Biology and ecology of the introduced snail Microxeromagna armillata in south eastern Australia

Abstract

Microxeromagna armillata ( Lowe, 1852 ) is a snail introduced snail to Australia which has established populations in the Riverland and Sunraysia citrus growing regions. Citrus exported from these regions to the USA has been rejected due to contamination with M. armillata, causing significant economic losses. The life history, phenology and activity of Microxeromagna armillata has not been studied in Australia : this forms the basis of this thesis. Microxeromagna armillata employs an iteroparous egg laying strategy in semi - field conditions and lays approximately 500 eggs per year. Field populations can reach high densities ( ∼ 4000 snails / m ² ), particularly during the winter months when juvenile recruitment occurs. Snails reach sexual maturity at ∼ 6mm in shell diameter and can grow to this size from a juvenile stage ( 2mm ) within six weeks. Microxeromagna armillata can reproduce successfully by self-fertilisation, and juveniles are able to aestivate with little reduction in subsequent fecundity. These traits make control of this pest a significant challenge. Leaf litter is the preferred habitat of M. armillata, but snails do move in the tree canopy. Cues for snail activity in the leaf litter and canopy appear to differ, as does the size of active snails in these areas. Microxeromagna armillata activity was low in the tree canopy during harvest compared to post harvest, intimating that fruit contamination is either occurring infrequently or post - harvest. Copper trunk bands were shown to minimise snail movement into the canopy and may be an important preventative measure. These findings have changed the recommendations for M. armillata management in citrus groves of south eastern Australia.