This Anoplophora chinensis (order Coleoptera, family Cerambycidae) is known as the Citrus Longhorn Beetle and is said to occur in China, Taiwan and Japan. There is apparently only one generation per year. The Cerambycidae are renowned as timber pests, and the larvae bore in living trees, usually deep in the wood, sometimes causing the death of the host trees. The adults are large robust beetles, although a few small slender species are known, who sometimes do some damage to trees by gnawing off patches of bark. The larvae are legless with a well-developed head and round thorax, consequently they make round or cyclindrical tunnels in the tree branches or trunk. As the larvae tunnel through the wood, they make small holes to the exterior at intervals and push out quantities of frass-this consists of their faecal pellets together with pieces of chewed wood.

Citrus Longhorned Beetle(CLHB), Anoplophora chinenis, is a serious pest of citrus in China.

With a host range of more than 40 hardwood species, CLHB is a potential threat to natural areas as well as fruit trees and woody ornamental plants. Unlike many other native borer pests that primarily attack dead trees, CLHB attacks apparently healthy trees. Once established, it can be extremely difficult and expensive to eradicate.

Distribution

CLHB primarily occurs in China, Korea, and Japan but it is also found in Taiwan, the Philippines, Indonesia, Malaysia, Myanmar, and Vietnam.

Description

Adult: The beetle is large, stout, and approximately 21 to 37 mm (~1 - 1.5 inch) long with shiny black elytra marked with 10 to 12 white round spots. Males are generally smaller than females, and have their abdomen tip entirely covered by the elytra, in contrast to the partially exposed abdomen of females. Also, the male elytra are narrowed distally compared to the rounded female elytra. Another difference between males and females is antennal size. The male's antennae are approximately twice as long as the body when compared to the female's antennae which are only slightly longer than the body. Each segment of the long, 11-segmented antennae is basally marked with white or light blue bands. The anteriorly and posteriorly narrowed pronotum has a pair of stout spines extending from its sides.

The base of the elytra has numerous short processes (tubercles) called granulae, a morphological character that may help to differentiate CLHB from the Asian longhorned beetle, Anoplophora glabripennis.

Egg: The egg is 5.5 mm (0.22 inch) long and 1.7 mm (0.07 inch) wide, elongate, sub-cylindrical, smooth-surfaced, and tapering at both ends; it is initially creamy white but gradually turns yellowish brown when ready to hatch.

Larva: The legless larva, which is 5 mm (0.2 inch) long at the time of hatching, grows to a size of 52 mm (2 inch). It is creamy white with some yellow, chitinized patterns on the prothorax.

Pupa: The pupa is 27 to 38 mm (1 to 1.5 inch) long; it has elytra that only partially covers the membranous hind wings and curves around to the ventral surface of the body.

Life Cycle

In China, CLHB is known to emerge from April to August but is most abundant from May to July. Soon after emergence, the adult feeds on leaves, petioles, and bark of twigs of preferred host plants. Most activity, including feeding and mating, occur during the day. Eggs are deposited under the bark through a T-shaped oviposition slit made at the base of the trunk or exposed roots. Under rearing conditions, observed an average fecundity of 15 eggs, but some sources mention that a single female is capable of laying as many as 200 eggs.

The young larva hatches out in one to three weeks and initially feed on the green, sappy portion of the inner bark. During its later instars, the larva makes irregular tunnels in the wood, and continue to do so until pupation. The pupal stage lasts for four to six weeks until a pre-adult is formed with the final molt. The pre-adult is inactive and takes about one to two weeks to mature and emerge out of the tunnel. CLHB takes approximately one year to complete its development.

Host Plants

The citrus longhorned beetle is a polyphagous pest attacking living trees of over 100 species. It is a pest of major concern for citrus growers in parts of China. Its primary hosts include, lime/lemon/oranges/tangor (Citrus), trifoliate orange (Poncirus trifoliata), apple (Malus pumila), Australian pine (Casuarina equisetifolia), poplars (Populus), and willows (Salix). However, it attacks a wide range of trees and shrubs in 26 different families and more than 40 genera.

The Washington State Department of Agriculture declared the following genera (species) of plants as potential hosts for CLHB: maples (Acer), silk tree (Albizzia), alders (Alnus), birch (Betula), Camellia, hickory/pecan (Carya), chestnut (Castanea), Japanese cedar (Cryptomeria), wild olive (Elaeagnus), loquat (Eriobotrya japonica), beech (Fagus), fig (Ficus), 'Nagami' kumquat (Fortunella marginata), ash (Fraxinus), mallow (Hibiscus), holly (Ilex), walnut (Juglans), spicebush (Lindera), amur (Maackia), mulberry (Morus), Photinia, sycamore/plane tree (Platanus), trifoliate orange (Poncirus trifoliata), poplars (Populus), cherry/peach/apricot/plum (Prunus), firethorn (Pyracantha), pears (Pyrus), oaks (Quercus), sumac (Rhus), locust (Robinia), rose (Rosa), blackberry/raspberry (Rubus), willows (Salix), pagoda tee (Sophora), Stransvaesia, snowbell tree (Styrax), and elm (Ulmus).

Damage

The majority of damage associated with CLHB is caused by the larval stages which feeds and tunnel on the woody portion of the host plant trunk. The wounds created during the course of feeding increase the host susceptibility to various secondary plant pathogens. Later instar larvae have stronger mouthparts and are able to burrow deep into the wood and create irregular tunnels that interfere with the water and nutrient transportation resulting in rapid tree decline. As compared to the younger trees, older trees with larger trunk diameters are able to sustain more damage. Although adults do feed on leaves, and bark of twigs, the damage is usually not considered severe.

Management

Natural control. CLHB larvae are most susceptible to natural enemies in the early larval instar stage, or approximately the first two months of development. In China, predation by the weaver/red ants, Oecophylla smaragdina (Fab.) prevented the need for chemical control.

Sanitation. Field sanitation including cutting and burning/chipping of infested plant parts can eliminate immature stages.

Mechanical exclusion. Since eggs are laid under the bark at the base of the trunk, wire nettings or spiral guards at the trunk base can serve as physical barrier for female oviposition.

Biological control. The pathogenic fungi Beauveria brongniartii (Sacc.) is known to cause high adult mortality. In Japan, studies demonstrated adult mortality of 46 to 100% when sheets of polyurethane forms impregnated with Beauveria brongniartii were wrapped around the lower portion of the trunk or hung from the crotch.

Chemical control. Systemic insecticides are injected into base of a tree from where it is circulated to the branches, twigs and foliage. The tree injection has been a successful component of the Asian longhorned beetle eradication program and imidacloprid was recommended for use during the eradication program for CLHB. Both adults and larvae are exposed to insecticides when treated by tree injection.***