Abstract
Defense can be induced in conifer seedlings to reduce pine weevil (Hylobius abietis) damage, by treatment with the plant hormone methyl jasmonate (MJ). Few studies have addressed important practical issues regarding the use of MJ such as treatment incidence and timing, seedling age and its compatibility with plant nursery practices. We examined if levels of pine weevil damage depend on seasonal timing and recurrence of MJ treatment, and if the observed effects depend on plant age. Norway spruce (Picea abies) seedlings from two age cohorts (1 year and 1.5 years old) received four MJ treatments: MJ application before winter storage in the previous year, after winter storage but before spring/summer planting, repeated MJ application (both before winter storage, and before planting) or no MJ application at all. Pine weevil damage was evaluated in a lab and field experiment. We found that the timing and recurrence of MJ treatment affected the amount of damage inflicted by pine weevils in different ways, but these effects were consistent among age cohorts. MJ application before winter storage provided the most effective protection, and this reduction in damage was comparable to that provided by a currently used physical protection method against pine weevil feeding. Our results indicated that MJ can be applied in line with nursery practices (before winter storage) and provides adequate protection for two growing seasons.
Highlights
Insects are one of the major agents of damage to European forests (Matyjaszczyk et al 2019)
There was a significant difference in area debarked by pine weevils among methyl jasmonate (MJ) treatments differing in timing and recurrence, but the effect of age and the interaction effect of age and MJ treatment were not significant (Table 1)
Our results show that MJ treatment reduces pine weevil damage and that the protective effects vary with the timing and recurrence of treatment, but not with the seedling age cohort
Summary
Insects are one of the major agents of damage to European forests (Matyjaszczyk et al 2019). The problems caused by insects are usually more prominent in clear-cut forests as they are often regenerated through planting, and the seedlings are susceptible to insect herbivory during establishment. In these newly planted forests, the pine weevil (Hylobius abietis) is one of the most destructive insect pests because it consumes the stem cambium, often girdling seedlings (entire ring of bark removed), causing high levels of plant mortality (Hagner and Jonsson 1995; Långström and Day 2007). Even though various silvicultural practices and physical protective methods against the pine weevil are available, their effects are variable depending on site conditions (Nordlander et al 2011; Wallertz et al 2018; López-Villamor et al 2019); complementary and sustainable methods of seedling protection are needed
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