Host-plant acceptance on mineral soil and humus by the pine weevil Hylobius abietis (L.)

1 The pine weevil Hylobius abietis (L.) (Coleoptera, Curculionidae) is an economically important pest of conifer forest regeneration in Europe and Asia. 2 Soil scarification, which usually exposes mineral soil, is widely used to protect seedlings from weevil attack. However, the mechanism behind this protective effect is not yet fully understood. 3 Field experiments were conducted to determine the pine weevil's responses to visual and odour stimuli from seedlings when moving on mineral soil and on undisturbed humus surface. 4 One experiment measured the number of pine weevils approaching seedlings, with and without added host odour, on mineral soil and undisturbed humus. Seedlings with added host odour attracted more weevils on both soil types. Unexpectedly, somewhat more weevils approached seedlings surrounded by mineral soil. 5 In a similar experiment, feeding attacks on seedlings planted directly in the soil were recorded. Only half as many seedlings were attacked on mineral soil as on undisturbed humus. 6 In the first experiment, the weevils were trapped 2.5 cm from the bases of the seedlings' stems, whereas they could reach the seedlings in the experiment where seedlings were planted directly in the soil. We conclude that the pine weevils' decision on whether or not to feed on a seedling is strongly influenced by the surrounding soil type and that this decision is taken in the close vicinity of the seedling. The presence of pure mineral soil around the seedling strongly reduces the likelihood that an approaching pine weevil will feed on it

Local host-dependent persistence of the entomopathogenic nematode Steinernema carpocapsae used to control the large pine weevil Hylobius abietis

Entomopathogenic nematodes (EPN) applied inundatively to suppress insect pests are more likely to persist and establish in stable agroecosystems than in annual crops. We investigated a system of intermediate stability: three stumps harbouring the large pine weevil (Hylobius abietis L.; Coleoptera: Curculionidae), a major European forestry pest. We tested whether persistence of EPN Steinernema carpocapsae Weiser (Rhabditida: Steinernematidae) applied around stumps is maintained by recycling of EPN through pine weevils developing within stumps. Steinernema carpocapsae was detected in soil around and under the bark of treated tree stumps up to two years, but not 4–5 years after application. Differences in nematode presence between sites were better explained by tree species (pine or spruce) than soil type (mineral or peat). Presence of S. carpocapsae in soil was positively correlated with the number of H. abietis emerging from untreated stumps the previous year, which was greater for pine stumps than spruce stumps

A herbivore tag-and-trace system reveals contact- and density-dependent repellence of a root toxin

Foraging behavior of root feeding organisms strongly affects plant-environment-interactions and ecosystem processes. However, the impact of plant chemistry on root herbivore movement in the soil is poorly understood. Here, we apply a simple technique to trace the movement of soil-dwelling insects in their habitats without disturbing or restricting their interactions with host plants. We tagged the root feeding larvae of Melolontha melolontha with a copper ring and repeatedly located their position in relation to their preferred host plant, Taraxacum officinale, using a commercial metal detector. This method was validated and used to study the influence of the sesquiterpene lactone taraxinic acid β-D-glucopyranosyl ester (TA-G) on the foraging of M. melolontha. TA-G is stored in the latex of T. officinale and protects the roots from herbivory. Using behavioral arenas with TA-G deficient and control plants, we tested the impact of physical root access and plant distance on the effect of TA-G on M. melolontha. The larvae preferred TA-G deficient plants to control plants, but only when physical root contact was possible and the plants were separated by 5 cm. Melolontha melolontha showed no preference for TA-G deficient plants when the plants were grown 15 cm apart, which may indicate a trade-off between the cost of movement and the benefit of consuming less toxic food. We demonstrate that M. melolontha integrates host plant quality and distance into its foraging patterns and suggest that plant chemistry affects root herbivore behavior in a plant-density dependent manner. © 2017, Springer Science+Business Media New York

Influence of climate and forest management on damage risk by the pine weevil Hylobius abietis in northern Sweden

The pine weevil Hylobius abietis (L.) is an economically important pest insect that kills high proportions of conifer seedlings in reforestation areas. It is present in conifer forests all over Europe but weevil abundance and risk for damage varies considerably between areas. This study aimed to obtain a useful model for predicting damage risks by analyzing survey data from 292 regular forest plantations in northern Sweden. A model of pine weevil attack was constructed using various site characteristics, including both climatic factors and factors related to forest management activities. The optimal model was rather imprecise but showed that the risk of pine weevil attack can be predicted approximatively with three principal variables: 1) the proportion of seedlings expected to be planted in mineral soil rather than soil covered with duff and debris, 2) age of clear-cut at the time of planting, and 3) calculated temperature sum at the location. The model was constructed using long-run average temperature sums for epoch 2010, and so effects of climate change can be inferred from the model by adjustment to future epochs. Increased damage risks with a warmer climate are strongly indicated by the model. Effects of a warmer climate on the geographical distribution and abundance of the pine weevil are also discussed. The new tool to better estimate the risk of damage should provide a basis for foresters in their choice of countermeasures against pine weevil damage in northern Europe

Structure-Activity Relationships of Phenylpropanoids as Antifeedants for the Pine Weevil Hylobius abietis<i/>

Ethyl cinnamate has been isolated from the bark of Pinus contorta in the search for antifeedants for the pine weevil, Hylobius abietis. Based on this lead compound, a number of structurally related compounds were synthesized and tested. The usability of the Topliss scheme, a flow diagram previously used in numerous structure-activity relationship (SAR) studies, was evaluated in an attempt to find the most potent antifeedants. The scheme was initially followed stepwise; subsequently, all compounds found in the scheme were compared. In total, 51 phenylpropanoids were tested and analyzed for SARs by using arguments from the field of medicinal chemistry (rational drug design). Individual Hansch parameters based on hydrophobicity, steric, and electronic properties were examined. The effects of position and numbers of substituents on the aromatic ring, the effects of conjugation in the molecules, and the effects of the properties of the parent alcohol part of the esters were also evaluated. It proved difficult to find strong SARs derived from single physicochemical descriptors, but our study led to numerous new, potent, phenylpropanoid antifeedants for the pine weevil. Among the most potent were methyl 3-phenylpropanoates monosubstituted with chloro, fluoro, or methyl groups and the 3,4-dichlorinated methyl 3-phenylpropanoate

Hydroxy-methoxybenzoic methyl esters : Synthesis and antifeedant activity on the pine weevil, Hylobius abietis

The pine weevil Hylobius abietis (L.) (Coleoptera: Curculionidae) feeds on the bark of coniferous seedlings and is the economically most important forestry restocking pest in large parts of Europe. Substances with an antifeedant effect may offer an environmentally friendly alternative to insecticides for the protection of planted seedlings. Bioassays were performed on commercial and synthetic methyl hydroxy-methoxybenzoates in order to determine their possible antifeedant activity. Two methyl hydroxy-methoxybenzoates were synthesized by esterification and mono-O-methylation of two dihydroxybenzoic acids. A regioselective protection-deprotection strategy was used in the synthetic pathway of the other non-commercial esters, esterification and selective pivaloylation of the less-hindered hydroxyl group of other commercial dihydroxybenzoic acids gave diester intermediates, which then were O-methylated before methanolysis of the pivaloyl group which yielded the desired non-commercial methyl hydroxy-methoxybenzoates. The five synthesized methyl hydroxy-methoxybenzoic esters were complemented with commercial samples of the five other isomers of methyl hydroxy-methoxybenzoate and spectrometric data were collected for the complete set of isomers. All ten isomers were tested for their antifeedant effect on the pine weevil. The effect varied considerably among the hydroxy-methoxybenzoic esters. Methyl 2-hydroxy-3-methoxybenzoate showed the highest effect and may thus be a candidate for practical use in pine weevil pest management.841SN Times Cited:8 Cited References Count:12</p

Quantitative Structure-Activity Relationships of Pine Weevil Antifeedants, a Multivariate Approach

Antifeedant activity of mainly phenylpropanoic, cinnamic, and benzoic acids esters was tested on the pine weevil, Hylobius abietis (L.). Of 105 compounds screened for activity, 9 phenylpropanoates, 3 cinnamates, and 4 benzoates were found to be highly active antifeedants. To understand the structure-activity relationships of these compounds, a multivariate analysis study was performed. A number of molecular and substituent descriptors were calculated and correlated to results from two-choice feeding tests with H. abietis. Three local models were developed that had good internal predictive ability. External test sets showed moderate predictivity. In general, low polarity, small size, and high lipophilicity were characteristics for compounds having good antifeedant activity