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.
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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.