Oranges (Citrus sinensis) are one of several economically important citrus tree species -- including grapefruit and lemon -- in North America, Europe and Asia. These trees are regularly attacked by various insect pests, including several species of worms and caterpillars. Infestations of these insects are not usually fatal for mature plants, but a serious outbreak can kill healthy adult trees. Young trees and saplings are more fragile and can easily die from an infestation of one of these parasitic worms.
Orange Dog Caterpillar
The orange dog caterpillar is the larval form of the giant swallowtail butterfly (Papilio cresphontes), which has a wingspan of up to 6 inches. The caterpillar is brown and white and is between 1 and 2 inches in length. According to the Texas AgriLife Extension, the larvae are capable of spraying a foul toxin that discourages predators and can kill other insects. They damage citrus trees by eating leaves and other green growth in the tree's canopy. Each caterpillar can destroy a significant amount of foliage. Even a few of them can completely defoliate a young orange tree if they aren't removed or treated with insecticide.
The citrus blackfly (Aleurocanthus woglumi) is a non-native pest of orange trees throughout North America. According to the University of Florida IFAS Extension, these Asian pests were detected and eradicated in the United States multiple times during the 1900s, but they have since established themselves in various counties in several states. Both larval worms and adult blackflies drain fluids from their host tree's tissues to sustain themselves. They also release a substance that allows sooty mould to establish itself on orange trees.
Citrus leafminers are the larval form of a tiny moth species (Phyllocnistis citrella), which has a wingspan of around 1/4 inch. Like other leafminers, these small worms are compact enough to fit between the two surfaces of orange tree leaves. They consume the insides of the leaf without piercing the surface. Damage caused by leafminers is often quite obvious, thanks to visible tunnels through dying leaves. According to the University of California, the wounds caused by citrus leafminers often allow bacterial canker to infect the host tree.
The citrus spreading decline nematode (Radopholus citrophilus) is one of the most insidious worms that attacks orange trees. Individual worms are nearly microscopic -- they measure less than 1mm long. Nematodes live in the upper layers of the soil and infect host plants through their root tissue. The root damage they cause decreases the host tree's growth rate and vitality, leaving it vulnerable to bacterial and fungal infections. According to a publication of the European and Mediterranean Plant Protection Organization, a local population of nematodes can increase up to 10 times its original number in less than two months.
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- Purdue University Center for New Crops & Plant Products; Orange; Julia F. Morton; 1997
- European and Mediterranean Plant Protection Organization: Radopholus Citrophilus and Radopholus Similis
- University of California Integrated Pest Management Program; Citrus Leafminer; January 2011
- University of Florida IFAS Extension; Citrus Blackfly; Ru Nguyen and Avas B. Hamon; September 1993
- Texas AgriLife Extension; Orange Dog Caterpillar; Jo McPherson and Camille Goodwin