Get Rid of These Invasive Pests
Mole crickets are a serious problem for many Floridians. These insects can do major damage to any species of turfgrass, as well as to flowers and vegetables. So how can you get rid of them? New research suggests that biocontrol with Larra bicolor wasps may be more effective than pesticides.
WHAT ARE MOLE CRICKETS?
Mole crickets are common turfgrass pests. Three species of mole crickets are considered pests in the Southeast United States.: tawny, southern, and short-winged mole crickets.
This insect’s "hands" are uniquely adapted for digging, allowing it to tunnel through the soil. Sod farms, home lawns, golf courses, and pastures can all play host to mole crickets. Any species of turfgrass can be damaged by mole crickets, but they particularly like bahiagrass and bermudagrass.
WHAT DO THEY DO?
Mole crickets make tunnels in the ground, severing grass roots and causing the earth to bulge upwards. They also eat the roots and shoots of grass. Mole cricket damage looks like ugly brown patches. Predators such as raccoons and armadillos may further dig up the turf to snack on the crickets.
WHEN ARE THEY ACTIVE?
Mole crickets do the most damage from late August to early October. There is one generation of mole crickets per year, with eggs typically being laid in April and May. Mole crickets are nocturnal, which means they do their dirty work at night.
HOW CAN I TELL IF I HAVE MOLE CRICKETS?
An easy way to determine whether there are mole crickets in your yard is to mix 1.5 ounces of liquid dishwashing soap into 2 gallons of water and sprinkle the mixture over 4 square feet of turf. If two to four mole crickets appear within three minutes of application, corrective action is justified.
For many years, pesticides have been used to combat these winged pests, but University of Florida researchers have recently been looking at alternative methods of control. While liquid and granular insecticides do remain an option, UF scientists think that using beneficial insects on your lawn or golf course will more easily do away with the little diggers--at virtually no cost to you.
BIOCONTROLS: A SAFE, THRIFTY APPROACH
What Is a Biocontrol?
Many insects have become pests in the United States because they came from other countries and had no predators here. With nothing to keep them in check, their populations exploded. The mole cricket, which arrived as a stowaway from South America, is a perfect example.
Biocontrol (short for "biological control") means using a beneficial insect to combat a pesky one. Scientists look to the homeland of a foreign invader to find its natural enemies and then import them into our environment.
What Are the Benefits?
The benefits of biocontrols are many. They are cheap to establish; safe for humans, pets, and livestock; require little to no maintenance; and do not pollute. They are also often more effective than pesticides.
Why Not Pesticides?
Pesticides are a valid option for dealing with mole crickets--and a sometimes necessary one--but they do have drawbacks. Pesticides require regular reapplication, which costs you money. They also create potential hazards. Beneficial pollinators such as bees may suffer from pesticides. Rain or sprinklers may wash pesticide runoff into groundwater, which comes up through our taps.
Biocontrols are most successful when the control is very specific to the pest. Biocontrols seek to reestablish population equilibriums rather than bombard a lawn or garden with chemicals that target every insect.
The Larra Wasp
The Larra bicolor wasp--one of the mole cricket's natural enemies--is called a "parasitoid" because its young feed off mole crickets, though the adults live on nectar. The wasp lays an average of two to three eggs per day, or up to one hundred in a lifetime. Each one of these eggs is laid on a mole cricket.
When an egg hatches, the wasp larva sticks to the cricket, feeding off its blood. When the wasp is fully grown, it eats the mole cricket it has lived on. There is a one hundred percent death rate for mole crickets that play host to a Larra wasp.
Each generation of wasps kills about twenty-five percent of the local mole cricket population--and there are three generations of wasps per year to one generation of mole crickets.
Larra bicolor wasps do not sting humans unless caught and held in the hand. They are solitary, which means they have no nest to defend. It is more beneficial for them to flee than to sting.
At least thirty-one Florida counties are home to the wasp today, and they’re spreading. It’s simple to encourage these wasps to visit your property. Simply plant their favored host wildflowers--Spermacoce verticillata and/or Chamaecrista fasciculata--in the vicinity of your lawn, golf course, or pasture; sit back; and watch nature work.
Host Plants for the Larra Wasp
Commonly known as "shrubby false buttonweed" and "partridge pea," respectively, Spermacoce verticillataand Chamaecrista fasciculata are much cheaper than chemical treatments to install and require little to no maintenance. Because they are wildflowers--weeds, in essence--they are used to growing without fertilizer, irrigation, or other assistance from humans.
Both shrubs are perennials and can grow up to two feet tall. They produce yellow, odorless compound flowers with leaflets roughly 2/3" in length. In North and Central Florida, shrubby false buttonweed provides great coverage from July through the first freeze. Partridge pea blooms from May to October. In South Florida, they may bloom year-round.
UF’s Department of Entomology and Nematology recommends installing these plants before mole crickets are a problem on your property. This preemptive action will greatly reduce your risk of ever having mole crickets. Should the little pests find their way to your turf, the wasps are already on hand to deal with them.
You can plant buttonweed and partridge pea from seed or as a whole plant. The shrub can take up to a year to grow if you plant from seed, so if you’re in a hurry, purchasing and installing a fully-grown plant is probably the best option. Contact your county Extension office for information about where to purchase these plants. Nurseries specializing in Florida native plants are likely to stock one or both of them.
For more information on mole crickets and biocontrols, visit IPM Florida's Mole Cricket Success Story, and refer to the following publications:
- Larra Wasps, Larra analis Fabricius; Mole Cricket Hunters, Larra bicolor Fabricius
- Shortwinged Mole cricket, Scapteriscus abbreviatus Scudder; Southern Mole Cricket, Scapteriscus borellii Giglio-Tos; and Tawny Mole Cricket, Scapteriscus vicinus Scudder
Georgia Gelmis, Environmental Horticulture Department (8/2007).
Dr. J. Howard Frank, Professor of Entomology and Nematology, UF/IFAS
Scott Portman, Masters candidate, Entomology and Nematology Department, UF/IFAS