Aphid Complex

Over many decades, studies of hyperparasitism have been conducted on the primary parasitoid microwasps in the Hymenoptera that attack the Hemiptera in the suborder Sternorrhyncha, and in particular the superfamily Aphidoidea, with special emphasis on the family Aphididae. The aphid-primary parasitoid-hyperparasitoid food web has been used as a model system in community ecology partly because of the economic importance of aphids as worldwide pests on a variety of agricultural crops and forests, but also because of the relative ease of rearing aphids, their primary parasitoids, and hyperparasitoids in the laboratory and/or greenhouse for precise behavioral and ecological studies. Primary aphid parasitoids are found in only two families of Hymenoptera: all genera of the Aphidiidae (Braconidae: Aphidiinae), and the Aphelinidae (Aphelinus and related genera). These primary parasitoids of aphids are in turn attacked by many genera of hyperparasitoids in three hymenopteran superfamilies such as Chalcidoidea (Pteromalidae: Asaphes; Encyrtidae: Syrphophagus; Eulophidae: Tetrastichus), Cynipoidea (Alloxystidae: Alloxysta), and Ceraphronoidea (Megaspilidae: Dendrocerus).

Aphid hyperparasitoids can be divided into two categories based on adult ovipositional and larval feeding behaviors:

FIGURE 1 Female ovipositional behavior of four genera of aphid hyperparasitoids. (A) Endophagous koinobiont Alloxysta victrix jumps on a live parasitized aphid and deposits her egg internally inside the primary parasitoid microwasp larva while the aphid is still alive, but before mummy formation. (B) Ectophagous idiobiont Asaphes lucens stands on top of a dead aphid mummy, drills a hole, and deposits her egg externally on the surface of the primary parasitoid larva developing inside the mummy. (C) Ectophagous koinobiont D. carpenteri stands on the leaf, backs into the dead aphid mummy, drills a hole, and deposits her egg externally on the surface of the primary parasitoid larva developing inside the mummy. (D) and (E) "Dual ovipositional" behavior of endophagous koinobiont S. aphidivorus. (D) Syrphophagus stands on top of a live parasitized aphid and deposits her egg internally inside the primary parasitoid larva while the aphid is still alive, but before mummy formation. (E) Syrphophagus stands on top of a dead aphid mummy, drills a hole, and deposits her egg internally inside the primary parasitoid larva developing inside the mummy. [Reprinted from Sullivan, D. J. (1988). Aphid hyperparasites. In "Aphids, Their Biology, Natural Enemies and Control" (A. K. Minks, and P. Harrewijn, eds.), Vol. 2B, 192, with permission from Elsevier Science.]

1. The female wasp of endophagous species such as Alloxysta (Charips) victrix (Fig. 1A) deposits her egg inside the primary parasitoid larva while it is still feeding on and developing inside the live aphid, but before the aphid has become mummified (a mummy is the hardened exoskeleton of the dead aphid that remains attached to the leaf). Being a koinobiont hyperparasitoid, the larva usually does not hatch until after the mummy has been formed by the primary parasitoid larva. Then the hyperparasitic larva feeds internally on the primary parasitoid larval host.

2. The female wasp of ectophagous species such as Asaphes lucens (Fig. 1B) and Dendrocerus (Lygocerus) carpenteri (Fig. 1C) deposits her egg on the surface of the primary parasitoid larva after the aphid has been killed and mummified. To do this, the female must first drill a hole in the mummy in which to deposit her egg. Then the hyperparasitic larva feeds externally on the primary parasitoid larva while both are still inside the mummy. The venom of species varies such that Asaphes is an idiobiont, whereas Dendrocerus is a koinobiont. An unusual species is Syrphophagus (Aphidencyrtus) aphidivorus, whose females display a "dual ovipositional" behavior by attacking primary parasitoid larvae within both living aphids (Fig. 1D), and also inside dead aphid mummies (Fig. 1E). Either way, S. aphidivorus develops as an endophagous koinobiont hyperparasitoid.

However, in all species of aphid hyperparasitoids, further development is similar to that of primary parasitoids, such that pupation is also inside the dead aphid mummy. Then the single adult hyperparasitoid emerges by cutting a hole in the dorsum of the mummy. After pulling itself out, the new adult male or female is ready for mating. From the time of the female's attack on the primary parasitoid larva/pupa, the period of hyperparasitoid development from egg deposition to adult emergence varies with different hyperparasitoid species from as short as 16 days to 25 or more.

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