Ants and mealybugs share a complex, symbiotic relationship- and this relationship can have consequences for your vineyard. Do you know why ant control can be important to your integrated pest management program for vine mealybug?
Grape growers who have experienced a mealybug infestation have likely encountered the sticky substance mealybugs excrete on the vines they infest, known as honeydew. Vine mealybugs are particularly known for producing excessive amounts of honeydew, which can be a sign of their presence. Honeydew is a sugar-rich substance that serves as a food source for other insects.
Ants have adapted to take advantage of the honeydew produced by mealybugs and will form a symbiotic relationship with the species, similar to the relationship shared by clownfish and anemones. As they go about their life cycle feeding on grape vines, mealybugs will excrete honeydew that provides a nutrient-rich substance for the ants to consume. To secure their consistent source of honeydew, ants will defend mealybugs from predators and parasitoids , keeping the mealybugs alive and moving them throughout the vineyard.
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 commonly 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.
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.
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 aforementioned 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.