Lorraine J Spohr

Models for the dispersal in Australia of the arbovirus vector, Culicoides brevitarsis Kieffer (Diptera: Ceratopogonidae).

Culicoides brevitarsis is the main biting midge responsible for the transmission of bluetongue and Akabane viruses to livestock in Australia. Models are given for its dispersal after winter from endemic areas at the southern limit of its distribution in New South Wales (NSW); the models might also be applicable elsewhere. Model 1 shows that dispersal can be explained by distance from a key point just outside the endemic area in mid-northern/northern coastal NSW. The model provides probability data for times of first occurrence at sites within regions down the southern coastal plain or up the Hunter Valley towards (but rarely reaching) the western slopes and tablelands. Model 2 shows that the movement depends on temperature and wind speed from northerly and easterly directions. Preliminary data also are given to suggest a relationship between density in the endemic area and the maximum distance that C. brevitarsis can travel in a given year. The models can be linked to other information which in combination can provide probabilities for winter survival outside the endemic area, times of occurrence at sites where it cannot survive winter and times when activity ceases naturally at these sites at the end of the season. This information can be used to predict the potential for virus transmission and indicate zones of seasonal freedom from both vector and virus for the export of livestock.

Antifungal effect of gaseous nitric oxide on mycelium growth, sporulation and spore germination of the postharvest horticulture pathogens, Aspergillus niger, Monilinia fructicola and Penicillium italicum

Aim:  To evaluate the antifungal activity of nitric oxide (NO) against the growth of the postharvest horticulture pathogens Aspergillus niger, Monilinia fructicola and Penicillium italicum under in vitro conditions.

Low Dose Gamma Irradiation Does Not Affect the Quality or Total Ascorbic Acid Concentration of "Sweetheart" Passionfruit (Passiflora edulis)

Passionfruit (Passiflora edulis, Sims, cultivar “Sweetheart”) were subject to gamma irradiation at levels suitable for phytosanitary purposes (0, 150, 400 and 1000 Gy) then stored at 8 °C and assessed for fruit quality and total ascorbic acid concentration after one and fourteen days. Irradiation at any dose (≤1000 Gy) did not affect passionfruit quality (overall fruit quality, colour, firmness, fruit shrivel, stem condition, weight loss, total soluble solids level (TSS), titratable acidity (TA) level, TSS/TA ratio, juice pH and rot development), nor the total ascorbic acid concentration. The length of time in storage affected some fruit quality parameters and total ascorbic acid concentration, with longer storage periods resulting in lower quality fruit and lower total ascorbic acid concentration, irrespective of irradiation. There was no interaction between irradiation treatment and storage time, indicating that irradiation did not influence the effect of storage on passionfruit quality. The results showed that the application of 150, 400 and 1000 Gy gamma irradiation to “Sweetheart” purple passionfruit did not produce any deleterious effects on fruit quality or total ascorbic acid concentration during cold storage, thus supporting the use of low dose irradiation as a phytosanitary treatment against quarantine pests in purple passionfruit.

Feeding and Development of the Glassy-Winged Sharpshooter, Homalodisca vitripennis, on Australian Native Plant Species and Implications for Australian Biosecurity

In any insect invasion the presence or absence of suitable food and oviposition hosts in the invaded range is a key factor determining establishment success. The glassy-winged sharpshooter, Homalodisca vitripennis, is an important insect vector of the xylem-limited bacterial plant pathogen, Xylella fastidiosa, which causes disease in numerous host plants including food and feedstock crops, ornamentals and weeds. Both the pathogen and the vector are native to the Americas and are considered to be highly invasive. Neither has been detected in Australia. Twelve Australian native plant species present in the USA were observed over two years for suitability as H. vitripennis feeding, oviposition and nymph development hosts. Hosts providing evidence of adult or nymph presence were Leptospermum laevigatum, Acacia cowleana, Eremophila divaricata, Eucalyptus wandoo, Hakea laurina, Melaleuca laterita and Swainsona galegifolia. An oviposition-suitability field study was conducted with citrus, a favoured oviposition host, as a positive control. Citrus and L. laevigatum, A. cowleana, B. ericifolia×B. spinulosa, C. pulchella, E. divaricata, E. wandoo, H. laurina, and S. galegifolia were found to be oviposition hosts. Egg parasitism by the mymarid parasitoid Gonatocerus ashmeadi was observed on all Australian plants. A number of Australian plants that may facilitate H. vitripennis invasion have been identified and categorised as ‘high risk’ due to their ability to support all three life stages (egg, nymph and adult) of the insect in the field (L. laevigatum, A. cowleana, E. divaricata, H. laurina, and S. galegifolia). The implications of these host status and natural enemy research findings are discussed and placed in an Australian invasion context.

Factors affecting the distribution of Culicoides spp. (Diptera: Ceratopogonidae) vectors of bluetongue virus (BTV) in Australia

This study examined environmental and geographical factors affecting the distribution of the bluetongue virus vectors Culicoides brevitarsis Kieffer, C. actoni Smith, C. fulvus Sen and Das Gupta and C. wadai Kitaoka in Australia using graphical analysis. Calculations and mapping were carried out in the R programming environment using freely available data. Average low temperatures of 13.5°C in June and in September were estimated as thresholds and expressed as contours at which C. brevitarsis activity ceases and then recommences during and after winter, respectively. The June threshold also designated areas where populations would be unable to survive the winter. There was substantial variability in the contours between years, around which the activity of C. brevitarsis would be correspondingly dynamic. Culicoides wadai, C. actoni and C. fulvus appeared to be less tolerant of low temperatures. A high temperature limit was proposed at a maximum 35°C during summer. Culicoides brevitarsis was found in areas above and below this temperature, while C. actoni, C. fulvus and C. wadai occurred mainly in coastal environments at maximum temperatures of less than 35°C. Possible effects of global warming were considered with 1°C or 2°C rises in temperature. Changes to low temperature thresholds could expose greater areas of southern Australia to vector activity, while temperature rises in the north could increase the size of areas in which temperatures are lethal to the vectors. Rainfall had no apparent effect on C. brevitarsis during the northern wet and dry seasons. Distributions of C. brevitarsis and cattle overlapped until both ended with the climatic change to desert, which formed a physical barrier preventing C. brevitarsis movement to the south. Temperature restricted associations between C. brevitarsis and sheep. The other Culicoides spp. were found outside major cattle and sheep production areas. Apart from seasonal and dynamic activity around the contours, cattle and sheep in areas below a June average temperature of 13.5°C should remain vector free at current climatic temperatures.

Phytosanitary irradiation of three species of spider mites (Trombidiformes: Tetranychidae): Phytosanitary irradiation of spider mite

The survival of three species of Tetranychidae mites: Tetranychus evansi (tomato red spider mite), Tetranychus ludeni (bean spider mite) and Tetranychus urticae (two‐spotted mite), exposed to gamma irradiation doses of 200, 300, 400, 500 and 600 Gy was investigated. The aim was to identify an irradiation dose capable of killing or sterilising mites infesting horticultural produce to prevent movement to and colonisation of host plants in non‐infested regions or countries. Eggs were irradiated separately; otherwise, to simulate naturally occurring mite populations, mixed life stages (immatures and adults) were combined and the treatment effects compared to non‐irradiated controls. Irradiated eggs of all species failed to develop and hatch at 200 Gy and above. Tetranychus urticae was the most tolerant species, requiring an irradiation dose of 300 Gy to ensure all adult females were sterilised. Sterilised adults continued to lay eggs, but these eggs failed to develop or hatch. Tetranychus evansi and T. ludeni were sterilised when irradiated at 200 Gy. Based on these results, a dose of 300 Gy is recommended as a phytosanitary measure to prevent the survival of these species of Tetranychidae pests of horticultural produce in non‐infested regions. Combined with data from other studies this study proposes a generic dose for Tetranychidae mites of 375 Gy.

Effects of gamma radiation on the survival of four species of thrips (Thysanoptera: Thripidae): Effects of irradiation on the survival of thrips

The survival of four species of thrips (Frankliniella occidentalis, Frankliniella schultzei, Thrips tabaci and Thrips imaginis) exposed to gamma irradiation at doses of 0, 200, 300, 400 and 500 Gray was investigated. The aim of the work was to identify a generic dose of gamma radiation capable of killing or sterilising thrips infesting horticultural produce to prevent movement to, and colonisation of host plants in noninfested regions or countries. To simulate naturally occurring thrips populations, mixed life‐stages were irradiated, and the effects compared with a nonirradiated control. The eggs of F. occidentalis and T. tabaci were more tolerant to irradiation than those of F. schultzei and Thrips imaginis, but none of the F. occidentalis or T. tabaci eggs developed beyond first stage larvae when irradiated at a target dose of 200 Gy. In mixed life‐stage tests, all species had a similar tolerance to gamma irradiation. At a target dose of 200 Gy, all species were sterilised and no further offspring were produced. Based on these results, a minimum generic dose of 200 Gy would be sufficient to control these species of thrips in fresh horticultural produce destined for export to thrips‐sensitive regions. A target dose of 250 Gy will provide a further margin of safety, until large‐scale confirmatory trials are completed.

A novel method for assessing the effect of photoperiod and temperature on reproductive biology of the predators Hippodamia variegata (Coleoptera: Coccinellidae) and Micromus tasmaniae (Neuroptera: Hemerobiidae)

A novel experimental approach for the simultaneous investigation of the effects of photoperiod and temperature showed evidence of diapause in Hippodamia variegata Goeze but not in Micromus tasmaniae Walker. Results are discussed in relation to their potential as greenhouse biocontrol agents.