Dialectica scalariella (Zeller, 1850)
Echium Leaf Miner
(previously known as Gracilaria scalariella)
Don Herbison-Evans,
Stella Crossley

Dialectica scalariella
(Photo: courtesy of Katarina Christenson, Melba, Australian Capital Territory)

This Caterpillar was introduced deliberately from the Mediterranean region into Australia to control :

  • Paterson's Curse ( Echium plantagineum, BORAGINACEAE ),

    which it attacks by mining the leaves.

    'Paterson's Curse' was accidently introduced into Australia, and is poisonous to cattle. However it is also known as 'Salvation Jane', as it is resistant to drought and is fodder for sheep in drought conditions. The flowers are also a good source of nectar for bees, and make the fields of New South Wales and South Australia an attractive and unusual purple colour when in flower.

    Dialectica scalariella
    (Photo: courtesy of Donald Hobern, Aranda, Australian Capital Territory)

    Biological control was first suggested for Paterson's curse in 1928, but it was 42 years before anything was done about it. Then, in 1972, CSIRO began surveying the western Mediterranean region for natural enemies of the plant. One was the caterpillar of Dialectica scalariella, and this was the first agent released (in 1980). It did not establish well, probably because of drought and grasshoppers. Shortly after the species was released, some beekeepers and graziers obtained a legal injunction preventing further releases. A legal battle followed for eight years. Eventually, the federal Government passed the 'Biological Control Act' in 1984. which prevents biological control programs being stopped by legal challenges if they aid the majority of the people. All state and territory governments passed complementary biological control legislation between 1986 and 1988. The injunction was then lifted in November 1988, allowing further releases of the moth. The moth was finally re-released in South Australia in 1988.

    Dialectica scalariella
    (Photo: courtesy of Ken Bond, Dept of Zoology, Ecology & Plant Science,
    University College, National University of Ireland, Cork, Ireland)

    The forewings of the adult moth have a brown front half, and a white rear half, with a wavy line separating the halves. The head and thorax have white dorsal patches. The wingspan is about 1 cm.

    The adult moth superficially resembles that of the Australian native species Dialectica aemula, which has made monitoring the progress of the species difficult, but the cocoons are more easily distinguished. The cocoons are in two layers. The inner cocoon of Dialectica scalariella is white, nearly filling the outer cocoon. The inner cocoons of Dialectica aemula are yellowish, and narrower than the outer cocoon.

    The species was originally found in:

  • Spain,

    but now can be found also in

  • New South Wales,
  • Australian Capital Territory,
  • Tasmania, and
  • South Australia,

    and has also accidently invaded

  • New Zealand.

    Further reading :

    T. Kumata and M. Horak,
    The native Dialectica aemula (Meyrick) and the introduced Dialectica scalariella (Zeller) (Lepidoptera:Gracillariidae) in Australia: characterisation of two closely related species on Boraginaceae/,
    Australian Journal of Entomology,
    Volume 36, No. 1 (1997), pp. 25-36.

    Philipp C. Zeller,
    Verzeichniss der von Herrn Jos. Mann beobachteten Toscanischen Microlepidoptera.,
    Stettiner Entomologische Zeitung,
    Volume 11 (1850), pp. 160-161, No. 208.

    Australian Butterflies
    Australian Moths

    (updated 17 September 2011, 27 February 2017, 19 January 2021)