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DIPTERA, Nemestrinidae -- <Images> & <Juveniles> This is a rare family of Diptera, several
species of which are known to parasitize larvae of Coleoptera and a few are
internally parasitic on locusts. Biology & Behavior
Handlirsch (1882, 1883) and Brauer (1883, 1884) gave early
accounts of the host preferences of the family on Hirmoneura obscura
Meig., parasitic on Amphimallus solstitialis L. (= Rhizotrogus sp.) pupae. Riley (1883a, 1884) elaborated on their
observations. Hirmoneura obscura
adults are present in the field during July and early August, when females
are frequently observed laying eggs in abandoned burrows of Anthaxia quadripunctata L., and probably of other coleopterous borers, in
broken branches, spruce poles, etc., from which bark had been removed. The parasitoid seems closely associated
with spruce, and adults could be found abundant only at the borders of spruce
forests where fallen trees or branches were common, or in fields bordered by
fences made of spruce. No oviposition
was observed in hosts in living trees.
During oviposition the female parasitoid inserts her abdomen tip
deeply into the exit hole of the beetle and lays a mass of eggs. After hatching, young larvae make their way to the surface of the
branch or pole, assume an erect position and are thought to then be blown
away by wind. Riley (1883a, 1884)
hinted that they might be carried into the soil by adult host beetles, but
Clausen (1940) thought this improbable, for the normal movements of the
beetles would not bring them into contact with the young larvae and in any
case just carrying them into the soil would not be advantageous to
establishing contact with a pupa or grub that was in a vulnerable stage for
attack. Brauer (1883, 1884) found
parasitization of Amphimallus pupae
to be highest within 3 m. of the spruce fence and that it decreased rapidly
with an increase in distance away. Second instar larvae are found in living host pupae during June
and 3rd instar soon thereafter. The
host beetle is fully formed and its integument heavily chitinized before it
dies. The parasitoid is oriented in
the same way as the host. After the
fluid contents are completely consumed, it makes a large hole in the venter
of the thoracic region and eventually pupates alongside the host remains or partly
extruded from the opening (Clausen 1940/1962). It is thought that the mature larva persists until the
following season, because some individuals that had emerged from host pupae
during June did not pupate by August.
In the field, the pupae work their way to the soil surface just before
they emerge as adult flies. The pupal
shells were observed in large numbers in the field, each standing upright
with its posterior end held in the burrow by the caudal fork and spines. Brauer (1883, 1884) concluded that the life cycle of Hirmoneura must cover two years just
as its host. Beetles lay their eggs
in late summer, with larval and pupal stages being completed by autumn of the
following year. Newly formed adults
hibernate in their pupal cells and then appear in the field in June of the
2nd year. Hirmoneura eggs hatch in July and early August. At this time no beetle pupae are
available, and thus they wait until the following May or June to
develop. If the protracted larval
diapause is normal, the 2-year cycle is obligatory; for larval development is
not completed until the season following oviposition, and the second winter
is then passed in the mature larval or pupal stage (Clausen 1940/1962). Brauer tried to determine how and when 1st instar larvae reach
their hosts. He noted that the in the
case of Anthrax sp. the 1st instar
larva enters the Agrotis larva and
then awaits its pupation before completing its own development. Also, Mantispa
hibernates in the first stage and then searches for the spider egg masses the
following spring. First instar larvae
of Hirmoneura were found to be very
long-lived, and Handlirsch (1882, 1883) found one that remained alive without
food from August 17th to October 29th.
This suggests the possibility of living overwinter in the free
condition, yet Clausen (1940) thought it more probable that they enter the
more mature beetle larvae during autumn, remaining inactive until after host
pupation in late springtime. In South America, Hirmoneura
exotica Wied. lays its eggs in the
tunnels of wood boring bees (Brauer 1883, 1884). Spencer (1931, 1932) observed the manner of oviposition of Parasymmictus clausus O.S. (= Rhynchocephalus
sackeni Will.). Females inserted their ovipositors in
holes and cracks of telegraph poles in which no borers of any kind were present. They remained in that position for an hour
or more. Circumstantial evidence
suggests that larvae of cerambycid borers of genera Asemum and Xylotrechus
are probable hosts. Stuardo (1935)
found females of H. articulata Ph. to oviposit principally
during late morning and early afternoon.
They were attracted only to poles or posts lacking bark, and the
ovipositor was inserted deeply into the crevices. While for one or more hours in that position, a female may lay
a mass of eggs exceeding 100. The behavior of lateral larval stages of two species that are
solitary internal parasitoids of locusts in South Africa (Potgieter 1929),
suggest that mature larvae of Symmictus
costatus Loew are on the ground
surface in association with Locusta
vardalina Wlk. nighttime resting
areas. An examination of living
parasitized locusts showed that the partly grown parasitoid larva fed only on
body fluids, with little injury to the host.
This was judged by the normal oviposition and development of the
female locust eggs. The Symmictus
larva leaves the dead host when mature, and burrows into the soil to 2.5-50.0
cm. Pupation takes place soon
thereafter if conditions are favorable, and the fly emerges ca. 14 days
later. However, mature larvae are
able to adapt themselves to adverse conditions by entering diapause
(Potgieter 1929). Diapause may
persist for 3.5 years, but normally the cycle is requires ca. one year
(Potgieter 1929). Trichopsidea ostracea Westw. in Australia is parasitic
in adults of the plague grasshopper, Chortoicetes
terminifera Wlk. Noble (1936) and Fuller (1938) published
notes on the immature stages. Larvae
are solitary, being found in the abdomen.
This parasitoid leaves the host while it is still alive, which differs
from Symmictus. The prepupal stage in soil extends over
several months, and the pupal stage lasts 3 weeks. Field parasitization was ca. 5%. For detailed descriptions of immature stages of Nemestrinidae
please see (Clausen 1940/1962). References: Please refer to <biology.ref.htm>, [Additional references
may be found at: MELVYL
Library] |