The preservation of infective spores of Octosporea muscaedomesticae in Phormia regina,of Nosema algerae in Anopheles stephensi,and of Nosema whitei in Tribolium castaneum by lyophilization

Infective spores of three species of microsporidia were subjected to the lyophilization process by employing varying media as cryoprotectants. The infectivity of the lyophilized spores was then tested against a standard fresh spore preparation in the appropriate host insect. Spores of Octosporea muscaedomesticae served as an experimental model and were rendered noninfective in host Phormia regina (Calliphoridae: Diptera) after lyophilization with the following cryoprotective agents: skim milk (12%), ascorbic acid (5%) combined with thiourea (5%), glycerol (10%), mesoinositol (5%), and equine serum. Spores of O. muscaedomesticae lyophilized or vacuum-dried in 50% sucrose as well as in the hosts' tissues remained highly infective for as long as 2 years at a dose of 10⁶ spores/fly and a trial length of 12 days. At a dose of 5 × 10⁴ spores/fly there was a slight decrease in infectivity of the spores which had been lyophilized in the host's abdomen after a 2-year storage period compared with that of fresh, nonlyophilized spores. Naked spores of Nosema algerae suspended in 50% sucrose and lyophilized produced infection in 50% of the host population of Anopheles stephensi (Culicidae: Diptera) compared with 70% infection produced by fresh non-lyophilized spores. Spores of Nosema whitei lyophilized within its host larva Tribolium castaneum (Tenebrionidae: Coleoptera) remained 100% infective at a dose of 5 × 10⁵ spores/gram diet. It is concluded that an aqueous solution of 50% sucrose and/or the host's tissues are excellent protectants for the cryogenic or vacuum-drying process of the above-named spores, and their protective function may apply also to other microsporidian species.