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HYMENOPTERA, Miscogasterinae (Pteromalidae) (Chalcidoidea) -- <Images> & <Juveniles> This subfamily was originally considered a separate family
Miscogasteridae. It is a small family
with species of Tomocera, Scutellista, Aphobetoideus and Anysis
that are predators on the eggs of lecaniine Coccidae. Miscogaster
is an internal parasitoid of the larvae of leaf-mining Agromyzidae, and Megorismus is parasitic in Aphididae,
and several genera are known from Hymenoptera. Some species of Dinarmus
are known as solitary external parasitoids of the larvae of Tephritidae. Host preferences are varied, and host
relationships include a wide range extending from predation on eggs and
larvae of other insects to true internal and external parasitism. Miscogasteridae are closely related to the
Pteromalidae. Scutellista cyanea Motsch. has been used in
biological pest control. This
parasitoid was originally introduced from Italy to Louisiana in 1898 to
combat Ceroplastes and from South
Africa to California in 1901 for biological control of black scale, Saissetia oleae Bern. Establishment
occurred in some areas, and although the parasitoids became abundant, there
was very little reduction in the host population density because the
parasitoid larvae did not consume the entire batch of eggs beneath the host
and thus a number of survivors remained to infest trees. In California S. cyanea has largely
replaced Tomocera californica How., which had similar
habits and which previously had effected about the same degree of natural
control. Biology & Behavior
Scutellista cyanea is predaceous on eggs of
various lecaniine Coccidae contained in the cell beneath the parent female's
body. When eggs are unavailable, the
larva is able to develop as an external parasitoid of the female scale. Preferred hosts are Saissetia oleae and Ceroplastes rusci L., although occasionally Coccus and Phenacoccus,
etc. are utilized. During host selection the female shows a preference for mature
females, usually those which have just laid a portion or all of their
eggs. The scale is first examined
with the antennae until the posterior arch is found, after which the position
is reversed and the ovipositor is inserted by a backward thrust through the
arch. Sometimes eggs are laid under
scales from which all young have already emerged and also under those which
have just completed the second molt and are without eggs. Normally the parasitoid eggs are found
among those of the host, where they may be distinguished by their larger size
and white color as compared to the pinkish host eggs. If no host eggs are present, the
parasitoid egg adheres to the scale's ventral portion. On hatching the young larva begins feeding on host eggs. At maturity a pupation cell is formed among
the mass of empty eggshells and debris.
The debris is matted together with small amounts of silk, which
strands also bind the inner edge of the scale to the substratum. The meconium is case and pupation
occurs. At emergence the adult
parasitoid cuts a circular opening in the dorsum of the dead host, similar to
but larger than those of true internal parasitoids. Old parasitized scales may adhere closely and remain on the
tree longer than unparasitized scales.
They may persist for 2-3 years.
The life cycle is about 41 days, of which 4-6 days are required
for egg incubation, 15-21 days for the larval stage and 15-20 days for the
pupa. Newly transformed adults may
remain under the scale for several days before leaving. Scutellista's seasonal
cycle is correlated with the host. In
areas of California where the host has a distinct annual cycle, the
parasitoids are abundant only during June and July, for there is no suitable
alternate host available in sufficient abundance to maintain a high density. Optimum conditions for the parasitoid
require a continuous supply of maturing scales, condition which is approached
only in coastal areas. There is no
definite hibernation stage in California, and development continues, although
at a reduced rate, through winter. In
Italy there are ca. 5 generations each year, the first being on Ceroplastes and the remaining four on Ceroplastes, Philippia and Saissetia. On small Saissetia
females, that can produce 500 eggs, a single parasitoid larva may consume the
entire lot, thereby being able to halt reproduction. However, in large scales, which may
deposit 2,500 or more eggs, only a portion can be consumed by a single
parasitoid larva. Thus, control is
considerable greater on small than large hosts (Clausen 1940/1962). There are distinct biological forms which are not easily
transferable from one host to the other.
In Australia, the parasitoid attacks only Saissetia, while the African form is on Ceroplastes. The first
introduction into the United States was of the wax-scale form from Italy to
Louisiana, while the California introductions were of the black scale form
from South Africa. Both of these
hosts are heavily attacked in Italy, although it is not known if there are
distinct parasitoid forms present. Behavior of other Miscogasteridae that attack coccids is similar
to that of Scutellista cyanea. Tomocera californica (Smith & Compere 1928)
on the same host sometimes oviposits through the posterior arch and other
times around the periphery of the scale.
Like Scutellista the larva
is able to develop as an external parasitoid of the female scale if eggs are
unavailable. Aphobetoideus comperei
Ashm. inserts the ovipositor underneath the lateral scale margin (Smith &
Compere 1928). Miscogaster sp. in
France develops as a solitary internal parasitoid of the larvae of Agromyza mining the leaves of alfalfa
(Parker & Thompson 1925). The
ovipositor is inserted through the leaf surface and into the body cavity of
the host. The tip of the egg stalk
remains fixed in the puncture in the host integument, but the larva does not
maintain a connection with it after hatching. The behavior of immature stages of Systasis dasyneurae
Mani differ in several respects from those of other Miscogasteridae by being
predaceous on 2nd instar larvae of the midge, Dasyneura lini Barnes
in linseed buds in India (Ahmad & Mani 1939). Eggs are deposited singly within the crumpled and unopened
flower buds containing well developed midge larvae, although not always in
their immediate vicinity. The newly
hatched larva is active and in most cases quickly finds the midge
larvae. The predators requires 3-4
midge larvae to complete development, but if more are present all are killed,
although they are not completely consumed.
Pupation is within the bud, and the cycle from egg to adult is 25-32
days at 18°C. For descriptions of immature stages of Miscogasteridae please see
Clausen (1940/1962). References: Please refer to
<biology.ref.htm>, [Additional references may be found at: MELVYL Library] |