Blattisocius cakmaki n. sp. (Acari: Mesostigmata: Blattisociidae), a mite invading phytoseiid mass-rearing, with a key to the world Blattisocius species

Blattisocius cakmaki Khanjani and Safiarian n. sp. is described from specimens infesting colonies of the predatory mite Neoseiulus californicus (McGregor) in Hamedan, Iran, raising the number of known Blattisocius species in the world to 20. Both sexes are described and illustrated. Key diagnostic characteristics of females include: a reticulate dorsal shield, with 18 podonotal and 15 opisthonotal pairs of setae; a ventrianal shield with three pairs of pre-anal setae; peritreme, extending only to the anterior margin of coxa III; fixed cheliceral digit short (≈18 µm), toothless, with a robust pilus dentilis; and movable digit with four teeth. Males also with 18 podonotal and 15 opisthonotal pairs of setae, ventrianal shield with six pairs of pre-anal setae, and peritrematic plate with a short structure external and parallel to the proximal part of the peritreme, with multiple transverse ridges. This new species has been a major obstacle to the mass production of N. californicus in Iran, as it voraciously feeds on eggs and larvae of the predator, leading to rapid extinction of the colony. The species is compared with the morphologically similar B. tarsalis (Berlese, 1918), which primarily differs by featuring three teeth on the female movable cheliceral digit and by not having the short structure external to the base of the male peritreme. This is the sixth Blattisocius species recorded from Iran. A key to the known world Blattisocius species is included.