Biology Reference
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allowed Josens and Farina (2001) to manipulate the concentration and vis-
cosity of hawkmoth diets independently. The dependence of intake rate on
concentration did not change in solutions to which tylose was added to main-
tain constant high viscosity, although all intake rates were reduced. If
viscosity were the only physical factor affecting ingestion dynamics, solu-
tions of equal viscosity would be ingested at the same rate. For butterflies,
there is evidence that they compensate for increased food viscosity by in-
creasing suction pressure (May, 1985; Pivnick & McNeil, 1985). A noctuid
moth, Anticarsia gemmatalis , illustrates the ability of adult Lepidoptera to
cope with a broad range of sugar concentrations under laboratory conditions;
the moths regurgitate a clear, sugar-free liquid from the proboscis after feed-
ing on sucrose solutions below 20%, or use saliva to dissolve solid sucrose
(Wei et al., 1998). The Noctuidae, the largest family of moths, includes
many pest species, but adult feeding has received little attention.
Sugar preferences have been tested in Macroglossum stellatarum , and
this moth strongly prefers sucrose to fructose and fructose to glucose (Kelber,
2003). The same order of preference has been recorded in tests involving
butterflies (Rusterholz & Erhardt, 1997; Romeis & Wäckers, 2000). The
ecological relevance of testing pure solutions of glucose and fructose is
questionable, but the use of mixed sugar solutions also shows a clear prefer-
ence of the peacock butterfly Inachis io for high sucrose levels (Rusterholz
& Erhardt, 1997). Behavioural responses to sugars are not necessarily corre-
lated with their nutritional importance to the insects. Although glucose is not
selected by butterflies in choice tests, it usually occurs in nectar at similar
levels to fructose and has high nutrititional value for adult Pieris brassicae
(Romeis & Wäckers, 2002). In three Japanese butterfly species that feed on
exuded tree sap and rotting fruit, Ômura and Honda (2003) have shown that
ethanol and acetic acid have synergistic effects on the butterflies' response to
low hexose concentrations.
Adult feeding in Lepidoptera is not just for energy. Butterfly nectars are
thought to contain relatively high levels of amino acids compared to those
consumed by other pollinators (Baker & Baker, 1982). Artificial nectar that
resembles that of Lantana camara has often been used in experimental tests
(with varied results) of whether butterflies select for high levels of amino
acids in nectar. Female butterflies are generally more responsive to diets
enriched with amino acids than males, and female Inachis io were found to
select low concentrations of amino acids (Erhardt & Rusterholz, 1998; Mevi-
Schütz & Erhardt, 2002). Until recently, it has been assumed that female but-
terflies obtain nitrogen from several sources which do not include nectar:
these are larval feeding, sometimes pollen feeding ( Heliconius species), and
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