conditions. In temperate Europe, bees experience a
brief abundance of floral resources in summer fol-
lowed by a long cold winter, fostering biological traits
that are not well suited to conditions in the tropics.
Consequently, although the European bees that were
shipped to Latin America during colonial times re-
sulted in a beekeeping industry, these races generally
did not survive without management and rarely es-
tablished feral populations.
To obtain larger honey crops, Brazilians imported
breeder queens predominantly from South Africa (A.
m. scutellata) in 1956. Their extreme defensive behav-
ior was a concern and, after their escape, quickly led
them to become known as "abejas asesinas," or
"killer bees." They reproduced extensively and ab-
sconded during periods of low nectar availability.
These traits did not endear them to beekeepers, but
they thrived in the New World. In 1995, approxi-
mately one trillion bees were forecasted to occupy
16,000,000 km^2 (Roubik 1989). This colonization has
been remarkably rapid; within only a few years of
their release, they expanded their range at rates of
300-500 km/yr, a rate virtually unchecked until 1994.
They frequently attain densities of 10-15 colonies/
km^2 (ca. 90,000-450,000 bees/km^2 ) 2-4 years after
arriving to a new area.
Starting in 1976, I followed individual bee colo-
nies in French Guiana over time. By quantifying their
birth (swarming) and death rates, I modeled the dy-
namics of a population in its initial growth period.
Beginning with a single established colony, the high
swarming rate was estimated to yield an average of
60 "daughter" swarms per year. Colonies lived an
average of only seven months, but I estimated that the
population grew 16-fold during a single year (Otis
1991). These data support the numerous observations
of rapid population growth in many areas of Latin
America. The first Africanized bees in Costa Rica were
discovered near San Isidro del General on 2 Febru-
ary 1983. Within a month, they were observed forag-
ing in Santa Rosa National Park near the Nicaraguan
border. In seasonally dry areas of the Pacific slope,
the feral population grew quickly, and by 1986, most
beekeepers' colonies had become Africanized. At
higher elevations, swarms have been less common
and Africanization has proceeded more slowly (Spivak
1991). In Monteverde, the cool, damp, windy weather
slows colony growth and reduces swarming rates.
Although Africanized bees are probably present in the
area, they are uncommon and have caused little dis-
ruption to humans or livestock. They are much more
common in the warmer, drier region of San Luis.
The invasion of Apis into areas previously lacking
honey bees has potential consequences for the diverse
community of native bee species. In French Guiana
the proportion of foragers at a patch of Mimosa pudica
flowers that were Africanized bees increased from 7%
in 1977 (two years after they arrived) to nearly 75%
in 1982. This increase in Apis was accompanied by a
corresponding decrease in the proportion of two sting-
less bee species (Melipona), presumably due to com-
petition with Honey Bees (Roubik 1987).
Such changes in the native bee fauna are likely
to affect "buzz-pollinated" plant populations. Afri-
canized bees are not capable of buzz pollination, so
as they reduce the populations of other bees through
competition, they may indirectly reduce the repro-
ductive success of some plants (Roubik 1989). These
long-term processes are poorly understood. Because
Africanized bee density is low in highland regions,
the impact on Monteverde plant communities is ex-
pected to be negligible, but there may be effects on
plant species in the Pacific lowlands.
A contentious issue is the significance of hybrid-
ization between European and Africanized bees. The
two races interbreed (Rinderer et al. 1993), but con-
troversy surrounds the ecological fitness of those
hybrids. Some studies suggest that they disappear in
tropical regions, perhaps because of genetic incom-
patibility that is expressed in second- and third-gen-
eration hybrids (Harrison and Hall 1993). The estab-
lishment of Africanized bees in the New World has
provided biologists with an opportunity to study a
biological invasion. Surprisingly few studies have
been conducted in Costa Rica, given the large data-
base that was assembled on pollination systems prior
to the arrival of Africanized bees. Repeat studies un-
der conditions of high densities of Africanized bees
will provide insights on the impact of these bees on
plant communities.4.8. Arachnids: Spiders, Scorpions,
and Mites4.8.1. Introduction
Paul Hanson
The other major group of terrestrial arthropods besides
insects are the arachnids, which include scorpions
(Fig. 4.18), pseudoscorpions, solifugids (sun spiders
or wind scorpions), whip scorpions (uropygids), am-
blypygids, spiders, daddy longlegs, mites, and a few
lesser known groups. The largest (most speciose) of
these groups are the mites (order Acarina), which
occur in almost every type of habitat and include
fungivores, predators, ectoparasites of animals (e.g.,
chiggers and ticks), endoparasites of animals, and
plant sap suckers (e.g., spider mites and gall mites).
Most other arachnid groups are predatory.139 Insects and Spiders