File:
<thynnid.htm> [For educational purposes
only] Glossary <Principal
Natural Enemy Groups >
<Citations> <Home> |
HYMENOPTERA, Thynnidae (Vespoidea) (grouped with Sapygidae) -- <Images>
& <Juveniles>] Description & Statistics
There are noticeable differences in size between males and females
in Thynnidae. Females are apterous
and mating flights occur among males in most species. This family is common only in South
American and Australia. Insects
attacked are primarily grubs of Scarabaeidae in the soil or in decaying
wood. Many species may be parasitic
on other aculeate Hymenoptera (Clausen 1940/62). Australian Diamma bicolor Westw. is parasitic on the
mole cricket, Gryllotalpa coarctata Wlk., but Clausen (1940)
wondered if this species actually belonged in the family. Janvier (1933) studied a number of species
principally of the genus Elaphroptera
in Chile and Burrell (1935) several species in Australia. Elaphroptera dimidiata Guer. of Chile is solitary
and external on grubs of scarabaeid genera Amblyterus, Oryctomorphus
and Liogenys. Adult males are active in the field soon
after sunrise when they may be observed in groups circling above the ground
surface. They concentrate around
areas that contain females about to emerge.
The female is dragged from her burrow and the mating flight begins,
covering a period of 1 hr. or more, such mating flights occurring quite
frequently during the life of the female.
At night females occur singly under rubbish on the ground surface, and
at dawn they ascend tree trunks, where they wait in an inverted
position. Females exercise an
attraction for males only when in this position and not when moving about,
the mating stimulus being visual.
Males cluster at night in galleries in the soil or on plant
foliage. Males feed extensively at
blossoms and sap exuding from wounds in trunks of trees caused by boring
beetles. Females also feed on plant
sap but not at blossoms, their main food being body fluids of host grubs. In most species of Thynnidae, the males carry diminutive wingless
females around for an hour or more in the mating flight. However, D. bicolor does not
because the male is smaller than the female (Turner 1907). In this case females and not males were
found to feed at blossoms during the flight period (Burrell 1935), which is
contrary to earlier reports. This
brings to mind the possibility of the existence of different races, as has
been discerned with many parasitic species in the latter part of the 20th
Century. The mating flight in
thynnids secures food for the female and disseminates the species. The host grub is permanently paralyzed during oviposition, and
the egg is laid longitudinally at the lateral margin of the thorax opposite
the last pair of legs. The egg is a
bit cylindrical, curved and with one end lightly broader than the other, and
is apparently attached to the integument by a short filament (Clausen
1940/62). Hatching occurs 10 days
after deposition, and the entire host body, with exception of the head and
integument on the anterior portions, is consumed by the larva. Feeding is completed in 15 days and there
is a resting period of ca. one week. before the cocoon is formed. There is a single annual generation and
winter is passed as adults in the cocoon in the soil. Females of Elaphroptera
in Chile feed extensively on the body fluids of the host. E.
atra Guer. does not sting grubs
upon which it feeds, the female rather chewing the posterior portions of the
body. In the process, some host grubs
do eventually die, however. About 50%
of field collected grubs of Athlia rustica Er. had feeding wounds
produced by E herbsti André, and this parasitoid may thus be of greater
significance as a predator than a parasitoid. This chewing behavior is not mentioned with regard to
Australian thynnids (Burrell 1935). All Thynnidae, except Diamma,
attack the host grub in its cell from which it is never removed. Such hosts are permanently paralyzed. D.
bicolor stings the host and drags
it to a previously prepared burrow, in which it resumes movement within about
1 hr. (Clausen 1940/62). The side of the thorax is preferred for oviposition by some
Chilean Elaphroptera. The egg lies parallel with the host's body
axis. However, five Australian
species studied were found to place the egg on or near the median ventral line
of the 2nd to 4th abdominal segments (Burrell 1935). This is also found in Epactiothynnus opaciventris
Turn. in Australia (Williams 1919d).
The anterior end of the egg lies toward the host's head. In most species the life cycle is about one year, which conforms
to the host cycle. Elaphroptera dimidiata requires 10 days for egg incubation, while eggs of
Australian species hatch in 2-3 days, the larval feeding period is usually
short (5-10 days). Janvier (1933)
noted a longer developmental period at higher elevations in South America. Thynnid eggs are rather elongate, have the anterior end slightly
broader, and are a bit curved.
Janvier (1933) mentioned a "filament" that attached eggs of
several species of Elaphroptera to
the host integument. Larval feeding
habits are similar to those of Campsomeris
and Scolia, where a large hole is
torn in the host's integument wherein the parasitoid embeds its head. This hole is very large, causing
considerable exudation of body fluids from around the head. However, the newly hatched larva moves
considerably and its point of feeding is not determined by the egg's
position. Larvae of thynnids are easily distinguished from those of
Tiphiidae and Scoliidae, by the very faint segmentation of the body as
compared with a pronounced segmentation in the other groups. Several species of Elaphroptera have mature larvae with tridentate mandibles, and
the spiracles occur only on the first 9 abdominal segments (Janvier
1933). Such an arrangement of
spiracles is not found elsewhere in Hymenoptera, but it serves as a good way
to distinguish larvae from those of Scoliidae and Tiphiidae that have the
same host preferences (Clausen 1940/62). Thynnid cocoons are similar to Scoliidae, and the posterior end
is not as pointed as in the Tiphiidae.
The cocoon wall consists of many closely oppressed layers of silk, and
varying quantities of loosely woven strands may fill the space between the
cocoon and the cell wall. A circular
cap is cut at the anterior end for adult emergence. Brothers & Finnamore (1993) placed this family in the
subfamily Thynninae in the Tiphiidae.
Subfamily Diamminae was listed with Thynninae, and they noted that
they are found only in the Southern Hemisphere in Australia and
Neotropics. There are many species in
52 genera. Sexual dimorphism is
great, with males being usually mostly dark but often with extensive bright
markings, especially yellow or white, and females are generally mostly dark
without bright markings. The larvae
are ectoparasitoids on the larvae of Scarabaeoidea (Coleoptera); one species
parasitizes Gryllotalpidae (Grylloptera).
A few species have been used for biological control. Kimsey (1991) recognized a separate
subfamily, Diamminae, for the gryllotalpid parasitoid. Females are recognized by their metallic
bluish body color and the reduction of the metapleuron to a strip hidden by
the mesopleuron, except at its dorsal fringe. = = = = =
= = = = = = = = = References:
Please refer to <biology.ref.htm>, [Additional references may be
found at: MELVYL Library] Ashmead, W. H.
1898. Thynnidae in the United
States. Psyche, Volume 8 (268): 251-251. Burrell, R.
W. 1935.
Notes on the habits of certain Australian Thynnidae. J. NY. Ent. Soc. 43: 19-28. Given, B. B.
1954: A catalogue of the Thynninae (Tiphiidae, Hymenoptera) of
Australia and adjacent areas. New Zealand Department of Scientific and
Industrial Research bulletin, 109: 1-89. Given, B. B. 1954:
Evolutionary trends in the Thynninae (Hymenoptera; Tiphiidae) with special
reference to feeding habits of Australian species. Transactions of the
Royal Entomological Society of London, 105: 1-10. Given, B. B.
1954: Notes on Australian Thynninae I. Ariphron bicolor
Erichson. Proceedings of the Linnean Society of New South Wales, 78:
258-261. Given, B. B.
1958: Notes on Australian Thynninae II. The genera Dimorphothynnus,
Rhagigaster and Eirone. Proceedings of the Linnean Society
of New South Wales, 83: 309-326. Given, B. B.
1959: Notes on Australian Thynninae III. The genus Thynnoides. Proceedings
of the Linnean Society of New South Wales, 83: 327-336. Pilgrim, E.
M., C. D. Von Dohlen & J. P. Pitts.
2008: Molecular phylogenetics of Vespoidea
indicate paraphyly of the superfamily and novel relationships of its
component families and subfamilies. Zoologica scripta, 37: 539-560. |