly invaded Florida and the other areas, attached to imported woody plants, probably from Asia or Australia because all other Paratachardina species are native from India to Australia. Attempts were made to trace the introductions of host plants that may have carried this insect from this huge area to Florida. The number of host plants, imported plants, absence of plant import records, and diverse potential pathways made this effort fruitless. A visit to Christmas Island was made to attempt to trace the insect’s introduction. Christmas Island is recently populated and has only 2000 people who are mostly ethnic Chinese and a few Malays.

Results/Conclusions

We learned that most of the island’s immigrants, who also grow imported garden plant hosts of the scale, came after WW II and were recruited from Penang and Malacca in peninsular Malaysia by the island’s phosphate mining company. Subsequent surveys in Penang and Malacca found scales that morphologically matched P. pseudolobata. Molecular analysis of these Malaysian scales found them to be identical to P. pseudolobata. P. pseudolobata thus appears to be native to Peninsular Malaysia, where it behaves as a native insect, occurring at low densities with high rates of parasitism.