A new diamondback moth

The tiny diamondback moth (Plutella xylostella) gets its common name from the array of diamond-shapes along the margin of its forewing. Despite their small size, the caterpillars of the diamondback moth exert tremendous damage on many crucifers including cabbage and broccoli. More than $1 billion is spent globally each year in efforts to control damage by this moth, reflecting its amazing capacity to evolve resistance to both insecticides and biological control agents.

A global study of DNA Barcodes revealed unexpected complexity: the occurrence of two distinct species among Australian diamondback moths. One of them is the well-known diamondback pest which is found nearly everywhere. The other is a new species, named Plutella australiana by Jean-François Landry of the Canadian National Collection in Ottawa and Paul Hebert from BIO, the authors of the study. The new species has so far been found only in Australia, where it occurs together with typical Plutella xylostella.

The new species was initially detected by Paul Hebert in a general survey of Australian moths aimed at developing a library of DNA Barcodes representing all the species of the fauna. One part of this effort (sequencing the lepidoptera of the Australian National Insect Collection) I described a few days ago but the specimens of this study were caught in the wild. Subsequent study of the anatomy revealed significant, previously unsuspected, differences in internal reproductive organs between typical diamondbacks and the new species.

Although the new species of diamondback moth has now gained recognition and a name, key aspects of its biology remain uncertain. For example, what is its role as a crop pest in Australia and does it pose a threat to agriculture? The presence of these two species also has implications for past evaluations of biological control strategies, particularly since both species appear to be abundant and widely distributed in eastern Australia. The next step could be to find the host plant(s) of Plutella australiana to ascertain if it is also a crop pest. If so, it likely represents a new risk to international trade which should be subsequently evaluated.