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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 18C.


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]