The effect of flooding on population density of the gum leaf skeletonizer moth, Uraba lugens Walk., in Barmah State Forest.  J.A. Harris.  October 1972.  11 pp. (unpubl.)

SUMMARY

The gum leaf skeletonizer moth, Uraba lugens Walk., (Lepidoptera: Nolidae), from time to time causes widespread defoliation of river red gum, Eucalyptus camaldulensis Dehn, forests, and the flooding which is characteristic of these forests has been regarded as a factor controlling populations of this insect.

In the Barmah State Forest the population level of insects in the generation before, and the generation after a single flood in March, 1966, were compared numerically on seven areas with different intensities of flooding. Population level increased on the only dry area, decreased slightly on an area with floodwater nearby, and was reduced on all other areas in the presence of floodwater.

All seven areas were flooded from August to December, 1966, during the second generation of the insect, and were free from floods during the third generation studied (December, 1966 to March, 1967). Comparison of population levels of the third generation, sampled in December, 1966, with those of the second generation, oviposited after the March, 1966 flood, showed that there had been a non-significant increase on one area and significant decreases on all other areas, whereas in the fourth generation, sampled in March, 1967, population levels had increased on all areas in the absence of flood water.

Comparison of March, 1967 defoliation on the sampled the areas with defoliation on four additional areas which had been dry during the August-December, 1966 floods, showed negligible defoliation on the original seven areas and on one of the additional areas which had had floodwater nearby, and widespread defoliation on the remaining three additional areas which had had no adjacent floodwater.

Flooding of the Bamah State Forest, which occurs whenever the flood regulators along the Murray River are opened, will reduce the population of this insect, and less oviposition will occur. In the subsequent generation, defoliation is unlikely to occur on areas which have been flooded, as the insect requires at least one generation, without flooding, before oviposition is sufficient to produce a plague population. Moderate defoliation may occur on these flooded areas in the second generation after a flood, unless a further flood occurs during that generation.