Dissertation•
Pine Weevil Feeding Behaviour in Relation to Conifer Plant Properties
01 Jan 2014-
TL;DR: The results from a no-choice and a choice experiment indicate that the protective effect of MeJA-induced defences is, besides an overall reduction of feeding, mainly due to the reduced amount that a pine weevil can feed at one place.
Abstract: The pine weevil (Hylobius abietis (L.)) is a forest insect distributed over the Palearctic region. The adults feed on the phloem of young conifer plants causing high economic losses for the European forest industry. Still, there is very little knowledge about the structure of its feeding behaviour. Feeding behaviour can be studied in several different temporal resolutions, from differences in feeding after several weeks to diel patterns and short-term feeding, i.e. feeding patterns at the level of feeding events and meals. The aim of this thesis was to increase the knowledge about the pine weevils’ feeding patterns and the underlying behavioural mechanisms.
I studied the pine weevils’ time budget and diel behaviour as well as its short-term feeding behaviour based on video recordings. In addition, I assessed how changes in plant properties due to girdling or induction of plant defences with a chemical elicitor, methyl jasmonate (MeJA), affect the feeding pattern and preferences of the pine weevil.
Pine weevils allocated only 6 % of the time to feeding. Most of the time was spent away from the plant (70 – 80 %). Damaged plants appeared to attract the weevils because they spent more time while not feeding on damaged plants than on undamaged plants. Feeding behaviour was mostly concentrated to the second half of the dark phase, after a peak of locomotion behaviour during the first part of the dark phase. During the light phase, pine weevils mostly rested. Analysis of the short-term feeding behaviour showed that pine weevils made 4-5 meals per day, removing about 13 mm2 during about 24 minutes in each meal. Some of the feeding properties, such as how much time was spent not feeding during a meal, differed between male and female weevils. Girdling did not affect the time budget or feeding properties.
The induced plant defences with MeJA caused a reduction in meal duration. When meals consisting of only phloem, only needles or both were compared, the meal duration and the time until the initiation of a meal were more similar between the different meal contents on induced plants. In addition, the results from a no-choice and a choice experiment indicate that the protective effect of MeJA-induced defences is, besides an overall reduction of feeding, mainly due to the reduced amount that a pine weevil can feed at one place. Thus the risk of girdling and death of the plant is reduced.
References
More filters
TL;DR: It is suggested that weevil aggregations are formed in response to host volatiles and that weevils feeding increases amounts of these volatile released.
Abstract: Field tests were conducted with Hylobius abietis (L.) in Sweden during 1982 and 1983 to study how weevils feeding on host material affect attractivity of this host material to other H. abietis Pitfall traps baited with a combination of male or female weevils and cut stems of Scots pine caught more weevils of both sexes than pine alone. Weevils of either sex were not attractive in absence of host material. Attractivity of ground phloem containing weevil frass was not significantly different from that of ground phloem alone. In a laboratory test, feeding by weevils of either sex on pine about doubled the release of monoterpene hydrocarbons and ethanol compared with pine alone. Existence of an aggregation pheromone could not be confirmed. We suggest that weevil aggregations are formed in response to host volatiles and that weevil feeding increases amounts of these volatiles released.
70 citations
"Pine Weevil Feeding Behaviour in Re..." refers background in this paper
...Damaged plants have been shown to be more attractive to pine weevils (Tilles et al., 1986; Nordlander, 1991)....
[...]
...In insects that do not produce long-range signals for attracting mates, as the pine weevil, it is common that males are more active in looking for mates (Tilles et al., 1986; Brown et al., 1997)....
[...]
TL;DR: Screening trees based on their capacity to produce traumatic resin canals may be useful in selecting genotypes resistant to white pine weevil, suggesting that other resistance mechanisms might be important.
Abstract: The traumatic wound response of families of white spruce, Picea glauca (Moench) Voss, resistant or susceptible to the white pine weevil, Pissodes strobi (Peck), were compared after simulated weevil damage. Leaders from 331 trees were wounded just below the apical bud in the spring, coinciding with the natural time of weevil oviposition. A portable 1-mm diameter drill was used to drill 24 holes per leader. Leaders were removed in the fall and examined for evidence of traumatic resin canal formation. Drilled trees had a traumatic wound response 8 times greater than that of undrilled trees; however, undrilled trees also formed some resin canals in response to unknown causes. In the drilled trees, the traumatic wound response extended into the lower part of the leader, where it could possibly affect older larvae. Trees from resistant families responded with greater intensity than trees from susceptible families, by producing multiple rings of traumatic resin canals. Trees from resistant families also responded more rapidly than trees from susceptible families based on number of cells to the first ring of traumatic resin canals. Trees from some resistant families exhibited no traumatic resin canal formation, showing considerable within-family variation and suggesting that other resistance mechanisms might be important. In the year after drilling, there was a reduction in tree diameter growth and trees suffered a reduction in constitutive resin canals in the bark, which suggests some energetic cost of traumatic resin production. There was no indication that the extent of constitutive defenses, as measured by density of cortical resin canals before wounding, was related to the ability to produce traumatic resin canals. Screening trees based on their capacity to produce traumatic resin canals may be useful in selecting genotypes resistant to white pine weevil.
66 citations
"Pine Weevil Feeding Behaviour in Re..." refers background in this paper
...These bouts are called meals and are commonly used as a unit of short-term feeding behaviour (e.g. Simpson, 1981; Raubenheimer & Bernays, 1993; Mitchell & Low, 1994; Bernays & Singer, 1998; Tomlin et al., 1998; Daoust et al., 2010)....
[...]
TL;DR: This work explored the allocation of constitutive and methyl-jasmonate inducible chemical defenses in six half-sib families of Pinus radiata juveniles, and studied the quantitative allocation of resin and polyphenolics to tissues with contrasting fitness value across three parts of the plants, using nitrogen concentration as a proxy of tissue value.
Abstract: Optimal defense theory (ODT) predicts that the within-plant quantitative allocation of defenses is not random, but driven by the potential relative contribution of particular plant tissues to overall fitness. These predictions have been poorly tested on long-lived woody plants. We explored the allocation of constitutive and methyl-jasmonate (MJ) inducible chemical defenses in six half-sib families of Pinus radiata juveniles. Specifically, we studied the quantitative allocation of resin and polyphenolics (the two major secondary chemicals in pine trees) to tissues with contrasting fitness value (stem phloem, stem xylem and needles) across three parts of the plants (basal, middle and apical upper part), using nitrogen concentration as a proxy of tissue value. Concentration of nitrogen in the phloem, xylem and needles was found to be greater higher up the plant. As predicted by the ODT, the same pattern was found for the concentration of non-volatile resin in the stem. However, in leaf tissues the concentrations of both resin and total phenolics were greater towards the base of the plant. Two weeks after MJ application, the concentrations of nitrogen in the phloem, resin in the stem and total phenolics in the needles increased by roughly 25% compared with the control plants, inducibility was similar across all plant parts, and families differed in the inducibility of resin compounds in the stem. In contrast, no significant changes were observed either for phenolics in the stems, or for resin in the needles after MJ application. Concentration of resin in the phloem was double that in the xylem and MJ-inducible, with inducibility being greater towards the base of the stem. In contrast, resin in the xylem was not MJ-inducible and increased in concentration higher up the plant. The pattern of inducibility by MJ-signaling in juvenile P. radiata is tissue, chemical-defense and plant-part specific, and is genetically variable.
65 citations
"Pine Weevil Feeding Behaviour in Re..." refers background in this paper
...Nitrogen concentrations can be used as a proxy of the relative importance of different tissues (Moreira et al., 2012)....
[...]
...For example, in the stem tissue of Pinus radiata concentrations of nitrogen correlate with the concentration of non-volatile resin, which is part of the plant defences (Moreira et al., 2012)....
[...]
TL;DR: New statistical methods have allowed a quantitative comparison of a number of causal factors affecting feeding in fifth-instar nymphs of the migratory locust, and the effect of recent defaecation was unexpectedly large, increasing the probability of feeding seven-fold.
64 citations
TL;DR: D ifferences in inducibility by and tolerance to native enemies between exotic and native host congeners emerge as key traits for understanding how native enemies might contribute to preventing an introduced species from becoming invasive.
Abstract: Summary 1. Current hypotheses predict contrasting roles for natural enemies in determining the success or failure of plant invasions. Differences in plant-induced resistance and tolerance to native herbivores between native and exotic species might contribute to resolve this controversy. 2. We examined the differences between the native Pinus pinaster and the exotic P. radiata in constitutive resistance, inducibility of chemical defences, realized resistance and tolerance to the large pine weevil Hylobius abietis in NW Spain. In this region, both pine species closely coexist and are threatened by the weevil, a harmful phloem feeder that causes extensive mortality and growth reduction in young pine stands. 3. We performed two in vitro cafeteria bioassays, two induction experiments with direct exposure to the weevil and spraying methyl jasmonate and an exhaustive field study of the genetic variation in tolerance and resistance in forestry genetic trials. 4. The weevil significantly preferred the native to the exotic pine when twigs were offered as cut material in Petri dishes. However, the pattern in the field was the opposite, with greater damage on the exotic. Inducibility of stem oleoresin did not differ between species when elicited by the application of methyl jasmonate. However, after a 72-h experimental exposure to the weevil, stem resin content in the native pine was double that in the exotic pine, suggesting a lower capability of the exotic pine to respond to the insect damage. In the field, family relationships between early damage and several pine fitness correlates revealed a significantly greater tolerance of the native pine to the insect damage. Furthermore, only the native pine showed genetic variation in tolerance to the damage. 5. Synthesis. The preference of the herbivore for the native species was counterbalanced by a lower capability for expressing induced resistance to the weevil and reduced tolerance in the exotic species, resulting in no apparent fitness advantage of the exotic P. radiata over the native P. pinaster .D ifferences in inducibility by and tolerance to native enemies between exotic and native host congeners emerge as key traits for understanding how native enemies might contribute to preventing an introduced species from becoming invasive.
61 citations
"Pine Weevil Feeding Behaviour in Re..." refers background in this paper
...During choice experiments, animals have access to several different food sources, most commonly two but more are possible, while they only have one food source during no-choice experiments (e.g. Roa, 1992; Zas et al., 2011; Meier et al., 2014)....
[...]
...It is therefore not unexpected that this is by far not the first study concerned with pine weevil feeding (e.g. Hesse et al., 1955; Christiansen & Bakke, 1968; Christiansen & Bakke, 1971; Pohris, 1983; Manlove et al., 1997; Nordlander et al., 2003; Zas et al., 2011)....
[...]