- Author: Saoimanu Sope
Sugar-feeding ants protect pests that infect trees and damage the fruit they bear. Insecticides are often a go-to solution, but may kill beneficial insects in the process, too. Thankfully, Mark Hoddle, University of California Cooperative Extension entomologist and biological control specialist at UC Riverside, together with UCR colleagues in chemical engineering, developed a biodegradable hydrogel baiting system that targets ant populations, which protect sap-sucking pests from their natural enemies. Control of ants allows beneficial parasitoids and predators to greatly reduce pest populations.
Deciding to expand Hoddle's research was a “no-brainer” according to David Haviland, UC Cooperative Extension farm advisor in Kern County.
Haviland is investigating active ingredients that can be effectively used in hydrogel baiting systems. His research builds on Hoddle's use of alginate gels, also known as water beads, soaked in sugar water to control Argentine ants.
“What we're doing in California can benefit places like Florida, Texas, Mexico and beyond,” Haviland said.
The Hoddle lab conducted two years of orchard research showing that when ants are controlled, the amount of citrus flush infested with Asian citrus psyllid (ACP), a mottled brown insect that vectors the pathogen causing citrus greening, decreases by 75%. Citrus flush refers to newly developed leaves.
“But benefits are not restricted to just ACP with Argentine ant control, as natural enemies destroy colonies of other sap-sucking pests too,” said Hoddle. “For example, citrus mealybug infestations on leaves were completely eliminated by natural enemies, 100% control, while densities of fruit infested by mealybugs were reduced by 50%.”
The Hoddle lab's success inspired Haviland to consider how this approach will fare in different regions of the state where there are different crops, different pests and different ant species.
Haviland has worked for many years on solid baits that are effective and affordable for ants that feed primarily on protein, like fire ants in almonds, but successful control measures for sugar-feeding ants that drink their food have been elusive.
“Therefore, we're using hydrogels to essentially turn a liquid bait into a solid, making it effective and commercially adoptable,” Haviland said. He and his team are assessing whether active ingredients that undoubtedly work against ants, like thiamethoxam, maintain their effects in a hydrogel system.
Unlike Hoddle's biodegradable alginate gels, Haviland is relying on acrylamide gels that are similar to the absorbing material you would find in a diaper. These gels are not organic, but are currently accessible on a commercial scale, and have been shown to be effective in wine grapes on the North Coast by a Cooperative Extension advisor in Napa County, Monica Cooper. Haviland's current research efforts are focused on citrus, table grapes and wine grapes in the San Joaquin Valley, and on lemons on the coast.
The primary challenge now is navigating pesticide regulations and registration.
“This is cutting-edge research,” Haviland said, and manufacturer labels for the products being used need to be updated to include hydrogels as an approved use. This process takes time. Additionally, adding new product uses needs to make economic sense for the manufacturer.
Hoddle and Haviland's research can provide data for adding these methods to the product labels.
“If we can show that this tech works against lots of pests, lots of ant species, in lots of different crops across California, hopefully we'll achieve a critical mass of benefits that motivates product manufacturers to make modifications to their labels,” said Haviland.
Haviland is hopeful about the process, and said he believes that UC ANR is in a prime position to lead innovation for an issue that requires collaboration among specialists, advisors and the industry.
- Author: Ben Faber
Dr. Hoddle presented about how to monitor and manage Argentine ant in citrus orchards with liquid baiting systems and discussed why ant management has such strong benefits for the suppression of sap-sucking pests by natural enemies. This information is critical for PCAs and growers to better understand why managing Argentine ant is important. (Presentation slides in the PDF format)
From: https://www2.ipm.ucanr.edu/agriculture/citrus/Ants/
There are numerous species of ants present in citrus orchards, however, the most common are the Argentine ant (southern and coastal California), the native gray ant (San Joaquin Valley) and the southern fire ant (statewide). The red imported fire ant has been found in Southern California, but is not yet established in citrus orchards. It is important to identify the primary ant species in the orchard, because management tactics depend on which ant species is present.
The Argentine ant, is a small, uniformly deep brown ant. Worker ants travel in characteristic trails on trees, the ground, or irrigation lines and build their nests underground. Ant populations peak in mid-summer through early fall.
The southern fire ant is light reddish brown with a black abdomen. These ants build nests of loose mounds or craters near bases of trees, do not aggregate in colonies as large as those of the Argentine ant, and will sting and bite.
Native gray ants are gray and considerably larger than the other two species. They nest in topsoil or under rocks and debris and move in irregular patterns. In contrast to Argentine and fire ants, the native gray ant is solitary and its importance in disrupting biological control is often underestimated.
Red imported fire ant is new to California and can make large, dome-shaped mounds. They feed on almost any plant or animal material.
Damage
Most ant species feed on honeydew excreted by various soft scales, mealybugs, cottony cushion scales, whiteflies, psyllids, and aphids. As part of this relationship, they protect these pest insects from their natural enemies, thus interrupting biological control. They also protect some non honeydew-producing pests, such as California red scales.
Argentine and native gray ants are the most common ant species that aggressively protect pest insects. In addition, Argentine ants and fire ants can plug up irrigation sprinklers. Fire ants directly damage citrus by chewing twigs and tender bark of newly planted trees; they also sting people working in the orchard and may cause allergic reactions.
No effective natural enemies of ants are known.
Cultural Control
Skirt prune trees, i.e., remove branches within 12 to 30 inches of the ground, and apply sticky material to the trunk to prevent access to the trees by ants. Use polybutenes, as oil-based materials may cause phytotoxicity and should not be used.
The application of sticky polybutene materials directly to the trunk of citrus trees can cause bark cracking, especially if multiple applications are applied to the same area of the trunk, the area is exposed to sunlight (topworked trees), or both. The sticky material can be applied on top of a tree wrap or a base layer of latex paint. Young trees, which have a very thin cambium layer, are most susceptible to damage.
Sticky material should last from 1 to 4 months and will also prevent the access by Fuller rose beetles. If the sticky material contains tribasic copper sulfate, it will also control brown garden snails. The persistence of sticky material can be increased by applying it higher above the ground to reduce dust and dirt contamination and to decrease irrigation wash-off.
Baits
Argentine ant adults are liquid-feeding only and have physical digestive "blocks" in the mouth and gut to prevent them from swallowing and digesting solid food particles. They may bring back solid food to the colony to feed the brood (but solid-food digestion not been confirmed in Argentine ant brood), or harvest the bodily fluids inside of insect prey/moisture in food items. Dry insects or food items are of little use to them, even though they may pick these things up. Feeding studies have shown ants feed several times faster on liquids than gels and gels than solids. This faster feeding resulted in much higher toxicity with liquid. Gel was intermediate, and solids provided the lowest control.
Put out bait in the shade to increase feeding and overall kill. You do not need to obscure it. The soil temperature and moisture are going to be more moderate in the shade, particularly under the canopy. This is the environment the ants will prefer to feed in. There will be less evaporative loss in the shade, as well. Sometimes when the toxins become too concentrated they are less attractive to the ants. The other issue is that many toxins (like borax products) may photodegrade at a faster rate in direct sunlight.
Ants often enter buildings seeking food and water, warmth and shelter, or refuge from dry, hot weather or flooded conditions. They may appear suddenly in buildings if other food sources become unavailable or weather conditions change.
One such ant we see headed indoors during rainy conditions in California, is the Argentine ant. The Argentine ant is about 1/8 of an inch long and dull brown in color. It's normally found living in the landscape in shallow nests, and might even be living just outside your building. When rainy weather floods their nest, Argentine ants may use your home or office as a warm and dry place to relocate.
This rainy season, before ants have a chance to invade your home, be proactive and “ant-proof” your buildings ahead of time Determine what the ants are attracted to and eliminate the food or water source. Monitor the places in and around your home where ants are often found. Follow ant trails to find where they are entering, and seal them off using caulking or other sealants.
Of the 270 species of ants in California, fewer than a dozen are pests, and although ants can be bothersome pests indoors, it's important to remember that outdoors they sometimes also play a beneficial role in the environment.
Visit the Ants section of UC IPM's home and landscape web pages for more information about preventing or managing ant invasions. There you will find videos about ants including, “What to do if you have an ant emergency” and “Why do ants invade?” as well as other resources to help identify ants and know what to do indoors or out.