Abstract
The increases in temperature have recently allowed the southern pine beetle (Dendroctonus frontalis Zimm.; SPB) and its associated fungi to expand its natural range to northern pine forests. In this study, vigorous eastern white pine mature trees were used to evaluate constitutive and induced response to the southern pine beetle, using O. minus as a proxy. We evaluated histological and chemical changes in P. strobus in response to the fungus at 28- and 65-days post inoculation (dpi). Inoculation with O. minus resulted in an induced defense response as evidenced by the increased production of traumatic resin duct, and lesion development surrounding the site of infection. Starch granules accumulated in the epithelial cells surrounding the resin ducts of inoculated trees. Chemical analyses showed that among phloem phenolics, epi/catechin and three unknown compounds were significantly upregulated at 28 dpi due to fungal inoculation. Several phloem terpenoids (α-pinene, β-myrcene, limonene, terpinolene and β-pinene) were significantly increased in inoculated trees compared to controls at both, 28- and 65-dpi. Continuous production of these terpenoids (up to 65 dpi) can be energetically costly for P. strobus as carbohydrate reserves fund monoterpene synthesis, reducing carbon availability necessary for tree development. Induced phenolics along with monoterpenes production and traumatic resin ducts observed in these trees, suggests that vigorous white pine may sustain endemic populations of southern pine beetle and vectored fungi.
Highlights
The southern pine beetle (SPB) is one of the most damaging agents of conifers in the United States, changing forest dynamics and structure [1]
Twenty-two healthy pine trees, with similar size and diameter at breast height (DBH, 48 ± 14 cm) were used in a randomized experiment design with two treatments, control and O. minus inoculated at two heights 140 cm and 180 cm, to study the defense response of eastern white pine to the SPB-vectored fungus
Recent expansion of the southern pine beetle into areas previously unsuitable for this insect has brought interest in understanding how northern pine species will respond to unforeseen beetle attack
Summary
The southern pine beetle (SPB) is one of the most damaging agents of conifers in the United States, changing forest dynamics and structure [1]. The insect bores under the bark of the host tree allowing its associated fungus to colonize the phloem and overwhelm the tree defense system. The geographical range of SPB extends from the southern United States, north to New Jersey, Delaware, Pennsylvania and. It appears that a warming climate has allowed this insect to expand its range into northern areas where beetles had previously been precluded by cold temperatures [2]. The beetles moved from New Jersey to Long Island (NY) in 2014, infesting approximately 3500 acres, and were. Forests 2018, 9, 690 later found in Connecticut in 2015 where they attacked Pitch (Pinus rigida Mill), Red
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