Biology Reference
In-Depth Information
feed exclusively on nectar, while in females, nectar meals are directed to the
crop and blood meals to the midgut. The suborder Brachycera is more im-
portant in nectar feeding. Adult fruit flies (Tephritidae) commonly feed on
nectar, as well as honeydew and the juices from damaged fruit. Major dip-
teran pollinators occur in the families Syrphidae and Bombyliidae (bee flies,
which possess a long but non-retractable proboscis), and in the muscoid
families with lapping labellae (Kearns, 1992). The Syrphidae (hover flies)
are important pollinators, but eat mainly pollen (Gilbert, 1981; Haslett,
1989). The most specialized dipteran nectar feeders are long-tongued flies in
southern Africa (Johnson & Steiner, 1997). Some of these Tabanidae and
Nemestrinidae hover at flowers with very long floral tubes (Fig. 4F), and
their slender mouthparts require low viscosity nectars of 25-30% (Goldblatt
& Manning, 2000).
Like beetles, flies are associated with a heterogeneous group of flowers,
and flies are often considered to be minor pollinators because of their small
size, inconstancy, and varied food sources. However, most species of Dip-
tera feed on nectar or other plant exudates and their sheer numbers may
compensate for their low effectiveness as pollinators (Larson et al., 2001).
Flies are important in the Arctic areas and at high altitude, in part because
other pollinator groups are less well-represented (Hocking, 1968; Kearns,
1992; Larson et al., 2001). They tend to replace bees as pollinators in New
Zealand where there are few indigenous bees (Godley, 1979). This is a wide-
spread pattern: recently Devoto et al. (2005) examined plant-pollinator
interactions along a steep rainfall gradient in southern Argentina, and found
that as rainfall increased in a westerly direction there was a gradual replace-
ment of bees by flies.
The success of flies at high latitudes and high elevations has been attrib-
uted to the moist larval habitats available, the low energy requirements of
the adults, and their use of microhabitats for thermoregulation (Kearns,
1992). These microhabitats include heliotropic flowers, which offer basking
sites and possibly increased nectar yield owing to the higher temperatures
(Hocking, 1968). The short proboscis of most flies limits them to open flowers
with exposed nectar, such as the inflorescences of Apiaceae and Astera-
ceae—described as flowers that “cater for the mass market” (Proctor et al.,
1996). Owing to the minute volumes of nectar produced, detailed study of
nectar in such flowers is a challenge. In flowers of caraway (
Carum carvi
,
Apiaceae), Langenberger and Davis (2002) measured nectar volumes of
0.039 μl and 0.108 μl per floret in the male and female phases, respectively,
and consistently high concentrations of 66.5% w/w or 2.5 M! This nectar is
