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In the case of honeydew, the volume pro-
duced and its composition depend on the
sap-feeding species, as well as on plant para-
meters and environmental factors (Kloft et
al., 1985). Sap feeders can actively increase
the quantity of excreted honeydew when
tended by ants (Takeda et al., 1982; Yao and
Akimoto, 2001).

Sugar composition

Floral nectar, EFN and honeydew are princi-
pally sugar solutions. However, the sugar com-
position can vary in respect of both the types of
saccharides and their relative proportions.
Floral nectar is generally dominated by
the monosaccharides fructose and glucose

and the disaccharide sucrose (Baker and

Baker, 1982b). The proportions of the three

main sugars are rather constant within a

species, but can show wide differences

between flowering species. Percival (1961)

and Baker and Baker (1982b), for instance,

showed that the sucrose/hexose ratios of

flowering plants can vary from less than 0.1

to more than 0.999. In addition to these main

nectar sugars, nectar may contain low con-

centrations of other carbohydrates (Table 5.1).

EFN is typically dominated by sucrose

and its hexose components glucose and

fructose. These are also the three most com-

mon sugars in EFN. Unlike the species-

characteristic sugar ratio in floral nectar,

however, the ratio of sucrose to hexose in

the EFN of a given species can be much

Food Ecology and Mass Rearing in Biocontrol 63

Table 5.1.Sugars reported to occur in floral nectar, extrafloral nectar and honeydew.

Reported to occur in References

Monosaccharides
Glucose Various (extra)floral nectars Bentley, 1977
Honeydew Baker and Baker, 1983; Kloft et al., 1985
Fructose Various (extra)floral nectars Bentley, 1977; Baker and Baker, 1983
Honeydew Kloft et al., 1985
Galactose Extrafloral nectar Bory and Clair Maczulajtys, 1986; Olson
and Nechols, 1995
Floral nectar Gottsberger et al., 1973
Honeydew Byrne and Miller, 1990
Mannose Traces in floral nectar and fruits Barnavon et al., 2000
Rhamnose Extrafloral nectar Bory and Clair Maczulajtys, 1986

Disaccharides
Sucrose Various (extra)floral nectars Bentley, 1977; Baker and Baker, 1983
Honeydew Kloft et al., 1985
Maltose Floral nectar Baker and Baker, 1983; Belmonte et al.,
1994
Coccid honeydew Ewart and Metcalf, 1956
Melibiose Floral nectar Baker and Baker, 1983
Eucalyptus manna (plant exudate) Steinbauer, 1996
Trehalose Honeydew Kloft et al., 1985
Trehalulose Honeydew (whitefly) Hendrix et al., 1992

Trisaccharides
Raffinose Floral nectar Baker and Baker, 1983
Honeydew Byrne and Miller, 1990
Melezitose Primarily in honeydew Kloft et al., 1985; Hendrix et al., 1992
Some floral nectars Baker and Baker, 1983
Erlose Honeydew Kloft et al., 1985

Tetrasaccharide
Stachyose Floral nectar (orchids) Baker and Baker, 1983
Honeydew Byrne and Miller, 1990; Davis et al., 1993