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File: <platy1.ima.htm> [For educational purposes only] Terminology Glossary <Principal Natural
Enemy Groups > <Citations> |
Immature Stages of Platygastridae
Immature stages of Platygastridae (= Platygasteridae) were
discussed in detail by Clausen (1940), as follows: The egg of Platygastridae is always of minute size, ranging in
length from 0.02 to 0.1 mm. The main body
is usually lemon‑shaped; with a stalk at the anterior end which, in L. rhanis (Fig. 108A), is 3X the length of the egg
body. In other species, this stalk is
shorter, and the extreme is shown in P.
herrickii (Fig. 108C), which
has the posterior end somewhat, attenuated and bears several short flagellum‑like
processes at the anterior end.
Several species that have a pronounced stalk also bear a blunt
protuberance at the posterior end. Please CLICK on pictures to view details:
The first‑instar larvae of the polyembryonic species is the
form that frees itself from the enveloping trophamnion; it does not
necessarily differ from those of the monoembryonic species. There are two types of larva of this
instar, the first being hymenopteriform and the second cyclopoid. The hymenopteriform first‑instar
larva is elongate‑oval to almost spherical in form and distinctly
segmented, with the head small, the mandibles relatively large, no fleshy
processes on the body, and three pairs of spiracles, situated on the second
and third thoracic and the second abdominal segments. P.
hiemalis (Fig. lO9B) P. ornatus, and P.
dryomiaee are. of this
type. A large discoidal body replaces
the spiracle on the first abdominal segment, and a spiracular branch leads
to it. In P. zosine
(Fig. IO9A), the body is more elongated, with a constriction between the head
and thorax, but it lacks any further indication of segmentation. There are no spiracles. Please CLICK on pictures to view details:
The cyclopoid type of first‑instar larva is characterized
by a cephalothorax usually larger than the remainder of the body and somewhat
flattened dorsoventrally, which bears enormous falcate mandibles and
conspicuous antennae. The abdominal
segments are narrowed and reduced in number. The mandibles are widely spaced, being set near the lateral margins,
and they lie transversely. The body
terminates in one or more fleshy processes of diverse form. This type was first studied and figured by
Ganin (1869) (Fig. 110) for several species parasitic in cecidomyiid larvae;
it was described as "cyclops‑like." Two of them described by him have a pair
of large fleshy processes lateroventrally on the cephalothorax near the
posterior margin, and the caudal segment bears two or more long spine‑like
processes which themselves are armed with numerous spines. Marshal has described a similar larva for Leptacis rhanis (Fig. 108B).
A second form described by Ganin shows the caudal appendage bifurcate,
with the inner margins serrate. That
described by Marchal for Inostemma
piricola (Fig. 109C) bears a
close resemblance to it. In P. lineatus, P.
herrickii, Misocyclops marchali (Fig. 108D), and Sactogaster pisi Foerst (Kutter 1934), the
caudal appendage is broad, terminating in a pair of lobes which, in the last
named species bears short, heavy spines.
In T. remulus
(Fig. 111), the abdominal segments are very narrow and the caudal process is
short and bilobed, with the tips rounded and curved inward. An undetermined species of Platygaster figured by Marchal
(Fig. 109D) has the last abdominal segment somewhat expanded, with the
posterior margin serrated. In some
species, such as M. marchali, the paired fleshy
processes that generally occur ventrally on the cephalothorax are entirely
lacking. Spiracles are not known to occur upon any cyclopoid larvae, in contrast
to the three pairs occurring upon most hymenopteriform larvae of the family. There is considerable question as to the body parts that make up
the so‑called cephalothorax of the cyclopoid larva. Some authors consider it to consist only
of the head, and illustrations show the mandibular muscles attached near the
posterior base, though Marchal considered it to include the thoracic
segments, also. The fleshy paired
ventral processes are presumably borne on the first thoracic segment. The fact that the visible segments
following the cephalothorax number only 5-7 lends weight to this conclusion
and accords with the reduced number of body segments found in the mature larva. The consideration of the instars following the first is
complicated by a variation in the number of molts recognized among the
different species. According to Hill,
P. hiemalis has only a single larval instar. It is of considerable size when separation
is effected from the trophamnion, and a relatively slight growth brings it to
larval maturity. In P. zosine, according to the same author, there is only one
molt, and the mature form immediately succeeds the first instar. The second instar, as here discussed, includes only those of
species in which three larval instars have been noted. That described and figured by Ganin for Platygaster sp. is oval in form
with no indication of segmentation; during its early period, it is enclosed
within the distended skin of the preceding instar. There are no fleshy or cuticular process any sort, and no open
spiracles are present. Other species
that have been studied by various authors possess second‑instar larvae
that likewise present no distinguishing characters. The mandibles are small in all species. The mature larvae, which may be of the first, second, or third
instar, depending on the species under consideration, present no characters
by which they may be readily separated.
The body is oval in form and distinctly segmented and comprises the head
and 10-11 body segments. No cuticular
spines or fleshy processes are to be found.
The mandibles are small and widely spaced. The tracheal system possesses three pairs of spiracles,
situated on the second and third thoracic and the second abdominal
segments. The first abdominal segment
bears the large discoidal body mentioned in the discussion of the first
instar larva of P. hiemalis and others. This organ has been detected only in
species of Platygaster but
may occur in other genera also. References: Please refer to <biology.ref.htm>, [Additional references may be found at: MELVYL Library] |
