Ozone as a toxicant was evaluated against the stored product pests Plodia interpunctella and Tribolium confusum. Ozone was introduced into the continuous air stream flowing through a chamber made of high-density polyethylene and polycarbonate. By decreasing the flow of ozone and/or air in the chamber, various concentrations of ozone were obtained. The eggs, larvae and pupae were exposed to ozone at varying duration (1 to 18 h). The developmental stages exhibited delayed reactions to toxicity. Even high concentrations of 200-500 ppm (v/v) required up to 18 h to kill the insects. Mortality was first observed among the adults, followed by larvae, pupae and eggs. Carbon dioxide and reduced pressure were also evaluated for the stimulation of the opening of the spiracles of the insects as a means to increase the penetration of ozone into the insects. All the stages responded to the treatment except the eggs, which were unaffected. The pupal and larval stages were the most susceptible.
Twenty-three essential oils and six antioxidants were screened for control of growth of the mycotoxigenic species Fusarium culmorum. Of these, three essential oils (bay, clove and cinnamon oil) and two antioxidants (propyl paraben and hydroxymethylanisole) were found to be effective in controlling growth in the at concentrations of 50-200 ppm at 15°C and 25°C over the range 0.995 to 0.955 water activity (aw). More detailed studies were carried out to examine the efficacy of interactions between water activity aw (0.955, 0.995), temperature (15°C and 25°C) and these control treatments (100 ppm; 500 ppm) on growth and both deoxynivalenol and nivalenol mycotoxin production by F. culmorum on irradiated wheat grain. Higher concentrations of these control treatments (500 ppm) were needed to reduce or inhibit growth significantly on wheat grain when compared to that in vitro. Growth of F. culmorum was significantly affected by temperature, aw and antifungal treatment. At 100 ppm concentration the essential oils/antioxidants stimulated growth under some of the experimental conditions. Growth was significantly inhibited by 500 ppm concentration. Cinnamon and clove essential oils were the most effective inhibitors of growth regardless of temperature or aw level used. The control treatments had a variable effect on the production of mycotoxins by F. culmorum. Butylated hydroxy anisole and clove oil inhibited nivalenol and deoxynivalenol production at both 100 and 500 ppm concentration on wheat grain. However, propyl paraben and cinnamon oil enhanced nivalenol production at 100 ppm and intermediate aw levels.
From an ecological point of view a bulk of grain is a huge potential source of food for a succession of organisms to exploit. These include pests as well as the human "owners". The success or otherwise of individual species depends on complex interactions between the commodity, environment, and interactions between species and control measures. The speed at which these interactions take place is most rapid in warm to hot climates like Australia, where pest populations can develop very rapidly. From time to time the status of pests can change. Before the early 1990s, psocids (Liposcelis species) were pests of no great significance to the Australian grain bulk-handling industry. Since that time, in some areas they have become the most frequently encountered storage pest. The paper summarizes efforts to understand the growth of psocid pests in the Australian grain bulk-handling industry. In particular, it demonstrates the need to understand pest behaviour and biology in addition to the more frequently examined toxicological and engineering aspects.
The Australian grain industry relies heavily on phosphine to meet domestic and international market demand for high-quality grain, free of insects. Phosphine usage has increased markedly over the past 10 years, because of market reluctance to accept chemical residues and resistance in target pests to grain protectants. The threat that insects may also develop resistance to phosphine led to resistance-monitoring projects being initiated across all cereal-growing regions of Australia. The rationale was that the industry needed to be proactive in developing strategies to combat resistance when it evolved, and required early warning of the development of resistance and a scientific assessment of its likely impact. With industry support, these projects have now amalgamated to form a national phosphine resistance monitoring and management programme. Insect population samples are collected from farms, grain merchants, mills and central storages, and tested for resistance. If the resistance is classified as significant, then action is taken to eradicate or control the strain and, where feasible, to prevent its further distribution. In addition, research is undertaken to fully characterize the resistance and to develop control options such as changes to fumigation concentrations and exposure periods. Although the three collaborating laboratories are widely spaced geographically, they maintain close links through data sharing on an Internet-accessible database. They share a common procedures manual, and the groups independently confirm diagnoses of significant resistance made in other laboratories. They also hold regular national workshops to benchmark their suite of bioassays and other techniques and report at least annually to the industry through various forums. The Australian approach is unique in that it has drawn together primary producers, bulk handlers, chemical companies, industry funding organizations and government research institutions from across the country to combat the national threat of phosphine resistance.
Laboratory bioassays were conducted to compare the efficacy of spinosad dust (0.125%) admixed with shelled wheat grains with that of a cocktail of pirimiphos-methyl (1.6%) and permethrin (0.3%) as actellic super dust against Sitophilus zeamais, Tribolium castaneum, Rhyzopertha dominica and Prostephanus truncatus. Spinosad dust was applied at 0.35, 0.7 and 1.44 ppm, and actellic dust at 10.5 ppm. All treatments were significantly (P=0.05) better than the control except when applied against T. castaneum. Spinosad at 0.7 and 1.44 ppm controlled S. zeamais over the 24-week period. All treatments gave good control of P. truncatus and R. dominica, with no apparent significant differences (P=0.05) between treatments on the latter. On P. truncatus, spinosad showed better performance than actellic super dust (P=0.05). All levels of spinosad dust appeared to perform better on P. truncatus compared to actellic super; however, spinosad dust, unlike actellic super, was unable to control T. castaneum. The results suggest that spinosad dust may have potential in controlling major storage insect pests, with special applicability against the destructive larger grain borer, P. truncatus.
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