A molecular method for biomonitoring of an exotic plant-pest: leafmining for environmental DNA

1. Understanding how invasive species respond to novel environments is
limited by a lack of sensitivity and throughput in conventional
biomonitoring methods. Arthropods in particular are often difficult to
monitor due to their small size, rapid lifecycles, and/or visual
similarities with co-occurring species. This is true for the agromyzid
leafminer fly, Liriomyza sativae, a global pest of vegetable and nursery
industries that has recently established in Australia. 2. A robust method
based on environmental DNA (eDNA) was developed exploiting traces of DNA
left inside ‘empty’ leaf mines, which are straightforward to collect and
persist longer in the environment than the fly. This extends the window of
possible diagnosis to at least 28 days after a leaf mine becomes empty.
The test allowed for visually indistinguishable leafmining damage caused
by L. sativae to be genetically differentiated from that of other flies.
 3. Field application resulted in the identification of new local
plant hosts for L. sativae, including widely distributed weeds and common
garden crops, which has important implications for the pest’s ability to
spread. Moreover, the test confirmed the presence of a previously unknown
population of L. sativae on an island in the Torres Strait.   4.
The developed eDNA method is likely to become an important tool for L.
sativae and other leafmining species of biosecurity significance, which,
historically, have been difficult to detect, diagnose and monitor. More
generally, eDNA is emerging as a highly sensitive and labour-efficient
surveillance tool for difficult to survey species to improve outcomes for
agricultural industries, global health, and the environment.