SATI Beyond The Bunch 4th Quarter 2025

A year in the life

LIAAN JANSE VAN VUUREN

Female mealy bugs don’t have a pupal stage. Adult female mealy bugs overwinter in cracks or under bark. Vine mealy bugs can also survive underground on roots. The females lay eggs that hatch into mobile first instars called crawlers. These energetic juveniles can scale a grapevine in a day. Female crawlers moult several times before adulthood. Vine mealy bug females can lay up to 750 eggs during a lifetime of several weeks to several months. Male crawlers also moult before pupating to become winged adults. Adult males only live a few days and don’t feed. Their only goal is to seek and mate with females. Vine mealy bugs require temperatures of ± 16–36 °C to

develop. The optimum range for development is 23–27 °C. The insects can complete their life cycle in 3–4 weeks during summer and have 3–7 generations per year. Crawlers start surging up the vine trunks in September or October. They prefer soft, nutritious tissues and start by targeting new stem growth, then move on to leaves, and finally bunches. Stem infestations of vine mealy bugs peak during January in Stellenbosch and Robertson and during February in the Hex River Valley. Peak crawler activity is associated with favourable weather, but females lay eggs throughout the year so that crawlers may be present in small numbers even in winter. Mealy bug populations tend to decline later in summer, even though temperatures are still favourable for reproduction. This may be partly due to increased activity by predators and parasitoids. Adult females also move to winter hiding places as sap flow slows.

Mealy bug females like to shelter in crevices and under bark.

Ants Mealy bugs can spread by hitching a ride on people and equipment, and crawlers can be carried by the wind. However, ants are largely responsible for transporting mealy bugs within vineyards. Mealy bugs and ants go together like coffee and rusks. Besides carrying mealy bugs to new locations, ants defend them against enemies. The mealy bugs reward this behaviour by excreting sticky honeydew that the ants consume eagerly. Ants form similar relationships with other sucking insects, including aphids and scales. Due to the close association between mealy bugs and ants, ant control is an essential component of mealy bug management, which is discussed in the following section.

GRAEME HATLEY

BEYOND THE BUNCH • 5 • QUARTER 4 • 2025