Phloem-sap feeding by animals: problems and solutions. J Exp Bot

Department of Biology, University of York, PO Box 373, York YO10 5YW, UK.
Journal of Experimental Botany (Impact Factor: 5.53). 02/2006; 57(4):747-54. DOI: 10.1093/jxb/erj067
Source: PubMed


The incidence of phloem sap feeding by animals appears paradoxical. Although phloem sap is nutrient-rich compared with many other plant products and generally lacking in toxins and feeding deterrents, it is consumed as the dominant or sole diet by a very restricted range of animals, exclusively insects of the order Hemiptera. These insects display two sets of adaptations. First, linked to the high ratio of non-essential:essential amino acids in phloem sap, these insects contain symbiotic micro-organisms which provide them with essential amino acids. For example, bacteria of the genus Buchnera contribute up to 90% of the essential amino acids required by the pea aphid Acyrthosiphon pisum feeding on Vicia faba. Second, the insect tolerance of the very high sugar content and osmotic pressure of phloem sap is promoted by their possession in the gut of sucrase-transglucosidase activity, which transforms excess ingested sugar into long-chain oligosaccharides voided via honeydew. Various other animals consume phloem sap by proxy, through feeding on the honeydew of phloem-feeding hemipterans. Honeydew is physiologically less extreme than phloem sap, with a higher essential:non-essential amino acid ratio and lower osmotic pressure. Even so, ant species strongly dependent on honeydew as food may benefit from nutrients derived from their symbiotic bacteria Blochmannia.

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    • "In many cases, this involves symbiotic interactions with microorganisms that produce essential amino acids whose synthesis is not encoded in animal genomes (Crotti et al., 2010; Defossez et al., 2011; Nardi et al., 2002; Oh et al., 2010; Russell et al., 2009; Schloss et al., 2006; Spiteller et al., 2000). Some of the best-studied symbioses of this type are found in aphids, whiteflies and other phloem-feeding Hemiptera (Braendle et al., 2003; Douglas et al., 2006; Kikuchi et al., 2007, 2009; Wilkinson et al., 2001). Phloem-feeding insects benefit from having evolved rapid and efficient pathways for the uptake and metabolic conversion of glutamine, glutamic acid, asparagine and aspartic acid into essential amino acids. "

    Full-text · Article · Dec 2015 · Journal of Experimental Biology
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    • "2004; Chau et al., 2005). However, N fertility, with increasing amino acid and nitrate level in host plant (Mengel and Kirkby, 2001) can enhance nutritional quality and attractiveness of plants for herbivorous insects; therefore, it improves performance parameters of phloem feeders (Mattson, 1980; White, 1993; Douglas, 2006; Fallahpour et al., 2015). For instance, results of a study conducted by Aqueel and Leather (2011) showed that 0.4 g plant -1 N fertilizer in the form of ammonium nitrate significantly enhanced the fecundity and longevity of Sitobion avenae (F.) and Rhopalosiphum padi (L.) in comparison to those by 0.1 g plant -1 N fertilizer level. "
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    ABSTRACT: Reducing nitrogen status of floriculture plants is an effective tactic in pest management by decreasing host plant quality. Life table parameters and population growth rate of Aphis craccivora (Hemiptera: Aphidiae), as well as cosmetic and qualitative parameters losses associated with aphid infestation were evaluated in relation to N fertilization levels on Gomphrena globosa, under greenhouse condition. Four N fertilization levels (0, 30, 60, and 100% of recommended 2 kg m-3) were used. The results indicated that aphid’s intrinsic rate of natural increase on plants fertilized with 100% of the recommended N level was the highest. Abundance and population growth rate of aphid also positively correlated with N fertilization levels. The interactive effect of aphid population and N fertility significantly affected growth parameters of the plants. In the absence of aphid, plant yield improved linearly with increasing N levels. However, aphid population highly decreased shoot to root ratio and the number of flowers in plants fertilized with 100% of the recommended N level. According to our findings, fine-tuning fertility to reduce A. craccivora population is a steadfast tactic to produce marketable globe amaranth ornamental plant.
    Full-text · Article · Nov 2015 · Journal of Agricultural Science and Technology
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    • "-chain oligosaccharides and excrete them as honeydew (Douglas, 2006). Phloem sap-sucking insects are also able to get their amino acids from symbiotic microorganisms and amino acids synthetase enzymes (Wilkinson, 1998; Douglas, 2006). "
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    ABSTRACT: The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Liviidae), transmits the citrus greening pathogen 'Candidatus Liberibacter asiaticus' (CLas) by feeding on citrus phloem sap. Because phloem sap is rich in sugars but low in amino acids, ACP sucks large quantities and excretes most of it as honeydew. We studied the chemical composition of ACP honeydew on various host plants. Honeydew samples were analyzed with gas chromatography-mass spectrometry. Fourteen sugars, 13 amino acids, and six organic acids were detected in the honeydew of ACP. Sugars composed about 95% of the total compounds. Sucrose and trehalose were the predominant sugars, composing about 58 and 23% of the total sugars, respectively. Proline, asparagine, aspartic acid, and glutamic acid were the most abundant amino acids in ACP honeydew. The host plant and its infection with CLas had some effect on the honeydew composition. Glucose, chiro-inositol, myo-inositol, inositol, maltose, and turanose were lower in honeydew collected from CLas-infected citrus compared to that collected from non-infected trees. In CLas-infected citrus (pineapple sweet orange, Citrus sinensis L. Osbeck) and Bergera koenigii (L.) Spreng. [curry leaf tree (both Rutaceae)] honeydews, valine, alanine, serine, glutamine, glycine, and the organic acids were lower than in honeydew from healthy citrus. Mannose, galactose, inositol, mannitol, an unknown disaccharide, and proline were higher in the honeydew collected from B. koenigii than in honeydew collected from healthy citrus (pineapple sweet orange), whereas fructose, chiro-inositol, myo-inositol, trehalose, and lactic acid were lower. The findings of this study help us understand the metabolism and the nutrient needs of ACP that transmits CLas, the pathogen of huanglongbing in citrus.
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