3.3.3. Hymenoptera

Few hymenopteran parasitoids of soil-inhabiting wireworms are known. For Europe, Subklew [106] lists records mainly of *Paracodrus apterogynus* (Proctotrupidae), but other *Proctotrupidae* and partly unidentified Hymenoptera also appear. *P. apterogynus* is a gregarious parasitoid with several individuals (Figure 4B), but a low percentage of males, emerging from a single wireworm [117]. Known hosts of *P. apterogynus* are *Agriotes obscurus, Agriotes lineatus*, and *Athous* sp. [113,117–120], indicating that different genera and species are attacked. Another species, *Pristocera depressa* (Bethylidae), is a solitary parasitoid of *Agriotes obscurus* [121] and perhaps further species. Females of *P. apterogynus* and *P. depressa* are wingless, indicating that both species search for their wireworm hosts underground. According to D'Aguilar [113], only five of several thousand *Agriotes* larvae from a site in Brittany (France) were parasitized. The parasitism rate seems to be similarly low in Germany, with only two of several thousand wireworms from all over the country being parasitized by a gregarious hymenopteran, most likely *P. apterogynus* (Lehmhus, unpublished). In a few cases, parasitoid Diptera larvae were also found [106,122]. Due both to the rare occurrence of insect parasitoids in economically relevant wireworms and to specific parasitoid biology, they are unlikely to be suitable for mass rearing and augmentative biocontrol.

**Figure 4.** Illustrations of wireworm biocontrol agents. (**A**) Mite infestation of an *Agriotes ustulatus* wireworm; it is unclear if these mites are parasitic or phoretic, but heavy infestations appear to affect wireworms negatively; (**B**) *Agriotes* sp. wireworm with gregarious hymenopteran parasitoid, most likely *Paracodrus apterogynus*; (**C**) *Agriotes sordidus* infested by the nematode *S. boemarei* (strain FRA48, Lee etal. 2009) carrying the symbiotic bacterium *Xenorhabdus kozodoii* FR48; and (**D**) *Agriotes lineatus* wireworm with *Metarrhizium brunneum* infestation. Photographs A, B, D: JKI.Photograph C: INRAE-DGIMI.
