Ants and Their Symbiotic Relationship with Vine Mealybug

Ants and mealybugs share a complex, symbiotic relationship and this relationship can have consequences for your vineyard.

Understanding Mealybug Infestations: The Symbiotic Relationship Between Mealybugs and Ants in Vineyards

Grape growers dealing with mealybug infestations are often confronted with the sticky residue left behind on their vines, known as honeydew. Vine mealybugs are notorious for producing large quantities of honeydew, which is a telltale sign of their infestation. This sugar-rich substance not only indicates mealybug presence but also attracts other insects, making it a key concern for vineyard health.

As mealybugs feed on grape vines, they excrete honeydew, a nutrient-dense food source for ants. To maintain their supply of honeydew, ants actively protect mealybugs from predators and parasitoids. This defense mechanism ensures the mealybugs’ survival and enables ants to move them throughout the vineyard, perpetuating the infestation.

The relationship between ants and mealybugs is not particular to one species - multiple species of ants, both native and invasive, will take advantage of and defend multiple species of mealybug. In California, vine mealybug is most defended by the native gray ants found in the region, although invasive Argentine ants are also significant defenders of mealybugs, and in some vineyards may be the predominant species.

Natural Pest Control in Vineyards: Predators, Parasitoids, and the Impact of Ants on Mealybug Management 

The unsung heroes of many vineyards are the predator and parasitoid species that provide natural pest control as part of their life cycle. These can be either naturally occurring or intentionally released (augmentative biological control) to help control pests.

Cryptolaemus beetles, also known as mealybug destroyers, are a widely used form of augmentative biocontrol for mealybugs. Some parasitoid wasp species, such as Anagyrus pseudococci, are also released in many vineyards. In addition to these species, other naturally occurring predators including lady beetles, lacewings, and spiders, readily feed on mealybugs. Vine mealybugs are relatively immobile and have few defenses against natural enemies.

However, the ants that ‘farm’ them for their honeydew are not. Parasitoid wasps are particularly vulnerable to ants defending mealybugs. The presence of ants can reduce the effectiveness of biological control of mealybugs, impacting the success of the overall integrated pest management program.

Effective Ant Control Strategies in Integrated Vine Mealybug Management

In addition to more direct measures of controlling vine mealybug, such as mating disruption, an integrated pest management program for vine mealybug should include controlling the ants that defend them.

Using vetch as a cover crop can keep native gray ants off vines, as vetch produces nectar that is more attractive to ants than nutrients provided by the grape vines. Tilling soil and using a French plow in vineyards can also disrupt ant hives in fully organic blocks.

In some cases, chemical control targeting ants may be necessary. In general, using bait to kill ants is the most effective and is least disruptive to the beneficial species that may be present in vineyards. The type of bait and overall treatment will depend on the species of ant you are treating and your location; consult UC IPM and your Pest Control Adviser for more information.

If you have questions about ant management and other strategies for mealybug management, Suterra is happy to help. Request support from a local technical representative and we can connect you with somebody who can provide you with advice for your unique situation.