Bark beetles attacking conifer seedlings: picking on the weakest or feasting upon the fittest?

Abstract

Summary1. Plant stress from causes such as drought is thought to increase the susceptibility of plants to herbivore attack and damage. Although this forms the basis of the widely cited plant stress hypothesis, there are few cases where this has been tested thoroughly. 2. We compared the frequency of attack and damage of an invasive pine bark beetle Hylates ater, on seedlings of Pinus radiata, using a 2 9 2 factorial design with artificially induced stress and insecticide application to distinguish effects of beetle attack and direct effects of stress. 3. Contrary to expectations based on the plant stress hypothesis, twice as many unstressed seedlings (22%) were attacked than stressed seedlings (11%). However, stressed seedlings were twice as likely to experience sustained bark beetle feeding resulting in girdling, than unstressed seedlings (31% and 15%, respectively). 4. In response to beetle attack, unstressed seedlings showed much stronger resin production than stressed seedlings, which is likely to explain the greater survival of unstressed seedlings after attack. 5. Experimental drought stress caused a 50% reduction in shoot growth. 6. Synthesis and applications. Maximizing seedling vigour and minimizing (pre-)planting stress are key for the resilience of planted forests. Managers should emphasize a stress-free transition of seedlings from nursery to field as well as correct planting techniques, in order to safeguard this vulnerable stage. This is particularly crucial since drought stress and insect invasions are likely to increase as a result of global change.

Predicting forest insect flight activity: A Bayesian network approach

“…Similarly Sopow et al . [ 10 ] report a strong autumn peak of activity, but like Reay et al . [ 7 ] their sampling did not encompass early spring conditions.…”

Long‐distance dispersal of non‐native pine bark beetles from host resources

“…Previous studies indicate that H. ligniperda is the more abundant species in New Zealand and Chile (Reay & Walsh, ; Brockerhoff et al ., ; Mausel et al ., ; McCarthy et al ., ), but all of these studies took place in or near pine plantations. We propose five possible (not mutually exclusive) explanations for finding greater abundances of H. ater in remote locations: (i) H. ater can colonise the root systems of damaged trees (Chararas, ; Sopow et al ., ) in pine windbreaks, thereby using these resources as ‘stepping stones’ (Saura et al ., ) to spread through and persist in the landscape. In a recent study, H. ater was captured in emergence traps placed around the buttresses of damaged windbreak trees in New Zealand (Be et al ., unpublished data); (ii) H. ater has been in New Zealand c .…”

“…Previous studies indicate that H. ligniperda is the more abundant species in New Zealand and Chile (Reay & Walsh, 2001;Brockerhoff et al, 2006b;Mausel et al, 2007;McCarthy et al, 2010), but all of these studies took place in or near pine plantations. We propose five possible (not mutually exclusive) explanations for finding greater abundances of H. ater in remote locations: (i) H. ater can colonise the root systems of damaged trees (Chararas, 1962;Sopow et al, 2015) in pine windbreaks, thereby using these resources as 'stepping stones' (Saura et al, 2014) to spread through and persist in the landscape. In a recent study, H. ater was captured in emergence traps placed around the buttresses of damaged windbreak trees in New Zealand (Be et al, unpublished data); (ii) H. ater has been in New Zealand c. 35 years longer than H. ligniperda which might have allowed it to colonise more remote sites with low-density host material; (iii) within pine plantations, H. ater could be an inferior competitor compared to H. ligniperda, which would be consistent with the greater abundance of the latter in areas with a high density of pines; (iv) H. ater may be able to better tolerate colder temperatures and wetter climates than H. ligniperda.…”

Approaches to Forecasting Damage by Invasive Forest Insects and Pathogens: A Cross-Assessment

“…Caged, potted European conifer seedlings were exposed under quarantine conditions to Siberian moth (Dendrolimus sibiricus) larvae, which developed successfully on most of these species (Kirichenko et al 2011), suggesting that host-plant availability would not limit its establishment and spread if introduced into Europe. Among insects that feed on stems of young trees, a field bioassay was conducted to determine the extent of maturation feeding on P. radiata by the invasive bark beetle Hylastes ater (Sopow et al 2015). Likewise artificially infesting C. fagisuga eggs on potted seedlings and grafts, and trees in the field, has been used to identify scale-resistant lines for beech bark disease management and tree improvement programs (Koch et al 2010, Koch et al 2012.…”