Reproductive development and maternal effects in the pine weevil Hylobius abietis

1. In a laboratory study of maturation feeding of female pine weevil Hylobius abietis on current and 1‐year‐old stem bark of transplants of Scots and Corsican pine, Norway and Sitka spruce, Douglas fir, and hybrid larch, the length of the pre‐oviposition period was influenced by the species on which weevils fed. The shortest pre‐oviposition period was on hybrid larch (11.8 days) and the longest on Douglas fir (15.5 days). 2. The species on which weevils fed also affected fecundity but there was evidence of a species–year interaction. Over a period of 36 days, most eggs were laid by weevils feeding on current stem of Norway spruce and Corsican and Scots pine and fewest on current stem of Sitka spruce. 3. Significant maternal effects on egg size were observed both in relation to female size and conifer species. The largest eggs were laid on Corsican pine and the smallest on Douglas fir, with no evidence of a trade‐off between number of eggs laid and their size. 4. There was a positive relationship between egg and larval size and between larval size and survival on logs of four conifer species. Residual resistance mechanisms in the bark of recently cut stumps and larval competition are discussed briefly in relation to the importance of the observed maternal effects on weevil population dynamics.     

Non-pesticide alternatives for reducing feeding damage caused by the large pine weevil (Hylobius abietis L.)

The large pine weevil (Hylobius abietis L.) is an important pest of young forest stands in Europe. Larvae develop under the bark of freshly cut pine and spruce stumps, but maturing weevils feed on the bark of coniferous seedlings. Such seedlings frequently die because of bark consumption near the root collar. We tested the effect of three treatments (the insecticide alpha cypermethrin, a wax coating and a glue coating) on the feeding damage caused by H. abietis on Douglas fir (Pseudotsuga menziesii) and Norway spruce (Picea abies) seedlings under semi-natural conditions. In two experiments (one in 2016 and another in 2017) seedlings in cages were subjected to pine weevil feeding for 16 weeks under shaded outdoor conditions. The experiment in 2016 compared insecticide and wax treatments and an untreated control on Douglas fir and Norway spruce, and the experiment in 2017 compared insecticide, wax and glue treatments and an untreated control on Norway spruce. In both experiments, all treatments significantly reduced H. abietis feeding damage at week 8 at the end of both experiments (week 16); the effect of treatments was significant only on spruce seedlings. The damages on Douglas fir seedlings was less on treated seedlings than on untreated control seedlings but differences were not significant. Coating stems with glue and especially with wax was generally effective at reducing weevil damage and in most cases provided control that was not significantly different from that provided by insecticide treatment. Our results suggest that a wax coating has the potential to replace the protection of seedlings provided by insecticides.     

Adult large pine weevils Hylobius abietis feed on silver birch Betula pendula even in the presence of conifer seedlings

1 The feeding preference of the adult pine weevil Hylobius abietis (L.) (Coleoptera: Curculionidae) for Betula pendula Roth was studied in no‐choice and paired‐choice feeding experiments. 2 In the first no‐choice test, large quantities of silver birch bark in Petri dishes were consumed; on average, the daily consumption of each weevil was 67 mm². 3 In the second no‐choice test, the weevils were offered 1‐year‐old silver birch seedlings for 6 days. Initially, the weevils fed mostly on the stem bases; later, they moved upward to feed on other parts of the stems. In addition to the main shoots, scars caused by gnawing were also found on leaf bases, blades, veins and petioles. Feeding resulted in the death of the main stems in 15% of the seedlings. 4 In the paired‐choice tests, the conifers were preferred to silver birch, even though a large amount of silver birch was also consumed in the presence of conifers. 5 In the paired‐choice tests, equal amounts of Scots pine and Norway spruce were always consumed. When hybrid aspen was offered, only small amounts were gnawed.     

Ants protect conifer seedlings from feeding damage by the pine weevil Hylobius abietis

• 1 Ants that protect food resources on plants may prey on (or deter) herbivores and thereby reduce damage. Red wood ants (of the Formica rufa group) are dominant ants in boreal forests of Eurasia and affect the local abundance of several herbivorous species.
• 2 The pine weevil Hylobius abietis (L.) is a herbivore that causes severe damage by feeding on the bark of coniferous seedlings within areas of forest regeneration.
• 3 We investigated whether ants can protect conifer seedlings from pine weevil feeding. In a manipulative experiment, ants were attracted to sugar baits attached to spruce seedlings and the damage caused by pine weevils was compared with control seedlings without ant‐baits.
• 4 The feeding‐scar area was approximately one‐third lower on the seedlings with ant‐baits compared with the controls. Besides red wood ants, Myrmica ants were also attracted in high numbers to the ant baits and the relative effects of these species are discussed.
• 5 The results obtained in the present study support the trophic cascade hypothesis (i.e. damage to herbivores is suppressed in the presence of predators). The decreased pine weevil feeding on the baited seedlings was probably a result of nonconsumptive interactions [i.e. the presence of (or harassment by) ants distracting pine weevils from feeding].
• 6 Understanding the role of ants may have important implications for future strategies aiming to control pine weevil damage. For example, maintaining suitable conditions for ants after harvesting stands may be an environmentally friendly but currently unexploited method of for decreasing weevil damage.

     

Flight ability and reproductive development in newly‐emerged pine weevil Hylobius abietis and the potential effects of climate change

• 1 Adult pine weevils Hylobius abietis emerge from conifer root‐stumps, on which larvae develop, over an extended period during summer and autumn. Newly‐emerged weevils were tested for their ability to fly and assessed for wing muscle and reproductive development. In addition, the effect of summer–autumn maturation feeding on reproductive development was assessed in field bioassays.
• 2 There was considerable variation in development between newly‐emerged weevils that was related to the timing of emergence. The first weevils, emerging in early July, weighed less than later‐emerging ones, had undeveloped flight muscles and did not fly. Over the emergence period, wing muscle size and flight ability increased markedly, with 50–60% flying by mid‐September. Differences between emerging adults are likely to have been affected by temporal changes in the quality of the bark on which the larvae feed.
• 3 Reproductive development lagged behind that of wing muscles but, in early August, there was a rapid increase in the proportion of weevils with immature eggs and a corresponding increase in oocyte size. However, although wing muscles were fully formed in later‐emerging weevils, immature eggs were only approximately 10% of the volume of mature eggs.
• 4 In field bioassays of summer–autumn maturation feeding, eggs continued to develop and some weevils laid mature eggs. Feeding and development during the pre‐overwinter period is likely to influence winter survival and also dispersal and reproduction in the following spring.
• 5 The potential effects of climate change on the weevil life cycle are briefly discussed. Weevils are likely to benefit from the higher temperatures and later autumns predicted under climate change, resulting in an increase in damage to transplants.

     

Interaction between flight,reproductive development and oviposition in the pine weevil Hylobius abietis

• 1 The development of reproductive and flight capacity of pine weevils Hylobius abietis during the spring and their dispersal to, and subsequent development at, new clearfell oviposition sites comprise key phases in their life cycle in managed forests. At an old clearfell site where autumn‐emerging weevils had overwintered, weevils were trapped as they re‐emerged in the spring and tested for their ability to fly and then dissected to determine the degree of wing muscle and egg development.
• 2 Re‐emerging weevils were most abundant in pine growing at the edge of the clearfell and, over most of the trapping period (April to June), their capacity for flight (proportion flying and wing muscle width) was more advanced than in weevils from the clearfell itself, with a similar trend in the degree of reproductive development (proportion with mature eggs and egg volume).
• 3 In weevils from the clearfell, flight capacity and reproductive development increased concurrently to a peak around mid‐May. In weevils from pine, wing muscles were already well developed at the start of trapping, although few of them flew. Their more advanced development was attributed to the increased opportunities for maturation feeding after emergence in the previous autumn.
• 4 In the spring, weevils reached the canopy of trees for maturation feeding by walking and, to a lesser extent, by flight. Weevils dispersed by flight to oviposition sites in mid‐May when most of them were reproductively mature. After arrival, flight ability and wing muscle size declined rapidly but egg production was maintained until most weevils had stopped flying. When wing muscles reached their minimum size, there was a marked decline in egg size, suggesting that wing muscle breakdown is important in maintaining egg production at oviposition sites. Prospects for further wing muscle and reproductive development are discussed.

     

The effect of red wood ant abundance on feeding damage by the pine weevil Hylobius abietis

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The impact of host plant species on the larval development of the large pine weevil Hylobius abietis L.

• 1 The developmental performance of the large pine weevil Hylobius abietis was studied in the laboratory on four species of conifer, Corsican pine Pinus nigra var. maritima, Sitka spruce Picea sitchensis, Douglas‐fir Pseudotsuga menziesii and Japanese larch Larix kaempferi.
• 2 All species supported development, but, there was considerable variation in larval mortality, development time and weight of adults on emergence between host species.
• 3 Levels of mortality were highest in Japanese larch (77%) and lowest in Corsican pine (8.2%), and the heaviest adults emerged from Corsican pine (130 mg) and the smallest from Douglas‐fir (74 mg).
• 4 A constitutive plant defence chemical, lignin, found to vary within a northern provenance of Sitka spruce, also strongly affected larval development.
• 5 The significance of these findings is discussed in relation to the management of H. abietis.

     

White pine weevil performances in relation to budburst phenology and traumatic resin duct formation in Norway spruce

1 As the phenological window hypothesis was reported to be significant in influencing the fitness of many herbivores feeding on tree foliage, could it also explain the performance of an insect such as the white pine weevil Pissodes strobi mainly attacking the bark phloem of conifers? 2 Under field conditions, adult weevils were caged on Norway spruce trees presenting a natural variation in their shoot growth phenology. 3 We evaluated white pine weevil biological performances, including oviposition, the number of emerged insects, survival, adult mean weight and tree defense responses as reflected by the production of induced resin canals. 4 None of the white pine weevil biological parameters was significantly affected by Norway spruce phenology. 5 The number of eggs per hole, the number of oviposition holes per leader, the number of emerged adults and their mean weight were not affected by host phenology. 6 The intensity of the traumatic response observed was variable and not correlated with budburst phenology. 7 Trees with higher traumatic responses, forming two or more layers of traumatic ducts, had lower adult emergence and estimated survival. 8 The distance between the first layer of traumatic resin ducts and the start of the annual ring was not correlated with the number of emerged weevils. 9 Norway spruce, which is an exotic tree in North America and a relatively recent host for the white pine weevil, might not possess the defense mechanisms necessary to fight off the white pine weevil.     

Oviposition and feeding behaviour by the vine weevil Otiorhynchus sulcatus on red raspberry: effects of cultivars and plant nutritional status

• 1 The vine weevil Otiorhynchus sulcatus is a major pest of horticultural crops worldwide, with root‐feeding larvae causing most damage. Adult oviposition aboveground may therefore influence levels of damage as the larvae are relatively immobile after oviposition.
• 2 The present study investigated feeding and oviposition behaviour on red raspberry Rubus idaeus using intact plants, ensuring that choices reflected the realistic differences in cultivar appearance and chemical composition. Previous studies investigating vine weevil feeding and oviposition on other crops have used excised plant material, which may inadvertently influence behaviour.
• 3 Adult weevils significantly preferred to feed on particular cultivars in the choice experiment (e.g. Tulameen), although they consumed significantly more foliage (0.22–1.03 cm²/day) on different raspberry cultivars (e.g. Glen Moy, Glen Rosa and a wild accession) in no‐choice situations.
• 4 In choice experiments, weevils tended to avoid laying eggs on some cultivars (e.g. Glen Moy and the wild accession). The number of eggs laid (1.91–4.32 eggs per day) did not, however, differ significantly between the cultivars in a no‐choice situation. Foliar nitrogen and magnesium concentrations were positively, although weakly, correlated with the total number of eggs laid.
• 5 The present study highlights the importance of considering both choice and no‐choice tests when assessing crop susceptibility to attack because weevils may avoid feeding on certain cultivars (e.g. Glen Moy) when given a choice, although this would cause significant damage to such cultivars if they were grown in monoculture (i.e. when there is no alternative).

     

Comparisons of mountain pine beetle (Dendroctonus ponderosae Hopkins) reproduction within a novel and traditional host: effects of insect natal history,colonized host species and competitors

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Hylobius pine weevils adult host selection and antifeedants: feeding behaviour on host and non-host woody scandinavian plants

Abstract 1 We searched for antifeedant activity in predomonantly non‐host woody plants to find new compounds for seedling protection of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) against feeding by pine weevil Hylobius abietis. In total, 38 species from 25 families were compared in choice and no‐choice tests. 2 In choice tests with Empetrum, Juniperus, Ledum, Populus, Betula, Evonymus, Sorbus, Salix, Myrica and Pinus, the weevils preferred Pinus to all others. In no‐choice tests with the same species, the insects removed a similar or even greater area of the bark in three of 10 species than Pinus. The results were clearly different between the test modes. 3 In experiment 4, the areas of outer and inner bark (phloem) removed were quantified separately.The weevils removed significantly less of both outer and inner bark in Ilex, Evonymus, Populus, Syringa, Taxus, Tilia, Viburnum, Lonicera and Sorbus than Pinus. 4 Large areas of outer bark were removed in Juglans, Fraxinus, Sambucus, Aesculus, Quercus, Corylus, Fagus, Salix, Alnus and Acer. However, in the latter cases the insects stopped when reaching the inner bark. Thus, certain plant species have the outer bark removed by the insects but possessed an inner bark with antifeedant qualities.     

Primary attraction and kairomonal host discrimination in three species of Dendroctonus (Coleoptera: Scolytidae)

Abstract 1 Synthetic blends of bole and foliage volatiles of four sympatric species of conifers were released from pheromone‐baited multiple‐funnel traps to determine if three species of tree‐killing bark beetles (Coleoptera: Scolytidae): (i) exhibited primary attraction to volatiles of their hosts and (ii) discriminated among volatiles of four sympatric species of host and nonhost conifers. 2 Bole and foliage volatiles from Douglas‐fir, Pseudotsuga menziesii (Mirb.) Franco, increased the attraction of coastal and interior Douglas‐fir beetles, Dendroctonus pseudotsugae Hopkins, to pheromone‐baited traps. Primary attraction to bole volatiles was observed in interior D. pseudotsugae. Beetles were significantly less attracted to the pheromone bait when it was combined with volatiles of lodgepole pine, Pinus contorta var. latifolia Engelm. or interior fir, Abies lasiocarpa × bifolia. 3 The monoterpene myrcene synergized attraction of mountain pine beetles, Dendroctonus ponderosae Hopkins, to their aggregation pheromones, but there was no evidence of primary attraction to host volatiles or discrimination among volatiles from the four conifers. 4 There was significant primary attraction of the spruce beetle, Dendroctonus rufipennis Kirby, to bole and foliage volatiles of interior spruce, Picea engelmannii × glauca, but beetles did not discriminate among volatiles of four sympatric conifers when they were combined with pheromone baits. 5 Our results indicate that host volatiles act as kairomones to aid pioneer Douglas‐fir beetles and spruce beetles in host location by primary attraction, and that their role as synergists to aggregation pheromones is significant. For the mountain pine beetle, we conclude that random landing and close range acceptance or rejection of potential hosts would occur in the absence of aggregation pheromones emanating from a tree under attack.     

Ethylene in induced conifer defense: cDNA cloning, protein expression, and cellular and subcellular localization of 1-aminocyclopropane-1-carboxylate oxidase in resin duct and phenolic parenchyma cells

Members of the Pinaceae family have complex chemical defense strategies. Conifer defenses associated with specialized cell types of the bark involve constitutive and inducible accumulation of phenolic compounds in polyphenolic phloem parenchyma cells and oleoresin terpenoids in resin ducts. These defenses can protect trees against insect herbivory and fungal colonization. The phytohormone ethylene has been shown to induce the same anatomical and cellular defense responses that occur following insect feeding, mechanical wounding, or fungal inoculation in Douglas fir (Pseudotsuga menziesii) stems (Hudgins and Franceschi in Plant Physiol 135:2134–2149, 2004). However, very little is known about the genes involved in ethylene formation in conifer defense or about the temporal and spatial patterns of their protein expression. The enzyme 1-aminocyclopropane-1-carboxylate oxidase (ACO) catalyzes the final step in ethylene biosynthesis. We cloned full-length and near full-length ACO cDNAs from three conifer species, Sitka spruce (Picea sitchensis), white spruce (P. glauca), and Douglas fir, each with high similarity to Arabidopsis thaliana ACO proteins. Using an Arabidopsis anti-ACO antibody we determined that ACO is constitutively expressed in Douglas fir stem tissues and is up-regulated by mechanical wounding, consistent with the wound-induced increase of ethylene levels. Immunolocalization showed cytosolic ACO is predominantly present in specialized cell types of the wound-induced bark, specifically in epithelial cells of terpenoid-producing cortical resin ducts, in polyphenolic phloem parenchyma cells, and in ray parenchyma cells.J.W. Hudgins and Steven G. Ralph contributed equally to this work.     

Stimulating effect of bark polar fraction from the terminal leader of Norway spruce, Picea abies, on white pine weevil, Pissodes strobi, feeding and oviposition

Abstract:  The objective of the study was to demonstrate the importance of bark polar fraction from Norway spruce [ Picea abies (L.) Karst.] terminal leaders on the feeding activity and oviposition process of the female white pine weevil, Pissodes strobi (Peck). The bark polar fraction was extracted with a ternary solvent [chloroform, methanol and water (12 : 5 : 3)]. This extracted fraction was added, at different concentrations, to an artificial diet on which mated female white pine weevils could feed and oviposit. The bark polar fraction of Norway spruce terminal leaders promoted white pine weevil oviposition compared with untreated artificial diet. The results of this study contributed to the development of an efficient artificial rearing substrate required to better understand the interactions between white pine weevil and its host plants. The importance of more specific compounds found in the polar fraction could eventually help produce more resistant trees.     

The structure of feeding behavior in a phytophagous insect (Hylobius abietis)

Analysis of the feeding behavior of animals using such a high temporal resolution that meals can be defined may improve our understanding of the mechanisms regulating feeding. Meals can be distinguished in an ethologically meaningful manner by using the ‘meal criterion’, the shortest non‐feeding interval between feeding bouts recognized as meals. However, such a criterion has only been determined for a few insect species. Applying a recent method developed for assessing meal criteria for vertebrates, we determined the meal criterion for Hylobius abietis (L.) (Coleoptera: Curculionidae) based on data from video recordings of single individuals feeding on seedlings of Norway spruce, Picea abies (L.) Karst. (Pinaceae). The pine weevil is an economically important pest insect, because it feeds on the stem bark of planted conifer seedlings. Weevils had 4–5 meals per day. Each meal lasted about 24 min during which about 13 mm² of bark per meal were removed. Females had longer total meal durations and longer non‐feeding intervals within meals than males. Girdling seedlings did not affect the weevils' feeding properties. The size of meals was significantly correlated with the duration of non‐feeding intervals before and after them. This study is one of few describing the feeding behavior of an insect at a temporal resolution that allows individual meals to be distinguished. With more meal‐related data from insects available, differences in meal properties may be interpreted based on phylogeny, ecology, and physiology. Our results may also assist in the setup and interpretation of studies of plant‐insect interactions, and facilitate the evaluation and development of methods to protect plants against herbivores.     

Soil type and microtopography influencing feeding above and below ground by the pine weevil Hylobius abietis

Abstract 1 The influence of soil type and microtopography on above and below ground feeding by adult pine weevils Hylobius abietis (L.) (Coleoptera: Curculionidae) was evaluated in a field experiment with enclosed weevil populations of known size. 2 Four soil treatments, each with a food source at the centre, were presented within each enclosure: (i) a flat surface with fine‐grained, cultivated humus; (ii) a flat surface with sand; (iii) a conical mound of sand; and (iv) a conical pit in sand. The food source consisted of a stem section of Scots pine Pinus sylvestris L. extending both above and below ground. 3 The majority of feeding on the half buried stem sections occurred below ground; only 2.7% of the total bark area consumed was situated above ground. The variation over time in bark area consumed was not significantly associated with any of the tested weather factors. 4 The amount of feeding was 10‐fold higher on food sources placed in fine‐grained humus than those in areas of flat sand. 5 Less pine bark was consumed on mounds of sand than flat sand surfaces, and there was more feeding in sandy pits than on flat sand. These effects on feeding are explained by the observation that the weevils had difficulties climbing the sandy slopes (27° gradient). 6 We conclude that pine weevil damage to conifer seedlings can be considerably reduced by planting on mounds of pure mineral soil and that planting deeply in the soil increases the risk of damage.     

Feeding by the pine weevil Hylobius abietis in relation to sun exposure and distance to forest edges

Abstract 1 The intensity of feeding by adult pine weevils Hylobius abietis (L.) on the stem bark of Norway spruce Picea abies (L.) Karst. seedlings planted in rows with a north–south orientation across a clear‐cutting, was measured throughout a growth season. The feeding was then correlated to light interception, soil temperature and distance to the nearest forest edge. 2 Feeding was at least twice as intense on seedlings in the central part of the clear‐cutting compared to those at the edges. The decline began approximatety 15 m from the edge and was of similar proportions on both the sun‐exposed and shaded sides. 3 Measures of global radiation and soil temperature correlated well with consumption on the shaded side. However, on the sun‐exposed side, there were no apparent correlations with global radiation or soil temperature that could explain the decline in consumed bark area. 4 We conclude that the decline in feeding towards the forest edges was mainly due to factors other than the microclimate variables we monitored. We suggest that the presence of roots of living trees along the forest edge may reduce damage to seedlings, since they provide an alternative source of food for the weevils. This alternative‐food hypothesis may also explain why seedlings in shelterwoods usually suffer less damage from pine weevils than seedlings in clear‐cuttings.     

The effect of cold temperature exposure and long-day photoperiod on the termination of the reproductive diapause of newly emerged female Pissodes strobi (Coleoptera: Curculionidae)

Abstract

• 1 There is confusion in the literature concerning a possible reproductive diapause in the adult white pine weevil Pissodes strobi.
• 2 We evaluated the effects of temperature, photoperiod, feeding substrate and mating status on the sexual maturation and oviposition of female white pine weevils.
• 3 Less than 30% of female P. strobi became sexually mature and laid eggs without experiencing dormancy under a temperature regime of 2 °C for 4 weeks.
• 4 Among the females that experienced a cold temperature treatment after emergence, 80% laid eggs after dormancy when exposed to a long‐day (LD 16 : 8 h) photoperiod and 17.6% laid eggs when exposed to a short‐day (LD 8 : 16 h) photoperiod.
• 5 Significantly more eggs were laid by all the females (with and without a cold treatment) when subjected to a long‐day photoperiod compared with a short‐day photoperiod.
• 6 A period of cold temperature followed by exposure to a long‐day photoperiod with warmer temperatures is required to break reproductive diapause and to obtain a good oviposition response in female P. strobi.
• 7 This study reveals the existence of much intraspecific variation in the response of the white pine weevil to temperature and photoperiod with respect to the induction and termination of reproductive diapause.