Female of Polynema
The family Myrmaridae is perhaps the most distinctive
of all taxa included in the superfamily. As mentioned previously, they are
likely the sister group of the rest of the chalcidoids and as a result,
their morphology is somewhat different. One such difference is that although
the prepectus is present, it is often quite reduced and in some species
it is fused to the pronotum and appears to reach the tegula, giving the
mymarids a "proctotrupoid" appearance. Another reason is that
the antennal toruli are quite far apart (3-5 times their own diameter) which
is not found in most other chalcidoids (normally at most 1 diameter apart).
A third reason (although one you are not likely to see) is that mymarid
larvae are similar to scelionid larvae (Nikol'skaya 1952). Burks (1979)
stated that they were derived from the same stem that produced Eulophidae.
Yoshimoto (1975) reviewed the placement of this family by earlier authors
who placed it "mid-way in the Proctotrupoidea," at "the beginning
of the Proctotrupoidea," and "after the primitive Chalcididae,
Torymidae, and Pteromalidae." Yoshimoto placed the mymarids as evolving
"independently from the primitive eurytomid-torymid-like ancestral
group before the branching of the chalcid-pteromalid and tetracampid-eulophid
lines." Recent work on the evolutionary relationships (Schauff l984,
Gibson 1986a) indicate the mymarids branched off early from the primitive
chalcidoid ancestor and represents a lineage independent of the other chalcidoids.
Huber (1986) wrote a complete review of the taxonomic history of the family
along with information on their biology and hosts.
As in Trichogrammatidae, these wasps are egg parasites and are very small (usually less than 1 mm). One genus (Alaptus), parasitic on Psocoptera eggs, approaches the record of 0.18 mm for a trichogrammatid claimed as the smallest of all insects.
The genera have been divided into subfamilies based upon either tarsal number or gastral attachment. Depending upon which character is used first, the placement of higher taxa will be subject to some confusion. Annecke and Doutt (1961) provided the most current world review of mymarids, but their system of classification is now regarded as highly artificial and in some cases misleading. Regardless, this system has been generally accepted since its publication. The system used by Debauche (1948) and several earlier authors, although far from perfect, provides a better approximation of the true relationships of the family. These authors simply split the family on the basis of tarsal segment number (the Gonatocerinae for those with 5 tarsi and Mymarinae for those with 4). Schauff (1984) revised the Holarctic genera of mymarids. Noyes and Valentine (1989) revised the mymarids of New Zealand. Yoshimoto (1990) reviewed the New World genera. A large part of North American Gonatocerus and Anaphes was revised by Huber (1988, 1992). Gordh and Dunbar (1977) reviewed Nearctic Anagrus and Schauff revised North American Acmopolynema (1981) and Omyomymar (1983). Huber (in Gibson, et al. 1997) keyed all the genera for North America.
STATISTICS: Number of world species: about 1400 (120 Nearctic); number of world genera: 100 (28 Nearctic).
BIOLOGY: Hosts of the Mymaridae include eggs of Hemiptera, Homoptera, Pscoptera, Coleoptera, Diptera, and Orthoptera. As in the trichogrammatids, several mymarids attack aquatic insect eggs. Huber (1986) published a comprehensive review of the host of mymarids. Mymarids are all believed to be internal, primary parasites of insect eggs. Other records of hosts (e.g. Peck, et al. 1964 of "coccoids, aleyrodids, etc.") are open to question (Annecke and Doutt 1961). Burks (1979) suggested that at least one of the species (Alaptus) thought to parasitize coccids probably was attacking a psocid egg. He also stated that one species (Arescon aspidioticola (Ashmead)) was an egg predator beneath the cover of scales. Recent work (Schauff 1984) indicates that this species is not a mymarid at all.
DISTINGUISHING CHARACTERS: Mymarids are fairly characteristic in habitus and do not closely resemble any other chalcidoids. The most easily observable characters are the stalked, narrowly elongate hindwing, the long clubbed female antennae (filiform in the male), and the greatly reduced venation which terminates within the first third of the wing (except in Arescon and Krokella) and lacks a discernible stigmal or postmarginal vein. Additional characters are the tarsi which may be 4 or 5 segmented, the widely separated antennal toruli and the vertex surrounded by thickened bands of cuticle and separated from the face by a suture.
COLLECTING: Although considered "rare" by many collectors, this is really an artifact of collecting techniques. When properly collected, mymarids are among the most abundant of chalcidoids. Mymarids and trichogrammatids may often be collected together because size and biology are nearly the same. A fine-mesh net or canvas sweepnet may be used for sweeping (this works best if the sweepings are dumped directly into alcohol and then the "mess" is sorted under a microscope). Rearing egg material will sometimes produce specimens of this family. Yellow pan-traps are very good for collecting both trichogrammatids and mymarids. We have also found that a low, long malaise trap (5 feet high by 20 feet long) based on Gressitt and Gressitt's model (1962) works very well. The trap should be made of very fine-mesh dacron.
DISTRIBUTION: Mymarids are found worldwide throughout temperate and tropic latitudes. Their presence at high altitudes (see Annecke and Doutt 1961) indicates a probable wind dispersal as in the trichogrammatids.