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File: <mymar1.ima.htm> [For educational purposes only] Terminology Glossary <Principal Natural
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Immature Stages of Mymaridae
Immature stages of Mymaridae were discussed in
detail by Clausen (1940), as follows: There is little variation in egg form within
the family. The main body of the egg
is ellipsoidal, ovoid, or spindle‑shaped, with a slender tapering
peduncle at the anterior end ranging in length from one‑tenth that of
the egg body in Anaphoidea nitens and Caraphractus to equal its length in Polynema striaticorne
(Fig. 44A). The ovarian egg is practically identical with the oviposited
egg. These eggs are exceedingly minute,
ranging from O.06 mm. in length in Anagrus
atomus to 0.25 mm. in P. striaticorne. Please
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A great deal of confusion exists regarding the
larval forms of the Mymaridae. This
is primarily due to the exceedingly minute size of the early stages combined
with the lack, in the instars following the first, of heavily sclerotized or
indurated structures of fixed form.
Often several species have been involved in the descriptions of the instars
of what was supposedly a single species.
This was the case in the account given by Ayers (1884) of Teleas sp., a scelionid
parasite in the eggs of Oecanthus
in the United States. His figures 2,
3, 8, 12, and 13, of plate 24, are undoubtedly of Polynema (Fig. 46A), which is stated by E. W. Wheeler
(1923) to be P. bifasciatipenna Gir. The Polynema
sp. figured by Ganin is stated by
Bakkendorf to be Anagrus,
probably A. incarnatus
Hal., though Henriksen believed it to be A.
subfuscus Foerst. There are two general types of first‑instar
larvae. The first of these is oblong
or flask‑shaped, of the sacciform type, and occurs in the several
species of Anagrus that have
been studied and in Prestwichia
aquatica. The body is merely a bag, without segmentation,
and lacks any distinguishing characters.
Bakkendorf (1934) figures a somewhat intermediate form between this
and the next, in what are considered to be first‑instar larvae of Allaptus minimus Hal. and Lymnaenon
effusi Bakk. (Fig.
46B). These are rather spindle‑shaped,
with indications of segmentation, and have the caudal segment attenuated and
tapering to a point. There is no
distinct tail structure, nor are there spines or setae. The second and more common form of the first‑instar
larva is designated as mymariform and occurs in the described species of Polynema, Araphes, Ooctonus,
and Anaphoidea. The head is large, drawn out into a curved
median conical process, with a second smaller process beneath it,
representing the mouth. The thorax
and abdomen consist of six to eight segments, often indistinguishable, with
transverse rings of long hairs, which are most numerous upon the dorsum. The dorsal spines of P. euchariformis
(Fig. 45A) and Anaphoidea nitens are exceptionally long
and heavy. The caudal end of the body
bears a long, curved or abruptly bent process, often equal to the body in
length, which, in some species, is compressed laterally into blade‑like
form and bears a single large tooth or one or more smaller paired teeth on
the ventral margin. Clark (1931)
described two distinct mymariform instars in A. nitens;
the first of these has the tail slender and bent at right angles twice, first
ventrally and then dorsally, whereas in the second form it is constricted and
toothed at several points (Fig. 46C).
Clausen (1940) believed this to be highly improbable, and the two
forms doubtless represent either two species or different ages of the first
instar of the same species. In size
the first instar larvae of the Mymaridae are small and range from 0.1 to 0.3
mm. in total length at the time of hatching. The number of larval instars following the
first is very uncertain. Several
authors asserted that there are only the first and the mature forms, though
in most species there are said to be three.
Balduf described four in Polynema
striaticorne. The second‑instar larva of Anagrus is of distinctive form
and has been designated as "histriobdellid" by Ganin, who first
observed and described it. This larva
(Fig. 45C) is cylindrical in form and is divided by constrictions into six
segments, of which the first and last are largest. The head bears a pair of large, conical or cylindrical fleshy
processes lateroventrally, which are said to be the antennae, and the
extruded mandibles, which are long, slender, and curved, lie parallel to each
other. The last segment bears a pair
of large ear‑like organs, of unknown function, lateroventrally. This type of larva has thus far been
associated only with the sacciform first‑instar larva and is not known
in any species having mymariform larvae. The second‑instar larvae of Prestwichia, Anaphoidea, and Polynema (Fig. 45B, D) have few
digtinguishing characters except for the relatively large extruded mandibles,
which are somewhat fleshy. The body
is bag‑like, without segmentation, and lacks appendages, spines, or
setae. The mature larvae of Anagrus and Paranagrus
are similar to the histriobdellid form except that the ear‑like
processes of the last segment are lacking and the mandibles and antennal
processes are much reduced in size.
Those of Polynema
(Fig. 44C), Prestwichia, Anaphes, and Anaphoidia are indistinctly
segmented, and, aside from the large extruded mandibles, have no recognizable
characters. The larva of Erythmelus goochi Enock appears to be intermediate in form between Anagrus and the above genera. In no species is there any indication of an
internal tracheal system or spiracles in any of the larval instars.
References: Please refer to <biology.ref.htm>, [Additional references may be found at: MELVYL Library ] |
