Dendroctonus valens (insect)
Chemical: Bark beetles are good candidates for semiochemical-based control methods (Borden 1997, in Rappaport Owen & Stein 2001). The use of ecologically-selective semiochemicals are environmentally friendly and non-toxic (Carmona Undated). Research on bark beetle response to pine host volatiles and beetle pheromones in China and North America is on-going. Anti-aggregation pheromones such as verbenone repel red turpentine beetles. Verbenone acts as a chemical message to D. valens that host food resources are limited. Release rates of the pheromone must be carefully controlled as low release rates of verbenone will actually increase D. valens response to host attractant molecules.Pine monoterpenes are highly attractive to bark beetles (Liu & Dai 2006) and have applications in the monitoring and trapping of beetles. (+)-3-carene and the standard North American D. valens lure of a 1:1:1 ratio of (+) alpha-pinene & beta-pinene (+)-3-carene are effective in attracting D. valens (Erbilgin et al. 2007). The standard lure was used in a mass-trapping program in the Guandi Mountains (west of Shanxi province, China). The proportion of infested forest decreased by 64.4% and the average number of attacks per tree decreased by 59.2% (Guo et al. 2003, in Yan et al. 2005). Ethanol attracts various scolytid beetles including D. valens when released at relatively low or medium concentrations (Yan et al. 2005). A 1:1 ration of ethanol:turpentine captured 60 times more D. valens than turpentine alone (Klepzig et al. 1991, in Yan et al. 2005). 4-Allylanisole (4AA), released by some pines, may prove useful in protecting high-value logs or individual trees by it ability to reduce bark beetle attraction to ethanol (in combination with alpha-pinene & beta-pinene) (Jospeh et al. 2001).
Insecticides: Fumigation or injection of beetle galleries or spraying of basal tree trunks with insecticides may result in 90 to 98% beetle mortality (Shanxi Forestry Bureau Unpub. Data). Fumigation is costly and difficult and is not effective at controlling beetle populations over large areas. It can result in environmental contamination and decreased natural enemy populations.
Biological: Research from the Université Libre de Bruxelles showed that Rhizophagus grandis is able to successfully complete its life-cycle with D. valens. R. grandis responds to attractants produced by D. valens, enters D. valens galleries and oviposits a relatively high number of eggs. (LUBIES 2004). Steinernema ceratophorum, a nematode isolated from Jilin province in northeast China, has also produced high infection rates of D. valens larva, causing a larval mortality rate of 90% (Jian et al. 2002).
Please follow this link for detailed information on the management of the Red turpentine beetle (Dendroctonus valens).
The importance of synchronised bark beetle attacks is poorly understood. In southwest North America ponderosa pine forests D. adjunctus and D. valens often occur from the base of the tree to half a meter in height. Beetle success in killing a vigorous host by a synchronised attack could offset costs of inter-specific competition. Alternatively, niche overlap of two or more species may prevent an individual species from ever dominating utilisation of the resource and reaching outbreak levels. Inter-specific competition for resources may hold invasive species in check in their native range. This lack of inter-specific competition in introduced areas may explain the severity of outbreak of D. valens in northern Chinese forests. Sakai and colleagues (2001, in Erbilgin et al. 2007) reported that the reasons underlying the greater tree mortality in China could include a lack of evolutionary adaptation to this new insect-host (Dendroctonus valens-Pinus tabulaeformis) association.
Wallin and colleagues (2008) found that the thinning of ponderosa pine Pinus ponderosa near Flagstaff (Arizona, USA) decreased the percentage of trees with bark beetle infestations. Beetle attacks were induced by beetle community response to a Dendroctonus brevicomis pheromone; the D. brevicomis pheromone attracts several bark beetle species. The positive affect of restoration treatments on tree resistance may be due to the underlying stimulation of resin defenses. Thinning treatments have been reported to increase production of carbon-based defenses such as resin in some studies (Kolb et al. 1998, Feeney et al. 1998, McDowell et al. 2007, in Wallin et al. 2008). These findings along with those of the authors suggest that thinning reduces resource competition among trees and hence, tree stress, and increases carbon allocation to resin defenses in the tree. Resin flow after phloem wounding was greater in restoration treatments than in control in the first and second year after treatment. The authors found a negative correlation between resin volume and the number of D. valens brood which emerged from the bole.
Because the red turpentine beetle lives in a protected micro-habitat beneath the pine bark insecticides are not usually effective. Chemical spray applications made once the beetles have aggregated and penetrated the bark is ineffective. Treatment must target beetles during their flight activity preventing beetle attacking a new host tree. The bark of the tree is sprayed so that when the beetle lands on the pine to bore it is killed. Spraying a persistent insecticide on valuable uninfested pine at risk of infestation be warranted.
Protective spraying for bark beetles must be done by a licensed pesticide applicator. Pyrethroids (such as Astro or Dragnet) or any of the flowable (EC) formulations of carbaryl may be applied to protect healthy trees from bark beetle infestations. In most cases, the time to apply is in late winter to early spring in warm lowland areas.
Infested tree or tree limbs may be removed and chipped or burned. General hygeine principles should be followed. For example stumps of infested trees provide optimum breeding grounds for the red turpentine beetle and should be extracted and disposed of sensibly. No infested material should be piled next to, or anywhere near, a suceptible pine tree.
Only pine species adapted to a habitat should be planted. If bark beetles are a threat only non-host trees should be planted. In North America, appropriate species would include redwoods or atlas cedars. A mixture of tree species in planted landscapes will reduce mortality resulting from bark beetles and wood borers. Stresses placed on trees caused by poor planting, planting at the wrong time of year or lack of proper care afterwards will increase a trees susceptibility to bark beetles or wood borers. (Seybold, Paine & Dreistadt 2008)
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