Phoracantha semipunctata (Fabricius)
Taxonomic placing: Insecta, Holometabola, Coleoptera, Cerambycidae.
Common name: Eucalyptus longhorned borer.
Geographical distribution: This pest occurs wherever eucalypts are planted.
Host plants: Many species of Eucalyptus.
Morphology: The larva is yellowish-white, about 3 mm long, with a brown head. The adult: is 22-28 mm long, the body is dark-brown, with a yellowish band extending across the upper half of the elytra with yellow spots. The yellow-brown antennae are as long or longer than the body.
Life cycle: In the Middle East the pest has 2-3 partially overlapping annual generations, depending on the climate. Development from oviposition to adult emergence requires about 100-220 days. Females may live for 40-200 days and lay several hundred eggs from spring to late autumn. The eggs are placed under loose bark in groups of 3-30 eggs, hatching after a few days. The emerging larvae initially feed on the bark and then bore galleries along the stem. They grow and the size of the galleries increases correspondingly. Fully grown larvae burrow a short tunnel towards the bark surface and then construct a pupal chamber. The emerging adults gnaw their way out. They are usually active during warm nights, when the temperature at dusk is above 15ºC.
Economic importance: Infested trees bear dead branches with yellowing and wilting leaves and in some cases the whole crown may die. Heavy infestations can result in rapid tree death. When tree bark is removed, the larval tunnels are revealed, which lead into the inner bark and cambium and are filled with compressed frass. The numerous galleries start from the same point, usually along the stem. A single larval gallery may extend for more than 1 m and can girdle a tree, and can thus seriously harm and even kill young trees. Older, larger trees withstand the damage. Hot and dry summers, drought and infertile soils, along with the suboptimal state of many plantations and the dispersal capacity of the pest, promoted its rapid spread in the Mediterranean region. Unirrigated trees are more susceptible than well-watered ones. Death of apparently healthy trees can also occur when subjected to periodic moisture stress. Much damage to North African plantations was recorded following the pest’s introduction in 1963. An outbreak in Morocco in 1981 caused an estimated loss of 2 million trees. In other regions much damage may be caused even to apparently healthy trees, when subjected to periodic moisture stress. The main cause of the rapid spread of the pest throughout the world has been the transport of unprocessed logs and beetle-infested Eucalyptus firewood. When such wood is milled into timber used for packing material, the pupating insects complete development in the milled wood and the adults emerge at the destination of the cargo.
Management
Horticultural methods: Curative and preventive measures include clearance and cutting all attacked, weak and dead branches and even trees, and removing them from the forests. EPPO recommends that only debarked Eucalyptus wood should be traded. Such wood, including chips larger than 4 x 0.5 cm, should be kept in storage under supervision for at least 6 months after debarking, or should have been appropriately fumigated. Dry logs older than 9 months can be considered free from larvae and pupae.
Plant resistance: Certain Eucalyptus spp. are less susceptible to the borer. Selecting these trees is a major preventive measure against the pest.
Monitoring: Treating logs from recently cut timber (which are attractive to the beetle) with a persistent pesticide can be used to trap, monitor and kill the pest.
Chemical control: Freshly cut trap logs, treated with pesticides, are placed in woodlots to attract adult beetles. Females lay their eggs on the sprayed logs which are replaced every 2 weeks with fresh ones, and then destroyed within 2 months to prevent beetle emergence.
Biological control: Several natural enemies attack the pest in various parts of the world. These include braconid and encyrtid parasitoids, as well as predatory beetles and ants. In Israel Picoides syriacus (Hemprich & Ehrenberg), the Syrian woodpecker, excavates borer larvae out of trap-logs, causing up to 30% mortality.
References
CABI/EPPO, 2007. Phoracantha semipunctata Distribution map. Distribution Maps of Plant Pests, Map 272 (2nd Revision). Wallingford, UK: CABI.
El-Yousfi, M. 1989. The principles of control of Phoracantha semipunctata Fabr. Boletin de Sanidad Vegetal, Plagas 15: 129-137.
Hanks, L.M., Paine, T.D., Millar, J.G. and Hom, J.L. 1995. Variation among Eucalyptus species in resistance to eucalyptus longhorned borer in Southern California. Entomologia Experimentalis et Applicata 74: 185-194.
Joyce, A.L., Millar, J.G., Paine, T.D. and Hanks, L.M. 2002. The effect of host size on the sex ratio of Syngaster lepidus, a parasitoid of Eucalyptus longhorned borers (Phoracantha spp.). Biological Control 24: 207-213.
Luhring, K.A., Paine, T.D., Millar, J.G. and Hanks, L.M. 2000. Suitability of the eggs of two species of eucalyptus longhorned borers (Phoracantha recurva and P. semipunctata) as hosts for the encyrtid parasitoid Avetianella longoi. Biological Control 19: 95-104.
Mendel, Z. 1985. Seasonal development of the eucalypt borer Phoracantha semipunctata (Coleoptera: Cerambycidae) in Israel. Phytoparasitica 14: 85-93.
Mendel, Z. Golan, Y. and Madar, Z. 1984. Natural control of the eucalyptus borer, Phoracantha semipunctata (F.) (Coleoptera: Cerambycidae), by the Syrian woodpecker. Bulletin of Entomological Research 74: 121-127.
Way, M.J., Cammell, M.E. and Paiva, M.R. 1992. Studies on egg predation by ants (Hymenoptera: Formicidae) especially on the eucalyptus borer Phoracantha semipunctata (Coleoptera: Cerambycidae) in Portugal. Bulletin of Entomological Research 82: 425-432.