Tamarixia wasp

How it works

The female lays a single egg on the underside of a fourth- or fifth-instar psyllid nymph, beside the mid or hind leg. The larva feeds on the nymph from below and kills it before it can become an adult, passing through four instars in about 11 days at 77 °F (25 °C). The dead nymph darkens to a brown, crusty 'mummy' anchored to the leaf by beige silk, and the new adult chews its way out through a round hole about 0.5 mm across near the front of the body. Females also kill young nymphs (first to third instar) by feeding on them. UC Riverside puts the split at about 80% parasitism and 20% host feeding, for up to 500 nymphs per female; CDFA gives the adult an average life of 24 days.

It was first released in Southern California in 2011, from stock collected in Punjab, Pakistan, and CDFA and its partners now release it statewide in residential citrus, around HLB finds, along highways and along the Mexican border. Florida introduced it deliberately, and it reached the Rio Grande Valley of Texas on its own; Texas has released it widely since 2010, but a 2022 study there judged its control insufficient. In host-range tests it proved highly specific: the only non-target psyllid it attacked was the potato psyllid, at under 5%. A second parasitoid, Diaphorencyrtus aligarhensis, was also released, but in caged trials it parasitised about 28% of nymphs on its own and under 3% when Tamarixia was present.

The results vary a great deal. Parasitism can reach 70% where the wasp is established, but a 2012–2014 study of Southern California yards averaged under 5% year-round, UC Riverside field monitoring found up to 18.6%, and Florida typically sees 1–3%. Argentine ants are a large part of the difference. It reduces psyllid numbers; it does not cure or prevent HLB. A 2021 study found the wasp can pick up the HLB bacterium and pass it between nymphs it probes; how much that matters in the field is not known.

What it is confused with

The adult wasp is too small to watch for. What a homeowner can see, with a hand lens on new flush, is the difference between a living psyllid nymph and a parasitised one.

1. PestLiving Asian citrus psyllid nymph — Yellow-orange, flat and trailing curly white wax tubules. A parasitised nymph turns into a brown, crusty mummy stuck to the leaf; once the wasp has left it has a round exit hole near the front. A brown mummy without a hole may still hold a developing wasp, so leave it.
2. PestAdult Asian citrus psyllid — Three to four times the wasp's length at 3–4 mm, mottled brown, and feeds head-down with its body tilted at about 30–45°. Tamarixia is about 1 mm, black and yellow with yellow legs, clear yellow-veined wings and red eyes.
3. Also goodDiaphorencyrtus aligarhensis — The other psyllid parasitoid released in California. It develops inside the nymph rather than beneath it and attacks younger (2nd–4th instar) nymphs, with up to 280 killed per female. Both are beneficial; leave any mummy alone.