Emissions of biogenic volatile organic compounds (BVOCs) from the rhizosphere of Scots pine (Pinus sylvestris) seedlings exposed to warming, moderate N addition and bark herbivory by large pine weevil (Hylobius abietis)

Aims Biogenic volatile organic compound (BVOC) research has been mostly focused on foliar emissions. In this experiment, the main focus was on rhizosphere BVOC emissions of Scots pine seedlings under changing growth conditions. Methods Soil-growing Scots pines were exposed to increased air (0.5°C) and soil (4.0°C) temperature and N addition (30 kg N ha− 1 yr− 1) for three growing seasons in a field experiment. In addition to these factors, seedlings were exposed to bark herbivory by large pine weevils in two last seasons. Gas-chromatography and mass-spectrometry was used for analyzing the BVOC samples collected from pine rhizosphere. Results Almost 98 % of BVOCs were non-oxygenated monoterpenes (nMTs), 1 % oxygenated monoterpenes (oMTs), 0.5 % sesquiterpenes (SQTs), and 1 % other BVOCs. In both years, there was an interaction of warming, N addition and bark herbivory on rhizosphere BVOC emissions. In 2015, warming and N addition in single exposures decreased oMT emissions, while herbivory in single exposure increased oMT emissions. In 2016, the three-way interaction showed that the effects of warming, N addition and herbivory on BVOCs were mainly detected in single exposures. In 2016, warming decreased nMT, oMT, SQT and other BVOC emissions; N addition decreased oMT and SQT emissions; and herbivory decreased SQT and other BVOC emissions. Conclusions Warming and N addition in single exposures decreased the rhizosphere BVOC emissions. The effect of bark herbivory on BVOC emissions varied between the years from increase to decrease. It seems that under altered growth conditions Scots pine seedlings may reduce carbon investment to rhizosphere BVOCs.

Simple Is Best: Pine Twigs Are Better Than Artificial Lures for Trapping of Pine Weevils in Pitfall Traps

The large pine weevil Hylobius abietis (Linnaeus 1758) is the main pest of coniferous seedlings in Europe and causes substantial damage in areas that have been clear-cut or otherwise disturbed. We compared the efficacy of different attractants for the capture of H. abietis adults in white pitfall traps. The field experiment was performed from mid-April to the end of August 2018 at six plots in Central Europe located in spruce stands that had been clear-cut. At each plot, we compared five attractants: one pine twig with ethanol, Hylodor, alpha-pinene + ethanol, turpentine oil and ethanol (separated), and turpentine oil + ethanol (not separated). Traps without attractant served as a control. Six traps for each attractant or control were distributed at each plot. Of the total number of H. abietis adults trapped, 43.3%, 20.5%, 17.9%, 9.8%, 8.5% and 0.5% were captured in traps with pine twigs with ethanol, alpha-pinene, Hylodor, turpentine, oil + ethanol (separated), turpentine oil + ethanol (combined), and no attractant, respectively. The bottom of each trap contained propylene glycol to kill and preserve beetles. The small number of beetles captured in the control traps confirms that the propylene glycol:water mixture did not influence the trapping of H. abietis. The use of pitfall traps with a suitable attractant (especially pine twigs and ethanol) should be useful for monitoring of H. abietis, because it is simple and cost-effective. The use of such pitfall traps to control H. abietis by mass trapping would require 50 to 100 traps per ha.

Deep planting of Norway spruce seedlings: effects on pine weevil feeding damage and growth

As the use of mounding as a soil preparation method and mechanized planting become more common, the use of deep planting has increased. In deep planting, a greater portion of the stem is buried below the soil surface. However, it is feared that this increases the risk of insect damage, especially damage from the pine weevil Hylobius abietis (L.) (Coleoptera: Curculionidae). The effects of planting depth on the feeding preference of adult pine weevils in 1.5-year-old Norway spruce (Picea abies (L.) Karst.) seedlings were investigated using choice experiments. Seedlings were planted at two depths in a pot to compare (i) normal planting depth (target depth 3 cm) and (ii) deep planting (8 cm). In deep-planted seedlings, the number of feeding scars on lower stem parts above the soil surface, as well as severe feeding, was effectively reduced. After planting, the aboveground portion of the stem in deep-planted seedlings was clearly shorter and thinner, but the stems grew more both in height and diameter during the 5-week growing period than did normal-planted seedlings. At the end of the experiment, the deep-planted seedlings were still shorter, but there was no difference in diameter. In conclusion, deep planting protected 1.5-year-old seedlings from pine weevil feeding and improved seedling growth.

Gut microbiota of the pine weevil degrades conifer diterpenes and increases insect fitness

The pine weevil (Hylobius abietis), a major pest of conifer forests throughout Europe, feeds on the bark and cambium, tissues rich in terpenoid resins that are toxic to many insect herbivores. Here we report the ability of the pine weevil gut microbiota to degrade the diterpene acids of Norway spruce. The diterpene acid levels present in ingested bark were substantially reduced on passage through the pine weevil gut. This reduction was significantly less upon antibiotic treatment, and supplementing the diet with gut suspensions from untreated insects restored the ability to degrade diterpenes. In addition, cultured bacteria isolated from pine weevil guts were shown to degrade a Norway spruce diterpene acid. In a metagenomic survey of the insect’s bacterial community, we were able to annotate several genes of a previously described diterpene degradation (dit) gene cluster. Antibiotic treatment disrupted the core bacterial community of H. abietis guts and eliminated nearly all dit-genes concordant with its reduction of diterpene degradation. Pine weevils reared on an artificial diet spiked with diterpenes, but without antibiotics, were found to lay more eggs with a higher hatching rate than weevils raised on diets with antibiotics or without diterpenes. These results suggest that gut symbionts contribute towards host fitness, but not by detoxification of diterpenes, since these compounds do not show toxic effects with or without antibiotics. Rather the ability to thrive in a terpene rich environment appears to allow gut microbes to benefit the weevil in other ways, such as increasing the nutritional properties of their diet.

Response of adult large pine weevils (Hylobius abietis L.) to neonicotinoids (chloronicotinyls) and fenylpirazoles insecticides

Reakcja chrząszczy szeliniaka sosnowca (Hylobius abietisL.) na insektycydy z grupy neonikotynoidów (chloronikotynyli) i fenylopirazoli

Molecular characterization of the entomopathogenic fungi Lecanicillium spp. (Deuteromycota: Hyphomycetes) isolated from white pine weevil, Pissodes strobi (Coleoptera: Curculionidae), in British Columbia

The entomopathogenic fungal genus Lecanicillium Gams and Zare includes species that are highly pathogenic to many genera of insects. Three species, Lecanicillium longisporum (Petch) Zare and W. Gams, L. muscarium (Petch) Zare and W. Gams, and L. pissodis Kope and Leal, were found to be entomopathogens of adult white pine weevils, Pissodes strobi (Peck), in coastal British Columbia. Morphological characteristics were used to identify these species, but variation in conidial shape and size made it difficult to classify some of the isolates into the correct species of Lecanicillium. To confirm the identity of these Lecanicillium species, we used molecular tools such as polymerase chain reaction – restriction fragment length polymorphism and DNA sequencing.