Nosema

Nosema is a genus of microscopic, spore-forming parasites in the phylum Microsporidia. These obligate intracellular pathogens infect a broad range of invertebrate hosts, with insects being the most common hosts. The best known Nosema species affect honey bees, including Nosema apis and Nosema ceranae. Other species infect bumblebees (Nosema bombi), silkworms (Nosema bombycis), and, in some cases, grasshoppers (Nosema locustae), the latter used as a biological control agent.

Infection typically occurs when a host ingests environmental material containing spores. Inside the gut, spores germinate and inject the parasite’s contents into epithelial cells via a polar tube, initiating replication that produces meronts and eventually new spores. Spores shed in feces help spread the infection to other individuals or colonies.

Nosema infections in bees are collectively called nosemosis and can lead to decreased lifespan, reduced foraging efficiency, diminished colony growth, and, in severe cases, colony decline. Clinical signs in bees may be subtle, with dysentery or a mottled abdomen sometimes observed.

Diagnosis involves detecting Nosema spores in the gut or feces using light microscopy, often complemented by molecular methods such as PCR. Management focuses on improving overall colony health and sanitation, replacing contaminated combs, and reducing stressors. In some regions, chemical treatments such as fumagillin have been used, though their use is subject to regulatory and practical considerations. For pest management, N. locustae is deployed as a microbial control agent against grasshoppers.