Insects that attack citrus in Louisiana

5/2/2008 3:05:52 AM

The woolly white fly (right, secreting white and waxy filaments) and the citrus blackfly are new pests of citrus in Louisiana. These are piercing, sucking feeders in both the nymph and adult stages. The citrus black fly lays its eggs in a spiral fashion, making them easy to detect. The nymphs are clear when they first hatch and gradually change color as they mature, depending on species. The eggs are usually placed on the underside of the leaf surface, and the nymphs develop there. The nymphs develop through three instars and then pupate. These empty clear shells are often mistaken for developing nymphs. Large populations of white flies occur in March-April, June-July and September-October. Populations are easily managed when caught early, before multiple generations can develop. Whiteflies are also consumed by ladybugs.

The citrus blackfly nymphs are hidden under a black covering.

The citrus black fly lays its eggs in a spiral fashion, making them easy to detect.

Mining pattern in leaf is caused by citrus leafminers. These small pests affect the foliage of each flush of growth. The moths deposit their eggs on the underside of the foliage and, upon emerging, larvae tunnel into the leaf and create winding tunnels between the upper and lower surfaces as they develop and feed. At maturity, the larvae move to the edge of the leaf causing it to curl. This protected area is where the larvae pupate. The larval stage lasts from five to 20 days; pupation last six to 22 days. Adult females emerge in the morning and lay their eggs at night. Total development time takes from 13 to 52 days, depending on weather and temperature. Adults are short lived. There are multiple generations each year, which can occur every three weeks, depending on the environmental conditions.

The Western leaf-footed bug is widespread and a pest of many crops including fruits, vegetables, grains, nuts and ornamentals. It is a major pest of citrus where feeding on ripening fruit causes premature color break and fruit drop. Adults will fly considerable distances and enter orange groves at bloom time to feed on buds and young shoots. Later adult bugs will attack the ripening fruit, causing drop. Leaf-footed bugs transmit a yeast, Nematospora coryli, that causes a dry rot. Leaf-footed bugs primarily attack Satsuma mandarins. Injury usually occurs as the fruit matures in the fall. The leaf-footed bugs will aggregate in large colonies on individual trees while neighboring trees are completely free of bugs. Leaf-footed bugs are parasitized by a Tachinid fly which lays eggs on adults and nymphs. Immature flies hatch from the eggs and consume the leaf-footed bug internally.

Mealybugs are soft, flat, oval, distinctly segmented and covered with white or mealy wax that extends into spikes along the abdomen and posterior end. The citrus mealybug has a yellow-orange body covered with a powdery wax. The waxy spikes are not very long on the abdomen or posterior. The Comstock mealybug has a thicker wax covering, and the wax spikes on the abdomen and posterior are prominent.The female lays several hundred eggs within 10 to 20 days in waxy egg sacks attached to the plant and fruit. There are two to three overlapping generations a year. They overwinter as eggs or in various stages, weather permitting. Since they feed continuously, they excrete the excess sugary plant fluids onto the plant. This creates an ideal food for bees and wasps and an excellent medium for the growth of several species of fungi that develop into a black mat-like growth on the plants known as sooty mold.

Citrus blackfly adults hold their wings tent-like above their body.

The orange-dog caterpillar is often a pest of young trees. One or two of these caterpillars can completely strip a young tree of its foliage. The larva appears as bird droppings on the foliage and stems when small. When disturbed, they evert a pair of orange glands from the base of the head. This is caused by blood pressure, and these horn-like glands have a very pungent odor. The odor is used as a defense mechanism against predators. The adult butterfly is called the giant swallowtail. It is black with a series of yellow spots that form bands in both the fore and hind wings.

Citrus blackfly adults and immatures produce large amounts of honeydew.

The woolly white fly is a new pest of citrus in Louisiana. These are piercing, sucking feeders in both the nymph and adult stages. Large populations of white flies occur in March-April, June-July and September-October. Populations are easily managed when caught early, before multiple generations can develop.

The following images are of insects that attack citrus in Louisiana.  The purpose of this publication is to aid in identification of insects on your citrus trees.
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