Author
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Martin, Phyllis |
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Submitted to: Journal of Biological Control
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 5/9/2003 Publication Date: 1/1/2004 Citation: Martin, P.A. 2004. A freeze-dried diet to test bacterial pathogens of colorado potato beetle. Journal of Biological Control. Vol# 29 Pg. 109-114 Interpretive Summary: The Colorado potato beetle is a serious pest on potato, eggplant and tomato. Because Colorado potato beetle develops resistance to insecticides quickly, alternative methods are needed to control this pest. One of the difficulties developing new means to control this pest has been the lack of a synthetic food or diet that is less variable than potato plants grown year round. Our lab has developed such a diet, but it must be used fresh or the beetles will not eat it. One way of preserving food is freeze-drying as is done with instant coffee. The beetles readily eat a freeze-dried diet that has been re-hydrated. For the short term, some ingredients such as preservatives and plant material can be left out of this diet and the insects gain the same weight on these diets as on diets containing these ingredients. However, without the preservatives, for longer studies, the diet spoils because of the growth of mold. In the present study, the new diet was evaluated for its usefulness in determining the toxicity of bacteria to the Colorado potato beetle. The results indicated that the bacteria kill more insects and kill them quicker when used to re-hydrate a freeze-dried diet than when mixed into a fresh diet. Because bacteria must be added to a fresh diet while it is hot, the heat kills the bacteria and reduces toxicity. Like other freeze-dried foods, this diet has an extended shelf life of at least 4 months. Other scientists can use this diet to test bacteria or chemicals that are toxic to Colorado potato beetle. Companies that make components for insect diets may be interested in making pre-made diets for insect assays. Technical Abstract: The Colorado potato beetle is an important pest on potato, eggplant and tomato. Because Colorado potato beetles develop resistance to insecticides quickly, new methods are needed for control. Bacillus thuringiensis is the only bacteria to successfully control Colorado potato beetle. Until recently, one of the drawbacks to testing bacteria has been the lack of an artificial diet for screening. Colorado potato beetle larvae will, only consume previous artificial diets, when fresh. To improve storage, we developed a freeze-dried diet, based on a 96 well mold, suitable to feed larvae for the duration of a bioassay. Individual diet components were tested both for their effect on insect growth and on pathogen toxicity. When the preservatives, methylparaben and sorbic acid, were removed from the diet, the average weight of 2nd instar larvae increased from 7.9 mg to greater than 9.8 mg. The preservatives inhibited the growth of two of the bacteria tested, Photorhabdus luminescens HM and Chromobacterium sp. PRAA. The removal of these preservatives also allowed for fungal growth and reduced survival from 94% to 38%. Removing diet preservatives that inhibited bacterial growth increased the toxicity of Chromobacterium sp. PRAA as well as reducing the time needed to kill 50% of the larvae. Compared to diet incorporation, the total mortality of Colorado potato beetle fed either Photorhabdus luminescens HM or Chromobacterium sp. PRAA on freeze-dried diet doubled. Preparation of freeze-dried diet does not need to be synchronized with the insect or the pathogen. There is little waste of the diet. The freeze-dried diet gives consistent results as measured by control mortality and pathogen toxicity over time. |
