# The Current State and Future Potential of Microbial Control of Scarab Pests
## 6 Protozoa
### Gregarinasina  
Gregarines, sub-class Gregarinasina, are Apicomplexan protozoa that live as gut parasites of invertebrates, particularly arthropods and anneloids. It is not uncommon for an insect to be infected by multiple gregarine species. Approximately 500,000 gregarine species are estimated to infect cooleopteran hosts alone [187]. Gregarines exist in the environment as oocysts and are typically ingested by their hosts. The parasites grow in host intestinal epithelial cells and are released back into the environment as gametocysts, typically in the feces of the host, where they undergo gametogenesis and fusion to create zygotes that eventually develop into new oocysts. The two orders that are most relevant as scarab parasites are the Eugregarines and the Neogregarines. Eugregarines are the largest and most diverse order of gregarines, encompassing 27 families and at least 240 genera [188]. They routinely infect insects hosts and are the most common protozoa found in scarab species, where infection is typically associated with a reduction in fat reserves and failure of larvae to pupate [160]. _Euspora_ species have been documented to infect New Zealand grass grub (_E. zealandica_) and cockchafer (_E. fallax_) [189; 190]. _Stictspora_ species infect a wide range of grubs, including Japanese beetle, New Zealand grass grub (_S. costelytrue_), _Oryctes_ species (_S. kurdistana_), _Rhizotrogus_ and _Melolonthu_ species (_S. provincialis_) [156; 157; 158; 169; 168] and typically at high rates [156; 57; 159]. [PERSON] and [PERSON] [156] found _Stictspora_ in 36.1% of all Japanese beetle grubs collected in a Michigan study, making it the most common parasite found. [PERSON] and [PERSON] [70] also reported that 50-100% of Japanese beetle grubs collected in a Connecticut sample contained, what was believed to be, _Stictspora_[70]. An _Actinoccephalus_ species and an unidentified gregarine have also been documented in Japanese beetle [192], while other undescribed gregarines have been found in Asiatic garden beetle, oriental beetle, rose chafer (_Macodactylus subspinosa_), and Northern masked chafer [70]. _Didymophes_ species are found in _Geotrupe stercorarius_, _G. pyrenaeus_ (_D. paradoxa_), dune beetle (_Sisyplus schaefferi_) and European rose chafer (_Cetonia_ species) (_D. sisyphi_) [193], while _Monocystis_ and Pseudomonocystis hopliae_ are found in both cockchafer (_M. melolontha_) and monkey beetle (_Hoplia_ species) [177; 194; 195]. Neogregarinida is another gregarine order known to infect insect hosts. They have been studied most extensively in the boll weeevil (_Anthonomus grandis_) and the khapra beetle [196; 197; 198]. Of the 13 genera, only three are documented to infect scarabs [160]. The first is _Ophryocystis orycesi_, which was been found in rhinoceros beetle (_O. monoceros_) in Tanzania, where it infects the Malpighian tubules, causing hypertrophy and damage [199]. The other are species of the genus _Mattesia_, known to infect the New Zealand grass grub (C. zealandrica). These protozoa infect the fat body and can cause weight loss and larval mortality [200; 201]. _Aranciocystis mukarensis_ was also found infecting cereal chafer (_Anisoplia segetum_) in Turky [202]. Both species are transmitted by the ingestion of oocytes [160]. The potential use of neogregarines as biocontrol agents has been studied a little more extensively than the eugregarines, but this work is still in the early stages and not currently focused on any scarab species [203]. Although gregarines are commonly found infecting insect hosts, they're impacts on host survival and/or performance is usually limited and/or very slow-acting [204]. Due to this, epizootics are rarely observed, despite gregarines being persistent in insect populations. This low efficacy, along with a serious lack of information about host range and pathology, has limited the development of gregarines for insect biocontrol. However, given their ubiquity, future development is probative, and they may be particularly useful when combined with other microbial agents.