File: <tricm1.ima.htm> [For educational purposes only] Terminology Glossary <Principal Natural
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Immature
Stages of Trichogrammatidae
Immature stages of Trichogrammatidae were discussed in detail by
Clausen (1940), as follows: The egg
forms of very few species of the family were known by
1940 (Clausen 1940). Those of several
Trichogramma are somewhat
elongate, with the middle portion distinctly expanded, and both ends are
smoothly rounded (Fig. 48A). The egg
of Oligosita utilis. is of similar form, though with a short,
heavy peduncle at one end. In Poropoea stollwercki (Fig. 49A), the main body is 0.5 mm. in
length, elongate and irregularly curved, and it bears a slender peduncle at
the anterior end. The narrower
posterior portion represents a somewhat ringed appearance. The egg of P. defilippii
Rond. is similar, although the peduncle is shorter and more delicate. In Chaetostricha
pulchra, figured hy
Bakkendorf (1934), the main egg body is cylindrical, and the anterior
peduncle, which is half as long, is set at an angle with the main axis of the
egg.
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are two distinct types of first‑instar larva, the first
of which is sacciform almost globular or cylindrical, and lacks sensory and
integumentary setae and other external characters. The mandibles are minute but distinct. Those of Trichogramma (Fig.
48B), Chaetostricha,
and Oligosita are of this
type. The second is much more highly
specialized, being mymariform, with the head and thorax appreciably larger
than the abdomen, the segmentation distinct, the caudal segment drawn out
into a tail, and the thorax and abdominal segments bear long setae. This type occurs in Poropoea and Ophioneurus. The first‑instar larva of P. stollwercki (Fig. 49B), as described by Silvestri, is 0.28
mm. in length, with the head and thorax exceptionally large, and the abdomen
consists of six ring‑like segments and a seventh that is curved
ventrally and extended into a point.
There are 16-18 long, slender setae in a transverse row at the
posterior margin of the thorax, situated dorsally and extending to the lateral
margins. All abdominal segments
except the last bear a smaller number of these setae dorsally near the
anterior margins. The larva of Ophioneurus signatus Ratz. (Fig. 50),
described by Bakkendorf (1934), has a distinct head; but the thorax and
abdomen are unsegmented, almost spherical, and the last segment is produced
into a slender, curved tail which bears a tooth at the mid‑ventral
margin. In addition, there is a long,
heavy process or spine arising dorsally slightly in front of the base of the
tail. The
first instar. There has
been considerable disagreement as to the number of larval instars in the
family. Taylor stated that there is
only one in Oligosita utilis, and Bakkendorf was
unable to find evidence of intermediate molts in Chaetostricha pulchra. Flanders described three instars in Trichogramma, and Silvestri
recorded five for Poropoea stollwercki, though here, also,
the evidence of a corresponding number of molts is incomplete. The
second instar of Trichogramma
(Fig. 48C) is somewhat elongate and tapering anteriorly, and the
segmentation is indicated only on the anterior half of the body. The mandibles are extruded and only
slightly curved. The presumed second‑instar
larva of P. stollwercki (Fig. 49C) is still
mymariform, with the abdomen further reduced, and the tail exceeding the body
in length. It appears more probable
that this larva is still of the first instar rather than a distinct
second. Even the third instar as figured
(Fig. 49D) is identical with the first except for the elimination of the segmental
lines, possibly due to an increase in volume through feeding. The
mature larvae of all genera are of similar form,
being robust, more or less distinctly segmented, and without spines or
setae. The mandibles are elongate and
extruded and lie parallel to each other.
They are immovable and consequently not used in feeding, though they
may serve to lacerate the remaining embryonic tissues in the host egg. Several authors emphasized the complete
lack of a tracheal system in the larvae of Trichogramma, and it has not been mentioned in other
genera. References: Please refer to <biology.ref.htm> [Additional references may be found at: MELVYL Library] |