Geometrid “Looper” caterpillar populations have irrupted 4 times in the last 7 years over much of the 1 million hectare Bookmark Biosphere. They have extensively defoliated the mallee, with this year’s attack being probably the worst yet.
Over the summer period of 2021 – 2022 Adelaide University students Alexandra, Mia, Nicole, and Sophie undertook internships at Gluepot Reserve. Their task was to assess the defoliation damage looper caterpillars (seen in figure 1) are currently inflicting on the mallee trees on the reserve. Approximately 450 mallee covering the entire reserve were visually surveyed for damage and regeneration categorised into percentage brackets. Initial data has shown the majority of the trees surveyed have at least 25 % damage with most trees more likely to fall into the higher percentages of damage. See figure 2 for an example of the damage brackets. The four species of mallee found on the reserve include Eucalyptus gracilis, E. socialis, E. dumosa, and E. oleosa.
Loopers pictured below anecdotally appear to be a boom-and-bust species with instars noted in the thousands seen by Alexandra and Nicole within their first week of their stay in January. By the second week of their stay a vast reduction of loopers were noted with only minimal instars seen. Investigation into determining the species we are dealing with is underway, with specimens being sent off to various collaborating institutions. Students have also set up a “caterpillar hotel” in an attempt to pupate the looper into moths for more accurate species identification. We are hopeful that we can correctly identify the Geometridae moth species we are dealing with. Further understanding into the reasons why the extreme defoliation is occurring here at Gluepot may then open the possibility of solutions being implemented.
Figure 1: *Suspected instar stages of Geometridae looper caterpillars found on Gluepot Reserve. Image A; A looper instar within its earlier stages of development displaying a yellow – green colouration speckled with white and black dots along the side. Image B; As the instar develops its colouration changes to red – brown with the black dots along the sides increasing. Image C; Shows the instar in its final stages before pupation, its colouration may be slightly red to almost black with obvious black bands of colour along the sides. *This life cycle is based off anecdotal evidence noted in the field and references of known species of Geometridae instar stages.
Figure 2: An example of a healthy mallee tree verses an unhealthy mallee tree from left to right. Image A; A healthy mallee with a full canopy and 0 – 25 % damage present, which falls within the normal range. Image B; A mallee tree with 50 – 75 % canopy damage with 25 – 50 % regeneration seen. Image C; A mallee tree with 75 – 100 % canopy damage and 0 – 25 % regeneration seen. The defoliation seen has been caused by an unidentified Geometridae species within its instar stages over approximately 2 months.