When an Introduced Species Does the Job

Mole Cricket Hunter Wasp (Larra bicolor)

Yesterday, I spotted this wasp vigilantly hunting through the front meadow. Thought it was the perfect time to republish my lost article on why the Mole Cricket Hunter (Larra bicolor) was introduced.

Dateline:  June 14, 2014*

Meet the Mole Cricket Hunter (Larra bicolor). A beneficial wasp.

If you’ve ever seen a mole cricket, you’ll be glad these wasps are hunting them.  Mole Crickets are UGGGGG-LLLEEEEEEE…They also chew the heck out of root systems, damaging grasses and vegetable seedlings.

This pretty wasp was introduced intentionally in Florida from Bolivia in 1988 and again in 1989 for control of Scapteriscus mole crickets, which are also introduced from South America.  They are solitary wasps and do not build communal nests. Although they can sting, they have no real interest in attacking people so put away your DEET.

Lovely red and black coloring

Often when exotic insects are brought in for biocontrol of exotic pests, there is an uncomfortable feeling that they may eventually cause a different set of problems of their own making.  Luckily in the 25 years or so since introduction, this species has proved to only target the pest it was intended to control.

Larra bicolor adults are specialist parasitoids of Scapteriscus mole crickets and will not successfully attack the native mole cricket, Neocurtilla hexadactyla. Therefore, only the target pest species are affected by the presence of the wasp.”

The Larra wasp’s  lifecycle is pretty typical of a parasitoid.  The wasp locates its prey, often chasing it out of the “gallery” which is a horizontal tunnel that mounds up and runs along the ground.  It has the look of molehills, which is probably why the Mole Cricket was given its common name.

Here’s a group resting on Florida native Camphorweed

The wasp stings the mole cricket to temporarily disable it.  After the egg is laid, the cricket awakens and does what mole crickets do.  In about a week the egg hatches and the larva begins to consume the cricket.  This process takes about two weeks.  Then, the fully-grown wasp larva spins a cocoon in the mole cricket’s gallery, and pupates. The pupae stage lasts six to 10 weeks.

Golden markings on the back

There is a definite economic impact in the ranching world due to damage caused by mole crickets. There are three species of Scapteriscus introduced to Florida that serve as wasp hosts: S. abbreviatus, S. borellii and S. vicinus, All are attacked by L. bicolor.

Initially there were signs it would only nectar on Buttonweed (Spermacoce spp.)

In researching, early on it was reported that these wasps only used Shrubby False Buttonweed (Spermacoce verticillata), as a nectar source.  This particular species is not native to Florida.  There are several Spermacoce spp. that are Florida native plants.

But it makes use of several natives such as this Thoroughwort

Since that time there are indications of a lot more diversity in the plants used by the wasp, including a great many natives.  It appears the style of flower is the influence in the wasps choosing a nectar source. Shallow flowers fit the bill.

While I have many of the flower species listed in the link in my garden, the Larra wasps appear to be adapting to some of the other natives.  Some favorites in my yard are Peppervine (Ampelopsis arborea), Rosy Camphorweed (Pluchea baccharis) and Thoroughwort (Eupatorium mohrii). The wasps are pretty little things and based on the numbers, I am pretty certain that I won’t ever be complaining about mole crickets in my beautiful wildlife garden.

It isn’t afraid to share with Bees and Tumbling Flower beetles on this peppervine

Further reading: Frank, J.Howard & J. Walker, T. (2006). Permanent Control of Pest Mole Crickets (Orthoptera: Gryllotalpidae: Scapteriscus) in Florida. American Entomologist. 52. 10.1093/ae/52.3.138.

It also serves as a food source for our spiders

*This is an update of a tale originally published by Loret T. Setters on June 14, 2014 at the defunct national blog beautifulwildlifegarden[dot]com. Click the date to view reader comments.

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