Shepherd ant

Systematic position. The ant Plagiolepis custodiens belongs to the order Hymenoptera and the family Formicidae. Known as a shepherd ant, it is widely recognized in southern Africa for its complex symbiotic relationships with honeydew-producing insects, which leads to significant agricultural damage.

Crops and damage. This species poses a major threat to orchards, vineyards, and various ornamental plants. While the ants do not consume plant tissues directly, they protect and cultivate populations of aphids, mealybugs, and scale insects, which serve as their primary source of carbohydrate-rich honeydew.

The damage is severe: by shielding aphids from natural predators like ladybugs and lacewings, the ants ensure that aphid colonies grow unchecked. This leads to heavy infestation, leaf curling, stunted plant growth, and the development of sooty mold on the honeydew, which blocks sunlight and hampers the plant's photosynthetic capacity.

Biology and lifecycle. Plagiolepis custodiens colonies are highly organized and aggressive. The workers exhibit "herding" behavior, physically carrying aphids to fresh, nutrient-rich parts of the plant. Their lifecycle is tied to the availability of honeydew-producing insects, making the ant population explosion proportional to the success of the aphid colonies they manage.

Control measures. Controlling the shepherd ant requires a dual-action strategy. First, mechanical barriers such as sticky bands on tree trunks are essential to prevent access to the canopy. Second, targeted chemical control of the aphid population, often using systemic insecticides, makes the plant less attractive to the ants, effectively forcing them to abandon the site.

• Install physical sticky traps on tree trunks.
• Apply systemic insecticides to control aphid populations.
• Monitor for early signs of ant activity.
• Encourage local populations of natural aphid predators.