Vagrant status of lucerne seed web moth, Etiella behrii (Zeller 1848) (Lepidoptera: Pyralidae) in Tasmania

Abstract

The lucerne seed web moth or etiella moth, Etiella behrii (Zeller) (Lepidoptera: Pyralidae: Phycitinae: Phycitini) has been recorded as adults and larvae across mainland Australia on leguminous plants. Suitable host plants occur in Tasmania but detections are restricted to adults, mostly in one long-term light trap. A combination of methods is used to determine whether this pest is a non-breeding vagrant, a breeding migrant or resident in Tasmania. A degree-day development model for E. behrii showed that warmer source areas outside Tasmania better explained flight seasonality observed by light trapping in Tasmania than local source areas. Pest records of 119 Lepidoptera associated with Tasmanian Medicago plants do not include Etiella. The absence of records of larvae, the coincidence of adults with migratory insects and northerly airflows, flight seasonality and a requirement for a six month non-developmental period in the cool season indicate that E. behrii migrates to Tasmania where any breeding is below detection although two generations seem possible based on thermal requirements. The results provide another example of a pest that fails to establish, even ephemerally, in Tasmania despite repeated migration from mainland Australia. The precise impediments to seasonal establishment of E. behrii remain unclear but this would most likely occur in north-west or north-east Tasmania, which receive most migratory moths. E. behrii is one of a suite of native Australian pests that may extend its breeding range to Tasmania with global warming. Climate matching models are prone to error if they assume E. behrii is resident in Tasmania.