Ovavesicula popilliae (Microsporidia: Ovavesiculidae) spore production in naturally infected adult Japanese beetles (Coleoptera: Scarabaeidae)

Gradual Decline of Japanese Beetle (Coleoptera: Scarabaeidae) Populations in Michigan Follows Establishment of Ovavesicula popilliae (Microsporidia)

The purpose of this research was to document the incidence of Japanese beetle, Popillia japonica Newman (Coleoptera: Scarabaeidae), infection by the microsporidian pathogen, Ovavesicula popilliae Andreadis & Hanula (Microsporida: Pleistophoridae) while monitoring Japanese beetle populations at nine golf courses in Michigan from 1999 to 2018. We also compared the current distribution of the pathogen in Michigan to the known distribution in 1999. Beetles were sampled a total of seven different years, in three time periods: 1999-2000, 2005-2007, and 2015-2018. At these nine golf courses, O. popilliae infection rates of adults increased from 0.39% in 2000 to 29.5% in 2018, while Japanese beetle adult populations declined 73.2%, and Japanese beetle larval density declined 78.6% (from 1999 to 2018). In previous research, larval infection rates averaged at least twice the infection rates of adults, because all infections originate in the larval stage, and at least 75% of infected larvae die before pupation. This means that an adult infection rate of 29.5%, combined with previously observed 50% reductions in egg production by infected females, are consistent with the observed population declines. The current distribution of O. popilliae in southern Michigan was determined by sampling Japanese beetle larvae and adults at 38 sites in 2017 and 2018. Ovavesicula popilliae was found at 21 of 38 sites and in 16 of 21 counties, compared with two sites in one of 16 counties when it was first detected in Michigan in 1999 and 2000.

Geographic distribution of Ovavesicula popilliae in the United States and sensitivity of visual diagnosis compared with qPCR detection

The Japanese beetle (Popillia japonica) is one of the most destructive invasive pests in North America, causing significant economic impact to many fruit crops, turfgrass and the nursery industry. A microsporidian pathogen of Japanese beetle, Ovavesicula popilliae, discovered in 1985, proliferates in the Malpighian tubules of larvae and adults, disrupting waste-removal, mineral filtering, and fluid balance in heavily infected individuals. Most infected larvae do not survive from fall to spring, and egg production by infected females is reduced by 50%. Ovavesicula popilliae is promising as a classical biological control agent for Japanese beetle, but outside of surveys completed in Connecticut and Michigan little is known about its geographic distribution in North America. The objective of this research is to obtain a better understanding of the distribution of O. popilliae in North America. Japanese beetles were collected at 59 locations in a total of 19 different states in the USA for pathogen analysis. Overall, the proportion of Japanese beetle adults infected by O. popilliae was much greater in Michigan, Ohio, Tennessee and four states in the northeastern USA compared with sites located west of the Mississippi River (18.6 ± 13.3% and 0.6 ± 1.2%, respectively). Nucleotide sequences of the gene encoding a small subunit of nuclear ribosomal RNA (ssrDNA), obtained from GenBank for O. popilliae was used to develop a highly specific qPCR test for O. popilliae DNA. A subsample of 110 individual Japanese beetles were visually diagnosed first, then analyzed via qPCR. Visual diagnosis and qPCR detection agreed for 80.9% of the beetles tested. The qPCR assay is more sensitive than visual diagnosis (56 visually positive, 73 qPCR positive), is highly specific for O. popilliae, and will be useful for detecting the pathogen in large batches of beetles, or in beetle frass.

Survival of Japanese beetle, Popillia japonica Newman, larvae in field plots when infected with a microsporidian pathogen, Ovavesicula popilliae

Japanese beetle, Popillia japonica Newman, is an important invasive pest that causes significant damage to golf courses, blueberries, raspberries, hops and many other crops and ornamentals in the eastern United States. This study was conducted to determine the survival of Ovavesicula popilliae-infected larvae compared with uninfected larvae from October to May. Larvae were collected from two sites, one where O. popilliae was active and one where it had not yet been detected. Larvae were placed into plastic sleeve-pots containing 15 cm-diameter cores of turfgrass with roots and soil intact. Larvae collected from both locations were put into sleeve-pots at both locations to account for soil and site factors. Results of this experiment in both years confirm that Japanese beetle larvae infected with O. popilliae do not survive well from October to May. We estimate that at an epizootic location where the pathogen has been active for several years, at least 76.5% of the Japanese beetle larvae infected in October do not survive until May. When the observed amount of population reduction (27-29%) due to natural pathogen infection of larvae in our field plots is combined with a 50% reduction in eggs produced by infected females as previously reported, annual population declines due to O. popilliae would average 40% (assuming a typical adult female infection rate of 25%). This rate of population reduction is consistent with previous reports of Japanese beetle population decline over a period of several years at O. popilliae epizootic sites.

Ultrastructural characterization of Pleistophora macrozoarcidis Nigerelli 1946 (Microsporidia) infecting the ocean pout Macrozoarces americanus (Perciformes, Zoarcidae) from the gulf of Maine, MA, USA

Pleistophora macrozoarcidis a microsporidian parasite infecting the muscle tissue of the ocean pout Macrozoarces americanus collected from the Gulf of Maine of the Atlantic Ocean, MA, USA, was morphologically described on the basis of ultrastructural features. Infection was detected as opaque white or rusty brown lesions scattered throughout the musculature of the fish mainly in the region anterior to anus. Transmission electron microscopy showed that in individual parasitized muscle cells, the infection progresses within parasite formed vesicles which are in direct contact with muscle cell elements. The earliest observed parasitic stages are the globular multinucleated proliferative cells or plasmodia limited by a highly tortuous plasmalemma with intervesicular finger-like digitations projecting into the parasite cytoplasm. These cells divided through the invagination of the plasmalemma and the amorphous coat producing daughter-cells. Fine electron-dense secretion is deposited on the plasmalemma that causes its thickening which is a sign of commencement of the sporogonic phase. This phase is carried out by cytokinesis of the sporonts and results in the formation of sporoblasts and finally spores. Mature spore has a thin electron-dense exospore, a thick electron-lucent endospore, and the plasma membrane which encloses the spore contents. A single nucleus is centrally located with the posterior region containing a posterior vacuole. The majority of spores have 7-13 coils in 1-2 rows, and a small group of spores had about 23 coils forming two rows. Events of polar filament extrusion for penetration of uninfected cells were studied. The polaroplast membranes were expanded and occupy most of the length of the spore. The coils are dislocated from the sides of the spore to throughout the entire sporoplasm. The polar filament everts and extrudes through the polar cap with a sufficient force to pierce adjacent sporophorous vesicle walls. After eversion, the polar filament is referred to as a polar tubule, as it forms a tube through which the sporoplasm travels. It pierces anything in its path and deposits the sporoplasm at a new location to begin another infective cycle.

Multilamina teevani gen. et sp. nov., a microsporidian pathogen of the neotropical termite Uncitermes teevani

A new genus and species of microsporidia is described from adults of the termite Uncitermes teevani (Emerson) (n. comb., formerly Armitermes teevani), collected in Ecuador. Masses of elongate, ovoid, uninucleate spores were localized to the coelomic cavity of adult workers and measured 6.29×3.33μm (fresh) and 5.83×3.00μm (fixed). These spores were individually contained within a multi-layered sporophorous vesicle and contained an isofilar polar filament with 24-28 coils. Blast-n analysis revealed that the small subunit ribosomal DNA (ssrDNA) sequence of this new species exhibited 85% identity with that of a Varimorpha species from the fire ant, Solenopsis richteri, and slightly less (78-85% identity) to a large clade of microsporidian parasites from mosquitoes and microcrustacea. The morphological and sequence data support the conclusion that Multilamina teevani gen. et sp. nov. is a novel microsporidium and distinct from any previously described genera or species.