Trichogramma spp.
Tiny wasps, 0.25–1 mm long, that lay their eggs inside the eggs of moths. The wasp larva eats the developing caterpillar, so the host egg turns black and never hatches. They are sold as parasitised eggs glued to cards, and released weekly while moths are flying and laying. Timing is the whole game: a release that goes out before the moths lay, or after the caterpillars have hatched, finds nothing to attack. Suppliers sell T. pretiosum, T. minutum, T. brassicae and T. platneri for different pests and regions.
At a glance
- Mode
- Egg parasitoid — kills the egg, not the caterpillar
- Size
- 0.25–1 mm
- Rate
- 50k–100k /acre weekly; 1–2 /ft² in gardens
- Ships as
- Parasitised moth eggs on cards, ~100k per card
- Emerges
- 2–5 days after arrival, by temperature
- Life cycle
- 7–14 days, egg to adult
How it works
A female Trichogramma finds a freshly laid moth egg and lays her own eggs inside it. Her larvae eat the embryo, pupate inside the shell and chew their way out as adults, about 7 to 14 days later in the growing season. The host egg darkens as the wasps develop, because parasitism changes the pigment of the shell. That black egg is the sign of success. Wasps leave a neat round exit hole, while a caterpillar leaves a ragged one. UF/IFAS reports, for one species (T. fuentesi), that females prefer young host eggs, and that mated females stop parasitising about five days into adult life and unmated females after about three. A short working life like that fits the advice to release again every week.
Four species are sold, matched to pests and regions. T. pretiosum is the warm-weather species for field, row and vegetable crops, and the one used against tomato fruitworm, bollworms and budworms. T. minutum, native to eastern North America, is sold for cabbage looper, grape berry moth and codling moth. T. brassicae, from Europe, is sold for European corn borer and caterpillars on cole crops. T. platneri, from western North America, is sold for codling moth and leafrollers in orchards. UC IPM counts successful programmes against tomato fruitworm in tomatoes, amorbia in avocado and codling moth in walnuts. But UC also warns that released parasites are not always effective, and UF/IFAS notes their effectiveness is still debated. We found no controlled trial in home gardens.
Is it established?
The evidence is in the moth eggs, not the caterpillars. Find eggs on the leaves before and after each release, and compare how many have turned black.
- DAYS 1–5Adults emerge from the card — two to five days, depending on temperature
- WITHIN A FEW DAYSMoth eggs near the release points turning black; UC IPM advises checking within a few days
- WEEKS 1–2Black eggs with round exit holes — a new generation of wasps has emerged
- EACH WEEKRelease again until moth trap counts fall; this is a repeated programme, not a single release
Release & handling
The wasps arrive as pupae inside moth eggs glued to perforated cards, usually about 100,000–125,000 eggs a card, split into 30 tabs. Tear the card into tabs and hang them through the crop so the wasps are spread out. Suppliers disagree about holding the cards. Buglogical and Arbico want them warm, 80–90 °F (27–32 °C), for emergence. Rincon-Vitova holds some cards at 55–60 °F (13–16 °C) to slow hatching by half a day to a day, and Buglogical and Rincon-Vitova say never below 40 °F (4 °C).
Hang within days
Adults emerge 2–5 days after arrival. Release before most have hatched in the packaging.
Cool, not cold
55–60 °F (13–16 °C) slows hatching by up to a day (Rincon-Vitova); never below 40 °F (4 °C) (Buglogical, Rincon-Vitova).
Tabs in the shade
Hang below the tops of the plants, out of hot sun, in the early morning or evening (Arbico).
Every 7–10 days
From the first moths through the flight period (Arbico, Rincon-Vitova).
Pesticide sensitivity
UF/IFAS notes that Trichogramma are sensitive to most insecticides. For tomato fruitworm programmes, UC IPM names Bacillus thuringiensis as the only recommended material that will not harm the parasite. UC also advises controlling ants and growing nectar and pollen plants for the adults. Check a product →
When to choose something else
An egg parasitoid is a narrow tool with a narrow window. Reach for something else when:
- Caterpillars are already feeding — the wasps do nothing to them; hand-pick hornworms or use Bt kurstaki on small larvae
- A hornworm is carrying white cocoons — that is Cotesia at work; leave it on the plant
- No moths are flying and no eggs are on the leaves — a release then has nothing to parasitise; set a light or pheromone trap first
- You have a few plants and a few hornworms — hand-picking is the standard garden control and costs nothing
- You are spraying broad-spectrum insecticides — they kill the wasps; Bt is the only material UC IPM recommends alongside them
Where to buy
Suppliers listed alphabetically, not ranked. helpfulbugs takes no commission and does not sell insects.
- Arbico Organics (T. brassicae, pretiosum, minutum, platneri)10k tabs to 100k cardsUS
- Buglogical (T. minutum)100k / 200k / 1MUS
- Rincon-Vitova (T. pretiosum, minutum, platneri)Cards, ~120k eggsUS
- Sound Horticulture (T. brassicae, minutum, platneri)100k cardUS
Trichogramma spp. by target
Rate and timing differ by what you are releasing it against. Each page below is the program for one pest.