- Citrus

Citrus Citrus

Citrus Flatid Plant Hopper

Insect

Metcalfa pruinosa


In a Nutshell

  • White, woolly, waxy material on leafunderside, branches and fruits.
  • Honeydew, favoring sooty mold.
  • Adults are brown to gray, with bright orange eyes, triangular forewings.

Symptoms

The presence of this planthopper is often unraveled by the appearance of white, woolly and waxy material on the underside of leaves, as well as on branches and fruits. These deposits, produced by the nymphs, can sometimes be mistaken for those found during mealybugs or the cottony cushion scale infestations (and which are more damaging pests). In case of doubt, it may help to know, that contrarily to those, the planthopper will jumped when disturbed. Adults and nymphs have mouthparts that are adapted for piercing plant tissues and sucking the sap. Adults are often seen feeding gregariously, excreting the excess sugar as honeydew, which favors the growth of sooty mold. Dense populations of this insect may cause the stunting of new shoots and the weakening of the trees, either directly or through the growth of the opportunistic fungi. In other susceptible plant hosts, symptoms may be more dramatic, including chlorosis and necrosis of the leaves, withering of shoot tips and malformation and shriveling of seeds.

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Hosts

Trigger

Symptoms are caused by the adults and nymphs of the planthopper Metcalfa pruinosa, which has a broad range of tree hosts, among them citrus. It is a highly adaptable insect, that can thrive in a multitude of environments. They can disperse over short distances by flight and are extremely attracted to light. Bad field practices and human intervention can also be a decisive factor in their long distance spreading. Adults are brown to gray and have characteristic prominent, bright orange eyes and triangular forewings with scattered whitish spots. They may easily be mistaken for moths at first glance. Adults and nymphs can be covered with an abundant bluish white wax, that can take the form of dense white tufts of hair in the latter. Females lay about 100 eggs in the autumn, usually on pre-existing wounds on the bark of twigs, or on holes dug in softer bark. When conditions are favorable during the spring, the egg hatch and nymphs start to feed on plant tissues. They usually do very little damage but can become a problem in trees that have been injured previously, by freeze for example.

Organic Control

A parasitic wasp of the dryinid family, Psilodryinus typhlocybae, lay its eggs on the nymphs of Metcalfa pruinosa and can help to reduce populations. Soap solutions cause the young nymph stages of the pest to slide on the leaves and to fall to the ground. Moreover, it is ideal solution to wash the honeydew present on the leaves, which is later colonize by sooty mold. However, in the absence of insecticide treatments the insects will return.

Chemical Control

Always consider an integrated approach with preventive measures and biological treatments, if available. Chemical control of adults is difficult because of their mobility. A way to control dense populations might be the timely application of insecticides to control the nymphs. The control of sooty mold is generally more useful as this can be the most damaging factor. Where authorized, foliar or fruit sprayings with solutions containing deltamethrin, pyrethroids or dimethoate at the edge of the field can give a good control of the insect.

Preventive Measures

  • Use healthy plant material from certified sources.
  • This species may be subjected to quarantine regulations in some countries.
  • Use light traps to attract the adults and monitor numbers.

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