est, accompanied by phorids of the genera Acantho-
phorides and Dacnophora and the brachypterous
(short-winged) females of A contis top tern andAdelop-
teromyia. Unlike army ant swarms at lower elevations,
few Apocephalus are associated with these raids.
These ants occasionally attack millipedes, which
produce defensive secretions that attract parasitic
females of the genus Myriophora.
4.6.3. Syrphid Flies of Costa Rican
Cloud Forests
Manual A. Zumbado
Syrphids (family Syrphidae), known as "flower flies"
or "hover flies," are often confused with bees and
wasps. Mimicry of other insects is much more com-
mon in Syrphidae than in any other family of Diptera.
In Costa Rica, there are more than 300 species of syr-
phids in 50 genera. Among specimens collected from
the Monteverde cloud forest, about 40 species and 30
genera are represented, but the actual number is cer-
tainly greater. Although many of these genera are
present in the lowlands, Eoseristalis and Criorhina are
restricted to mid- to high altitudes.
Species in the subfamilies Eristalinae and Syr-
phinae visit flowers and are sometimes pollinators.
Some small species feed exclusively on pollen and
have broad mouthparts; species that also ingest nec-
tar have slender, elongate mouthparts. Species of the
subfamily Microdontinae do not visit flowers. A strik-
ing characteristic of syrphids is their extraordinary
maneuverability in flight. In the field, they are fre-
quently encountered hovering, and they can quickly
rotate their orientation and dart precisely in any di-
rection. The wing muscles in the thorax, which ac-
count for 15% of the total body weight, permit them
to move their wings with a frequency of 250 wing-
beats/sec.
The larval stages have a variety of habits. Species
of Microdontinae live in ant nests. Larvae of Syr-
phinae are predators of Homoptera and a few other
insects. A species o£ Allograpta is a predator on psyl-
lids in San Gerardo de Dota (2300 m), and a species
of Salpingogaster preys on spittlebugs (Cercopidae)
in Monteverde. Larvae of Eristalinae are varied in
their habits, depending on the tribe or genus: aquatic
filter feeders live in water with high organic content;
detritivores live in dung or other organic material;
predators of Homoptera live on plants. Aquatic spe-
cies have an elongated breathing tube extending from
the posterior end and are sometimes called "rat-tailed
maggots." Larvae of predatory species are often strik-
ingly colored (reddish, bright green); larvae of other
species are whitish. Information on syrphid biology
is in Gilbert (1986).
4.7. Hymenoptera: Sawflies, Wasps,
Ants, and Bees4.7.1. Introduction
Paul Hanson & Ian D. Gould
Hymenoptera is one of the largest insect orders. It
includes sawflies, wasps, ants, and bees. Although the
most familiar species are those that sting, most hy-
menopteran species are parasitoids (parasitic wasps),
which help control populations of other insects. They
have been frequently used in biological control
projects. Ants are one of the most abundant groups of
insect predators, though less so in cloud forests than
in lowland tropical forests. Bees are the most impor-
tant group of animals that pollinate plants. Fig wasps
are obligate pollinators of fig trees, whose fruits are a
vital resource for numerous frugivorous vertebrates.
There are at least 20,000 species of Hymenoptera
in Costa Rica (Hanson and Gauld 1995). Of the 78
families of Hymenoptera (including all bees as one
family), 61 have been collected in Costa Rica. The
largest families in Costa Rica (those with more than
500 species) are Diapriidae, Platygastridae, Scelioni-
dae, Encyrtidae, Eulophidae, Pteromalidae, Braconi-
dae, Ichneumonidae, Formicidae, and Apidae.Hymenoptera with carnivorous larvae. Like parasites,
parasitoids live in intimate contact with their hosts,
but unlike parasites, they always kill their hosts. Hosts
are usually immature stages of other insects or spiders.
The female wasp searches for a particular type of host,
and lays an egg on or in it, and the larva feeds on the
host, eventually killing it. Although the distinction
is usually made between parasitic and predatory
wasps, there is actually a continuous gradation be-
tween the two. For example, in Pompilidae (spider
wasps) most species build nests in the manner of
predatory wasps, but each larva is usually provisioned
with just one prey (spider), in the manner of parasi-
toids. A more useful distinction is that between
idiobionts, which permanently paralyze their host,
and koinobionts, which allow their host to continue
its development after being parasitized. The former
usually feed externally and include primitive parasi-
toids and most predators; the latter feed internally and
include physiologically more specialized parasitoids
(Hanson and Gauld 1995).
The most primitive type of parasitoid (idiobiont)
generally attacks concealed or well-protected hosts
such as borers in plant tissue, insect pupae, or egg
masses. The female wasp stings the host, injecting a
venom that causes paralysis. Examples include some
Ichneumonidae and all Scelionidae. In a very few
cases, the larva consumes more than one host indi-124 Insects and Spiders