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DIPTERA, Bombyliidae (Westwood 1840) -- <Images>
& <Juveniles> Description &
Statistics
The predaceous habit of locust egg
capsules was first found by Riley (1880) in studies on the Rocky Mountain
locust. Many species are external
parasitoids of the larvae, prepupae and pupae of Hymenoptera (Apoidea,
Sphecoidea, Vespoidea and at times Tenthredinoidea and Ichneumonoidea) in
their cells or cocoons, and other species are parasitic externally on
coleopterous larvae or pupae in the soil (Meloidae, Cicindelidae and
Scarabaeidae). Some species attacking
locust eggs also develop on the pseudo nymphs of meloid species that are
predaceous on the same host stage. Villa alternata Say was reared both from noctuid and tenebrionid
pupae. Anastoechus mylabricida
Zack. was found to attack prepupae and pupae of Zonabris and at times the larvae of Carabidae and other
insects in the soil (Zackvatkine 1934).
Anthrax oophagus Par. attacks locust
eggs and Zonabris larvae and
pupae as well as occasionally developing as a secondary parasitoid through
other Bombyliidae. Systropus conopoides Kunckel and other Systropus spp. are solitary parasitoids of Eucleidae
larvae in their egg-like cocoons (Clausen 1940/62). Other species develop internally in larvae or pupae of other
Lepidoptera (Pyralidae, Noctuidae, Tortricidae and Tineidae), in larvae and
pupae of Coleoptera (Tenebrionidae), and in pupae of Diptera (Muscidae,
Tachinidae and Asilidae). Species that parasitized pupae of
Lepidoptera enter the active caterpillar while it is feeding. Anthrax
lucifer F. was reared from
pupae of Laphygma frugiperda S. & A. that had
developed from larvae collected and isolated when about half grown (Allen
1921). First instar larvae had thus
entered the caterpillars prior to that time, though extensive feeding and
development did not occur until after pupation. Baer (1920) believed that the young larvae enter the mature
maggots at the time when they have left their hosts and are entering the soil
to pupate. Clausen (1940) commented that
it is not yet established that these species are true internal parasitoids,
for they may feed externally on the pupa within the puparium. Hemipenthes sp. was found to be
hyperparasitic in Lepidoptera through some Ichneumonidae, from the cocoons of
which several species of that genus were reared. Clausen (1940) noted that there was doubt as to the true host
relationships. First instar larvae
may enter the body of the caterpillar hosts and thus gain access to
ichneumonid larvae, or they may attack the latter directly and only after the
cocoon has been formed. It seems that
the family as a whole can probably be regarded as ore beneficial than
injurious because of the extensive attacks of many species on egg masses of
Acrididae. Apart from the species
attacking Tenebrionidae, Scarabaeidae, Lepidoptera and Tenthredinidae and
those attacking Glossina,
the long list of hosts of the parasitic species consists of insects that are
themselves entomophagous in habit (Clausen 1940/62). Bombyliidae, are cosmopolitan but
are most common in the Mediterranean area.
There have been more than 2,508 species described as of 2000. They are usually robust and densely covered with fine hair, and
usually have wings that are clouded. Parasitic Bombyliidae are solitary
and most are ectoparasitic, although endoparasitic species are known. Also, there are both primary and
hyperparasitic species known. Host
preferences are exceedingly varied, though the species themselves are
confined within relatively narrow limits (Clausen 1940). A number of species are predators in egg
pods of Orthoptera. Bombyliids also
attack various Hymenoptera, including beneficial species, or they are
larval-pupal parasitoids of Lepidoptera.
Other species at times will attack hosts in other insect orders. Bombyliids have not been deployed
extensively in biological control.
There have been a few species used against grasshoppers, with little
success. Early information regarding
host preferences were given by Bezzi (1924) and Painter (1932). Adult bombyliid flies are most
often observed during periods of bright sunshine, although some species
prefer shady places. Almost all
species are flower feeders, subsisting on nectar and pollen, although several
genera lack functional mouth parts and probably do not feed. Oviposition.-- The
manner of oviposition varies among the species. Callistoma desertorum, which develops in
acridid egg pods, lays its eggs (80-100 at a time) in holes and fissures in
the soil (Zackvatkine 1931). This
species is capable of laying 1,600-2,000 eggs, however. Eggs of Cytherea setosa
Par. are laid in groups of 1-5 on the soil surface in shaded places, or in
crevices. Anthrax oophagus
Par. and A. jazykovi Par. oviposit similarly. Female Glossista
infuscata Meig. probably
inserts her eggs directly into the freshly formed egg pod (De Lepiney &
Mimeur 1930). Meilis (1934) recorded
that female Bombylius variabilis Lw. apparently
oviposits while in flight, merely touching the abdomen to the ground near an
ovipositing locust or newly formed egg pod. Species attacking hosts which are
contained in open burrows or cells seem to have developed a method of
oviposition which is considerably different from that of those species that
develop as egg predators. Female Bombylius major L. insert the egg into the entrance of a Andrena sp. nest during the
absence of the female bee (Dufour 1858).
Female B. fugax Wied. projects the egg
into the nest opening of Panurgus
sp. while the latter is in flight, the same behavior being shown in Hyperolonia morio F., when parasitizing Monedula sp. (Seguy &
Bandot 1922). The eggs of Villa sp., developing in cells
of solitary bees, are readily projected into glass vials buried in the soil
(Painter 1932). Larvae.-- The
young larva in searching for a host has not far to seek as the egg is usually
deposited in the host's vicinity.
Such larvae are well equipped for movement in the soil and have little
difficulty reaching hosts. Species
developing as predators in locust egg capsules are usually solitary, although
some are gregarious. In B. variabilis Lw., after consuming one egg mass the larva
searches in the soil for a second mass.
Such species as A. trifasciata Meig. (Fabre 1886),
developing on larvae of the mason wasps, have to penetrate an exceedingly
hard cell well to reach the host.
Those attacking parasitic Hymenoptera seem to have to make their way
into the cocoon (Clausen 1940/62).
Larvae mature quickly after feeding begins on inactive host
stages. The larva of A. anale first attaches itself to the thoracic venter of a
3rd instar Cicindela larva
(Shelford 1913). A thickened
chitinous ring is formed around the feeding incision, and growth is slight
until the host forms its pupation cell, which may be 8 months after the
parasitoid larva has attached. From
then onward, development is rapid.
Larvae of Exoprosopa fasciata Macq. (Richter &
Fluke 1935), parasitizing Phyllophaga
pupae, attach themselves to
the pupa's venter. Sparnopolius fulvus Wied. is occasionally
found parasitic on grubs of the same genus (Clausen 1940/62). Young larvae of Spogostylum delita Lw. (Niniger 1916),
developing in cells of Xylocopa,
are frequently found in the cells even before host eggs have hatched. They may wander about over the food for a
month or more, feeding voraciously, before quieting down, during which period
very little growth occurs. A definite
feeding position is ultimately taken on the 3rd or 4th abdominal segment of the
bee larva, and the body contents are then consumed in ca. 5 days. First instar larvae of B. pumilis also feeds on food material stored in the cell of
the host, Colletes daviesana Smith (Clausen
1940/62). Pupation and Adult Eclosion.-- Pupation
sites differ considerably among species, being dependent on the kind and
stage of host attacked. Larvae that
develop in acridid egg capsules consistently leave the capsule and form a
pupal cell in the soil at some distance away. Larvae of Systoechus
albidus Lw. burrow downward
8-20 cm. in compact soil and form a distinct cell (Potgeiter 1929). A.
anale on Cicindela larvae and E. fasciata on Phyllophaga
pupae pupate in the host pupation cell.
Species that are externally parasitic on larvae of solitary bees,
sawflies and wasps, pupate within the host cell or cocoon, and those on or in
Diptera do so within the puparium.
Internal parasitoids of pupae of Coleoptera and Lepidoptera transform
within the host's pupal shell (Clausen 1940/62). Prior to adult eclosion, there is
a period of pronounced activity of the pupa, the purpose of which is to free
it from any covering or enclosing wall and to permit the adult fly to emerge
directly into the air. Species found
in soil come to the surface after traversing 1 m. or more of soil, and at
least the anterior portion of the body protrudes from the burrow before the
adult fly emerges. Pupae contained in
cells or cocoons must cut an opening equal to their body width, which
involves repeated body rotations to rasp away a hole large enough to permit
complete or partial extrusion. Those
pupating within the pupal remains of the host rupture the body wall ventrally
in the thoracic region before escaping.
Those contained in puparia either force off the operculum or cut away
a portion of the puparial wall. In
every case, repeated bending and twisting of the abdomen causes the head
crown of the pupa to penetrate the soil or rasp away the cocoon or cell wall
in its path (Clausen 1940/62). Systropus conopoides emerging from eucleid cocoons, has pupae that
can fill their digestive tubes with air, thus inflating the body in an aid to
emergence (Kunckel d'Herculais 1905).
Such inflation is not associated with a dilation of any part of the
tracheal system, and it gives the body greater leverage within the confined
space of the cocoon, and pressure is essential to the efficient use of the
specialized cutting structure on the head (Clausen 1940/62). The adult fly emerges from the pupal skin
through a longitudinal split along the dorsum, and this is done rapidly. The time elapsing between the cessation of
movement of the pupa of Thyridanthrax
lloydi Austen and the flight
of the fly is only 2-3 minutes (Clausen 1940/62). Life Cycle
Life cycles in
Bombyliidae of temperate regions generally take a full year. In tropical species this may be only two
months. Adverse environmental
conditions, such as a lack of moisture, profoundly influence development of
many species, causing them to enter diapause for long periods. Mature larvae of Systoechus albidus
were kept in dry sand for 4 years, after which completion of development and
emergence quickly followed when sufficient moisture was provided (Potgieter 1929). The incubation period has been
determined in Bombylius fugas as 8-12 days. However, in Anastoechus mylabricida
Zack. (Zackvatkine 1934) the egg persist through winter. The larval feeding period represents only
a very small portion of the entire cycle.
In Hyperalonia the
consumption of the mature Pseudagenia
larva is finished in 3-4 days, followed by a resting period of 5-6 days. Hyperalonia
oenomanus takes 5-8 days for
feeding. However, in most other
species a much longer feeding period exists, ca. on month in S. albidus and ca. 7 seeks in Spogostylum delila
Lw. Copello (1933) found that the 1st
instar larva of Hyperalonia morio reaches its Monedula host in late autumn,
feeds only slightly until spring, and then rapidly consumes the prepupa the
following spring. The winter is
passed as 1st instar larvae in B.
variabilis, B. pumilis and Hyperalonia
sp., but most species hibernate as mature larvae. However, the 2nd instar larva of Anthrax anale
is found in winter (Shelford 1913). The pupal stage lasts from a minimum of 7-9 days in Systoechus albidus to just lest of on month in H. oenomaus,
with 12-16 days as normal for most species.
Occasionally individuals of a few species hibernate as pupae (Clausen
1940/62). Parasitization
Rates.-- Field parasitization rates can be high, indicating a
considerable degree of natural control effectiveness. In those species which attack hosts in
soil, the condition of the soil seems to be the main factor governing
effectiveness. High mortality may
prevail in one locality, while in another there may be hardly any attack at
all. Usually the range of the
parasitic or predaceous species is more restricted than that of the host. Among species attacking egg pods of
Acrididae, Glossista infuscata Meig. destroys up to
85% of eggs of Dociostaurus macroccanus Thbg. in Morocco
(Lepiney & Mimeur 1930), while Zackvatkine (1931), as a result of
observations on several species in Turkestan, estimated that ca. 20% are
destroyed each year by Callistoma
desertorum and up to 40% by Cytherea setosa Par.Potgieter (1929) noted finding 1,143 larvae of Systoechus albidus in 1-sq-yd, which contained more than 100 egg pods
of Locustana. A large number of larvae may develop in
each egg mass. Wilson (1936) found 62.4%
of Camnula pellucida Scudd. egg pods
destroyed by Aphoebantus hirsutus Coq. This species and most others attacking
similar hosts are solitary. All eggs
in the cluster may not be consumed, but those remaining do not hatch, because
of desiccation and disease. In areas
with heavy attack by Aphoebantus,
the leafhopper emergence the following spring was very low. This predator is very scarce in arid
sections with sparse vegetation (Clausen 1940/62). When attacking other groups of
hosts, the parasitoid population also may be quite high, as revealed in the
55-65% parasitization of the cocoons of Tiphia
sp. by H. oenomaus in India (Clausen
1928b) and 18-25% of the pupae of Laphygma
frugiperda by Anthrax lucifer in the southern United States. Parasitization of the larvae of Monedula surinamensis is high among those which mature during
December to February (Copello 1933). For detailed descriptions of immature stages, please
see Clausen (1940). = = = = = = = = = = = = = = = References: Please refer to <biology.ref.htm>, [Additional references
may be found at: MELVYL
Library] Brooks, ?. 1952.
Canad. Ent. 84: 357-73. Cole, F. R. 1969. The Flies of Western North America. Univ. Calif.
Press, Berkeley & Los Angeles.
693 p. Hesse, A. J.
1938. Ann. So. Afr. Mus.
34: 1-1053. Hesse, A. J.
1956. Ann. So. Afr. Mus.
35: 1-464. Painter, R. H. 1932.
Lingnan Sci. J. 11: 341-74. |