LA VENTANA IN MONTEVERDE: A MIGRATION CORRIDOR FOR INSECTS
Michelle Williamson & Chris Darlingn the tropics, insects cross major barriers during
migration. Movements across mountains have
been recorded for members of 15 orders of insects
in Venezuela (Beebe and Fleming 1951) and for but-
terflies and moths in Costa Rica (Janzen 1987, Haber
and Frankie 1989, Haber 1993), Mexico (Young 1982,
Powell and Brown 1990), Panama (Robbins and Small
1981), and Venezuela (Beebe 1949a, b, 1950a, b, 1951a,
b; see also Johnson 1978). Migrating insects must cross
the Continental Divide as they move between Atlan-
tic and Pacific habitats in Costa Rica (Janzen 1987,
Haber and Frankie 1989). Migrants could cross the
MCFP along routes such as La Ventana, an abandoned
road traversing the divide, which can be easily trav-
eled by crawling insects because it contains low,
meadowlike vegetation. Haber (1993) observed nu-
merous butterflies traversing the divide via two fly-
ways including La Ventana; they move east to the wet
Atlantic forest in the dry season and then return to
the dry Pacific forest in the wet season (see Chap. 4,
Insects and Spiders).Eastward MigrationIn February 1988, during the dry season, we observed
insects moving across La Ventana from the Pacific to
the Atlantic side of the Cordillera. Most abundant
were beetles (Coleoptera), wasps (Hymenoptera), and
flies (Diptera). Although little is known about migra-
tion in these insects (Johnson 1978), many insects
traverse Venezuelan cloud forest passes: 198 species
in 17 families of beetles, 126 species in 20 families of
moths, 170 species in 7 families of butterflies, 34 spe-
cies in 17 families of flies, and 70 species in 15 fami-
lies of wasps (Beebe 1949a, b, 1950a, b, 1951a, b,
Beebe and Fleming 1951). In Costa Rica, insects may
migrate to avoid the dry Pacific forest during the dry
season (Janzen 1987, Haber 1993), when many plants
lose their leaves or deteriorate in quality. Some hy-
menopterans and dipterans are pollinators and may
migrate to exploit pollen in the Atlantic forest. Otherwasps and flies are parasitoids and may migrate with
their hosts. Tachinid flies, which parasitize Lepi-
doptera, may migrate east over the Costa Rican divide
during the dry season (Janzen 1987).Westward MigrationIn July and August 1988, during the wet season, we
confirmed that insects migrate west across La Ventana
to Pacific habitats based on 13 samples collected in a
trap placed at 0, 0.5, and 1.5 m above ground, which
simultaneously trapped insects moving in opposite
directions. The trap was rotated between samples to
ensure that both sides collected equally. Represen-
tatives of numerous species were collected with 20-
30 insects trapped per hour. The most abundant mi-
grants were beetles (e.g., Blue Scarab), wasps (e.g.,
velvet ants and parasitoids such as ichneumonoids
and proctotrupoids), and flies (e.g., muscids and para-
sitoids such as tachinids).La Ventana: A Migration Corridor?Strong winds at La Ventana force insects to travel
close to the ground. However, westbound butterflies
in Monteverde fly in relatively calm weather 1-2 m
above the surface and over trees and buildings (Haber
1993). Butterflies are better fliers and less susceptible
to wind than the small insects observed or trapped in
this study as they crawled westward along the ground.
Much of the migration of the insects across mountains
occurs along old roads or through passes at elevations
below the peaks surrounding Monteverde. Westbound
butterflies are not restricted to these corridors since
they can migrate through forest (Haber 1993). La Ven-
tana in Monteverde is an ideal migration corridor
for insects crossing the divide between Atlantic and
Pacific habitats. Corridors between Pacific and Atlan-
tic forests in Costa Rica (e.g., Harris and Gallagher
1990) may be crucial for connecting habitats occupied
by migrating animals.438 Conservation BiologyI