ness consequences. Carbohydrates can have
a strong impact on several key fitness para-
meters. Sugar feeding is indispensable to
parasitoid survival, a factor applying to both
females (Zoebelein, 1956; Syme, 1975; van
Lenteren et al., 1987; Idoine and Ferro, 1988;
Wäckers, 2001) and males (Zoebelein, 1956;
Wäckers and Swaans, 1993). In the ideal
world of the laboratory, sugar can increase
parasitoid longevity up to 20-fold
(Zoebelein, 1956; Syme, 1975; Idoine and
Ferro, 1988; Wäckers and Swaans, 1993; Dyer
and Landis, 1996).
Sugar feeding can also benefit a para-
sitoid’s fecundity, either through a positive
effect on the rate of egg maturation,
through an increase in reproductive life-
span or both (Zoebelein, 1956; Hocking,
1966; Syme, 1975; Baggen and Gurr, 1998;
van Lenteren, 1999; Schmale et al., 2001).
Finally, the feeding status can affect the
parasitoid’s propensity to seek out their
herbivorous hosts. Telenga (1958) and van
Emden (1962) found that parasitoids are
more active in habitats in which flowers are
in bloom than in nearby habitats without
flowers. Wäckers (1994) and Takasu and
Lewis (1995) demonstrated that sugar
deprivation reduces host-searching effi-
ciency, partly due to a general reduction in
activity and partly due to a shift from host
searching to food searching.
Each of the listed fitness parameters
translates directly into the number of herbi-
vores that can be attacked. The availability of
suitable plant-provided food sources conse-
quently has a strong impact on parasitoid
mass rearing, as well as on their efficacy as
biological control agents.
Choosing Food Supplements for Mass
Rearing
The basic concept that parasitoid fitness can
be dramatically enhanced through the sim-
ple provision of food supplements has been
long engrained in parasitoid rearing. It is
standard practice to provide adult insects
with honey, honeydew, sugar water, fruits
or other sugar sources. While the impor-
tance of food supplements is thus widely
acknowledged, often little attention is given
to the actual choice of the food source. This
choice may be based on issues like conve-
nience (honey can be easily obtained, does
not require preparation and does not spoil),
methodology (parasitoids can get stuck in
liquid food media, while they have trouble
imbibing solid food sources) and economy
(cost). Hardly ever is the choice actually
based on what should be the central issue:
the question of which substrate is the opti-
mal food for a given parasitoid.
This omission is hardly surprising in light
of the fact that few comparative data exist in
respect of the relative suitability of various
food sources. The low priority given to this
issue reflects the generally held conception
that any sugar-rich liquid makes a suitable
food supplement for parasitoids. In an
attempt to correct this notion, I shall com-
pare the main natural sugar sources in
respect of their composition, and discuss the
consequences for feeding parasitoids.Potential Sugar Sources and Their
Ecological Function
Most hymenopteran pollinators, ants and
parasitoids share a dependency on sugars as
their main source of energy. The ecological
importance of these species, in combination
with their dependency on carbohydrates,
explains the fact that sugars play a central
role in numerous types of mutualisms
involving Hymenoptera. Sugar-feeding
insects usually have a wide range of carbo-
hydrate sources available, the most impor-
tant being floral nectar, extrafloral nectar
(EFN) and honeydew.
Floral nectar serves as a food reward in
the mutualism between plants and their pol-
linators. Even though parasitoids in general
are ineffective pollinators, they can freeload
on this mutualism as they seek out flowers
and collect floral nectar (Kevan, 1973; Jervis
et al., 1993). Due to the fact that many plants
are pollinated by Hymenoptera (e.g. bee
species), their nectar can be expected to
cater to the taste and nutritional require-
ments of these species. As nectar require-
ments of hymenopteran parasitoids appearFood Ecology and Mass Rearing in Biocontrol 61