Dissected larvae revealed infections with pathogens. Fat body and hemolymph of the larvae were full of oocysts (Figs. 1 and 2). The oocysts were navicular in shape and possessed plugs at the two poles (Figs. 2 and 3). Typical fresh navicular oocysts of the pathogen were 14.23 ± 0.85 (12.14–16.18) μm in length and 7.63 ± 0.71 (5.89–8.49) μm in width (n = 50). Oocysts stained with Giemsa stain (Fig. 3) measured 12.88 ± 0.67 (11.70–14.18) μm in length and 6.58 ± 0.46 (5.89–8.49) μm in width. Polar plugs were recognizable by light and electron microscopy (Figs. 3, 4, and 5). The oocyst wall was quite thick, measuring 460 to 560 nm. Each oocyst contained 8 sporozoites (Figs. 6 and 7). Infective forms of the neogregarine and the sporozoite were observed freely in the hemolymph (Fig. 2). Occasionally in addition to neogregarine stages, yet undescribed polyhedral inclusion bodies of a nuclear polyhedrosis virus (NPV) were seen on ultrathin sections (Fig. 6).
The results show that the described neogregarine had the typical characteristics of members of the genus Mattesia (Family Lipotrophidae: order Neogregarinorida (Apicomplexa)). It closely resembles Mattesia dispora, which had already been recorded from the host E. kuehniella and was the type species of the genus Mattesia. Morphology and ultrastructural characteristics of the presented neogregarine looked very similar to the life cycle stages depicted by Weiser (1954), Žižka (1978), and Valigurova and Koudela (2006). In detail, the oocyst size matches quite well, being 12.1–16.2 × 5.9–8.5 μm in the present Mattesia, while it was 11.5–14 × 6.5–7.5 μm in Weiser’s study (1954). The infection sites (hemolymph and fat body) and the host species (E. kuehniella) were the same in the present study and Weiser’s (1954) and Valigurova and Koudela’s (2006) studies.
In the present study, occurrence of the neogregarine pathogens in the larvae, pupae, and adults of E. kuehniella in the laboratory populations was reported for 2 years following each other. Totally, 538 larvae, 20 pupae, and 63 adults were examined for the presence of the neogregarine pathogen, total infection occurred as 66.98%. Infection rates were 57.06% for larvae, 85% for pupae, and 3.17% for adults. The results confirm that the infected larvae and pupae could not reach adult stage mostly and the neogregarine pathogen was very effective on both stages.
In Turkey, the microbial control of E. kuehniella has been focused on the spore-forming bacterium, Bacillus thuringiensis (Azizoğlu et al. 2011b). There is no record on naturally occurring entomopathogenic protists of E. kuehniella in Turkey although several protists have been isolated from insects (Yaman et al. 2016 and 2019). The neogregarine presented here was the first one isolated from this pest in Turkey. Although neogregarines were found almost exclusively in insects (Lange and Lord, 2012), until today, there are only three neogregarine records from insects in Turkey, i.e., from Dendroctonus micans (Coleoptera: Curculionidae) (Yaman and Radek 2015) and its specific predator, Rhizophagus grandis (Coleoptera) (Yaman et al. 2012). Two of these neogregarine isolates could be identified as the genus Mattesia (Yaman and Radek 2015), and the third was Menzbieria chalcographi (Yaman et al. 2012). Neogregarines may disperse extensively in the host populations. A high dispersal potential is very important for the biological control of insect pests (Pereira et al., 2002). The genus Mattesia includes several pathogens of major pests, such as the well-studied M. dispora and M. grandis. M. trogodermae has a great potential as a suppressive agent for dermestid beetles, which are also pests of stored products (Lange and Lord 2012).