Each season we encounter different challenges when producing and maintaining food crops. Weather, pests, disease and even time can become huge obstacles in achieving our goals and a good harvest. This season there is a new challenge that has been absent in some years from the agricultural scene, the Rutherglen Bug (RGB).
The RGB is a native species to Australia that breed on a wide range of native plant species and plants considered to be weeds. RGB have eight generations a year. In spring and summer RGB eggs take 3-4 weeks to become an adult. Adults live up to four weeks, in this time females will lay up to 400 eggs.
RGB migrate in large numbers as adults, typically with storms or strong winds, once inland breeding areas start to dry. According to the Queensland Government’s Department of Agriculture and Fisheries, when there are larger populations of RGB in a season, populations are dominated by migrants from inland breeding areas.
Once the bugs arrive to Eastern Australian agricultural regions, they will breed on plants similar to the inland species they migrated from (weeds). RGB are predominantly a seed-feeding species, affecting plants mostly at the grain filling stage. Though little is known about the capacity of damage caused by RGB on crops other than Sunflower. Feeding wounds will allow entry by bacteria and fungi, facilitating disease and infection. Then once the host plant dies out, RGB move to crops or other plants.
The most commonly recorded predator of the RGB is egg parasitoids. Although, like all control methods for RGB, the contribution to population control will be limited depending on the density of RGB adults. There is little data on the natural enemies of the RGB but spiders are thought to play a role.
A Collective View of Past Studies
In an experiment by the Department of Agriculture at the Biological and Chemical Research Institute, Rydalmere N.S.W, different culturing methods for the RGB were undertaken. There were three approaches to culturing the RGB: 1. Feeding on Seed Only, 2. Feeding on Vegetative Growth Only, 3. Soil Selection Experiment.
The aim of the experiment was to provide necessary information so the laboratory could maintain a culture, without introduced RGB from wild populations. From the results, the lab was able to maintain large numbers of nymphs and adults from early 1971 to mid 1973.
Something that was Interesting in the soil experiment, female RGB showed a definite preference for a particular soil, of the ‘series’ of soils tested. The females prefered the dry, sandy loam with moisture content below 30 per cent, to lay their eggs.
After enormous numbers of RGB were recorded during early 2007-08 in Central Queensland, Darling Downs, and northern NSW, research funded by Grains Research and Development Corporation (GRDC) observed the impact and best control of RGB on Sorghum. Data on the RGB impact and best management method was collected with good results.
The research found that seed set in sorghum reduced if more than 50 RGB per head, when present during flowering. The most effective control methods were found to be using alphacypermethrin and deltamethrin for controlling high densities of RGB in sorghum. GRDC are researching further fungal biopesticides, which won’t disrupt the beneficial insects.
It is thought Metarhizium anisopliae, fungi in the phylum Ascomycota, could be effective. These fungi are an entomopathogenic fungi that grow naturally in soils throughout the world. Entomopathogenic fungi act as a parasitoid and kill or seriously disables insects by causing disease.
Further research seems like a good idea as the previously mentioned poisons both contain Pyrethrin, plus some other nasties (Piperonyl butoxide, google it). Pyrethrins attack insects nervous systems, effectively disrupting the life cycle of any treated insect. This knowledge has been used for thousands of years.
Pyrethrum is a known genus of several Old World plants, now classified as either Chrysanthemum or Tanacetum. By drying and crushing Chrysanthemum cinerariifolium and Chrysanthemum coccineum flower heads, different methods of extraction can be used. Individual research and experimentation is always the best approach from here. We have found that enriching the soil with plenty of organic matter and mulch keeps humidity levels low. RGBs prefer sandy soils to 'sticky,' rich soils. Compost also helps strengthen weakened affected plants.
Attia, F & Elshafie, M 1973, ‘A TECHNIQUE FOR CULTURING RUTHERGLEN BUG, NYSIUS VINITOR BERGROTH (HEMIPTERA : LYGAEIDAE)’, Biological and Chemical Research Institute, Department of Agriculture
Australian Grain, ‘Rutherglen Bugs Taint Harvested Grain’ [online], Vol. 17, No. 4, Nov/Dec 2007, viewed 20 December 2016, <http://search.informit.com.au.ezproxy.uws.edu.au/documentSummary;dn=273488473150890;res=IELHSS>
Queensland Government 2010, Department of Agriculture and Fisheries, ‘Rutherglen bug, grey cluster bug’, viewed 20 December 2016, <https://www.daf.qld.gov.au/plants/field-crops-and-pastures/broadacre-field-crops/integrated-pest-management/a-z-insect-pest-list/rutherglen-bug,-grey-cluster-bug>
Miles, M, Lloyd, R, Murray, D & Hauxwell, C 2008, ‘New research on the impact and control of Rutherglen bug in sorghum’, Australian Grain, Vol. 17, No. 5
McDonald, G, Broadley, RH, Smith, AM & Blackburn, MD 1986, ‘Evaluation of insecticides for 'Nysius vinitor' Bergroth’, General and Applied Entomology: The Journal of the Entomological Society of New South Wales, Vol. 18
Wikipedia, 3 June 2016, Metarhizium anisopliae, viewed 20 December 2016 https://en.wikipedia.org/wiki/Metarhizium_anisopliae
Wikipedia, 29 October 2016, Entomopathogenic fungus, viewed 20 December 2016, https://en.wikipedia.org/wiki/Entomopathogenic_fungus