The great spruce bark beetle, Dendroctonus micans (Kugelann) (Coleoptera: Curculionidae), has been a potential threat for Turkey and the entire Eurasian spruce forests for many years. Control strategies which have been applied so far are still insufficient to prevent its damage. A previous study has shown that a Beauveria isolate (ARSEF 9271) proved to be an efficient microbial control agent against the great spruce bark beetle. In this study, this isolate was identified as B. pseudobassiana based on the partial sequence of EF1-a and ITS sequence. A conidial suspension (1 9 10 8 / ml) of this fungus caused 100% mortality on both larvae and adults of D. micans within 5 and 6 days, respectively. Also, it caused 100% mycosis value on both larvae and adults. Mortality values of horizontal transmission experiments between larvae and adults which were contaminated with 1 9 10 6 /ml spore suspension at 25%, 50%, 75% and 100% rates were determined as 100% after 15 days at 20°C under the laboratory conditions. We also determined the decrease of the damage in spruce wood block (15 9 25 cm) when the contamination rate of the larvae was increased. Our results indicate that B. pseudobassiana ARSEF 9271 seems to be a very promising biocontrol agent against D. micans.
Summary
Mistletoe infection results in substantial growth losses in mistletoe‐infected forests. This study reports and evaluates the results of retrospective analyses of radial growth of Scots pine (Pinus sylvestris) in relation to the level of infection of pine mistletoe (Viscum album ssp. austriacum). A total of 43 Scots pine trees were destructively sampled from different sites. Of these trees, 14 were uninfected and 29 were infected. Infection classes were determined using six‐class dwarf mistletoe rating system (DMRS). All needle and mistletoe biomass were removed completely and weighed for each sampled tree. Subsamples from needles and all mistletoe biomass were taken to the laboratory for oven‐dried weight determinations. Five‐cm‐thick wood discs were cut from the stem at the breast height (1.3 m) to determine annual basal area increment for the last 25 years. In addition to DMRS, new infection classes were created using mistletoe‐to‐needle biomass (MB/NB) ratio. The results showed that the radial growth losses could be as much as 41% to 64% at different infection levels. The rate of growth loss in relation to DMRS and MB/NB ratio was similar, but with a larger variability in DMRS values. The results showed that both DMRS rating and MB/NB ratio seem to be important for quantifying growth loss on Scots pine trees infected with mistletoe. The results of this study can also be invaluable in modelling the effects of mistletoe on the growth of Scots pine trees.
Ips sexdentatus (Boerner) and I. typographus (Linnaeus) (Coleoptera: Curculionidae) are considered to be important destructive pests of coniferous forests in Europe and Asia. In this study, the efficacy of Beauveria pseudobassiana strain ARSEF 9271 isolated from Dendroctonus micans (Kugelann) (Coleoptera: Curculionidae) was evaluated against I. sexdentatus and I. typographus adults. Insects were treated with different conidial concentrations of the fungus to determine the virulence. A conidial suspension of 1 × 10 8 conidia mL -1 caused 100% mortality in both I. sexdentatus and I. typographus within 5 and 7 days, respectively. Additionally, 100% mycosis was obtained in the concentration-response experiments for both insects. LC 50 values of the fungus were calculated as 3.94 × 10 4 conidia mL -1 and 1.32 × 10 4 conidia mL -1 for I. sexdentatus and I. typographus, respectively. I. sexdentatus and I. typographus adults were also inoculated with a conidial suspension of 1 × 10 6 conidia mL -1 at inoculation rates of 0% (control), 25%, 50%, 75%, and 100% to determine the horizontal transmission of the fungus. Mortality values from horizontal transmission experiments were determined as 100% at all rates after 15 days at 20 °C under laboratory conditions. Our results indicate that B. pseudobassiana ARSEF 9271 is a promising microbial control agent against the tested Ips species and can horizontally spread among a population of both I. sexdentatus and I. typographus.
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