Pediobius foveolatus
A small black wasp, 1–3.5 mm long, that lays its eggs inside Mexican bean beetle larvae. About 25 wasp larvae feed inside each host, which stops eating, dies and turns into a brown mummy; the next generation then comes out and hunts for more larvae. The wasp comes from India and cannot overwinter in the US, so it has to be bought and released every summer, timed to the first egg hatch. The New Jersey Department of Agriculture rears it and sells it outside the state, and UMass Extension reports a good record in the mid-Atlantic and New England.
At a glance
- Mode
- Gregarious parasitoid — ~25 wasps per host
- Rate
- Home garden: 10–15 mummies minimum
- Field rate
- 160–640 mummies/acre, split over two releases
- Ships as
- Mummies (parasitised larvae) or adult wasps
- Timing
- Two releases in consecutive weeks from first egg hatch
- Winter
- Killed by frost; release again each year
How it works
The female wasp stings a Mexican bean beetle larva and lays eggs under its skin. The wasp larvae feed inside it, and the beetle larva stops feeding and dies. About a week after the sting it has turned into a brown mummy, and 10–14 days later a new batch of adults comes out — about 25 from each mummy — to search for more larvae (New Jersey Department of Agriculture). The sources differ on which larvae to aim for. UMass Extension says the wasps will lay in larvae of any size but advises targeting the newly hatched ones, to get control before the damage is done; the New Jersey laboratory's instar guide says the wasp is most effective at killing the larger instars.
Because it comes from India and cannot survive a US winter, the wasp has to be brought in every year. The sources describe it parasitising the larvae only, so a release has to land when larvae are present. The New Jersey laboratory recommends two releases, in consecutive weeks, starting at the beginning of egg hatch (as reported by UMass); UMass suggests two or three releases at 7–10 day intervals where beans are sown in succession. UMass treats the first bean planting as a 'nurse crop' where the wasps build up, and reports that control continues and gets better as the season goes on and later plantings are protected.
Is it established?
A working release shows as mummies: brown, dead beetle larvae stuck under the leaves. Look for them from about a week after the wasps went out.
- DAYS 2–3Adult wasps emerge from the shipped mummies and start searching
- ABOUT 1 WEEKParasitised beetle larvae stop feeding and turn into brown mummies
- 2–3 WEEKSNew wasps come out of the mummies, about 25 from each, and look for more larvae
- AFTERThe wasps carry on into later bean plantings; control improves through the season
Release & handling
Mummies usually arrive in a screen bag, and adults emerge within two to three days. Secure the bag to the underside of a bean leaf in the patch you want to protect. Arbico's instructions are to use the shipment within 18 hours and, if you cannot release at once, to keep it somewhere cool and out of direct sun. Order ahead: the New Jersey laboratory caps orders per location each week, and supply runs out.
Time it to egg hatch
Scout for yellow-orange egg clusters under the leaves. If in doubt, release as soon as you see eggs — waiting for larvae can mean playing catch-up (UMass).
Mummies or adults
Mummies when you see adults, eggs or young larvae; adult wasps when older larvae are already feeding (New Jersey laboratory).
Bag under a leaf
Secure the screen bag of mummies to the underside of a bean plant, out of direct sun.
Keep the first planting
UMass calls the first bean planting a 'nurse crop': the wasps build up there and go on to protect later sowings.
Pesticide sensitivity
UMass Extension warns that insecticides used against Mexican bean beetle and potato leafhopper can harm the wasp, adults especially. Avoid spraying shortly before or after a release, and treat any succession planting at least 5 days before the wasps go out. Check a product →
When to choose something else
The wasp is a summer, timing-dependent tool. Something else is the better answer when:
- You have a few plants and few beetles — row cover from planting, or crushing eggs and beetles by hand, is cheaper and needs no timing
- There are no beetle eggs on the plants yet — the wasp parasitises larvae, so wasps released long before the hatch have nothing to attack
- You cannot order in time — releases need to coincide with the first egg hatch, and suppliers cap orders and run short
- The pest is actually bean leaf beetle, which is not among the wasp's listed hosts — check for the black triangle at the top of the wing covers
Where to buy
Suppliers listed alphabetically, not ranked. helpfulbugs takes no commission and does not sell insects. Availability was checked on 23 September 2026.
- Arbico Organics20 / 80 mummies — listed as unavailable until further noticeUS
- New Jersey Dept. of Agriculture, Phillip Alampi Beneficial Insect Lab20 mummies (max 4 units per location per week); 1,000 adults (max 2,000 per location per week)US
Pediobius foveolatus by target
Rate and timing differ by what you are releasing it against. Each page below is the program for one pest.