HD - Superparasitism of Aprosthema tardum larvae by Terozoa quadridens

Terozoa quadridens Perkins, 1961 (Hymenoptera: Ichneumonidae, Tryphoninae) superparasitises two fifth instar larvae of Aprosthema tardum (Klug,1814)(Hymenoptera: Tenthredinoidea, Argidae)
Between 20 and 24 June 2019, the ectoparasitoid Terozoa quadridens monitors two Aprosthema larvae, feeding on a same plant. The wasp hoovers around them without parasitizing.
On 24 June, by late afternoon, the larvae are about to moult into fifth instar and have no external eggs.
25 June 2019, around 10:30 a.m, the two larvae have moulted into fifth instar. Terozoa quadridens carefully approaches one of the Aprosthema tardum larvae. This Aprosthema larva already has three typical Terozoa quadridens external eggs, like little antennae, on its head and therefore must have already been parasitized earlier in the morning.
Although Aprosthema larvae with two or more external eggs have regularly been found, it is not clear why this superparasitism occurs. The wasp approach the larva and parasitizes it a fourth time.
Superparasitism is remarkable because only one parasitoid larva can survive on one host larva. It is not clear whether these eggs are from the same female or from different females. When the eggs are deposited by the same female, it is called self-superparasitism.
Definition of 'superparasitism'
Superparasitism - the parasitiod deposit one or more eggs on a host already parasitized by a different member of the same species.
Self-superparasitism - the same parasitoid deposit two or more eggs on a host on which only one parasitic larva can survive.
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Shaw, M.R., Kan, P., Kan-van Limburg Stirum, B. & Wahl, DB. (2022) - Biological and morphological studies on the parasitoids (Hymenoptera, Ichneumonidae) of Aprosthema tardum (Klug) (Hymenoptera, Argidae, Sterictiphorinae) in Var, southern France. Journal of Hymenoptera Research.
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