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COLEOPTERA, Rhipiphoridae (Reitter 1911) -- <Images>
& <Juveniles> Description & Statistics
Adult beetles are rather striking with a markedly streamlined
body, pectinate male antennae, but the color pattern of many species is
variable. Females of Macrosiagon pusillum Gerst. may be completely red or black, or the thorax may
be of one color and the elytra and abdomen of the other. Silvestri (1905) described the genus Rhizostylops as having certain
characters and habits that seem to place it as an intermediate form between
Rhipiphoridae and Strepsiptera, and the adult females bear a striking resemblance
to those of the genera Mengenilla
and Eoxenos of Strepsiptera. Adult females of Rhizostylops as well as those of several species of Ripidius are apterous, degenerate and
larviform (Clausen 1940/62).
All species seem to be parasitic, passing at least a portion of the
larval period internally in the host body.
This adaptation is virtually unknown elsewhere in the Coleoptera. Development is accompanied by a hypermetamorphosis
that is comparable with that in Meloidae and certain parasitic Staphylinidae. Most Rhipiphoridae seem to attack larvae of Hymenoptera
in families Andrenidae, Scoliidae, Vespidae and Tiphiidae. Those most often encountered belong to the
genera Metoecus, Ripiphorus, and Macrosiagon. Rather extensive
parasitization of scoliid and tiphiid larvae in cocoons has been observed on
several occasions. In India, Tiphia pullivora A. & J., 28.4% of field collected cocoons yielded Macrosiagon pusillum adults.
Generally all representatives of the family developing on Hymenoptera
are harmful (Clausen 1940/62). This is a small, cosmopolitan family with over 200
species known. Characters include a
serrated female antenna, male antenna pectinate or flabellate, 11-segmented
in both sexes; humpbacked, wedge-shaped beetles; pronotum large, distinct,
narrowed anteriorly; tarsal formula 5-5-4; elytra entire; abdomen with 5
visible sternites, blunt at apex. The
maxillary palps are 4-segmented; labial palps 3-segmented; legs slender;
trochantin absent. In some species
females are apterous and larviform. All known species are solitary parasitoids during their
immature stages. Most attack larvae
of Hymenoptera in the family Andrenidae, Vespidae, Tiphiidae and Scoliidae. Some parasitize adult and nymphal
cockroaches. Both primary and
hyperparasitic species are known.
First instar larvae are phoretic.
Larvae under hypermetamorphosis.
Cockroach parasitoids are internal, while those species parasitizing
Hymenoptera are internal only during the 1st instar. Adults are free-living. Biology & Behavior
Ripidius spp.
departs from the normal behavior for the family, both in host preferences and
in relationships. Ripidius pectinicornis Thbg. was originally described as early as 1808, as
a parasitoid of Blatella germanica L. under the name of Symbius blattarum Sund. by Sundervall in 1831 (Clausen 1940). Mature larvae were found in the bodies of
cockroaches on a ship, and adult females were observed to lay their eggs
abundantly. Stamm (1935, 1936)
extended studies on the behavior and larval forms of this species. Schultze, cited by Clausen (1940) recorded
rearing R. scutellaris Hell. from Blattidae in the Philippines, and R. boissyi
Abeille is parasitic in nymphs of Ectobia
in Europe. The whole genus seems
restricted to Blattidae. It is also
distinguished in habit from those developing on larvae of Hymenoptera, by
passing its entire larval period within the host. R. pectinicornis is gregarious, with 1-5
developing in each host, while those on Hymenoptera are consistently
solitary. Extensive observations have been made on Metoecus paradoxus L., which is common in Europe as a parasitoid of Vespa spp. larvae. The parasitic relationship was recognized
early in 1864 by Westwood (cited by Clausen, 1940). Chapman (1870, 1891, 1897) first thought this species was a
commensal in the nest. Murray
(1870a,b) agreed with the conclusions of Westwood. Rouget (1873) obtained oviposition in the laboratory and
thought that under field conditions the eggs are laid on blossoms, foliage,
etc., and that the young larvae are then carried to the nest by Vespa adults. Chapman later found the much distended 1st
instar larva, 10X their original length, within the bodies of the host
larvae, just beneath the integument of the 4th of 5th segment. Only a part of the 1st stage is passed
internally, and the 2nd instar larva is found as a collar encircling the
cervix of the host. Reproductive capacity of Rhipiphoridae is relatively
high, which is expected because of a high mortality in the 1st larval
stage. Chobaut (1891) noted that the
female of Macrosiagon flabellatum F. lays ca. 500 eggs, and
Silvestri recorded ca. 3,000 for R.
inquirendus Silv. Eggs are usually laid in clusters, with
the site of oviposition being variable.
M. flabellatum lays its eggs in clusters in the soil, covering them
lightly with earth. jarvis (1922)
found that M. cucullatum Macl. laid the eggs close together among the hairs on
the undersides of the leaves of Urenia
and Ficus. Over 100 were found on a single leaf,
covering an area of ca. 9-10 sq-cm. Metoecus paradoxus lays the eggs in crevices in decaying wood. Ripiphorus
subdipterus Bosc. was found to
oviposit in the blossoms of Eryngium
(Chobaut 1906), and R. solidaginis Pierce does so in the
green buds of goldenrod, Solidago rigida (Pierce 1904). There are numerous adaptations correlated
with the location of the host stages and with the habits of the host adults
in case the latter serve as carriers of the triungulinids. In no case were eggs found to be placed on
or in close proximity to the host stages on which development of the larva
occurs (Clausen 1940/62). Of particular interest is the manner by which the
triungulinids gain access to the host, because it involves transportation by
some agency from the vicinity of hatching to the host larvae in their
cells. It is believed that the
triungulinids themselves do not take an active search for either the host stages
or the carrier but rather that they take up a position favorable to contact
with a carrier and then wait for it.
Triungulinids of M. flabellatum attach themselves to Odynerus adults and are thus carried
to the nest (Chobaut 1906). Pierce
(1904) thought that the triungulinids of R.
solidaginis are carried by the Ripiphorus adults themselves, which
are thought to hibernate in the holes of Epinomia. This explanation is in view of the
occurrence of the triungulinids on opening buds of Solidago, a plant that is not frequented by Epinomia adults. However,
many of them were found on the bodies of bees of various genera living in the
Epinomia community. Triungulinids of R. subdipterus are
found on Eryngium blossoms and are
thought to attach themselves to Halictus
adults frequenting this plant (Clausen 1940/62). Macrosaigon cucullatum is parasitic on larvae of Campsomeris spp. in Australia.
The wasps are external parasitoids of scarab grubs in soil. Triungulinids of Macrosaigon are found on the foliage of certain trees and the
problem of reaching host larvae in the soil, which are themselves parasitic
and thus receive no attention from the parent females, is more complex than
that facing the species mentioned previously. Laboratory studies indicated that the triungulinids probably attach
themselves to the Campsomeris
females and are thus carried into the soil at the time the latter oviposit
and that at this time they transfer to the scarab grub and await the hatching
of the Campsomeris egg and its
subsequent development as a larva. One
triungulinid was found to remain motionless on an egg on a paralyzed grub for
3 days, during which it made no effort to pierce the chorion. Although development is completed only on
the mature larva in the cocoon, it is probable that the triungulinid attaches
itself to the partially grown larva or enters its body prior to cocoon
formation (Clausen 1940/62).
Triungulinids do not effect parasitization of scoliid or tiphiid
larvae after the cocoon has been spun. Among scoliid and tiphiid hosts of various
Rhipiphoridae, it is evident that if the triungulinids of the parasitoid are
carried into the soil by the females at the time of oviposition, the extent
of parasitization of the different species will vary greatly in the same
locality, due to diverse feeding habits of the adults. Scoliid females feed mainly at blossoms,
while the spring species of Tiphiidae feed almost exclusively on insect
honeydew and the summer and autumn species mostly on the secretions from
various nectar glands of plants. The
relatively high mortality of Tiphia
pullivora previously mentioned, is
possibly linked to a more general tendency to feed at blossoms than is shown
by other species in the field during the same season (Clausen 1940/62). A simple parasitic relationship in this family seems to
exist in respect to the Ripidius
species which attack nymphs and adults of cockroaches. In this genus the eggs are thought to be
laid indiscriminately in crevices, etc., and the triungulinids attach
themselves directly to passing hosts and enter the body to develop, thus
eliminating the requirement of a carrier. Triungulinids of all species are equipped with a caudal
sucker and 1-2 pairs of cerci of varying length which they use to assume an
erect position, with the legs entirely free, while waiting to attach to
passing insects, etc. They are
thought to have the jumping habit which is common to larvae of this kind. The fee-living phase of larval life may extend over a
considerable length of time, during which food does not seem to be
required. However, Pierce (1904)
believed that the triungulinids of Ripiphorus
solidaginis fed on the plant
tissues or sap of Solidago soon
after hatching. He based this
conclusion on (1) that they are of considerably greater size than the egg,
and (2) that they are found only on Solidago,
which is not frequented by host bees.
It was assumed that this plant was utilized in preference to others,
in order to fulfill these food requirements.
A transitory plant feeding habit such as this is not in accord with
the habits of larvae of this type, and the evidence presented does not
definitely establish its occurrence.
The increase in size may possibly have been the result of imbibing moisture
from the leaf surface (Clausen 1940). With exception of Ripidius
pectinicornis and Ripidius spp. which pass the entire
larval feeding period within the cockroach host, all known species develop
externally, having an internal phase only in the 1st stage. Sometimes this internal period is short,
but in M. flabellatum, entry into the Odynerus
larva occurs during late summer, and the parasitoid larva does not emerge for
external feeding until the following June.
The developmental cycle and larval habits are comparable to those of
certain Perilampidae, in particular species with hyperparasitic habits. Usually the host larva is not killed until
it has completed feeding and it prepared to pupate. The cells containing parasitized Vespa larvae and those of
other host groups of similar habit as well are thus closed in the normal
way. In the case of Scoliidae and
Tiphiidae, the cocoons are spun before death (Clausen 1940/62). Transition from internal to external feeding has been
observed in Macrosiagon flabellatum and Metoecus paradoxus
(Grandi 1937). In the former species,
the greatly distended triungulinid, which is several hundred times as large
by volume as when newly hatched (see Clausen, 1940 for diagrams), emerges
through a puncture in the 3rd thoracic segment of the host, immediately casts
it exuviae, which remains in the puncture, and then assumes the feeding
position in which it is found as a collar around the 1st or 2nd thoracic
segment (see Clausen, 1940 for diagram).
The triungulinid increases in length from 0.5 mm. at hatching to 2.5
mm. just prior to the first molt. The
host larva is eventually consumed. Life Cycle
Most species of Rhipiphoridae seem to have only one
generation per year, which is closely correlated with the cycle of the host. Ripiphorus
solidaginis overwinters in the
adult stage and lays eggs early in springtime, with the adult stage attained
again in August (Pierce 1904).
However, Metoecus paradoxus lays its eggs in late
autumn, and the fully developed embryo persists in the egg until
springtime. Macrosaigon flabellatum
lays its eggs in late summer, and overwinters as 1st instar larvae within the
body of Odynerus larvae. M.
pusillum is thought to have the
same hibernation habit, for adults emerge from Tiphia cocoons during July.
Barber (1939) discussing observations of J. C. Bridwell on Ripiphorus sp., parasitic on Augochlora pura Say, mentioned that the triungulinids are found attached to
the hairs of hibernating inseminated female hosts. They overwinter in this way, on the hibernating female bee, and
transfer to her brood cells when these are formed in spring. R.
solidaginis is believed to have 2
generations annually; Ripidius pectinicornis, developing in
cockroaches in the tropics, probably has a short cycle, with several
generations each year (Clausen 1940/62). In M. flabellatum and M. cucullatum, the
incubation period i 17 and 7.5 days, respectively. Larval feeding of Metoecus
paradoxus covers only 12-14 days. For detailed descriptions of immature stages of Rhipiphoridae,
please see Clausen (1940/62). References: Please refer to
<biology.ref.htm>, [Additional references may be found at: MELVYL
Library] Linsley, E. G. & J. W. MacSwain. 1951.
Bull. Calif. Ins. Surv. 1:
79-88. Linsley, E. G., J. W. MacSwain & R. F.
Smith. 1952. Univ. Calif. Publ. Ent. 9: 291-314. Selander, R.
B. 1957. Ann. Ent. Soc. Amer. 50: 88-103. |