Survey Of Insect Taxa Displaying Type I Hypermetamorphosis

Neuroptera

Only the Mantispidae have true hypermetamorphosis. Most of the species feed on spider eggs associated with a single egg sac. The first instar either enters a previously constructed egg sac or attaches onto a female spider and enters the sac as she constructs it. Other species feed on the larvae of various aculeate Hymenoptera. Several of these are phoretic and reach the food source by attaching to the adult bee or wasp.

Lepidoptera

The only lepidopteran family with hypermetamorphosis is the Epipyropidae. This group is parasitic on various Homoptera, a unique association for the generally phytophagous Lepidoptera. The active first instar seeks out a host and the grublike instars that follow occur on the body of a single homopteran.

Coleoptera

Hypermetamorphosis occurs in several families of beetles. Most are parasitoids of other insects. The larvae of Bothrideridae, and a few Carabidae and Staphylinidae, attack the larvae or pupae of other coleopterans or dipterans. The genus Sandalus (Rhipiceridae) feeds on cicada nymphs. All are hypermetamorphic to some degree, with active and relatively long-legged planidia followed by short-legged, grublike feeding instars.

Hypermetamorphosis perhaps is best known in the Meloidae and Rhipiphoridae. Most meloids parasitize grasshopper eggs or, more commonly, the larvae and provisions of soil- or wood-nesting bees. The planidia of several groups are phoretic on adults of their hymenopteran host. There are four distinctive larval types in the typical meloid life cycle: planidium, first grub, coarctate, and second grub (Fig. 1). The planidium (Fig. 1a) encounters the food source. The first grub (Fig. 1b), consisting of four instars, is the primary feeding stage. The coarctate (Fig. 1c), a quiescent instar, is adapted for overwintering or aestivation. The second grub (Fig. 1d) is a nonfeeding instar that precedes pupation. Each has a distinct phenotype, the most unusual being the immobile coarctate with its thick, highly sclerotized cuticle, aborted appendages, closed mouth and anus, and vestigial musculature.

The Rhipiphoridae include parasitoids of immature Hymenoptera (Rhipiphorinae) and Blattodea (Rhipidiinae). The planidia of Rhipiphorinae are phoretic on adults of their host. After being carried to the host nesting cells, they burrow into the body of the host larva, eventually molting into a grub that emerges to feed externally. The planidia of Rhipidiinae attach directly to their cockroach host and eventually molt into a legless and amorphous larva, which enters the host to feed. The last instar regains poorly developed legs, exits the host, and moves away for pupation.

Among nonparasitoid groups of Coleoptera, hypermeta-morphosis is known to occur in one genus of Eucnemidae (Rhacopus) and in the Micromalthidae. The larvae of both groups feed in decaying wood and have a planidial-like first instar. The single species of Micromalthidae, Micromalthus debilis, has perhaps the most complicated life cycle known in insects, with several distinct morphological and reproductive types of larvae. Hypermetamorphosis has also been reported in the Megalopodidae.

Strepsiptera

The Strepsiptera parasitize Thysanura, Orthoptera, Hemiptera, Diptera, and Hymenoptera. The free-living planidium encounters the host. If parasitic on a hemimetabolous host, the larva may immediately penetrate its body and develop. Those parasitizing Hymenoptera are phoretic and are carried to the nesting site, where the immature stages are attacked. The planidium molts into an endoparasitic legless grublike larva, which may have several instars. This secondary larva lacks mouthparts and feeds by diffusion through the cuticle. Male Strepsiptera are free living; females are neotenic and most remain on their host.

Diptera

Hypermetamorphosis is known in the Acroceridae, Nemestrinidae, most Bombyliidae, and some Tachinidae. All have legless, well-sclerotized, and active planida that search for the host, followed by soft-bodied maggotlike larvae. The Acroceridae are internal parasitoids of spiders. The Nemestrinidae are endoparasites of grasshoppers and beetles. The Bombyliidae are parasitoids of immature Lepidoptera, Hymenoptera, Coleoptera, Neuroptera, and Diptera; some prey on grasshopper eggs. They are either endo- or ectoparasitic.

Hymenoptera

A legless planidial larva (Fig. 2a) is known in three families of Hymenoptera: Perilampidae, Eucharitidae, and Ichneumonidae (Euceros). It is followed by a soft-bodied, relatively immobile larva. The Eucharitidae are endoparasitic on mature larvae or pupae of ants and are phoretic. Eggs are laid on vegetation. The planidia of most groups attach to worker ants and are carried to the nest, where they transfer to larvae for feeding. The Perilampidae is a closely related family, similar bionomi-cally to the Eucharitidae but known to parasitize several orders of insects. In the Ichneumonidae, the planidium of E. frigidus attaches to the integument of sawfly larvae and eventually transfers to feed on the larva of other ichneumonid species that are primary parasites of the sawfly.

See Also the Following Articles

Host Seeking, by Parasitoids • Larva • Metamorphosis • Phoresy

Further Reading

Clausen, C. P. (1940). "Entomophagous Insects." McGraw-Hill, New York. Clausen, C. P. (1976). Phoresy among entomophagous insects. Annu. Rev.

Entomol. 21, 343-368. Crowson, R. A. (1981). "The Biology of Coleoptera." Academic Press, London.

Hagen, K. S. (1964). Developmental stages of parasites. In "Biological Control of Insect Pests and Weeds" (P. H. DeBach and E. Schlinger, eds.), pp. 168-246. Chapman & Hall, London. Snodgrass, R. E. (1954). "Insect Metamorphosis." Smithsonian Miscellaneous

Collections, 122 (9). Smithsonian Institution, Washington, DC. Stehr, F. W. (ed.) (1991). "Immature Insects," Vol. 2 (see Chaps. 33-35, 37). Kendall Hunt, Dubuque, IA.

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