# The Current State and Future Potential of Microbial Control of Scarab Pests
## 5 Fungi
### Microsporidia  
Microsporida are spore-forming unicellular parasites that were once classified as Protozoa but are now placed in the Fungi kingdom. Despite this, their biology and morphology are largely unlike most fungi. Microsporida persist in the environment as resistant spores, and once ingested by a host, the spore contents are inserted into gut epithelial cells through a polar filament. Vegetative growth occurs within the host cells and eventually infective spores develop. Often times, spores will move to other parts of their host, as certain species are often associated with specific tissues [143; 144]. Microsporida, as a phylum, infect a wide range of organisms, from protists to vertebrates, but are often species-specific [144; 145]. Infection gradually wears down the host and death takes a long time to occur. Several entomopathogenic microsporidia are known to infect coleopteran, dipteran, hypmenopteran, lepidopteran, and orthopteran species around the world [146]; however, only one species, _Paranosema locustae_, is currently registered as a microbial pesticide for grasshoppers ([PERSON], 1981). Only six microsporidian species have been documented to infect scarabs: _Nosema costelytrae_[147], _N. takapanensis_[147], and _Vavraia oncoperea_[148; 149; 150; 151], found in the New Zealand grass grubs (_C. zealandica_), _Pletsophora tanzaniae_ in coconut beetle (_Orytetes monoceros_) [152], _N. meloonthae_ in the cockchafer (_Meloontha meloontha_), [153; 154], and _Ovavesicula popilliae_ in Japanese beetle [57; 155; 156; 157; 158; 159]. The two _Nosema_ species found in _C. zealandica_ infect the fat body, causing developmental delays and larval mortality [147]. _V. onocoperae_ infects muscle tissue but is also found in several other tissues, including the Malpighian tubules, gut caecae, nerves, and gonads; however, the pathology is not well-understood [147; 160]. _P. tanzaniae_ was infects midgut epithelial cells in the coconut beetle, but again, information about its transmission and pathology are lacking [152; 160]. _O. popilliae_ is the only microsporidian known to infect Japanese beetle and has been detected in populations throughout the U.S. but is most common in the Northeast and Midwest [159; 161]. _O. popilliae_ is multi-sporous species that infects the Malpighian tubules. When _O. popilliae_ spores are ingested by larvae they infect midgut cells and eventually move to the hindgut, where they produces sporophorous vesicles that disrupt mineral reabsorption, waste-removal, and fluid balance. Spores are largely spread through frass. Larval infection increases overwintering mortality by as much as 100% [162] and reduces egg production by as much as 50% [157]. Research on _O. popilliae_ has increased over the last decade, improving our understanding of its distribution and potential use as a biocontrol agent for Japanese beetle, which is the most damaging scarab pest in the U.S. The fact that microsporidia must be produced in vivo, limits its potential for commercial formulations. They also slow-acting. Due to these factors, microsporidia are most appropriate for long-term biocontrol in areas where species can become established in the soil. _Nosema_ species have also been implicated in natural epizootics in grass grub and locut populations [150; 163]. For scarabs, natural epizootics of _O. popilliae_ have been reported to diminish local populations [164]. Although spores of some _Nosema_ species can persist for ~300 days under optimal temperature conditions [165], spores generally do not do well outside of hosts. As a result, horizontal and vertical transmission are key to the persistence of microsporidia. The inoculative release of _Nosema portugal_ to control spongy moth (_Lymantria dispar_), formerly gyppsy moth, was reported to persist in the population for ~1 year due to vertical and horizontal transmission [166]. _N. locustae_ and _Perezia dichrolusae_ have also been consistently documented in the same Argentinian grasshopper populations for nine years in some cases [163].