Rhopalosomatidae is an odd family of Hymenoptera whose species parasitize crickets, and also has a genus that closely resembles the Ophioninae (Ichneumonidae). Rhopalosoma, with a single species in the eastern United States, R. nearcticum Brues, can easily be mistaken for Ophion at the blacklight sheet, and may occasionally be included with them when the collection is sorted.
Mississippi Hymenopterist 1 is about Rhopalosomatidae. In Mississippi we have three species distributed in three genera, Rhopalosoma, Liosphex and Olixon. Olixon can easily be mistaken by beginners for a mutillid -and, in fact, the male genitalia are very mutillid-like. Liosphex can be mistaken for a pompilid, or spider wasp, but lacks several features, the most salient being the cross furrow of the mesopleuron. Rhopalosoma is quite ophionine in appearance, but the abdomen is rounded and not as compressed, and the wing veination of each is distinctive. They have very large ocelli, however, as do many Hymenoptera collected at blacklights. For detailed species descriptions and taxonomic treatment, see Townes, 1977.
Lionel Stange (1991) showed the range of this species as virtually throughout the southeastern United States and into Texas, but there were no specific collection records from Mississippi. Therefore, this is a new, but hardly unexpected record for the state. Rhopalosoma nearcticum is the most commonly collected rhopalosomatid in Mississippi since it frequents blacklight traps. On the other hand, it is probably overlooked just as often, since it resembles closely the large and ubiquitous ichneumons in the genus Ophion or Netelia. A quick look at the wing veins or antennae, or a number of other characters, will quickly dispell any doubts about it's identity. Stange (1991) briefly discussed the biology. A more detailed description is available from Gurney (1953).
Ours is, so far, the most northern record for L. varius. It is known from the gulf coast region to Brazil, but not from this far inland . Collected from the northern limits of the last oceanic invasion, it may be a relict from the last embayment - this, since it is ordinarily associated with coastal regions, although found north to Tallahassee prior to this addition. The biology of the species remains unknown, but it is presumably a cricket parasite, as are the other members of the family. Several of the specimens available to me have an anomalous, or extraneous small cell located at the tip of the discal cell. The extra cell may occur in one or in both wings, and varies some in shape and size. I associate characters such as this with range-edge effects, and have witnessed it numerous times among coastal populations of chalcidoid wasps. More specimens of Liosphex have been collected in the Mississippi delta (Nathan Schiff, pers. comm.), but are not yet recorded in the MEM. Liosphex can easily be confused with pompilids, but lacks the mesopleural cross furrow, and has an elongated petiole. The drawings presented here should be sufficient for identification.
Olixon is not a commonly collected wasp, but may be taken more frequently in pitfall traps.Terry Schiefer collected one or two while they were crawling on the sheets at a blacklight. Again, the species should be expected in Mississippi, but this is the first record of it here. Stange (1991) listed Arkansas, District of Columbia, Florida, Georgia, Kansas, Louisana, Maryland, New York, North Carolina, Ohio, Oklahoma, and Mexico. Therefore, it is widely distributed. Olixon is possibly a parasite of Nemobius, though I have no records of it's hosts. In this species, the wings are reduced , or may be absent.
Miss., Lowndes Co., T17N, R 16E, Sec. 34, Black Belt Prairie, 19 July 1993, R.L. Brown and D. Pollock, blacklight and sunlamp in oak hickory forest. 7 specimens, 1 dissected on card/slide, no. MWM 98.11.
Grenada Co., T21, R2E, Sec. 12 and 13N and R 2E, Sec. 7S and 18 N, 28 August -4 September 1991, M. and J. MacGown, pitfall in deciduous forest.
Oktibbeha Co., Longview, 27 August 1984, P.R. Miller, blacklight trap
Oktibbeha Co., Craig Springs, G.L.Snodgrass, pitfall peripheral to cultivated cotton, the following dates:
1979:19,21 June1980: 19 June, 22,23 July, 1,4,9 August, 15 October
Oktibbeha Co., 3 mi. west of Adaton, 27 June 1995, T. Schiefer, blacklight trap
Panola Co., 6 mi. southwest of Como, pitfalls in and peripheral to cultivated cotton, W. H. Cross, the following dates:
1979: 20 June, 1 August, 13 September (several specimens)
Pontotoc Co., 1 mi. southeast of Ecru, in pitfalls, Snodgrass and Cross, the following dates:
1980: 7, 17 July (in deciduous woods); 1, 13, 27 August, 26, 28 September (in swamp). Numerous specimens
Gurney, A. B. 1953. Notes on the biology and immature stages of a cricket parasite of the genus Rhopaldsoma. Proc. U. S. Nati. Mus. 103:19-34
Stange, L.A. 1991. The Rhopalosomatidae of Florida. Fla. Dept. Agric. and Consumer Services, Div. of Plant Industry Entomology Circular No. 341. ~
Townes, H. 1977. A revision of the Rhopalosomatidae (Hymenoptera). Contr. Amer. Entomological Institute 15: 1-34.
