Ecological studies of sheep blowfly in winter rainfall regions as a basis for strategic treatment in an IPM program

Research Need

Control programs for blowflies in South-eastern Australia rely more on management practices, such as time of shearing, lambing and cropping, than on specific knowledge of the parasite’s life cycle. Consequently, on many farms, chemical treatments are applied in response to the occurrence of blowfly strike.

A better understanding of the ecology of the sheep blowfly would allow strategic early treatment which may give better fly control and reduce chemical treatments. For example, one study showed that early treatment in Sept/ Oct reduced subsequent flystrike by limiting the number of sheep susceptible to attack by the first generation of flies.

While much is known about the biology of blowflies, there are gaps in this knowledge which hamper adoption of this strategic approach.

This integrated parasite management (IPM) approachwould give more effective control of blowfly strike and provide a more targeted use of chemicals. This would reduce residues in wool and occupational exposure to chemicals by shearers and others.

Key research questions

Obtain more information about the over-winter survival of blowfly larvae and the emergence of adult flies in spring to better design an IPM approach.

Methods

In 2005 & 2006, sheep blowfly larvae were put into PVC containers on a farm in western Victoria (see photo below).

Deposits were made at 3-5 weekly intervals, from early autumn through until late spring. Flies emerging each week were collected and counted to measure the mortality of over-wintered larvae and timing of the spring generation.

Measurements are being made of soil and weather conditions. This will enable environmental factors to be related to the emergence of flies, possibly allowing prediction of this phase of the life cycle.

Conclusions

The second year of the study has just started. In the first year, a ‘split emergence’ was seen when larvae were deposited on 26 April 2005, with 45% developing to flies before winter, and 5% emerging in spring (October).

Subsequent deposits showed between 85 and 100% of over-wintering larvae died. Data from both years will be used to predict the emergence of the first spring generation of flies.

Personnel

Sandra De Cat (Masters student), Dr Norman Anderson &  Dr John Larsen
The Mackinnon Project, University of Melbourne Faculty of Veterinary Science, Werribee

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