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Information on the biology, ecology and control of the small brown snail in citrus orchards in south-eastern Australia.

The Problem 

One of the key export markets for the Australian citrus industry is the United States of America. Several issues threaten access to this market, with one of them being the interception of foreign invertebrates. Microxeromagna armillata, the small brown snail (SBS), has been intercepted on shipments of Australian export navels by USDA quarantine authorities. This snail does not occur in the USA, and it is related to several well-known pest snail species. On this basis, the USDA declared M. armillata an actionable species. This means that if further detections occurred on Australian export fruit, market access could be threatened. For Australian growers, this means that any snail contaminated fruit detected would either need to be repacked and re-exported to another country, or fumigated and destroyed in the USA, at a considerable cost.

This project aimed to provide citrus growers with more information on the biology, ecology and control of SBS and tools to minimise the risk of fruit contamination.

The Project Science 

The research focused in a number of key areas:

• Studies of the lifecycle and reproductive characteristics of SBS, in both the laboratory and orchard environments.
• A study of the comparative distribution of SBS within different citrus orchard areas across seasons.
• Investigations to determine the movement of SBS in the tree canopy in different seasons and evaluating the risk of fruit infestation, using a new mucous trail staining technique
• Assessment of the efficacy of three different snail baits against SBS in autumn, winter and spring.
• Evaluating the potential of several copper trunk bands to prevent snail movement into the canopy.  

The Key Research Findings and Extension Highlights

• Studies of the reproductive characteristics of SBS indicate that egg laying can occur from Autumn to Spring, and;
• • Eggs are laid in clutches of approx. 20 eggs in the soil.
  • SBS can live for at least two years, and can lay an average of 550 eggs per year.
  • Juveniles can grow to maturity in just three months and begin reproducing in laboratory conditions.
  • Juveniles can survive without food and water for at least 10 months.
  • SBS can reproduce by self-fertilisation.
• Sampling of SBS in the orchard has shown that:
• • Snails are found in much higher densities in the leaf litter than in the sod at all times of year.
  • Snail density in the leaf litter increased from autumn to spring as a result of juvenile recruitment.
  • Numbers of snails on the tree trunks were low in autumn and winter and high in Spring
  • No snails were found in the outer tree canopy in autumn and winter, however snails were found in this area in spring.
  • Snails were more likely to be found on fallen fruit than on fruit in the canopy during harvest.
• Snail movement in the tree was low during autumn and winter when compared to spring and:
• • Few snails were active on the upper branches during autumn and winter when compared to spring.
  • Larger snails in the population moved higher in the canopy at all times of year
  • Different cues for activity appear to be acting on snail movement in the leaf litter compared to the tree canopy.
• Metaldehyde and methiocarb based baits were effective against SBS in semi-field conditions with the most consistent results achieved in autumn. Snail behaviour, environmental conditions and bait breakdown all influence bait efficacy.
• Copper bands can prevent snail movement into the tree canopy for up to two years, although efficacy depends on band type.
• Communication of these results has been successfully conducted through the production of 5 Snail Mail newsletters and CITTgroup meetings in the Riverland, Sunraysia and Western Australia citrus growing regions.
• Improving the identification and monitoring of snails in citrus orchards was achieved by the production and distribution of the infonote: Snails – a quarantine concern for export citrus to the USA.

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Recommendations 

For citrus growers exporting Navels to the USA to minimise the risk of snail contamination of fruit:

• Skirt trees so that fruit never touches the ground.
• Never harvest fallen fruit.
• Monitor for snail activity prior to application of snail baits.
• Apply metaldehyde or methiocarb based baits when snails are active in autumn.

For further research:

• Investigate the environmental and behavioural triggers for snail movement into the canopy and particularly the upper branches.
• Further study of the factors that contribute to variability of bait efficacy.
• The use of copper trunk bands to prevent snail movement shows promise, however further evaluation is needed.

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Management 

Small Brown Snail Monitoring  (PDF file)
Note: To view and print PDF files an Adobe Acrobat Reader is required.
A Monitoring Tool for Small Brown Snail Control  (PDF file)
Contemplating your navels... A monitoring tool for small brown snail control. 

Snail Mail 

View past editions of Snail Mail here 

Fact Sheets and Infonotes 

• Small Brown Snail Control in Citrus Orchards (PDF)
• Snails - A Quarantine Concern for Export Citrus to the USA (PDF)

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