Nosema locustae (Paranosema locustae)
A single-celled parasite, a microsporidian, sold as wheat-bran bait for grasshoppers. A grasshopper that eats the bait is infected. The spores multiply inside it, and it slows down, eats less and may die weeks later. It was first registered in the US in 1980, and EPA found it harmless to people, birds, fish and honeybees. The catch is the evidence. It works only on young nymphs, it is slow (the labels give 2–6 weeks before deaths begin), and it does not infect all species equally. UC IPM says it is not likely to be effective in California home gardens. In a 2019 University of Wyoming lab trial it killed no grasshoppers on its own within 14 days. Nolo Bait, the best-known brand, had its EPA registration cancelled at the maker's request in December 2025. Semaspore Bait remains registered.
At a glance
- Mode
- Microsporidian spores on bran — must be eaten
- Label rate
- 1 lb/acre; Nolo home label (cancelled) 5 tsp per 100 sq ft
- Active
- 0.05%, 1 billion spores per lb (labels)
- Target stage
- Nymphs, mostly ½–¾ in long
- Speed
- Deaths begin in 2–3 weeks (Semaspore) or 3–6 (Nolo)
- Evidence
- UC IPM: unlikely to work in home gardens
How it works
Nosema locustae, now often placed in the genus Paranosema, is a microsporidian, a spore-forming single-celled parasite. EPA's 2000 fact sheet classes it as a protozoan and notes it was then the only one registered as a pesticide. The products carry the spores on wheat bran. A grasshopper eats the bait, the spores become active in its gut, and the parasite multiplies. The Semaspore label says infected grasshoppers first weaken, move more slowly and eat less, and begin to die in about 2 to 3 weeks. The Nolo Bait label says 3 to 6 weeks. Uninfected grasshoppers eat the sick and dead ones and pick up a larger dose, so few dead grasshoppers are seen. The labels also claim that surviving females lay fewer eggs and that the pathogen can persist in a population for several years.
The independent evidence is thinner than the label. Colorado State says only young grasshoppers are susceptible, it cannot be used effectively once adults have migrated in, it is slow, and it does not infect all species equally. UC IPM is blunter. Because it acts slowly and only on certain species, it is not likely to be effective in California home gardens. A 2019 University of Wyoming and USDA trial fed treated bran to third-instar migratory grasshoppers. On its own, Nosema caused no deaths within 14 days in the lab, though it added to the effect of a fungal pathogen. A three-year study in China found the parasite persisting for up to two years in treated and neighbouring untreated areas, with grasshopper numbers falling in both. Taken together, it is a slow, area-wide tool for rangeland and cropland, not a rescue for a vegetable bed that grasshoppers fly into from next door.
Applying it
The bait is live spores on bran, so it does not keep. It goes on the ground where the young nymphs are hatching, not onto food crops. The figures below come from the Nolo Bait (EPA Reg. 46149-2, 2023) and Semaspore Bait (EPA Reg. 54735-5, now 95566-1, 2008) labels.
Young nymphs, ½–¾ in
Apply when most grasshoppers are nymphs ½–¾ in long. Nolo's label says to use it at 8 or more grasshoppers per square yard.
Hatching beds and margins
Grassy, unbroken ground where nymphs are seen, and around the garden perimeter as a buffer. Do not let bait touch fruit or vegetables.
No rain for 8 hours
Semaspore: do not apply if rain is expected within 8 hours. Grasshoppers take the bait best on warm, bright mornings.
Cool, and use it fresh
Nolo: best at 42 °F, used within 13 weeks of formulation. Semaspore: refrigerating at 40 °F adds 30 days to the expiry date.
Pesticide sensitivity
EPA found that Nosema locustae does not harm mammals, birds, fish, aquatic invertebrates or honeybees. It does not infect or replicate in mammals or birds. The Semaspore label requires no restricted-entry interval; the Nolo Bait agricultural label set 4 hours. Check a product →
When to choose something else
Nosema bait is a slow, area-wide treatment for young grasshoppers, and the case for it in gardens is weak. Choose something else when:
- The grasshoppers are already adults. Colorado State says it cannot be used effectively once adults have migrated in
- You need the plants protected this season. Deaths begin weeks after feeding; use row covers or metal screening instead
- The garden is small and the grasshoppers come in from surrounding land. The bait treats where you spread it, not where they hatched
- You can keep poultry. UC IPM calls chickens and guinea hens excellent grasshopper predators, though they can also damage some garden plants
- You are in California. UC IPM says it is not likely to be effective in home gardens there
Where to buy
These are the registered products whose labels we checked. They are not ranked. helpfulbugs takes no commission and does not sell either one. Check the EPA registration is current before you buy.
- Semaspore Bait (EPA Reg. 95566-1, Organic Fanatics Biologics)1 lb, 5 lb, 50 lb (2008 label)US · REGISTERED
- Nolo Bait (EPA Reg. 46149-2, M&R Durango)Registration cancelled Dec 2025US · CANCELLED
Nosema locustae (Paranosema locustae) by target
Rate and timing differ by what you are releasing it against. Each page below is the program for one pest.