Mattesia oryzaephili (Neogregarinorida: Lipotrophidae), a Pathogen of Stored-Grain Insects: Virulence, Host Range and Comparison with Mattesia dispora

The neogregarine, Mattesia oryzaephili (Neogregarinorida: Lipotrophidae) has only been reported from the sawtoothed grain beetle, Oryzaephilus surinamensis. The pathogen's presence in cadavers of the rusty grain beetle, Cryptolestes ferrugineus, in collapsed colonies prompted studies of its potential to control stored-product insects. Respective mortality rates in fourth instar C. ferrugineus and C. pusillus were 15.3 and 17.7% at 10² oocysts/g of diet and 89.4 and 80.5% at 10⁵ oocysts/g. The mortality of fourth instar O. surinamensis exposed to 10⁵ oocysts/g was only 12%. For C. ferrugineus larvae, there were no significant differences in mortality and infection between exposure to Mattesia dispora and exposure to M. oryzaephili (P>0.05), but for C. pusillus larvae, both responses were significantly higher for M. oryzaephili than M. dispora. Adult C. ferrugineus and O. surinamensis were similar in their responses to M. oryzaephili, with mortality not exceeding 20%, but differed in their responses to M. dispora, with O. surinamensis being more susceptible. The median lethal doses for larval Mediterranean flour moths, Ephestia kuehniella, were 7.9×10⁷M. oryzaephili oocysts/g of diet and 2.7×10³M. dispora oocysts/g of diet. In single dose assays of M. oryzaephili physiological host range, greater than 75% infection was achieved for Rhyzopertha dominica and Plodia interpunctella. More than half of oocysts germinated during passage through the guts of susceptible and resistant insects. Second and third instar Galleria mellonella were highly susceptible to M. oryzaephili infection, but fifth instars were not. Infection percentages in fifth instars exposed to 10⁶ oocysts/g were significant only when boric acid or the stilbene, Blankophor®RHK were incorporated into the diet. Host range and general morphology confirm the identity of Mattesia oryzaephili.