Bacillus thuringiensis tenebrionis
The strain of Bacillus thuringiensis that kills beetle larvae rather than caterpillars. It is the Bt for Colorado potato beetle. Like other Bt strains it must be eaten. The larvae stop feeding within hours and die over the next two to five days, and the first and second instars, under about ¼ inch, are the ones it kills well. Its labels cover larvae only; for adult beetles they call for a contact insecticide. The catch for gardeners is supply. Novodor FC is still EPA-registered and on its maker's product list, but it is a farm product dosed in quarts per acre and sold through farm distributors. Trident, which has a home-garden label, is still registered, but UMass Extension reported it off the market in 2022.
At a glance
- Mode
- Stomach poison — must be eaten by the larva
- Label rate
- Novodor FC 1–3 qt/acre on young larvae; 3–4 qt with older ones
- Target stage
- 1st–2nd instar, under ¼ in
- Speed
- Feeding stops within hours; death in 2–5 days
- REI / harvest
- REI 4 h; exempt from tolerance, and the Trident label allows use up to the day of harvest
- Availability
- Farm pack only (Novodor FC); no home product on sale
How it works
Bt tenebrionis (listed in some papers as B. thuringiensis subsp. morrisoni strain tenebrionis) makes a crystal protein that is activated only in the gut of certain leaf beetle larvae. The Novodor label lists two targets, Colorado potato beetle and elm leaf beetle. A larva feeding on a treated leaf swallows the protein, its gut is paralysed, and it stops feeding within hours and dies in two to five days. Because it has to be eaten, coverage matters. Both labels target the larvae only. When adults are present, or the population is mostly older larvae and adults, the labels call for a fast-acting contact insecticide.
Timing is everything. The Novodor and Trident labels both say to start at the first egg hatch, because it works best on first and second instars. Kentucky Extension puts the cut-off at larvae under ¼ inch. In USDA field plots, two weekly applications of Novodor gave 50–85% control of larvae within 14 days. Adding Beauveria bassiana gave a small extra kill. The Trident label says the bacterium also works on beetles resistant to chemical insecticides. That matters because, as Kentucky Extension puts it, Colorado potato beetle is notorious for rapidly developing resistance to insecticides used repeatedly.
Applying it
The figures below come from the Novodor FC label (EPA Reg. 73049-48) and the maker's product page. The Trident home-garden directions (EPA Reg. 70051-120) are given for anyone holding old stock.
Spray at first egg hatch
Start when the first orange egg clusters hatch, while larvae are under ¼ in. Scout afterwards and reapply as new larvae appear.
1–3 qt per acre (Novodor)
2–3 qt for heavy infestations of young larvae, 3–4 qt when older larvae are mixed in. At least 20 gal of water per acre from the ground.
½ cup per gallon (Trident)
The Trident home label mixes 4 fl oz per gallon and repeats every 7–14 days while larvae are hatching. UMass Extension reported the product off the market in 2022.
Keep it cool
Novodor: store at 40–50 °F for stability, avoid long spells above 90 °F, and do not keep the diluted spray more than 72 hours.
Not while bees are foraging
The Trident farm label warns it may be toxic to bees exposed to direct treatment. Do not spray while bees or other pollinators are visiting the crop, and keep it out of ponds and streams.
When to choose something else
Bt tenebrionis does one job: it kills young Colorado potato beetle larvae that eat treated leaves. Choose something else when:
- You have a garden-sized planting — no home pack is on sale, so hand-pick adults and larvae, which Kentucky Extension encourages, and crush the egg clusters under the leaves
- The beetles are adults or big larvae — the labels call for a fast-acting contact insecticide instead
- The pest is a caterpillar, such as a hornworm — use Bt kurstaki
- Your tomatoes are past 8 inches tall — Kentucky Extension says beetle feeding on larger tomato plants does not reduce yield
Where to buy
These are the Bt tenebrionis products registered with EPA whose labels we checked, as of 23 September 2026. They are not ranked. helpfulbugs takes no commission and does not sell either one.
- Novodor FC, Sumitomo BioRational / Valent BioSciences (EPA Reg. 73049-48)Flowable concentrate, sold through farm distributorsUS · FARM
- Trident, Certis USA (EPA Reg. 70051-120) — registered; reported off the marketHome-garden and farm labels; not currently soldUS · HOME
Bacillus thuringiensis tenebrionis by target
Rate and timing differ by what you are releasing it against. Each page below is the program for one pest.