Biocontrol News and Information 29(2), 19N–35N pestscience.com General News Storing Onions without Tears differential between premium- and lower-grade onions. Depending on the dose rate used, this repre- A study in Australia has shown that the onion thrips, sented a 10- to 20-fold benefit:cost ratio. Further- Thrips tabaci, which reduces crop yields and bulb more, they suspected that the percentage increase in quality worldwide, can be effectively and economi- premium-grade onions could be improved if the mites cally controlled by innundative releases of a were introduced soon after harvest, rather than a commercially available predatory mite. fortnight later as in this trial. Despite intensive field spray programmes, harvested The results of a more recent trial, using a lower onion bulbs in Australia are invariably infested by range of mite doses (0.1, 0.25 and 1.0 litres of ver- onion thrips, which continue to colonize, reproduce miculite–mite mix per bin), and testing two methods and develop during on-farm onion storage, causing tissue scarring and loosening of the outer layers of of application (top dressing and incorporating, which the bulb, which in turn cause the onions to be down- proved equally effective) confirmed the impact of N. graded in quality and thus market value. Red onions, cucumeris on thrips numbers and onion quality. In a premium salad type, are particularly prone to this trial, the mites were added to the bins on the day thrips tissue scarring and resultant quality loss in of harvest, but the numbers of thrips in the har- storage. No in-storage control options currently exist, vested crop were particularly low (0.075 thrips/bulb) in Australia or overseas. so although the results were even better than in the trial above, it is difficult to separate the effects of ear- In 2006, Greg Baker and Kevin Powis (South Aus- lier treatment and the very low ‘starter’ pest tralian Research and Development Institute – population. The dearth of prey did not, however, pre- SARDI) began by conducting a small laboratory trial vent mite populations from sustaining themselves to assess the potential of two commercially available and exerting control; thrips densities were signifi- predatory mite species, the phytoseiid Neoseiulus cantly suppressed by all six treatments and there cucumeris and the ascid Hypoaspis aculifer, to limit was very little decline in the number of premium- onion thrips damage in stored red onions. The mites, quality bulbs over the trial period (from 97.0% at which are used in greenhouses for thrips control, harvest to 93.8% and 95.0% in the 0.25- and 1.0-litre were obtained from Biological Services (Loxton, treatments at 45 days, respectively, with the 0.1-litre South Australia). Following encouraging results, a treatment giving a lesser but still significant effect, larger-scale on-farm trial was conducted in 2007 at compared with a decline to 46.3% premium-rate Mypolonga, South Australia. Three rates of each spe- bulbs at 45 days in the control). cies (0.25, 1.0 and 4.0 litres of vermiculite–mite mix containing ca. 40,000 N. cucumeris and ca. 15,000 H. These studies provide strong evidence that innunda- aculifer per litre of mix) were added to 600-kg bins of tive release of N. cucumeris into onion bins at or soon red onions two weeks after harvest. The density of after harvest provides reliable, cost-effective control thrips per bulb in each treatment was monitored of onion thrips in red onions for at least six weeks twice over the next 45 days. after harvest. On the basis of results so far and for South Australian conditions, the researchers recom- The H. aculifer treatments had no apparent effect on mend a rate of 0.25 litres vermiculite–mite mix (ca. the thrips, with pest numbers increasing in a 10,000 N. cucumeris) per 600-kg bin, applied as a top manner similar to the untreated control (which dressing (the simpler of the two methods tested). For increased from a pre-treatment density of 0.7 thrips an Australian grower and at current prices, an per bulb to 6.0 thrips 45 days post-treatment). How- investment of approximately $6 per bin could give a ever, thrips numbers were reduced to very low levels saving of up to $279 per bin. in all three N. cucumeris treatments (to 0.4, 0.3 and 0.03 thrips at 45 days, with the increasing dose rates). The suppression of the thrips by N. cucumeris Australian growers are very pleased with the novel was reflected by an increased proportion of premium- tactic, because they have no effective alternative and grade bulbs assessed post-storage in these treat- because of its benign nature and high benefit:cost ments (74–79%) compared with the H. aculifer ratio. The method is particularly applicable in coun- treatments, and the control (42%). Thus some 35 % of tries, such as Australia and New Zealand, where the onions were upgraded to premium quality as a much of the harvested onion crop is not cool stored result of N. cucumeris treatment. Concerns about (which would arrest thrips development and contamination were assuaged because the mites feeding). themselves declined to very low levels at all three dosages by six weeks after introduction. For 2008–09, there are plans to see how the above recommended treatment works over a three-month The researchers calculated that the 35% increase in period, and whether an additional ‘top-up’ treatment premium-grade onions represented a gain of nearly at six weeks is necessary to extend protection to Au$150 per 600-kg bin, using the contemporary price three months. Are we on your mailing list? Biocontrol News and Information is always pleased to receive news of research, conferences, new products or patents, changes in personnel, collaborative agreements or any other information of interest to other readers. If your organization sends out press releases or newsletters, please let us have a copy. In addition, the editors welcome proposals for review topics. 20N Biocontrol News and Information 29(2) This project has been funded by Horticulture Aus- presence of competition by other plants, weevil tralia Limited (HAL) using the onion levy and feeding caused mortality of mile-a-minute plants. matched funding from the Australian Government. Mile-a-minute weed was shown to produce about five Main source: Baker, G.J., Powis, K. & Altmann, J. times as many seeds in full sun as in the shade. (2008) Neoseiulus cucumeris control of onion thrips Clearly this plant is adapted for full sun, germi- in storage onions: new trick for an old dog. Paper pre- nating early in the spring, growing rapidly, and sented at the First Australian and New Zealand scrambling up and over any available bushes, trees, Biocontrol Conference, Sydney, 10–14 February or other substrates. Our hope is that with an inte- 2008. grated programme that combines several types of competitive and other stresses, with the ultimate Contact: Greg Baker, Entomology Unit, goal of producing a shaded environment at sites cur- South Australian Research and Development rently overrun with mile-a-minute, the weevil will Institute (SARDI), GPO Box 397, Adelaide, provide the ‘tipping point’ that will allow a sustain- SA 5001, Australia. able diverse plant community to develop. Our next Email: [email protected] step will be to test this theory, and also determine Fax: +61 8 8303 9542 whether it is possible to produce weevils in a field nursery rather than depending strictly on laboratory rearing. Asian Weevil Chews up Mile-a-Minute Weed in By: Judy Hough-Goldstein and Ellen Lake, Northeastern USA Department of Entomology & Wildlife Ecology, University of Delaware, 250 Townsend Hall, 531 Mile-a-minute weed, Persicaria perfoliata (formerly South College Ave., Newark, DE 19716-2160, USA. known as Polygonum perfoliatum), invaded eastern Email: [email protected] and [email protected] North America beginning in the 1930s at a nursery in Pennsylvania, where it most likely established as a contaminant in holly seed from Japan. The annual prickly vine has since spread widely in disturbed Rusty Future for Yellow Bells in South Africa sites in the Mid-Atlantic states, causing failure of Tecoma stans is a large perennial shrub native from tree regeneration by smothering seedlings, and the Neotropics southwards to Argentina. It has been making life miserable for land managers in wildlife introduced as an ornamental to countries in many preserves and other natural areas. Herbicides and parts of the world. Its common names – yellow bells, mechanical controls can be effective, but huge yellow trumpetbush – indicate its attraction: large, annual seed production, spread by birds, deer, and showy, bright golden-yellow trumpet-shaped water, and a seed bank that can last for as long as flowers, which attract nectar-feeding insects and seven years make any sort of long-term control a birds but also produce thousands of papery, winged challenge. seeds. It is drought-tolerant and readily colonizes roadsides, urban open spaces, watercourses, natural The US Department of Agriculture – Forest Service savanna and rocky sites. These attributes have initiated a search for natural enemies in China, the allowed it to become an invasive weed in many parts presumed centre of origin of the weed, in 1996. Ding of its introduced range in southern South America, Jianqing (Institute of Biological Control, Chinese western Australia and southern Africa. Academy of Agricultural Sciences, Beijing) and his associates found more than 100 insect species In South Africa, T. stans has become naturalized feeding on mile-a-minute weed in China. Host-specif- throughout much of the country and is emerging as icity tests conducted in China and in quarantine in an invasive alien weed in areas such as the Mpuma- Delaware showed that one species, Rhinoncomimus langa lowveld and the KwaZulu-Natal coast.