Wheat streak mosaic virus (WSMV) infection and infestation with its wheat curl mite (WCM; Aceria tosichella) vector were investigated in wheat crops at two sites in the low-rainfall zone of the central grainbelt of south-west Australia. In the 2006 outbreak, after a preceding wet summer and autumn, high WCM populations and total infection with WSMV throughout a wheat crop were associated with presence of abundant grasses and self-sown ‘volunteer’ wheat plants before sowing the field that became affected. Wind strength and direction had a major effect on WSMV spread by WCM to neighbouring wheat crops, the virus being carried much further downwind than upwind by westerly frontal winds. Following a dry summer and autumn in 2007, together with control of grasses and volunteer cereals before sowing and use of a different seed stock, no WSMV or WCM were found in the following wheat crop within the previously affected area or elsewhere on the same farm. In the 2007 outbreak, where the preceding summer and autumn were wet, a 40% WSMV incidence and WCM numbers that reached 4800 mites/ear at the margin of the wheat crop were associated with abundant grasses and volunteer wheat plants in adjacent pasture. WSMV incidence and WCM populations declined rapidly with increasing distance from the affected pasture. Also, wheat plants that germinated early had higher WSMV infection incidences than those that germinated later. The alternative WSMV hosts identified at these sites were volunteer wheat, annual ryegrass (Lolium rigidum), barley grass (Hordeum sp.), and wild oats (Avena fatua). In surveys outside the growing season at or near these two sites or elsewhere in the grainbelt, small burr grass (Tragus australianus), stink grass (Eragrostis cilianensis), and witch grass (Panicum capillare) were identified as additional alternative hosts.

There is growing evidence that potassium deficiency in crop plants increases their susceptibility to herbivorous arthropods. The ability to remotely detect potassium deficiency in plants would be advantageous in targeting arthropod sampling and spatially optimizing potassium fertilizer to reduce yield loss due to the arthropod infestations. Four potassium fertilizer regimes were established in field plots of canola, with soil and plant nutrient concentrations tested on three occasions: 69 (seedling), 96 (stem elongation), and 113 (early flowering) days after sowing (DAS). On these dates, unmanned aerial vehicle (UAV) multi-spectral images of each plot were acquired at 15 and 120 m above ground achieving spatial (pixel) resolutions of 8.1 and 65 mm, respectively. At 69 and 96 DAS, field plants were transported to a laboratory with controlled lighting and imaged with a 240-band (390-890 nm) hyperspectral camera. At 113 DAS, all plots had become naturally infested with green peach aphids (Hemiptera: Aphididae), and intensive aphid counts were conducted. Potassium deficiency caused significant: (1) increase in concentrations of nitrogen in youngest mature leaves, (2) increase in green peach aphid density, (3) decrease in vegetation cover, (4) decrease in normalized difference vegetation indices (NDVI) and decrease in canola seed yield. UAV imagery with 65 mm spatial resolution showed higher & Dustin Severtson classification accuracy (72-100 %) than airborne imagery with 8 mm resolution (69-94 %), and bench top hyperspectral imagery acquired from field plants in laboratory conditions (78-88 %). When non-leaf pixels were removed from the UAV data, classification accuracies increased for 8 mm and 65 mm resolution images acquired 96 and 113 DAS. The study supports findings that UAV-acquired imagery has potential to identify regions containing nutrient deficiency and likely increased arthropod performance.

Preparation of arthropods for morphological identification often damages or destroys DNA within the specimen. Conversely, DNA extraction methods often destroy the external physical characteristics essential for morphological identification. We have developed a rapid, simple and non-destructive DNA extraction technique for arthropod specimens. This technique was tested on four arthropod orders, using specimens that were fresh, preserved by air drying, stored in ethanol, or collected with sticky or propylene glycol traps. The technique could be completed in twenty minutes for Coleoptera, Diptera and Hemiptera, and two minutes for the subclass Acarina, without significant distortion, discolouration, or other damage to the specimens.

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