vidual and is a predator, for example, ichneumonids
that attack spider egg sacs. Although many idiobionts
occur in Costa Rican cloud forests, only one has been
documented in detail: the tiphiid, Pterombrus piceus,
which attacks tiger beetle larvae (Pseudoxychila tar-
salis) in their burrows (Palmer 1976b, 1983b).
These parasitoids do not generally attack exposed
hosts, since such hosts cannot be permanently para-
lyzed and simply left where they are, lest they be
consumed by a scavenger. The problem of attacking
exposed hosts has been solved in two ways: (1) by
ovipositing on but not incapacitating a host and de-
laying parasitoid development until after the host has
stopped feeding and sought out shelter for pupation
(i.e., the koinobiont strategy), or (2) by retaining the
primitive (idiobiont) strategy but actively conceal-
ing the host in a specially constructed nest. Female
koinobionts only rarely paralyze the host to allow
oviposition. By avoiding or suppressing the host's
immune system, the larva can remain within the host
until the latter conceals itself in a pupal retreat, a
strategy pursued by all Proctotrupoidea and some
Ichneumonidae.
Nest building occurs in Pompilidae, Vespidae (Ap-
pendix 7), Formicidae (ants), and Sphecidae. Many
cloud forest wasps dig burrows in the ground, for
example, pompilids (Caliadurgus) and sphecids
(Sphecinae, Pseneo, Crossocerus, Nyssoninae, and
Philanthinae). Others construct nests in hollow plant
stems or abandoned beetle burrows in wood, for
example, pompilids (Dipogon), eumenine vespids
(Parancistrocerus), and sphecids (Pemphredonini,
most Crabronini, Miscophini, and many Trypoxy-
lonini). After building the nest, the female wasp hunts,
and when prey is encountered she paralyzes it. She
then relocates the prey, either by dragging it over the
ground (most pompilids) or by carrying it in flight
back to the nest (eumenine vespids and most sphecids).
After provisioning the cell with paralyzed prey, the
female lays an egg, seals it off, and repeats the pro-
cess (Hanson and Gauld 1995).
Among these nest-building wasps, the only de-
tailed study of a Costa Rican cloud forest species is
on Trypoxylon monteverdae (Sphecidae) in Monte-
verde (Brockmann 1992), which constructs exposed
mud nests consisting of vertical tubes that open at
the bottom, similar to those of other pipe-organ mud
daubers. As in other species in the subgenus Trypar-
gilum, males guard the nest while the female pro-
visions it, a rare behavior among nest-building hyme-
nopterans. Even more unusual is that T. monteverdae
males assist in nest construction, which consists of
smoothing the wet mud inside walls of the nest. In
return for this help, the female allows the male to
copulate frequently.
Nest-building wasps are subject to attack by para-
sitoids and by cleptoparasites. In the latter, the female
lays an egg in the nest of another species and the larva
that hatches from this egg feeds on the stored food it
steals from the other species. Cleptoparasites have
evolved either from close relatives (members of the
same family) that have abandoned nest building or
from parasitoids that have switched from feeding on
the host itself to feeding on its stored food (e.g.,
Gasteruptiidae and Chrysididae).
Polistine vespids and ants have evolved eusocial
behavior, living in colonial nests with the occupants
showing a division of labor (castes). The queen lays
eggs while workers forage and care for the brood.
Eusocial hymenopterans are often aggressive toward
human intruders; they have more invested in their
nest than do solitary nest builders and have evolved
effective means of defending their nest, that is, pain-
ful stings. Eusocial behavior has evolved more fre-
quently in the order Hymenoptera than any other
group of animals.Hymenoptera with plant-feeding larvae. Whereas mem-
bers of the suborder Apocrita have larvae that are
maggotlike and predominantly carnivorous, members
of the more primitive suborder, Symphyta (sawflies),
have caterpillarlike larvae that feed on foliage. In the
neotropics, sawflies are less conspicuous than those
in the suborder Apocrita that have become second-
arily phytophagous (e.g., fig wasps, leafcutter ants,
and bees; Hanson and Gauld 1995). In Costa Rica, only
four families of plant-feeding sawflies are present:
Argidae, Pergidae, Tenthredinidae, and Xiphidriidae.
Plant host records are available for very few of the 150
species that occur in Costa Rica.
One of the most exciting recent discoveries about
the biology of cloud forest Hymenoptera is that the
larvae of the two genera of Perryiinae (Pergidae) oc-
curring in Costa Rica appear to be fungivores rather
than true phytophages. Little was known about the
biology of this subfamily until D. Olson and F. Joyce
encountered larvae feeding on a jelly fungus (Auricu-
laria) in Monteverde and obtained adults, which were
identified as a species of Decameria, the first record
of a hymenopteran feeding on the fruiting body of a
macrofungus. J. Ugalde and E. Quiros reared larvae
of Perreyia to adults by feeding them on mouldy leaf
litter, the former from larvae collected in the San Jose
area (1100 m) and the latter in Las Alturas Biological
Station (1500 m). Although the larval diet and iden-
tity of this sawfly were previously unknown, the mi-
grating masses of black caterpillars are familiar to
Monteverdans. Phytophagous species of the sub-
order Apocrita consume the most nutritious parts of
plants (gall tissue, seeds, and pollen), and are derived125 Insects and Spiders