How to Release Trichogramma Wasps the Right Way

How to Release Trichogramma Wasps the Right Way

Trichogramma are microscopic wasps that stop caterpillars before they ever chew a leaf, by laying their own eggs inside the eggs of moths and butterflies. They ship to you alive, as parasitized eggs on a short clock, so how you store them, when you put them out, and the way you release them decides whether they take hold or die in the container. Below are both release methods, the temperatures and timing that actually matter, and how many to set out.

What shows up at your door

Trichogramma arrive as pupae developing inside grain moth eggs, ready to emerge as adults within days. They come in one of two forms, and the form changes how you handle them.

• Cards. A standard card holds about 100,000 parasitized eggs, sometimes up to 120,000. It is perforated into 30 small tabs of roughly 3,300 eggs each, and every tab has a hook so you can hang it like a door tag. That works out to around 4,000 parasites per square inch, which spreads coverage evenly across a tree, vine, or row.
• Loose eggs. Loose parasitized eggs are sold by volume, about 20,000 eggs per cubic centimeter. You divide them into paper cups, jars, or bags and set those out, which lets you put more where moth pressure is heaviest.

Temperature and timing run the whole show

Wasps emerge from the eggs in two to five days, and warmth sets the pace. The sweet spot is 80 to 90°F. You can slow emergence by holding the eggs cooler, but never below 40°F, and expect some drop in emergence and searching ability after cold storage, so do not treat the fridge as a parking spot.

Emergence almost always happens in the morning. Males come out first and sit quietly, then the females emerge and mating starts, then the males die off within a day. Once adults are out, release them right away, because every hour in a container is an hour they are not hunting eggs. Keep cards and containers in full shade the whole time, never in direct sun.

Method 1: hang the cards

This is the simplest option and the one most home growers use. Snap the perforated tabs apart and hang each one by its hook on a twig or small branch, ideally in a sheltered spot where a limb meets the trunk. Space the tabs across the affected plants so coverage is even.

Ants are the main threat to a hung card. They will carry off the parasitized eggs before the wasps ever emerge, so in ant-prone spots, staple the tab to the underside of a leaf or straight to the trunk instead of dangling it where ants can climb to it. Cards take almost no effort, but a slightly smaller share of wasps survives to hunt compared with releasing them as emerged adults.

Method 2: hatch them first, then release the adults

Releasing wasps that have already emerged gives you better field survival, at the cost of a little more effort. The idea is to incubate the eggs in a container until the adults hatch, then let them go. Any of three containers works.

• Glass jars. Use any size with a tight lid. Drop in shredded paper, confetti, or yarn so the wasps have something to climb, which makes them easy to lift out to a branch. Use a wide-mouth jar if you add filler, and if they will not fly out on their own, wrap the jar so they head for the opening. The upside of glass is that you can see how many are left to release.
• Paper bags. Any clean bag with no holes works. Light-colored filler makes the moving specks easier to spot, and wasps leave a bag more readily than a clear jar. Bags are the easiest of the three to handle.
• Paper cups. Fold the mouth shut twice and fold the corners back like dog ears. Before release, poke small exit holes with a pin or a knife tip. The holes let the wasps out and keep ants and earwigs from getting in and eating the eggs first. Set the punctured cups on branches, staple them to leaves, or scatter them around the plants.

For a tighter adult release, incubate the eggs in vials at 70 to 80°F and about 60 percent humidity for one to four days, until you see them hatching. Wait until the day after the first wasps appear, then carry the vials to the field in a cooler with ice packs. Keep the vials off the ice with crumpled newspaper, because condensation inside the vial will trap wasps. At each plant, open a vial, let some wasps fly off, and move to the next. Clear any stragglers with a short length of rubber hose to puff them out, or just leave the open vial in place for the rest to leave on their own.

Feed them honey and they work harder

A quick meal before release pays off. Wasps that feed live longer and lay more eggs, which makes this one of the highest-return steps in the whole process. Add a very thin streak of honey inside the container with a pin, dry enough that the wasps cannot get stuck in it. For a cleaner version, make honey paper: mix a couple of drops of honey with a couple of drops of water on waxed paper, fold and cut it into quarter-inch strips, and tuck a strip in with the wasps. Do not overdo it, or you will lose wasps to the honey itself.

When to release

Trichogramma go after fresh moth eggs, up to about four days old, so the time to release is when moths are flying and laying. Pheromone traps or scouting for eggs on the undersides of leaves tell you when that window opens. Start early in the season, as soon as the crop is tall enough to shade the wasps. A common cue growers use is tomatoes standing 12 to 28 inches high.

Do not think of it as a single drop. A single female can parasitize up to 300 pest eggs, and a population can multiply every 7 to 10 days, so an early head start does most of the work while weekly releases keep the pressure on through the season. Expect to tolerate a few minor pests along the way, because that low-level food supply is what keeps your beneficial population alive and working.

Protect the wasps you paid for. Skip broad-spectrum insecticides anywhere near a release zone, since those chemicals are as lethal to trichogramma as they are to the pests. The UC IPM guidance on natural enemies also recommends controlling ants and growing nectar-rich flowering plants, both of which help every beneficial in your garden, not just these wasps. Trichogramma work best as one piece of a program: University of Florida Extension notes that egg parasites rarely carry pest control on their own and should sit alongside traps, cultural practices, and targeted treatments.

How many to put out

Release rates depend on the species, the crop, and how heavy the pest pressure is, so treat these as a starting reference and dial them in for your own situation.

Loose amounts are measured by weight of parasitized grain-moth eggs. For a backyard tree or a small garden, a fraction of a card, or one card split across a few plants, is usually plenty. If you are not sure where to land, that is exactly the kind of question our team likes: call 716-217-0353.