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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    • "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.
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    • "Thus, the expression of sucrose transporters seems to be tightly regulated in accordance with cell wall invertases in response to many environmental factors including biotic stresses (Bitterlich et al. 2014; Ferrieri et al. 2015). Sucrose taken by aphid is present in plant phloem sap at high concentrations, often in the range of 0.5–1 M and is responsible for high osmotic pressure, often up to five times that of the feeding Hemipteran body fluids (Douglas 2006). "
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    ABSTRACT: The perception of aphid infestation induces highly coordinated and sequential defensive reactions in plants at the cellular and molecular levels. The aim of the study was to explore kinetics of induced antioxidative defence responses in leaf cells of Pisum sativum Cysterski upon infestation of the pea aphid Acyrthosiphon pisum at varying population sizes, including accumulation of flavonoids, changes of carbon metabolism, and expression of nuclear genes involved in sugar transport. Within the first 96 h, after A. pisum infestation, flavonoid accumulation and increased peroxidase activity were observed in leaves. The level of pisatin increased after 48 h of infestation and reached a maximum at 96 h. At this time point, a higher concentration of flavonols was observed in the infested tissue than in the control. Additionally, strong post-infestation accumulation of chalcone synthase (CHS) and isoflavone synthase (IFS) transcription products was also found. The levels of sucrose and fructose in 24-h leaves infested by 10, 20, and 30 aphids were significantly lower than in the control. Moreover, in leaves infested by 30 aphids, the reduced sucrose level observed up to 48 h was accompanied by a considerable increase in the expression level of the PsSUT1 gene encoding the sucrose transporter. In conclusion, A. pisum infestation on pea leads to stimulation of metabolic pathways associated with defence.
    Protoplasma 08/2015; DOI:10.1007/s00709-015-0865-7 · 2.65 Impact Factor
    • "Phloem is a troublesome food source for insects, not only because it lacks essential components, but also because its sugar content and osmotic pressure are high. Many phloem feeders have adapted tolerance to this and display sucrose transglucosidase activity in their gut, which can transform the excess ingested sugar into long-chain oligosaccharides, which in turn can be excreted as honeydew (Douglas, 2006). Especially homopteran insects such as aphids, which live solely on plant sap (i.e. "
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    Annals of Botany 04/2015; 115(7):1015-1051. DOI:10.1093/aob/mcv054 · 3.65 Impact Factor
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