Hyperparasite

The most common examples are insects that lay their eggs inside or near parasitoid larvae, which are themselves parasitizing the tissues of a host, usually the larvae of another insect.

A well-studied hyperparasitic species is the small white butterfly (Pieris rapae), a serious horticultural pest of Brassica species such as cabbage and Brussels sprouts. Its larvae are parasitized by the larvae of the wasps Cotesia glomerata and C. rubecula, both of which are in turn parasitized by the wasp Lysibia nana.^[5][6]

Plants may defend against herbivory by emitting volatile compounds. The volatiles attract parasitic wasps that in turn attack the herbivores. Hyperparasitoids are known to find their victims through herbivore-induced plant volatiles emitted in response to attack by caterpillars that in turn had been parasitized by primary parasitoids. The larvae of parasitic wasps developing inside the caterpillar alter the composition of the oral secretions of their herbivorous host and thereby affect the cocktail of volatiles the plant produces.^[7]

Hyperparasites are not limited to insects. There are parasitic flatworms that are parasitic on crustaceans, which are themselves parasites on fish. An example is the monogenean Cyclocotyla bellones, found on Ceratothoa parallela, a cymothoid isopod parasite of the sparid fish Boops boops.^[8]

There are levels of parasitism beyond secondary parasitism, especially among facultative parasitoids. Three levels of parasitism have been observed in fungi: a fungus (Rhinotrichella globulifera) on a fungus (Gen. Hypomyces) on a fungus (Fomes hemitephrus) on a tree.^[9]

Hyperparasites can control their hosts' populations, and are used for this purpose in agriculture and to some extent in medicine. Damage caused by chestnut blight (Cryphonectria parasitica) in American chestnut trees can be contolled with CHV1 virus, and bacteriophages can limit bacterial infections. It is likely, though little researched, that most parasitic (disease-causing) micro-organisms have hyperparasites which may prove useful in both agriculture and medicine.^[10]

Hyperparasitism is to an extent analogous to predation on herbivores, which in turn eat plants, as there are three trophic levels involved. However, hyperparasites are smaller than predators, breed more rapidly than their hosts and are generally found in larger numbers. In the case of micro-organisms, hosts can sometimes clear their infection. Hyperparasitism may thus behave differently from three-level predator-prey systems where predators can exert control of prey populations. However, given the differences between hyperparasites and predators, their effects may need to be modelled differently.^[10]

Jonathan Swift refers to hyperparasitism in these lines from his poem "On Poetry: A Rhapsody":^[11]

So nat'ralists observe, a flea
Hath smaller fleas that on him prey;
And these have smaller fleas to bite 'em.
And so proceeds ad infinitum.

• Hyperparasitoid