File: <agrom1..ima.htm> [For educational purposes only] Terminology Glossary <Principal Natural
Enemy Groups > Citations> |
Immature Stages of Agromyzidae Clausen
(1940) commented that the egg increases considerably in size during
incubation. The first instar larva is
caudate, although it is often referred to in this family as embryonic, for
the body is a transparent cylindrical sac 0.3-0.4 mm. long and slightly
curved, with little indication of segmentation and with the caudal segment
bifurcate and the lobes finger-like, with tips broadly rounded. There is no trace of a tracheal system or
of heart or sensory organs. There are
apparently no distinguishable mouth parts.
The 2nd instar larva is a bit cylindrical and has 10 distinct
segments. The tails are of markedly
variable diameter, a bit shorter than the body and they terminate
bluntly. Several short pointed
cuticular spines occur in a transverse row on the dorsum of the 2nd abdominal
segment, and similar spines completely encircle the following 5 segments,
almost completely covering the 6th and 7th abdominal segments. A simple closed tracheal system is
present, and the longitudinal trunks, with little evidence of branching, extend
from the first thoracic to the posterior margin of the 7th abdominal
segment. During the latter part of
the stage, usually 6 fine branches are developed in the expanded bases of the
tails. There is very little growth in
this stage, and no blood flow can be detected.
Please CLICK on picture to view details: The 3rd
instar larva is similar in form to that of the 2nd, the greatest difference
being in the tails, which are now 1.5-2.0 times as long as the body. The bases of the tails are greatly
expanded, being as wide as the preceding body segments, and the fragile
filaments beyond the bulbs are of uniform diameter. The tail's hypodermis in this and preceding instars, consists
of a single layer of cells with enormous nuclei. The lumen of the tail is filled with blood, although no
circulation can be observed. The
tracheal system is still closed, and there is a dense network of fine
branches just beneath the epidermis, several of which extend into the tails
for ca. 2/3rds of their length. Two
transverse commissures occur in the anterior part of the body and one in the
last abdominal segment (Clausen 1940/62). The 4th
larval instar is quite different from preceding instars. It is very robust and each of the 10
distinct body segments bears a band of minute setae. The tails are exceedingly long, being 3-4
times the body length. Except for the
basal bulb, the tails are very slender, kinked and irregular. The tracheal system is complete, with
spiracles on the anterior margin of the 1st thoracic segment and on the
dorsum of the 7th abdominal segment.
The anterior spiracles are pointed, dart-like structures, heavily
sclerotized and set in pits, while the posterior pair are distinctly dorsal
and are in the form of very heavy, dark hooks directed toward the head. The latter are apparently completely
closed, and the anterior pair is not open until late in the stage (Clausen
1940/62). At first
the puparium is a pale yellow, but finally becomes black. There are 10 distinct segments, and the
dorsally located operculum extends to the posterior margin of the 3rd
segment. The anterior spiracles are
terminal in position when fully extended.
The tails remain attached to the puparium, but they are shrunken and
brittle. The prothoracic spiracles of
the pupa are internal and do not protrude through the integument. First
instar larvae derive their food directly from the host's body fluids, which
are absorbed through a delicate integument.
The third stage feeds on the fat body, and gross feeding occurs in the
final stage. The larva is virtually
incapable of movement prior to the 3rd molt.
Before pupation, when the host's body contents have been largely
consumed, the anterior spiracles are extruded to their full extent and forced
through the host integument, usually at the lateral margin. The host integument then dries and closely
envelops the puparium. Because of this,
the skin is broken at the time the puparial operculum is raised, allowing the
adult fly to escape. There are
1-6 individual flies able to attain maturity in each host. The life cycle takes ca. one month, and
5-6 generations occur per year in California. Vayssiere
(1926) and Thorpe (1934) studied another species, Cryptochaetum grandicorne Rond. This is a solitary internal parasitoid of Guerinia serratulae F. in Europe. There are several differences in the
morphology of the immature stages and in the manner of development when
compared to C. iceryae. There are only 3 larval instars rather
than 4. The life history is well
adapted to the cycle of the host, and the pupal period of 6 months or more
covers the time in which the host is in the dormant phase. Oviposition occurs only in 1st instar
hosts after they have become fixed on the food plant (Vayssiere 1926, Thorpe
1934). The egg is
longer and more curved and the anterior end is relatively wider than in C. iceryae. The increase in size during incubation is much less, and the
1st instar "embryo" larva is more elongate and may be distinguished
by a pair of unpigmented mandibles projecting from the open mouth. The 2nd instar larva has 11 body segments
and bears a transverse row of digitate spines on the dorsum and sides of the
3rd thoracic segment and 4 rows, completely encircling the body, on each of
the following 8 segments. The tubular
tails increase much in length during the 2nd stage. The tracheal system is similar to that for 3rd instar C. iceryae. This instar may persist for 3-4 months. The 3rd instar larva has the tail
filaments shrunken and often broken off, so that in the latter part of the
period they may be shorter than the body.
The anterior spiracles are palmate and lightly pigmented, while the
posterior pair show an opening near the base of the spine. Just before pupation, both pairs of
spiracles are thrust through the host integument. Vayssiere (1926) found that the hook-like posterior spiracles
of the 3rd instar larva are fixed in one of the large tracheae of the host,
but the occurrence of this habit was not found by Thorpe (1934). The
biology and behavior of Cryptochaetum
sp. parasitic in Drosicha corpulenta
and others of that genus in Japan differ in some respects from the two
species just discussed (Clausen 1940/62).
Adult flies feed mainly on honeydew secreted by Kermes miyasakii
Kuw., which occurs on the same trees as the host insect. There are two generation per year, and the
summer brood of females oviposit in the young scales, passing the winter as
young larvae within the living hosts.
In this generation both male and female scales are parasitized, with
development being completed in springtime.
These parasitized scales usually do not leave their hibernating sites
in crevices in the trunk of trees.
Male hosts are in the prepupal stage at the time of death, and
emergence of the spring brood of Cryptochaetum
coincides with that of male hosts, which is usually 10-25 May in central
Japan (Clausen 1940/62). Cryptochaetum sp. eggs in Japan measure
0.35 X 0.08 mm., and are thus much larger and more elongate than the eggs of
either C. iceryae or C. grandicorne. The mature larva is 3.2-4.0 mm. long, with
the caudal filaments measuring 4.0-5.5 mm.
The latter are uniformly thick for their entire length, except of the
basal portions, which are bulbous.
The puparium is a deep red, which shows through the host's
integument. The tails remain unbroken
nd turgid even after emergence of the adult fly from the puparium. Clausen
(1940) noted that the life cycle given above, in which the parasitoid passes
through two generations annually on the same host generation, is much
different from that given by Vayssiere and Thorpe for C. grandicorne,
which has only a single generation annually and which provides for the long
summer period when hosts are not available, by undergoing a prolonged pupal
diapause. References:
Please refer to <biology.ref.htm>, [Additional
references may be found at: MELVYL Library |