Aphids container plants

Aphids extract sap from plant stems, specifically the phloem tissue. They excrete honeydew which still contains plant sugars. Ants collect this honeydew, often by milking the aphids, and use it as food. In return, they protect the aphids against predators. Ants prey on predators of aphids such as ladybird beetles (coccinellids), thus defending the aphids. Ants also shelter aphids by taking them or their eggs into their nests during inclement seasons. In a sense, ants herd aphids like cows. Furthermore, without removal of honeydew, aphid colonies become fouled. 

Nicotine is used as a contact insecticide for aphids attacking fmits, vegetables, and ornamentals, and as a fumigant for greenhouse plants and poultry mites. Nicotine sulfate is safer and more convenient to handle and the free alkaloid is rapidly Hberated by the addition of soap, hydrated lime, or ammonium hydroxide to the spray solution. Nicotine sprays commonly contain 0.05—0.06% nicotine, and nicotine dusts, 1—2% nicotine. 

Elder leaves contain the alkaloid sambucine, a precursor of hydrocyanic acid, which is somewhat toxic. Thus, the leaves are used only topically in ointments for sprains or bruises. Bruised leaves can be rubbed on the body or worn under a hat to prevent being pestered by insects. Cooled strained leaf tea can be applied to plants to discourage aphids. 

A little tolerance is also to be advised. Plants are part of the natural world, and are inevitably going to be less than perfect a leaf spot here or a nibbled leaf there is not going to be life-threatening. The A-Z of Plant Problems (seepp.320-342) contains more detailed advice on specific problems affecting woody plants the entries on aphids, black spot, powdery and downy mildew, and rose rust are particularly applicable to roses. 

Effect of water stress on susceptibility of barley to aphids. Barley seedlings were subjected to water stress. These plants accumulated among other compounds proline and glycine-betaine (Table IV). Also, the more stressed plants were the most susceptible to aphids. The cultivar used in this experiment lacked gramine. However, when a gramine-containing cultivar was used gramine concentration was not affected by water stress. 

Alkaloids and Phenols from Tobacco, Tomato, and Potato. Tobacco, tomato, and potato plants contain a number of toxic alkaloids. Probably the most widely studied Is nicotine. The Insecticidal properties of this and other tobacco alkaloids have been reviewed (72). A study of Nlcotlana showed that alkaloids are secreted by trlchomes In the seven species tested (73). Nicotine was the major alkaloid Identified In the trlchome secretion (7A). Anabaslne and nornlcotlne were also Identified In two species (75). Other ether soluable constitutents have also been Identified (76). Aphids were killed by contact with these secretions. Trlchome secretions from Nlcotlana also were... 

Other benefits of large numbers of analogs to plants may include slower evolution of tolerance or lower rates of metabolism of mixtures compared with that of single compounds in herbivorous insects. Feng and Isman (1995) investigated the possibility of adaptation in herbivores by repeated selection of peach aphid colonies with either pure azadirachtin or neem seed extracts containing a large number of limonoids. The colonies treated with azadirachtin soon showed evidence of tolerance of this pure compound, whereas no evidence of tolerance was... 

Polyphenol Oxidases. Plant trichomes and their exudates confer resistance to a variety of insects (54-56). In solanaceous plants, such as the tomato and potato, trichomes contain polyphenol oxidases and catecholic phenolics (e.g., caffeic and chlorogenic acids), which contribute to resistance to a variety of insect pests. In the potato plant, the polyphenol oxidases and phenolics are separated in different trichomes. When insects, such as aphids or leaf hoppers, walk across the surface of the plant they break the two types of trichomes. Trichomal fluids are liberated and, upon mixing, polymerize as a result of polyphenol oxidase activity on catechols, forming an often lethal adhesive trap for the insects (52,58) In tomato plants, the polyphenol oxidase and chlorogenic acid are separated by intracellular compartments, but upon breakage of trichomes by insects, polymerization and physical entrapment occurs (54). 

Nicotine is a highly poisonous alkaloid, extracted from special tobacco selected for its high nicotine content. When used as an insecticide, nicotine products are poisonous to most plant pests, including aphids, mealybugs, scales, and spider mites. However, nicotine is also highly toxic to mammals when taken internally or absorbed through the skin— more toxic, in fact, than many synthetic pesticides. It remains toxic on leaf surfaces for several weeks after an application. Also, nicotine products may contain the pathogen that causes tobacco mosaic virus in related... 

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