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Feeding behavior of Melanaphis sacchari Zehntner ( Hemiptera: Aphididae) was studied on sugarcane, Saccharum spp. ( Poaceae), cultivars HoCP 91-555 (resistant), LCP 85-384 (moderately resistant), and L 97-128 (susceptible) using the electrical penetration graph ( EPG) technique. Constitutive concentrations of total phenolics and available carbohydrates, water potential at the whole-leaf tissue level, and free amino acids (FAAs) in phloem sap extracts, and in honeydew produced by aphids fed on L 97-128 and HoCP 91-555 were determined. Cultivar did not influence time for M. sacchari to access phloem sieve elements. Total time in sieve elements was ca. two-fold greater on L 97-128 than on HoCP 91-555, whereas it did not differ from LCP 85-384 in either cultivar. The mean duration of individual events associated with phloem sap ingestion was ca. 50% shorter on both HoCP 91-555 and LCP 85-384 than on L 97-128. Although cultivar effects were not detected for levels of total phenolics, available carbohydrates, and water potential, two free essential amino acids, histidine and arginine, were absent from phloem sap in HoCP 91-555. Two free essential amino acids, leucine and isoleucine, and two free non-essential amino acids, tyrosine and proline, were absent from honeydew of aphids fed on HoCP 91-555. These results suggest that despite apparent biosynthesis of some FAAs, the absence of important FAAs in the phloem sap of HoCP 91-555 and the inability of M. sacchari and its endosymbionts (e.g., Buchnera) to derive specific free essential and non-essential amino acids from other ingested molecules, possibly along with other unidentified factors, underlie the pest's decreased phloem sap ingestion and consequently reduced growth potential on HoCP 91-555. [ABSTRACT FROM AUTHOR]

The invasive Middle East-Asia Minor 1 ( MEAM1) cryptic species (formerly referred to as the B 'biotype') of the whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) complex has become a major crop pest worldwide due to its global invasion as well as epidemics of begomoviruses it transmits. Previous studies demonstrated that MEAM1 performed better on tobacco [ Nicotiana tabacum L. (Solanaceae)] plants infected by Tomato yellow leaf curl China virus ( TYLCCNV) than on uninfected plants. However, mechanisms underlying the interactions are not completely understood. In this study, we compared the composition of sugars and amino acids in the phloem sap of uninfected and TYLCCNV-infected tobacco plants with or without whiteflies feeding on the plants. No significant differences were detected in terms of amino acid profiles, percentage of essential amino acids, and sugars:amino acids ratio. However, whiteflies feeding on TYLCCNV-infected plants excreted comparatively a lower percentage of amino acids, especially essential amino acids, or proportionally a higher level of sugars than those feeding on uninfected plants, suggesting that whiteflies feeding on virus-infected plants are able to achieve a more balanced nutritional assimilation. We also compared the honeydew excreted by viruliferous and non-viruliferous whiteflies feeding on cotton [ Gossypium hirsutum L. (Malvaceae)], a non-host plant for TYLCCNV, to test the direct effects of the virus on whiteflies. Although the amino acids profiles in honeydew were similar between viruliferous and non-viruliferous whiteflies, the sugars:amino acids ratio in honeydew excreted by viruliferous whiteflies was lower than that of non-viruliferous whiteflies, suggesting that the viruliferous whiteflies assimilated a more imbalanced nutrition with proportionally more sugar. Taken together, our data indicate that although a plant virus may exert negative direct effects on its vector, feeding by the vector on virus-infected plants may improve nutritional assimilation and consequently performance of the vector. [ABSTRACT FROM AUTHOR]

The chemical elements Fe, Mg, Cu, Zn, and Mn are involved in the various physiological processes of plants. A change in the contents of some chemical elements in rice (Oryza sativa L.) plants is associated with resistance to pests; this includes the slow growth of rice brown planthopper (Nilaparvata lugens Stål) populations. By manipulating the concentrations of Zn, Mn, Fe, and Cu in a hydroponic solution, we tracked the flow of these elements from a hydroponic solution through the rice plant phloem sap, to planthoppers, and ultimately the honeydew excreted by N. lugens. The results showed not only that the contents of Zn, Mn, Fe, and Cu in the rice plants increased with their concentrations in the hydroponic solution but also that the increase in the levels of these four elements in the hydroponic solution affected the level (positively or negatively) of other chemical elements in the rice plants. Furthermore, some of the changes in element levels in the rice plants were reflected in the content of the phloem sap, N. lugens itself and its honeydew. Among the four chemical elements manipulated in the hydroponic solution, only elevated levels of Mn and Na were proportionally transferred to both the rice plants and N. lugens. Therefore, those particular elements could be used as markers to match N. lugens individuals to the rice plants on which they have fed. Our findings have potential applications for determining the provenance of N. lugens migratory populations by examining the levels of chemical elements in N. lugens immigrants, which would lead to a better understanding of the migration sources and routes of this insect. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]