Getting a Handle on the Giant Swallowtail

By Amir Rezazadeh

The giant swallowtail butterfly (Papilio cresphontes) is a beautiful insect, admired for its large wingspan and vibrant yellow and black coloration. However, for citrus growers, this butterfly is often viewed with less enthusiasm. The larvae of the giant swallowtail, commonly referred to as “orange dogs,” can cause significant damage to citrus trees. Understanding the nature of this damage, its effects on citrus plants and the management methods are crucial for maintaining healthy citrus groves.

DAMAGE AND IDENTIFICATION

The primary damage caused by giant swallowtail larvae is defoliation. The caterpillars consume the leaves of citrus trees, sometimes stripping young trees of much of their foliage. This defoliation can be particularly harmful to young citrus trees, which are less resilient and more dependent on their leaves for photosynthesis and growth. Mature trees, while more capable of withstanding defoliation, can still suffer reduced vigor and yield if the infestation is severe.

In addition to leaf damage, heavy infestations can weaken the overall health of the tree, making it more susceptible to diseases and other pests.

Giant swallowtail damage is typically easy to identify due to the presence of the larvae themselves. The “orange dogs” are relatively large and conspicuous, especially in their later instars. Additionally, the defoliation pattern is often concentrated on the outer canopy of the tree, where the butterflies prefer to lay their eggs.

Other signs of infestation include chewed leaves, frass (caterpillar droppings) and presence of pupae.

MANAGEMENT METHODS

Monitoring: Regularly inspect citrus trees, especially during the growing season, for signs of larvae or damage. Early detection is key to preventing significant defoliation.

Cultural Controls: Encourage natural predators like birds and parasitic wasps that feed on the larvae. Planting diverse crops around citrus groves can also help attract beneficial insects.

Mechanical Removal: On smaller trees or in home gardens, larvae can be manually removed and destroyed. This method is labor-intensive but effective for managing small infestations.

Chemical Controls: In cases of severe infestation, insecticides may be necessary. Bacillus thuringiensis is a biological pesticide that specifically targets caterpillars and is safe for use in organic farming. Other insecticides, such as spinosad or pyrethroids, can also be used but should be applied carefully to minimize impact on beneficial insects.

Treatment Timing: Target the larvae when they are young and more vulnerable. This timing reduces the amount of foliage lost and minimizes the need for multiple treatments.

Amir Rezazadeh is a fruit and alternative crops agent for University of Florida Institute of Food and Agricultural Sciences Extension in St. Lucie County.

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