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.     

A flexible sand coating (Conniflex) for the protection of conifer seedlings against damage by the pine weevil Hylobius abietis

1 A new method for the physical protection of conifer seedlings against feeding damage by Hylobius abietis (L.), is described and evaluated in field trials in Swedish forest plantations.
2 The lower 60% of the stem of the seedling is protected by the Conniflex coating, consisting of fine sand (grain size = 0.2 mm) embedded in an acrylate dispersion that remains flexible after drying.
3 Seedlings are treated in the nursery by a large-scale application procedure involving four steps: (i) spraying the seedlings with water; (ii) application of fixative to the lower sections of the stems, (iii) application of fine sand to the fixative; and (iv) drying of the fixative.
4 A field experiment over three seasons demonstrated a significant increase in survival for coated seedlings compared with untreated seedlings. The survival rate increased from 29% to 97% for Scots pine and from 26% to 86% for Norway spruce. Coating the lower 30% of the stem (instead of 60%) provided inferior protection, resulting in only 64% survival in spruce.
5 Field trials in 11 commercial plantation areas indicated that the Conniflex sand coating was as effective in protecting seedlings as treatment with the insecticide imidacloprid.
6 The new method of coating conifer seedlings with fine sand provides an effective and environmentally sound alternative to insecticide treatment.     

Monoterpenes emitted by the large pine weevil, Hylobius abietis (L.) feeding on Scots pine, Pinus sylvestris L.

Abstract. Attraction of the large pine weevil, Hylobius abietis (L.) (Coleoptera: Curculionidae) to pine logs was enhanced by the presence of weevils already on the logs. We investigated the volatiles emitted by insects feeding on host trees to determine the mechanism of the attraction. Chemical analyses of the collected volatiles showed large amounts of monoterpenes. There were no qualitative differences in the collections, between Scots pine alone and pine plus feeding weevils, nor between males and females, mated or virgin. Strong quantitative differences in monoterpenes existed that were correlated to the surface of cut bark. Electroantennograms (EAGs) were recorded on male and female antennae stimulated by increasing doses of collected volatiles. EAGs for pine alone and pine plus weevils at the same stimulus loading in (a + P)-pinene gave superimposable curves. EAGs of male and female volatiles were also identical. These results suggest an attraction mediated by host plant allelochemicals rather than by an aggregation pheromone.     

Steinernema kraussei,an indigenous nematode found in coniferous forests: efficacy and field persistence against Hylobius abietis

1 More than 100 ha of forest restocking sites in Northern Britain are treated annually with the entomopathogenic nematode Steinernema carpocapsae to control larvae of the large pine weevil, Hylobius abietis. However, data on geographical distribution, thermal niche breadth and foraging strategy suggest that S. carpocapsae may be a poor choice for this application. 2 We undertook laboratory and field experiments that compared S. carpocapsae with Steinernema kraussei for efficacy towards H. abietis. Steinernema kraussei is indigenous to Northern Britain, active at low temperatures and is thought to adopt a ‘cruise’ foraging strategy particularly suitable for finding subterranean sedentary insects such as H. abietis. Conversely, S. carpocapsae has not been recorded in Northern Britain, prefers warmer temperatures and is thought to remain at the soil surface adopting an ambush foraging strategy. 3 There were no differences in the ability of the two nematodes to infect and kill larvae of H. abietis in laboratory experiments and, in two field experiments, both species were equally effective both in terms of parasitizing larvae within the stumps and reducing emergence of adult H. abietis. In one experiment, we monitored persistence of nematodes for 1 year after application and found S. kraussei persistence was much greater than that of S. carpocapsae. 4 The greater persistence of S. kraussei suggests that this nematode is better adapted to conditions in Northern Britain, but this may potentially represent a greater threat to nontarget insects. 5 Our data suggest that there would be little benefit associated with substituting S. kraussei for S. carpocapsae in integrated pest management systems for H. abietis.     

Influence of insecticide, wax and biofungicide treatments, applied to Pinus sylvestris and Picea abies, on the olfactory orientation of the large pine weevil, Hylobius abietis L. (Coleoptera: Curculionidae)

1 A four-arm olfactometer was used to test the effect of permethrin ‘Gori 920^®’ and the wax treatment ‘CereNat^® E30’ on the response of mature adult Hylobius abietis to olfactory stimuli from seedlings of Pinus sylvestris and Picea abies. 2 Also investigated in the olfactometer was the effect of Rotstop^®, a biofungicide for the control of Fomes root and butt rot, Heterobasidion annosum, on the responses of mature adult female H. abietis to stump material of both P. sylvestris and P. abies. 3 Hylobius abietis was significantly more attracted to untreated P. sylvestris seedlings compared to those treated with CereNat^® E30 or permethrin Gori 920^®. No differences in response to P. abies seedlings were found. 4 With Rotstop^®, no changes in the attractiveness of P. sylvestris stump material were found, but that of P. abies was significantly increased compared to untreated material.     

Oviposition patterns of the pine weevil Hylobius abietis

Spatial and temporal distributions of eggs laid by the pine weevil Hylobius abietis (L.) (Coleoptera: Curculionidae) were studied by taking root and soil samples around pine stumps on a clear-cutting in central Sweden. In addition, first-instar larvae migrating in the soil were sampled using traps baited with host-odour. Eggs were found in the soil rather than in the bark of stump roots, which previously has been regarded as the usual oviposition site. Based on an oviposition experiment and additional field observations we conclude that eggs are laid in the bark of roots only when the surrounding material is likely to dry out. We suggest two explanations for why weevils oviposit mainly in the soil, although they are known to show stereotypic behaviour when inserting eggs in stump roots: (1) egg predation by other arthropods or by conspecifics is avoided, and (2) newly hatched pine weevil larvae are better than ovipositing females at locating suitable sites for larval feeding.