Spatial analysis of an outbreak of Uraba lugens (Lepidoptera: Noctuidae) in the southwest of Western Australia: does logging, vegetation type or fire influence outbreaks?

Summary

There was an outbreak of gumleaf skeletoniser (GLS, Uraba lugens Walker) in the southern jarrah forest in 1982–1988. Aerial and observational survey data were used in a Geographic Information System analysis of the possible impact of forest management practices on this insect. In addition, this allowed investigation of the influence of vegetation type on the distribution of GLS. A total area of 6.7 million ha was interrogated, including 89 900 ha of land infested with GLS. Neither logging nor prescribed burning induced increases in GLS populations. However, a decrease in area infested with GLS was indicated for prescribed burning up to 3 y prior to the outbreak. Interrogation of vegetation complexes indicated that the GLS outbreak was initiated on marginal jarrah forest on poorly drained sites that are prone to inundation in winter and drought in summer. In addition, bivoltine GLS populations were discovered on the fringes of the southern jarrah forest during the observational surveys. This supports the hypothesis that bivoltine GLS were more prevalent in the southern jarrah forest during the outbreak as opposed to univoltine GLS during non-outbreak periods.

Keywords:

• insect pests
• population dynamics
• defoliation
• outbreak
• landforms
• vegetation types
• forest management
• logging
• controlled burning
• gumleaf skeletoniser
• Uraba lugens:
• jarrah
• Eucalyptus marginata
• marri
• Corymbia calophylla
• Western Australia