HYDRILLA TIP MINING MIDGE
UF/IFAS Photo by Tyler Jones
You could call the hydrilla tip mining midge a “big money bug hopeful.” This insect may help the state of Florida manage the invasive weed hydrilla in public lakes, springs and other surface waters.
Potential savings: a large fraction of the estimated $12 million in state funding spent annually to fight hydrilla.
The hydrilla tip mining midge is a VERY small flying insect that UF/IFAS researchers are evaluating as a biocontrol organism to help manage the invasive freshwater weed Hydrilla verticillata, a once-popular aquarium plant that is commonly known simply as “hydrilla.” Since the early 1990s, hydrilla has been Florida’s most troublesome aquatic weed, present in at least 70 percent of the state’s watersheds and believed to infest about 90,000 acres of surface waters, including lakes, ponds, rivers and springs (basically any water that is not salty).
Although hydrilla is commonly managed with chemical herbicides, UF/IFAS personnel believe that an ingenious three-pronged approach may offer better long-term prospects for hydrilla management. One prong of the approach involves the hydrilla tip mining midge. The adult midge spends its time on land but its larvae live underwater and feed on hydrilla shoot tips, inhibiting the plant’s vertical growth. Researchers believe that a treatment protocol combining the midge with an herbicide and a plant-pathogenic native fungus could prove successful. The scientists want to find a cost-effective way to change the architecture of submerged hydrilla beds and prevent shoots from reaching the water’s surface and forming dense mats that harm native ecosystems and interfere with navigation, drainage and recreational activities.
Common Name: Hydrilla tip mining midge
Scientific Name: Cricotopus lebetis
Good Bug or Bad Bug? Good Bug
What It Is: As an adult, the hydrilla tip mining midge is a flying insect that superficially resembles a tiny mosquito. It’s a member of the insect order Diptera, the true flies. Within the Diptera order, the hydrilla tip mining midge is part of a large family of non-biting flies that’s known scientifically as Chironomidae and known informally by many names, including chironomids, non-biting midges and a slang term common in Florida, blind mosquitoes. However, unlike many chironomids, the hydrilla tip mining midge is not found in large swarms and, thus, does not present a nuisance to people.
What It Does: The larvae of midges in the Chironomidae family are aquatic, and they typically feed on algae and/or decaying plant matter. The hydrilla tip mining midge is an exception – its larvae feed on living tissue in the tips of hydrilla shoots, an area of the plant that’s technically called the apical meristem.
Each larva tunnels or “mines” straight down the center of an individual hydrilla shoot tip, consuming tissue and generating damage that kills the shoot tip and causes the plant to branch, something that hydrilla plants normally do only after they have grown all the way from the bottom of a water body to its surface, a phenomenon called “topping out.” When the midge causes a hydrilla plant to branch, the plant devotes less energy to vertical growth, slowing its progress toward the surface. The more midges that feed on an individual hydrilla plant, the more it branches and the less likely it is to reach the water’s surface.
Who Is Affected: Because hydrilla is established statewide and is capable of tolerating a wide variety of environmental conditions, successful use of the midge in biocontrol programs could help swimmers, divers and boaters who dislike the thick mats that result when hydrilla plants “top out” and clog the surfaces of lakes, ponds, etc. Improved hydrilla management would also be welcomed by environmentalists who’d like to see a reduction in herbicide use and at the same time have Florida’s surface waters cleared of invasive plants to whatever degree is possible. Finally, anglers should appreciate the fact that the midge is expected to reshape submerged hydrilla beds, rather than eliminate them altogether, so that established beds will continue to offer cover for largemouth bass and other game fish.
Where It’s Found in Florida: The hydrilla tip mining midge’s range in Florida has not been determined. It has been collected from several locations statewide but thus far has not been found in the Panhandle. Noteworthy populations have been found in the Crystal River springshed in Citrus County, at Lake Rowell in Bradford County, and at Lake Istokpoga in Highlands County.
Native to Florida? Right now, scientists are uncertain where the hydrilla tip mining midge originates. In the United States, the adult midge was initially detected in Louisiana in 1960. In Florida, the first reported detection of the midge came in 1992, when larvae were found feeding on hydrilla plants in the Crystal River springshed. However, the midge is so small that it may have been overlooked by earlier researchers.
Until recent years, research on the hydrilla tip mining midge has been sparse. It’s unclear whether the midge is a native insect that has become associated with hydrilla, or a non-native insect that was introduced to Florida along with the plant itself. If the midge was introduced to Florida in shipments of hydrilla, then it is probably native to Southeast Asia, possibly Sri Lanka, the putative source of the first hydrilla populations found growing in Florida’s wild ecosystems.
Big Money Associates: UF/IFAS researchers study the hydrilla tip mining midge because its larvae feed on the invasive aquatic weed Hydrilla verticillata, which is native to Southeast Asia and Northern Australia. Hardy and eye-catching in freshwater fish tanks, hydrilla was once popular in the aquarium trade, though state and federal laws now prohibit its possession in Florida without a permit. It’s believed that hydrilla was deliberately placed in wild Florida ecosystems near Tampa and Miami in the 1950s, possibly by individuals who hoped to ensure a plentiful supply of the plant for commercial use.
Hydrilla tolerates wide variation in water temperature, light availability, water turbidity and nutrient availability. It can reproduce via five modes of action, though only four of those are reported to occur in Florida. Established populations of the weed were first reported in two Florida locations in 1960, the Crystal River springshed in Citrus County and Miami-Dade County. Hydrilla currently infests about 90,000 acres of Florida surface waters.
Interesting Fact: The family Chironomidae includes the largest purely terrestrial animal that is native to Antarctica, a flightless midge known as Belgica antarctica. “Largest” is a relative term here – this insect only reaches a maximum length of 6 millimeters. Though semi-terrestrial birds and seals are common along the Antarctic coast, those animals are at home in the water, whereas Belgica antarctica completes its life cycle entirely on land. As you might expect of an organism native to Antarctica, this is one tough bug – it’s able to survive freezing solid, dehydrating to 35% of its original body weight, and going without oxygen for up to one month.
Estimated Benefits per Year – If UF/IFAS evaluations demonstrate that a combination of the midge, the herbicide and the plant-pathogenic fungus provide a satisfactory return on the investment required to implement them, state authorities may eventually adopt this approach to hydrilla management in selected surface-water bodies. Ultimately, this approach might enable the state to significantly reduce its current hydrilla-management expenditures for public surface waters, which total about $12 million annually.
Estimated Hydrilla Control Costs per Year in Florida: The state of Florida spends an estimated $12 million annually to fight hydrilla in public surface waters, including lakes, ponds, rivers and springs.
What Is Currently Done About It: The state of Florida currently uses several techniques to fight hydrilla in public surface waters. They include mechanical removal using harvesting equipment, biocontrol using a specially bred fish that cannot reproduce, and chemical control using herbicides. From about 1990 to 2010, the most commonly employed management technique involved treating hydrilla beds with the herbicide fluridone. However, scientists began noting fluridone-resistant hydrilla in Florida in 2000, indicating that a recent genetic mutation or an existing genetic variation enabled some of the plants to tolerate the herbicide. Since about 2010, fluridone has been used less often, as scientists search for viable alternatives.
So far, fluridone-resistant hydrilla has been found only in Florida, not in any of the other two dozen U.S. states where hydrilla has been reported.
What Is UF/IFAS Doing About It? For almost 20 years, UF/IFAS research teams have made remarkable progress investigating the hydrilla tip mining midge as a potential biocontrol organism for use in Florida.
Upon recognizing the insect’s potential to fight hydrilla infestations, researchers launched a suite of projects to address a wide range of basic and applied-science issues surrounding the species. They have conducted projects ranging from a formal taxonomic re-description of the midge, to studies on its reproductive capacity, its feeding habits, the damage it causes in hydrilla, and the potential for the midge’s eggs to survive periods of cold storage to facilitate transportation.
Furthermore, it became apparent to researchers that the midge might have greater effectiveness when used in combination with an herbicide called imazamox, which also promotes branching in hydrilla plants, and a plant-pathogenic fungus, Mycoleptodiscus terretris, which infects hydrilla plants through wounds created by the midge, further inhibiting the plant’s vertical growth. Research on imazamox and the fungus commenced about a decade ago and continues today. The team has created and distributed a variety of educational materials as well.
This overall effort has been supported by a five year, $512,000 grant from USDA to a team that included personnel with UF/IFAS, Florida A&M University and the U.S. Army Corps of Engineers. Additional funding was supplied by a three-year, $249,000 grant awarded in 2014 to a team that included UF/IFAS and USDA-ARS personnel. Researchers are currently evaluating several combinations of midge, herbicide and fungus, using experimental ponds at the UF/IFAS Center for Aquatic and Invasive Plants in Gainesville; their findings will be disseminated in 2017.
UF/IFAS personnel also provided leadership for an earlier aquatic weed management program based in Osceola County and supported by $2.9 million in federal funds. The team accomplished numerous research and Extension goals, including evaluations of more than 150 herbicides, creation of an educational website and publication of multiple outreach documents aimed at the public.
What YOU Can Do About It? Everyone who enjoys recreational activities at Florida’s freshwater destinations should be careful to avoid transporting aquatic weeds from one body of water to another.
Steps to take after visiting surface waters include visual inspection of boats, boat trailers, outboard motor propellers, personal watercraft, oars and paddles, fishing tackle, etc. Remove any weed fragments by hand and discard them in a trash receptacle on-site before departing the location. This precaution will help reduce the risk of hydrilla and other noxious aquatic weeds fouling currently pristine surface waters. Furthermore, it will reduce the risk that additional hydrilla biotypes – genetic variants within the same plant species – will become established in lakes that are already infested, potentially complicating management efforts.
To learn more about the hydrilla tip mining midge, visit this “Featured Creatures” document produced by the UF/IFS Entomology and Nematology Department.
To learn more about Hydrilla verticillata, visit this UF/IFAS document from the EDIS online Extension library.
To see all the management options recommended for hydrilla, visit this EDIS document.
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