Synergistic effects of methyl jasmonate treatment and propagation method on Norway spruce resistance against a bark-feeding insect.

Utilizing plants with enhanced resistance traits is gaining interest in plant protection. Two strategies are especially promising for increasing resistance against a forest insect pest, the pine weevil (Hylobius abietis): exogenous application of the plant defense hormone methyl jasmonate (MeJA), and production of plants through the clonal propagation method somatic embryogenesis (SE). Here, we quantified and compared the separate and combined effects of SE and MeJA on Norway spruce resistance to pine weevil damage. Plants produced via SE (emblings) and nursery seedlings (containerized and bare-root), were treated (or not) with MeJA and exposed to pine weevils in the field (followed for 3 years) and in the lab (with a non-choice experiment). Firstly, we found that SE and MeJA independently decreased pine weevil damage to Norway spruce plants in the field by 32-33% and 53-59%, respectively, compared to untreated containerized and bare-root seedlings. Secondly, SE and MeJA together reduced damage to an even greater extent, with treated emblings receiving 86-87% less damage when compared to either untreated containerized or bare-root seedlings in the field, and by 48% in the lab. Moreover, MeJA-treated emblings experienced 98% lower mortality than untreated containerized seedlings, and this high level of survival was similar to that experienced by treated bare-root seedlings. These positive effects on survival remained for MeJA-treated emblings across the 3-year experimental period. We conclude that SE and MeJA have the potential to work synergistically to improve plants' ability to resist damage, and can thus confer a strong plant protection advantage. The mechanisms underlying these responses merit further examination.

Efficacy of four systemic insecticides for reducing Nantucket pine tip moth (Rhyaciona frustrana) (Lepidoptera: Tortricidae) infestation levels and improving growth metrics in loblolly pines.

The Nantucket pine tip moth (NPTM) (Rhyacionia frustrana Comstock) is a native, regeneration pest of young loblolly pines (Pinus taeda L.), causing shoot dieback, tree deformity, and growth and volume declines. Soil applications of systemic insecticides may be an effective strategy to suppress NPTM populations. The study objective was to assess the efficacy of four systemic insecticide treatments (chlorantraniliprole, dinotefuran, fipronil, and imidacloprid) for two growing seasons in outplanted bareroot and containerized seedling trials. Response variables included NPTM infestation rates, along with tree height, groundline diameter, volume index, and stem form. Infestation rates significantly decreased for each systemic insecticide treatment during the first year compared to controls, although dinotefuran and imidacloprid provided season-long control in one trial. Chlorantraniliprole reduced NPTM infestation rates for two growing seasons in both trials. While imidacloprid treatments did not alter growth metrics except for one comparison, fipronil and dinotefuran treatments improved several growth metrics. Chlorantraniliprole consistently improved growth metrics throughout the study.

Management Implications for the Nantucket Pine Tip Moth From Temperature-Induced Shifts in Phenology and Voltinism Attributed to Climate Change.

Forest insect pest phenology and infestation pressure may shift as temperatures continue to warm due to climate change, resulting in greater challenges for sustainable forest management . The Nantucket pine tip moth (NPTM) (Rhyacionia frustrana Comstock) (Lepidoptera: Tortricidae) is a native forest regeneration pest in the southeastern U.S. with multiple generations per year. Changes in NPTM voltinism may result from temperature-induced shifts in NPTM phenology. Degree-day models have been used to develop optimal spray dates (OSDs) for NPTM. The 2000 Spray Timing Model (STM), based on temperature data from 1960 to 2000, provided generation-specific 5-d OSDs to effectively time applications of contact insecticides. An updated degree-day model, the 2019 STM, is based on temperature data from 2000 to 2019 and was used to detect changes in voltinism as well as shifts in phenology and OSDs. Based on the model, increased voltinism occurred at 6 of the 28 study locations (21%). Changes in voltinism occurred in the Piedmont and Coastal Plain of Georgia, U.S., with shifts from three to four or four to five generations a year, depending on location. The OSDs from the 2019 STM were compared to the 2000 STM OSDs. Over half (57%) of the OSDs differed by 5-15 d, with the majority (66%) resulting in earlier spray dates. The 2019 STM will help growers adapt NPTM control tactics to temperature-induced phenology shifts. NPTM serves as an example of temperature-induced changes attributed to climate change in a forest insect pest with important implications to forest management.

Limited Scope Risk Assessment for Nontarget Ground-Dwelling Arthropods From Systemic Insecticide Applications to Young Pines.

The Nantucket pine tip moth (NPTM) [Rhyacionia frustrana (Comstock)], a native regeneration pest on young loblolly pines (Pinus taeda L.), negatively impacts pine growth. An emerging management approach is to apply systemic insecticides to seedlings to reduce NPTM damage. These systemic insecticide applications generally occur once, perhaps twice, during the first few years of loblolly pine growth. However, these applications could lead to unintended environmental consequences to nontarget organisms. The purpose of this study was to assess potential nontarget effects from four systemic insecticide applications by assessing ground-dwelling arthropod trap catch, with a focus on collembolan trap catch and genera richness. Loblolly seedlings (24 seedlings per plot) at three sites in southeast Georgia were treated with either chlorantraniliprole, dinotefuran, fipronil, or imidacloprid or left untreated as a control. Arthropods were collected with pitfall traps that were deployed for 5 d in July, August, and September 2019, 7-9 mo after treatment. Ground-dwelling arthropod trap catch, arthropod order trap catch, collembolan trap catch, and collembolan genera richness did not vary among insecticide treatments and the untreated control in this mid-term insecticide risk assessment. While no significant effects of insecticide treatment were observed, ground-dwelling arthropod trap catch, collembolan trap catch, and collembolan genera richness differed among collection times. This study was the first of its kind in a young pine stand setting and is an important first step to understanding risk in these settings. Information on nontarget risks of management practices informs growers of the level of environmental risk associated with systemic insecticides.