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Butterflies of
the Amazon and Andes
Onega Glasswing
Oleria onega
HEWITSON, 1852
Family - NYMPHALIDAE
subfamily -
DANAINAE
Tribe - ITHOMIINI
subtribe -
OLERIINI
introduction
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habitats |
lifecycle |
adult behaviour
Oleria onega, Satipo,
Peru
Introduction
The
genus
Oleria
comprises of about 50 known species, recognisable from the distinctive venation
of the hindwings.
The
butterflies are varied in their habitat requirements - most species occur in
lowland rainforests, many others specialise in cloudforest habitats, and a few
occur in deciduous forests.
Oleria
onega is found
from Colombia to southern Peru.
Habitats
This species is
associated primarily with wet tropical rainforest habitats, and is most commonly
found in shady damp areas in the vicinity of rivers or streams, at altitudes between 200-800m.
Lifecycle
In
common with all other Ithomiines, females of
Oleria onega normally lay their eggs directly on the
underside of leaves of their foodplants. In the case of
onega the preferred foodplant is
Solanum mite, although other species
including S. anceps,
S. angustialatum and
S. uleanum are also used.
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In 2002 Gallusser published research
findings following a study of 2
onega subspecies found near
Tarapoto in Peru. The two colonies are very close to each
other, O. onega agarista
being found on the relatively cool wet
NE slope of the Cerro Escalera mountain range, while
subspecies O. onega
"ssp. nov" ( as yet unnamed ) is found
on the hot sunny SW slope.
O. onega agarista behaved as
expected, always laying their eggs on
Solanum;
but onega
ssp. nov laid them instead on rocks, stems, dead leaves and
other substrates up to a metre distant from the foodplants.
Gallusser
suspected that the different oviposition strategy was
influenced by egg predation, and found that the main threat
came from Ectatomma
ants, which were common on the SW
slope, but entirely absent from the NE slope. She also noted
that partial deforestation and path clearance on the SW
slope allowed more sunlight to penetrate, so that eggs laid
on Solanum
in these situations would be easier for predators to locate.
The implication is that ssp. nov is evolving different
egg-laying behaviour as a direct result of human
interference in its habitat.
As part of the research, Gallusser
moved eggs from one site to another, and from one substrate
to another, and studied the survival rates of 400 eggs on
both mountain slopes. She found that on the SW slope, eggs
positioned away from Solanum
had a much higher survival rate than those on
the plants. Laboratory and field
studies however failed to provide observations of predation,
even when the eggs were offered directly to the ants, so it
seems possible that the mere
presence of the aggressive ants on the foodplants may be
enough to discourage the females from ovipositing, forcing
them to lay elsewhere. |
The
eggs are white, oval, and laid singly, although several may be dotted about in
close proximity by one or more females. The egg stage lasts about 3 days.
The caterpillars when newly hatched are transparent, and
consume their egg shell before beginning to feed on the foodplant. After each
moult the caterpillar consumes its shed skin, leaving only the chitinous head
capsule remaining. When fully grown the caterpillar is grey, with a yellow line
along the length of the body on each side. It takes about 12 days from hatching
to being ready to pupate.
The
chrysalis is pale green, with shiny metallic golden reflections. The abdominal
segments are compressed, and there is a dorsal hump. The overall impression is
of a small leaf dripping with rain. The butterfly emerges after about a week.
The entire lifecycle of the
butterfly from egg to adult takes about 3 weeks to complete, so in theory up to
17 generations could be produced annually. However during the dry season
reproductive activity is minimal. During this period the adults aggregate with
numerous other Ithomiine species in small pockets within the forest. In Brazil
and Ecuador for example I have found several such aggregations along the beds of
small dry streams, where as many as 100 Ithomiines of up to 10 different species
could be found aestivating among the stilt-like rootlets of palms.
Adult behaviour
The adults are normally found in small "leks" of up to a dozen
butterflies.
The males fly
very slowly and almost incessantly around the lek area, only
pausing to settle for a moment here and there, at which time they
slowly fan their wings, probably to aid dissemination of
pheromones from the androconial "hairs" on their wings.
Males of most
Oleria species visit
Eupatorium, from which they
acquire pyrrolizidine alkaloids which they pass to the females
during copulation, and which is believed to be essential for the
production of viable eggs.
Females visit
various flowers for nectar and pollen - the latter may be
essential in the production of eggs and the maintenance of
ovaries, as has been demonstrated by Dunlap-Pianka to be the case
with Heliconiines. Females also receive proteins during sperm
transfer.
Gravid females fly very slowly,
periodically dipping down to investigate
Solanum plants. Having found the foodplant they then spend
2 or 3 minutes testing it, using olfactory sensors on their legs,
antennae and abdomens, to determine whether it is
Solanum mite or another related
species.
In common with
most other Ithomiines, lateral and altitudinal migrations of
Oleria species are triggered by
seasonal changes in humidity.
Oleria onega, Satipo,
Peru
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