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HYMENOPTERA, Trigonalidae (Trigonaloidea) -- <Images> & <Juveniles> Please refer also
to the following link for details on this group: Trigonalidae = Link 1 Description & Statistics
Trigonalidae. -- Trigonalids
are a small group of rare hymenopterans that are of average size and quite
brightly colored. Their bodies are
stout and they resemble wasps, but have long and multisegmented antennae. Trigonalids are parasitoids of Vespidae or
hyperparasitoids of caterpillars. The very small eggs are laid in large
numbers on plant foliage. In the case of the species attacking caterpillar
parasites, the eggs hatch when eaten by a caterpillar, and the wasp larvae
attack the ichneumon, tachinid, or other parasitoid larva that may be
present. In the species that attack vespid larvae, the eggs are eaten by a caterpillar,
which is in turn eaten by a vespid wasp, which in regurgitating the
caterpillar and feeding it to its young, transfers the trigonalid larvae from
the caterpillar to the wasp larvae (Borror & DeLong, 1954). This is a little known family
represented by relatively few genera and species, but is nevertheless
distributed worldwide. Wheeler (1923)
considered it to be one of the most archaic groups of Hymenoptera. Some researchers consider the family to be
most closely allied to Vespoidea, although its habits and parasitic life link
it closely with Ichneumonoidea, in which superfamily is usually placed. Host preferences are obscure. Various species have been reared from the
nests of Vespoidea and several from cocoons of ichneumonoid Hymenoptera and
from puparia of Tachinidae. In the
case of Vespidae, the species reared from the nests appear to be primary
parasitoids, while those from ichneumonid cocoons and dipterous puparia are
hyperparasitoids, through these hosts, of caterpillars and sawfly
larvae. Australian Trigonalys maculatus Smith, however, is a primary parasitoid of sawfly
larvae in the genus Perga (Clausen
1940/1962). Mason (1993) noted that in
trigonalyids the antennae are inserted on the frons under a small lobe, and
there are >20 flagellar segments.
The forewing has 10 closed cells, the costal cell being wide. The hind wing has 2 closed cells. Tarsomeres 1-4 has apicoventral plantar
lobes. The metasoma is pedunculate,
and the ovipositor is reduced. Life histories are complex, with
many details being unknown. These
parasitoids lay thousands of minute (0.1 mm) but thick-shelled eggs on the
underside of leaves near the margin.
The eggs remain unhatched until they are eaten by a caterpillar
(either Symphyta or Lepidoptera).
Cracks are made by the jaws of the caterpillar and its digestive
juices cause hatching. The newly
hatched larva makes its way into the body cavity of the caterpillar. If the host already has a parasitoid
larva, that parasitoid is attacked.
Otherwise the trigonalyid larva seems to wait until the caterpillar is
parasitized when it attacks only the parasitoid, not the primary host. Some trigonalyids have been roared from
larvae of Vespula. They are thought to reach their host by
way of infested caterpillars that are fed to the wasp larvae by worker
wasps. There are ca. 75 rare species
in 22 genera worldwide. In North
America only 4 rare species are found in Canada (Mason 1993). Schultz (1907) revised the world
genera and Bischoff (1938) and Weinstein & Austin (1991) did a catalogue
of the species of the world. Clausen (1940) and Weinstein & Austin
(1991) reviewed their biology. Other
Key references are Townes (1956), Oehlke (1984) ,Tsuneki (1991) and (Mason
1993). Biology & Behavior
Detailed biological studies were
made by Clausen (1929, 1931a) on Poecilogonalos
thwaitesii Westw. and species of
several other genera, van der Vecht (1933) on Nippogonalos jezoensis
Uch., parasitic in larvae of Vespa
spp., and Raff (1934) on T. maculatus. All species seem solitary in habit and develop internally in
the mature larvae and prepupae of the various hosts. A complete life history, with descriptions
of immature stages, was not available for any species when Clausen (1940/1962)
wrote his monumental book, Entomophagous
Insects. Thus, it is not known how the young larva gains access to its
primary host. Oviposition habits of the family
are quite uniform. Bugnion's (1910)
study of the anatomy of Pseudogonalos
hahni Spin, revealed 3-4,000 minute
eggs in the ovaries of each female.
Wheeler surmised that oviposition would be found to take place upon
foliage and that the first instar larva would be an active form of the
planidium type. The first part of
this conjecture was proven correct.
Leaf oviposition trigonalids was first observed by Teranishi (1929) in
Poecilogonalos maga Tera, and a similar habit has since been noted by other
researchers in P. thwaitesii, P. henicospili Roh, Orthogonalos debilis Tera, Nippogonalos
jezoensis Uch, and Pseudogonalos sp. (Clausen
1940/1962). The female stands on the
upper surface of the leaf, curves the tip of the abdomen beneath the margin,
and deposits the egg on the lower surface at a distance of 0.5 to 1.0 mm from
the edge. In N. jezoensis, a
modification of this habit was noted by van der Vecht, where the eggs were
placed singly in minute incisions in the leaf tissue but near the margin, and
the leaf tissue was damaged on both sides.
They are placed in the foliage of a wide variety of plants and, in
some cases, in the petals of the blossoms. The eggs of a particular species
under field conditions in a given locality are usually deposited on a single species
of plant, although in another locality the plant chosen may be entirely
different (Clausen 1940/1962).
Physical qualities of the leaves have a direct bearing on the
readiness with which females oviposit on different plants, but the principal
influence may be the occurrence of the caterpillar or sawfly host on the
foliage (Clausen 1940/1962). There is
no direct evidence to indicate that the latter is true, and caged females
oviposit quite as readily on clean foliage as on that on which caterpillars
are present or on which they had previously fed. Oviposition capacity is
exceedingly high, as found by Bugnion.
Actual oviposition records show the deposition of 3,559 eggs in four
days by a female P. maga, while 10,641 were secured from a
single P. thwaitesii female in 14 days and 5,782 in 6 days from P. henicospili. The P.
thwaitesii individual referred to
by Clausen (1940/1962) deposited 4,376 eggs in a single day. This high reproductive capacity was
considered essential in view of the mortality factors operating prior to the
time the primary host is found. Clausen (1940/1962) noted that the
microtype eggs of trigonalids consistently fail to hatch when left on
foliage, although eggs several months old were determined to contain viable
larvae. Experiments with chemicals,
such as a weak solution of K(OH), induced emergence provided that the chorion
was first ruptured. This led to the
belief that the eggs must be eaten by the host in order to secure normal
hatching, a conditions already known in Tachinidae. Tests with lepidopterous larvae proved this to be true, and
hatching resulted from the cracking of the chorion by the mandibles of the
caterpillar followed by the stimulating effect of digestive juices. The larvae were found free in the
alimentary tract 1-6 hrs after ingestion of the eggs by the caterpillar and
shortly thereafter they entered the body cavity. Several 1st instar larvae of P. maga were found
within the body of a sawfly larva collected in an area where the species was
known to occur, thus verifying the conclusions arrived at experimentally
(Clausen 1940/1962). The larger larvae of Vespa velutina Lep. and V. analis F., which are the hosts of N. jezoensis,
are fed mainly, if not exclusively, with fragments of bees, flies, ants,
etc., and there is thus no direct clue as to the means by which the Nippogonalos larva reaches its host
(van der Vecht 1933). First to third instar larvae
develop internally in the body of the host, and the surplus individuals are
eliminated in the 3rd stage. The
mandibulate 3rd instar larvae show a strong cannibalistic tendency. Just prior to issuance, the parasite larva
assumes a position immediately beneath the derm of the thorax, with the head
embedded in an eye of the developing host pupa, and emergence of the 4th
instar larva always occurs at this point.
Emergence from the host prepupa or pupa occurs immediately after the
third molt of the parasitoid, and death of the host follows. Feeding then takes place externally until
the 4th molt. Despite its heavy
tridentate mandibles, the 5th instar larva feeds very little; only a portion
of the fluid contents of the host body is removed, and no solid tissue is
eaten. Mature larvae spin irregular
cocoons within that of the host, and partitions off the meconium of the host
and its putrefying remains. Raff
(1934) found that Trigonalys maculatus does not spin a cocoon. Instead, a transverse partition of host
origin in the Perga cocoon
separates the pupa from the exuviae of the sawfly host, and the prepupal
remains of the latter are within the cell occupied by the trigonalys pupa. Van der Vecht (1933) thought that the
larva of Nippogonalos emerged from
the body of its Vespa host after
the latter had closed its cell in preparation to pupation and that the mature
parasitoid larva, after completing its feeding externally, made a cross wall
of silk at the middle of the Vespa
cell, thereby isolating the host remains in the lower portion. This lower compartment was apparently
opened and cleaned by the Vespa
workers, and the parasitoid adult later emerged through a hole made in the
cross wall. The life cycle has not been
definitely determined for any species, but evidence points to a general one
year cycle in temperate regions, while in tropical areas it must be longer
than that of the host, for the duration of the egg stage is exceedingly
variable and may extend over several months (Clausen 1940/1962). Development of the early stage larva is
then delayed until the host approaches the prepupal stage. Please refer to Clausen
(1940/1962) for an account of the developmental cycle of members of this
family. = = = = = = = = = = = = = = References: Please refer to
<biology.ref.htm>, [Additional references may be found at: MELVYL Library ] Bennett, D.J.
& A. S. Lelej. 2003. To the knowledge of trigonalyid wasps (Hymenoptera) of the
Sakhalin. Far Eastern Entomologist 130:8 Lelej, A.S. 1995. [Fam. Trigonalidae -
Trigonalid wasps]. In: Kupianskaya A.N., Lelej, A.S., Storozheva, N.A. (eds)
[Keys to the insects of Russian Far East]. IV(2): 8-14 Lelej, A.S. 2003. A review of the Family Trigonalyidae
(Hymenoptera) of the Palaeartctic Region. Far Eastern Entomologist 130:1-7. Nel A., V. Perrichot & D. Néraudeau 2003. The oldest trigonalid wasp in the
Late Albian amber of Charente-Maritime (SW France) (Hymenoptera:
Trigonalidae). Eclogae Geologicae Helvetiae 96: 503-508. Poinar G.
2005. Fossil Trigonalidae and
Vespidae (Hymenoptera) in Baltic amber Proc. Ent. Soc. Wash. 107 (1): 55-63 Smith, DR & I. C. Stocks. 2005. A new
trigonalid wasp (Hymenoptera : Trigonalidae) from eastern north America.
Proc. Entomol. Soc. Wash. 107: 530-535 |