James Ridsdill Smith
CSIRO and UWA, Australia

Halotydeus destructor is a major invasive pest in the winter rainfall regions of southern Australia. We carried out ecological and biological studies to identify strategies to control the mites, which are polyphagous and breed opportunistically. They complete three generations in winter and pass the summer as diapausing eggs. Chemical sprays do not kill the eggs so populations are only partially controlled. It has proved possible to accurately predict the onset of diapause in spring.  We found that 80% of the variability between sites is predicted by daylength, and built a database, TIMERITE™, to provide individual farmers with the optimal date for spraying, using GPS co-ordinates. A single spring spray resulted in 97% mite control 8 months later in autumn, a 45% increase of clover seed yield and a 60% increase of clover seedling density. TIMERITE™ has been widely adopted and is estimated to deliver $AUD37 million a year benefit to farmers. We have also looked at mite feeding. Mites feed on the upper surface of the leaf canopy, piercing the cells and sucking up sap. Feeding mites aggregate in groups of 5-6, and are attracted to damaged cotyledons by low concentrations of 2-E-hexenal, a green leaf volatile. Another induced volatile, 1-octen-3-one, deters mite feeding in clover varieties causing resistance, and several varieties have been bred with mite resistance and released to farmers.