Dendroctonus valens (insect)
The most heavily attacked forests in China are located in mountains ranges in the Shanxi province from 600 to 2000 meters elevation (Zhang et al. 2002, in Yan et al. 2005). P. tabuliformis is a major reforestation species widely planted on degraded land; this increases tree stress and predisposes it to D. valens attack (Li et al. 2001 Yan et al. 2005). Mature and over-mature P. tabuliformis forests are infested, while younger forests are seldom attacked (Miao et al. 2001, in Yan et al. 2005).
D. valens occurs within a climatic region of China described as “warm temperature semi-moist” (Wu and Feng 1994, in Yan et al. 2005). Precipitation in northern China is generally lower than in other regions, especially from October to May (Sun et al. 2002, Yan et al. 2005), which may create favourable conditions for D. valens. High humidity and consecutive rainfall disrupts the growth of larvae and eggs of D. valens (Miao et al. 2001, in Yan et al. 2005). Parts of Northern China are becoming drier, hotter and plagued by drought leaving the primary pine host P. tabuliformis stressed and contributing to the current outbreak of D. valens (Sun & Shuqing et al. 2002, Li et al. 2001, Miao et al. 2001, in Yan et al. 2005). Winter temperatures, in particular, have been warmer than in previous years and appear to be a critical factor for beetle survival (Xu et al. 1986; Li et al. 2001).
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).
Adult colonisation: In spring beetles locate suitable plant host by detecting chemicals such as ethanol, monoterpenes (eg: alpha pinene and beta pinene) and pheromones (Byers 1995, LUBIES 2004). The female bores a hole in the bole of the tree and is soon joined by a male. Resin and frass pitch tube are formed on the bark or drop to the ground in pellets. Boring may exceed 2.5cm per day and the gallery may be extended to the larger roots. One or two pairs of beetles may be found per gallery. Beetles remain in their pine for several months, enlarging their galleries laterally.
Egg stage: 2 weeks in California, USA 1 to 2 weeks in China (Yan et al. 2005). The female red turpentine beetle oviposits (lays its eggs) within the phloem of trees or fresh stumps. Eggs are laid in an elongate mass along the side of the gallery.
Larval stage: Length = 8 weeks in California, USA; 8 to 10 weeks in China (Yan et al. 2005). Larvae live in groups in communal chambers within the phloem. A unique feature of the beetle is that the larvae are gregarious whereas most other bark beetle larvae maintain separate feeding tunnels. Gregarious insects live and feed in communities (of the same kind). The larvae tunnels appear as irregularly-margined fan-shapes.
Pupa stage: Length = 1 week in California, USA; 1 to 2 weeks in China (Yan et al. 2005). As larvae complete their feeding they scoop out bits of wood or bark to make separate pupation cells. In the pupal, or resting stage, the wings, legs and antennae are held against the body. Pupation of over-wintering larva begins in early June, and eclosion (emergence) begins in early July; adults can be detected from May to October (Miao et al. 2001 in Yan et al. 2005).
Adult emergence & flight: Length of young adult stage = 1 week (Yan et al. 2005). Within a few days to several months warm Spring weather induces emerged beetles to bore out, take flight and disperse in the search for a suitable new host. Flight temperature ranges have been recorded from 19 degrees C to 23 degrees C. In relatively warmer regions emergence and new attacks may occur at nearly any time of the year. In colder regions winter hibernation of the adult or larva may occur, often taking place under root bark (Britton and Sun 2002, Wu et al. 2002, in Yan et al. 2005). (Pupae and eggs rarely overwinter.)