Platypus quercivorus
(oak ambrosia beetle)

P. quercivorus is widely distributed in Asia, including temperate, subtropical and tropical ecosystems in India, Indonesia (Java), Japan, Papua New Guinea and Taiwan (Beaver and Hsien-Tzung Shih, 2003). In Japan, this insect is found from the island of Ishigaki Shima to Honshu (Hamaguchi and Goto, 2003).

The adults are capable of sustained flight for at least 1 km and may also be dispersed on air currents. All life stages are subjected to human-assisted dispersal. The use of oak crating, pallets or dunnage in international trade could result in the inter-continental spread of all the life stages of P. quercivorus. The localized spread of newly established infestations could be facilitated via the transport of logs and firewood.

P. quercivorus can be found in temperate, subtropical and tropical forests. It is presently a pest of mixed oak forests in parts of Japan.

P. quercivorus has a wide host range. It attacks many species of the family Fagaceae but it is also known to attack trees from other families including Aquifoliaceae, Lauraceae, Rosaceae and Cupressaceae (Wood and Bright, 1992).

The genus Platypus is exceptionally large within the Platypodidae, with several hundred recognized species. These are distributed throughout the world's temperate and tropical forests, and attack both broadleaf and coniferous trees (Bright and Skidmore, 2002). Eight species are known to occur in North America (Furniss and Carolin, 1977; Drooz, 1985; Cibrián Tovar et al., 1995). These include Platypus flavicornis [Myoplatypus flavicornis], which invades the basal portions of pines in large numbers in south-eastern USA following attacks by bark beetles, and Platypus parallelus [Euplatypus parallelus], a tropical species present in southern USA and Mexico, which is regarded as the most destructive ambrosia beetle in the world (Drooz, 1985).

Members of the genus Platypus are ambrosia beetles and breed in the wood of host trees. White splinters are produced during gallery construction as opposed to fine sawdust, which is produced by other ambrosia beetles. Also, unlike other ambrosia beetles, the galleries of Platypus spp. often penetrate into the heartwood. The larvae and adults feed on ambrosia fungi, which are stored and disseminated by the adult female. The fungal associates of several species of Platypus are members of the genus Raffaelea. In western North America, the ambrosia fungus associated with Platypus wilsoni is Raffaelea canadensis (Furniss and Carolin, 1977). In Argentina, Raffaelea santoroi is associated with Platypus mutatus (Giménez and Etiennot, 2003). In Europe, Raffaelea ambrosiae is associated with the oak ambrosia beetle, Platypus cylindrus (Babuder and Pohleven, 1995).

Adult ambrosia beetles vector their associated ambrosia fungi via structures known as mycangia, which store fungal spores. In the family Platypodidae, if mycangia are present, they are simple; usually small pits or notches in the integument. These structures are often present only on the females although the males typically initiate the attacks. For example, in the case of Platypus hintzi the mycangia consist of a pair of small hollows on the pronotum. In contrast, P. wilsoni has numerous small punctures on the pronotum (Cook, 1977). Ito et al. (2004) suggested that P. quercivorus has mycangia similar to P. hintzi.

Male P. quercivorus initiate the attacks on the boles of host trees and excavate galleries for mating from June to October (Soné et al., 2000). Apparently the first entry holes bored by male beetles trigger a mass attack (Kobayashi and Ueda, 2003). The attacks generally occur near ground level (Hijii et al., 1991). A single female joins the male and constructs the oviposition gallery after mating. This is kept clean by the male who expels the residues to the outside of the tree. During gallery construction, the females inoculate the gallery surface with spores of the ambrosia fungus, which the larvae feed on. The adult females begin to deposit eggs at the terminal parts of the tunnels, 2 to 3 weeks after gallery construction begins. The eggs are deposited in individual niches. An average of 50 to 60 larvae develop in a single gallery system but the number of larvae can be as high as 161. The larvae feed on the ambrosia fungus that develops on the walls of the galleries. Pupation occurs in the larval galleries. The majority of new adults leave their maternal galleries in September and October but some adults remain in the galleries until the spring and then die. In other cases the larvae reach the fifth-instar by late November and overwinter in pupal chambers. Pupation begins in the following May and the adults emerge in June and July. They emerge through entry holes made by the parents (Soné et al., 1998).

In Japan, Quercus mongolica and Quercus serrata that are mass-attacked by P. quercivorus, are usually killed later in the summer. Two fungi have been recovered from trees attacked by this insect and described as new species. Ophiostoma longicollum was described from Q. mongolica infested by P. quercivorus in 1998 (Masuya et al., 1998). The fungus, Raffaelea quercivora was isolated from discoloured sapwood, necrotic inner bark, the body surfaces of beetles, female beetle's mycangia and beetle galleries of symptomatic trees in 2002. Inoculation tests indicated that R. quercivora is the causal agent of Japanese oak disease and P. quercivorus is its vector. This is the first known occurrence of mass-mortality of trees in the family Fagaceae, caused by a species of Platypus and an associated ambrosia fungus of the genus Raffaelea (Ito et al., unda).

No natural enemies have been reported.

Lumber, crating, pallets and dunnage made from oak should be inspected for ambrosia beetle galleries and an associated brown discoloration caused by Raffaelea quercivora. Infestations in standing trees can be detected by the presence of white boring dust near the root collar and late summer tree mortality.

Most species of Platypus are similar in appearance. Species identification of ambrosia beetles (families Platypodidae and Scolytidae) must be carried out on the adults. A taxonomist, with expertise in the family Platypodidae, should identify specimens suspected of being exotic species of Platypus.

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

The management of Platypus spp. beetles includes the application of contact insecticide sprays to the bark of high value trees to prevent attack. Systemic insecticides can be applied to the soil or bark of infested trees. Attacks in harvested logs can be prevented by the timely removal of them from forested areas and rapid processing or debarking at the sawmill (Cibrián Tovar et al., 1995).

Pest management methods that are designed to reduce the rate of oak mortality caused by the combination of P. quercivorus and Raffaelea quercivora are being developed in Japan. Recent studies indicated that both P. quercivorus and its associated fungus can be controlled by the injection of NCS [metam-ammonium] (N-methyldithiocarbamate) into holes bored in the stems of host trees (Weng PuJin et al., 2000).