Larra bicolor — THE BENEFICIAL WASP: HOW TO USE IT

What is this wasp?

There are thousands of species of wasps in Florida. They range from smaller than a pinhead to almost 2 inches long. A few of them are social and build big nests (watch out for these!). But almost all are solitary wasps that do not build nests and rarely bother people. Larra bicolor (sometimes called “mole cricket hunter”) is a solitary wasp species native to South America.

Where is this wasp?

Larra bicolor wasps were imported from Bolivia by University of Florida/IFAS entomologists in 1988. They were released in Alachua County and they spread. Now they are present in at least 47 counties in Florida, and are in southern Georgia, and coastal Alabama and Mississippi. We hope that in a few years their presence will be documented in all Florida counties . We hope that county-level collaborators will report further spread of the wasps, with specimens or photographs to Dr. Howard Frank, because there is no longer a project to do so. .

Adult wasps need nectar from plants.

The best way to attract butterflies to your property is to plant a butterfly garden. Then you see butterflies taking nectar from the flowers. It works just the same for Larra bicolor wasps, except that the plants they use are not the ones that butterflies use. Two species of plants have been shown as good nectar sources for these wasps. They are Spermacoce verticillata, also known as shrubby false buttonweed, whitehead broom, botón blanco, and southern larraflower; and Chamaechrista fasciculata, also known as partridge pea.

Where to get nectar-source plants for wasps.

Spermacoce verticillata is native to the West Indies and Central and South America. Botanists detected it in Florida in the 1960s. It is not toxic. It is not invasive. In central and northern Florida it flowers from April to the first hard frost, at which time above-ground parts of it are killed, but it regenerates from its roots in spring. In southern Florida it may flower all year.

Chamaechrista fasciculata is native to the eastern United States. In northern Florida, it flowers during the summer months, then declines and dies during the fall. It regenerates from seed in spring. A USDA report indicates there is some evidence of toxicity from cattle ingesting large quantities of seed, so it is not a good idea to plant partridge pea where cattle can reach it, even though we are not aware of poisoning incidents in Florida. You can dig up these plants in the wild, or buy them from (a few) plant nurseries. They grow best in full sun. They do not like to be flooded. If you plant them in deep sand, you may have to water during dry spells. If you install these plants through a sheet of 6 mil black polyethylene, this will stop seeds from germinating outside the patch where you want them.

You can plant them grouped together in a patch alongside a pasture. If you plant them alongside a pasture they had best be outside the fence because cattle may destroy them by eating them. Not only Larra bicolor wasps but other kinds of wasps, too, will come looking for nectar. Some of these other wasps, too, are beneficial, attacking white grubs.

How it works.

Larra bicolor wasps should find your patch of plants and “move in” if there are mole crickets anywhere near. They will spend a lot of time during daylight hours sucking nectar from the plants. The female wasps will forage out at least 200 yards from the plant patch to hunt for adult mole crickets and mole cricket nymphs that are at least half-grown. They enter mole cricket tunnels and chase out the mole crickets to the surface. They lay an egg on each mole cricket they can catch. From the egg in a few days hatches a wasp grub that feeds by sucking the juices of the mole cricket for about 10 days, killing it. Then the wasp grub makes a cocoon in the ground and becomes a pupa inside that cocoon. After at least six weeks a new adult wasp emerges from the cocoon, digs to the soil surface, and flies off in search of nectar. The wasps provide you with free control of mole crickets. They cost you nothing (and nobody sells them). Wasps are not active in the winter - they survive underground as pupae in cocoons.

How safe is this wasp to have around?

Only the female Larra bicolor wasp can sting, but you really have to provoke her. If you grab her in your hand she may or may not sting. If she does, the sting is so mild that you will hardly notice. Larra bicolor attacks only pest mole crickets and is harmless to all other animals and plants. For more information on Larra wasps, see http://entnem.ifas.ufl.edu/creatures/beneficial/Larra_wasps.htm.

Questions and answers

Q. Can I buy these wasps?
A. No, because it would be too expensive to rear enough of them in a laboratory to do any good. Instead, they already are in your county, free, or should show up in your county in a year or two.

Q. Why can't I plant a butterfly garden to attract these wasps?
A. Butterflies have long tongues and use them to access nectaries deep in flowers. These wasps have short tongues and cannot reach deep nectaries - they prefer other kinds of flowers.

Q. Are there other species of plants useful to these wasps as nectar sources, besides Spermacoce verticillata and Chamaecrista fasciculata?
A. Yes, but we have not yet found any as good as these two.

Q. How many plants should be in a plot?
A. The idea is to make available hundreds of flowerheads to attract the wasps and keep their attention, so a minimum of a dozen good-sized plants is the best guess.

Q. Where can I buy Spermacoce verticillata and Chamaecrista fasciculata plants?
A. Search on the WWW for Florida nurseries offering them for sale. Few nurseries do so now because there has been very little demand, but this should change. At installation in a pasture setting, the plants must be watered in. They may need more water until they are firmly established, especially if there is a dry spell, so check them and water when necessary. At present, there seems to be only one company (Turf-Tec International of Tallahassee, Florida) supplying Spermacoce verticillata (larraflower). Several nurserymen supply Chamaecrista fasciculata. But that can change, and the plants are easy to grow.

Q. What happens to the plants during winter?
A. In northern and central Florida, Spermacoce verticillata freezes to the ground at the first hard frost, but regrows from the roots and should be flowering again by late April or early May. In northern Florida, Chamaecrista fasciculata stops flowering by early October then dies, but reseeds itself and the new plants should be flowering again by June.

Q. How many plots of plants do I need?
A. Plots could be 400 yards apart, outside a fenceline or even inside it if you install some posts and barbed wire around the plot.

Further reading:

Larra wasps, mole cricket hunters.
Also as IFAS/EDIS EENY-268/IN 451
Other information: http://entnem.ifas.ufl.edu/fasulo/molecrickets/mcri0007.htm