**5. Topical applications to the tree bole**

Topical applications to protect trees from bark beetle species such as western pine beetle, *Dendroctonus brevicomis* LeConte, mountain pine beetle, *D*. *ponderosae* Hopkins, and spruce beetle, *D*. *rufipennis* (Kirby), are applied with ground-based sprayers at high pressure [e.g., ≥2,241 kPa] to the tree bole. Insecticides are applied on all bole surfaces up to a height of ~10.6 to 15.2 m until runoff generally from the root collar to mid-crown (Fig. 4). For engraver beetles, *Ips* spp., that typically colonize smaller diameter hosts branches >5 cm diameter should also be treated. The amount of material (product + water) applied varies with bark and tree architecture, tree size, equipment and applicator, among other factors, but ranges from ~15 to 30 L per tree under most circumstances [12-14]. Application efficiency, the per‐ centage of material applied that is retained on trees, ranges from ~80 to 90% [14].

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**Figure 4.** A common method of protecting trees from bark beetle attack is to saturate all surfaces of the tree bole using a ground-based sprayer at high pressure. Photos: C.J. Fettig, Pacific Southwest Research Station, USDA Forest Service.

Bole sprays are typically applied in late spring prior to initiation of the adult flight period for the target bark beetle species. However, bole sprays require transporting sprayers and other large equipment, which can be problematic in high-elevation forests where snow drifts and poor road conditions often limit access. Additionally, many recreation sites (e.g., camp‐ grounds) where bole sprays are frequently applied occur near intermittent or ephemeral streams that are associated with spring runoff, limiting applications in late spring due to re‐ strictions concerning the use of no-spray buffers to protect non-target aquatic organisms. For these and other reasons, researchers are evaluating alternative timings of bole sprays and less laborious delivery methods.

#### **5.1. Carbaryl**

ence efficacy. However, results are rapidly obtained with limited risk and loss of scientif‐

A second design involves field assays in which insecticides are applied to an experimen‐ tal population of ~25−35 uninfested trees [8]. Trees are often baited with a bark beetle species-specific attractant to increase beetle "pressure" and challenge the treatment fol‐ lowing application. Efficacy is based on tree mortality and established statistical parame‐ ters [8]. This design is accepted as the standard for evaluating preventative treatments for tree protection in the western U.S., and provides a very conservative test of efficacy [9]. However, it is laborious, time-consuming (i.e., generally efficacy is observed for at least two field seasons) and expensive. Experimental trees may be lost to woodcutting or wildfire, and ≥60% of the untreated control trees must die from bark beetle attack to demonstrate that significant bark beetle pressure exists in the area or the experiment fails and results are inconclusive [8]. Some have argued that the design is perhaps too conser‐ vative as under natural conditions aggregation pheromone components would not be re‐ leased for such extended periods of time as often occurs with baiting. Finally, bark beetles may initiate undesirable infestations near experimental trees as a result of baiting,

The "hanging bolt" assay [10], "small-bolt" assay [11] and similar variants have received limited attention in the western U.S. Typically, insecticides are applied to individual, unin‐ fested trees that are later harvested and cut into bolts for inclusion in laboratory and/or field experiments. Alternatively, freshly-cut bolts may be treated directly in the laboratory. Effica‐ cy is often based on measures of attack density or gallery construction by adult beetles. Compared to [8], these methods allow for rapid acquisition of data; reduced risk of loss to scientific infrasture; and increased probability that a rigorous test will be achieved as bolts are transported to active infestations or brought into the laboratory and exposed to beetles. While these methods account for some host factors (e.g., bark architecture), others such as host defenses and environmental factors are ignored. Furthermore, the hanging bolt and small bolt assays do not provide an estimate of tree mortality, while the effectiveness of any

Topical applications to protect trees from bark beetle species such as western pine beetle, *Dendroctonus brevicomis* LeConte, mountain pine beetle, *D*. *ponderosae* Hopkins, and spruce beetle, *D*. *rufipennis* (Kirby), are applied with ground-based sprayers at high pressure [e.g., ≥2,241 kPa] to the tree bole. Insecticides are applied on all bole surfaces up to a height of ~10.6 to 15.2 m until runoff generally from the root collar to mid-crown (Fig. 4). For engraver beetles, *Ips* spp., that typically colonize smaller diameter hosts branches >5 cm diameter should also be treated. The amount of material (product + water) applied varies with bark and tree architecture, tree size, equipment and applicator, among other factors, but ranges from ~15 to 30 L per tree under most circumstances [12-14]. Application efficiency, the per‐

centage of material applied that is retained on trees, ranges from ~80 to 90% [14].

ic infrastructure compared to field studies.

476 Insecticides - Development of Safer and More Effective Technologies

which may be unacceptable under some circumstances.

preventative treatment is defined by reductions in tree mortality.

**5. Topical applications to the tree bole**

Carbaryl is an acetylcholinesterase inhibitor that prevents the cholinesterase enzyme from breaking down acetylcholine, increasing both the level and duration of action of the neuro‐ transmitter acetylcholine, which leads to rapid twitching, paralysis and ultimately death. Carbaryl is considered essentially nontoxic to birds, moderately toxic to mammals, fish and amphibians, and highly toxic to honey bees, *Apis mellifera* L., and several aquatic insects [15]. However, carbaryl is reported to pose little or no threat to warm-blooded animals. Several experts report that carbaryl is still the most effective, economically-viable, and ecologicallycompatible insecticide available for protecting individual trees from mortality due to bark beetle attack in the western U.S. [9,16]. Today, carbaryl (e.g., Sevin® SL and Sevin® XLR Plus, among others) is commonly used to protect trees from bark beetle attack, and is the mostextensively studied active ingredient registered for use. Failures in efficacy are rare and typ‐ ically associated with inadequate coverage, improper mixing (e.g., using an alkaline water source with pH >8) [17] or inaccurate mixing resulting in solutions of reduced concentration, improper storage, and/or improper timing (e.g., applying treatments to trees already suc‐ cessfully attacked by bark beetles).

**Mountain and western pine beetles.** Several rates and formulations of carbaryl have been evaluated, and most research indicates two field seasons of protection can be expected with a single application. The effectiveness of 1.0% and 2.0% Sevimol® was demonstrated in the early 1980s [18-22]. This and other research [23-24] led to the registration of 2.0% Sevimol® as a preventative spray, which was voluntarily canceled in 2006. [22] evaluated the efficacy of 0.5%, 1.0% and 2.0% Sevimol® and Sevin® XLR and found all concentrations and formula‐ tions were effective for protecting lodgepole pine, *P*. *contorta* Dougl. ex Loud., from mortali‐ ty due to mountain pine beetle attack for one year. The 1.0% and 2.0% rates were efficacious for two years. [9] reported 2.0% Sevin® SL protected ponderosa pine, *Pinus ponderosa* Dougl. ex Laws., from western pine beetle attack in California; ponderosa pine from mountain pine beetle attack in South Dakota; and lodgepole pine from mountain pine beetle attack in Mon‐ tana (two separate studies) for two field seasons. Similar results have been obtained else‐ where [12]. Ongoing research is evaluating the efficacy of fall versus spring applications of 2.0% Sevin® SL for protecting lodgepole pine from mountain pine beetle attack in Wyoming. Both treatments provided 100% tree protection during the first field season while 93% mor‐ tality was observed in the untreated control (C.J.F. and A.S.M., unpublished data). A similar study is being conducted for mountain pine beetle in ponderosa pine in Idaho.

mulations of carbaryl are effective for protecting Monterey pine, *P*. *radiata* D. Don, [35], but

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**Engraver beetles.** A single application of 2.0% Sevin® SL was effective for protecting singleleaf pinyon, *P*. *monophylla* Torr. & Frem., from mortality due to pinyon ips, *I. confusus* (Le‐ Conte), for two field seasons in Nevada [9]. A similar study in pinyon pine, *P*. *edulis* Engelm., on the Southern Ute Reservation in Colorado found 2.0% Sevin® SL was efficacious for one field season, but bark beetle pressure was insufficient the second year of the study to make definitive conclusions regarding efficacy [9]. [9] also evaluated the efficacy of 2.0% Sevin® SL for protecting ponderosa pine from pine engraver, *I*. *pini* (Say), but very few trees were attacked during the experiment. Approximately one year later, trees in this study were harvested and cut into bolts that were then laid on the ground in areas containing slash piles infested with pine engraver, sixspined ips, *I. calligraphus* (Germar), and Arizona five-spined ips, *I. lecontei* Swain [13]. From this and related research, the authors concluded 1.0% and 2.0% Sevin® SL were effective for protecting ponderosa pine from engraver beetle attacks for one entire flight season in Arizona. [36] reached similar conclusions for 2.0% Sevin® 80 WSP for a complex of engraver beetles, including sixspined ips, that colonize loblolly pine in the

Pyrethroids are synthesized from petroleum-based chemicals and related to the potent in‐ secticidal properties of flowering plants in the genus *Chrysanthemum*. They are axonic poi‐ sons and cause paralysis by keeping the sodium channels open in the neuronal membranes [37]. First generation pyrethroids were developed in the 1960s, but are unstable in sunlight. By the mid-1970s, a second generation was developed (e.g., permethrin, cypermethrin and deltamethrin) that were more resistant to photodegradation, but have substantially higher mammalian toxicities. Third generation pyrethroids (e.g., bifenthrin, cyfluthrin and lambdacyhalothrin) have even greater photostability and insecticidal activity compared to previous generations. Pyrethroids are one of the least acutely toxic insecticides to mammals, essential‐ ly nontoxic to birds, but are highly toxic to fish, amphibians and honey bees [38]. Today, permethrin (e.g., Astro® and Dragnet®, among others) and bifenthrin (e.g., Onyx™) are com‐ monly used to protect trees from bark beetle attack, and following carbaryl are the most-ex‐

**Mountain and western pine beetles.** Several active ingredients and formulations of pyreth‐ roids have been evaluated as preventative treatments, and most research indicates at least one field season of protection can be expected with a single application. [8] evaluated 0.1%, 0.2% and 0.4% permethrin (Pounce®) for protecting ponderosa pine from mortality due to western pine beetle attack, and reported that 0.2% and 0.4% provided control for four months. Permethrin plus-C (Masterline®), a unique formulation containing methyl cellulose (i.e., "plus-C") thought to increase efficacy and stability by reducing photo-, chemical- and biological-degradation of the permethrin molecule, exhibits efficacy similar to that of other formulations of permethrin [12]. [39] examined several rates of esfenvalerate (Asana® XL) and cyfluthrin (Tempo® 20 WP) as preventative treatments. In California, 0.025% and 0.05%

residual activity is generally short-lived (<1 yr).

tensively studied active ingredients registered for use.

southeastern U.S.

**5.2. Pyrethroids**

**Southern pine beetle.** Southern pine beetle, *D*. *frontalis* Zimmerman, occurs in a generally continuous distribution across the southern U.S., roughly coinciding with the distribution of loblolly pine, *P*. *taeda* L. However, southern pine beetle also occurs in portions of Arizona and New Mexico where it colonizes several pine species, and is therefore considered here. While preventative treatments have not been evaluated in western forests, carbaryl is inef‐ fective for protecting loblolly pine from mortality due to southern pine beetle attack in the southern U.S. [25-26]. This was later linked to insecticide tolerance in southern pine beetle associated with an efficient conversion of carbaryl into metabolites, and a rapid rate of ex‐ cretion [27-29]. Therefore, despite important environmental differences between the south‐ ern and western U.S., carbaryl is regarded as ineffective for preventing southern pine beetle attacks and subsequent tree mortality in the western U.S. [30].

**Spruce beetle.** Most research suggests that three field seasons of protection can be expected with a single application of carbaryl. In south-central Alaska, [31] reported that 1.0% and 2.0% Sevin® SL protected white spruce, *Picea glauca* (Moench) Voss, and Lutz spruce, *P*. *glau‐ ca* X *lutzii* Little, from attack by spruce beetle for three field seasons, despite early work indi‐ cating carbaryl was ineffective in topical assays [32]. One and 2.0% Sevimol® were effective for protecting Engelmann spruce, *P. engelmannii* Parry ex. Engelm., from spruce beetle attack for two field seasons in Utah [33], which agrees with results from [9] for 2.0% Sevin® SL. However, the two latter studies were concluded after two field seasons. In the case of [9], all Sevin® SL-treated trees were alive at the end of the study.

**Red turpentine beetle.** Red turpentine beetle, *D*. *valens* LeConte, usually colonizes the basal portions of stressed, weakened, or dead and dying trees. Therefore, the species is not consid‐ ered an important source of tree mortality in the western U.S., and limited work has occur‐ red regarding the development of tree protection tools. [34] reported that 2.0% Sevin® XLR and 4.0% Sevimol® 4 were effective for protecting ponderosa pine in California. Several for‐ mulations of carbaryl are effective for protecting Monterey pine, *P*. *radiata* D. Don, [35], but residual activity is generally short-lived (<1 yr).

**Engraver beetles.** A single application of 2.0% Sevin® SL was effective for protecting singleleaf pinyon, *P*. *monophylla* Torr. & Frem., from mortality due to pinyon ips, *I. confusus* (Le‐ Conte), for two field seasons in Nevada [9]. A similar study in pinyon pine, *P*. *edulis* Engelm., on the Southern Ute Reservation in Colorado found 2.0% Sevin® SL was efficacious for one field season, but bark beetle pressure was insufficient the second year of the study to make definitive conclusions regarding efficacy [9]. [9] also evaluated the efficacy of 2.0% Sevin® SL for protecting ponderosa pine from pine engraver, *I*. *pini* (Say), but very few trees were attacked during the experiment. Approximately one year later, trees in this study were harvested and cut into bolts that were then laid on the ground in areas containing slash piles infested with pine engraver, sixspined ips, *I. calligraphus* (Germar), and Arizona five-spined ips, *I. lecontei* Swain [13]. From this and related research, the authors concluded 1.0% and 2.0% Sevin® SL were effective for protecting ponderosa pine from engraver beetle attacks for one entire flight season in Arizona. [36] reached similar conclusions for 2.0% Sevin® 80 WSP for a complex of engraver beetles, including sixspined ips, that colonize loblolly pine in the southeastern U.S.

#### **5.2. Pyrethroids**

**Mountain and western pine beetles.** Several rates and formulations of carbaryl have been evaluated, and most research indicates two field seasons of protection can be expected with a single application. The effectiveness of 1.0% and 2.0% Sevimol® was demonstrated in the early 1980s [18-22]. This and other research [23-24] led to the registration of 2.0% Sevimol® as a preventative spray, which was voluntarily canceled in 2006. [22] evaluated the efficacy of 0.5%, 1.0% and 2.0% Sevimol® and Sevin® XLR and found all concentrations and formula‐ tions were effective for protecting lodgepole pine, *P*. *contorta* Dougl. ex Loud., from mortali‐ ty due to mountain pine beetle attack for one year. The 1.0% and 2.0% rates were efficacious for two years. [9] reported 2.0% Sevin® SL protected ponderosa pine, *Pinus ponderosa* Dougl. ex Laws., from western pine beetle attack in California; ponderosa pine from mountain pine beetle attack in South Dakota; and lodgepole pine from mountain pine beetle attack in Mon‐ tana (two separate studies) for two field seasons. Similar results have been obtained else‐ where [12]. Ongoing research is evaluating the efficacy of fall versus spring applications of 2.0% Sevin® SL for protecting lodgepole pine from mountain pine beetle attack in Wyoming. Both treatments provided 100% tree protection during the first field season while 93% mor‐ tality was observed in the untreated control (C.J.F. and A.S.M., unpublished data). A similar

478 Insecticides - Development of Safer and More Effective Technologies

study is being conducted for mountain pine beetle in ponderosa pine in Idaho.

attacks and subsequent tree mortality in the western U.S. [30].

Sevin® SL-treated trees were alive at the end of the study.

**Southern pine beetle.** Southern pine beetle, *D*. *frontalis* Zimmerman, occurs in a generally continuous distribution across the southern U.S., roughly coinciding with the distribution of loblolly pine, *P*. *taeda* L. However, southern pine beetle also occurs in portions of Arizona and New Mexico where it colonizes several pine species, and is therefore considered here. While preventative treatments have not been evaluated in western forests, carbaryl is inef‐ fective for protecting loblolly pine from mortality due to southern pine beetle attack in the southern U.S. [25-26]. This was later linked to insecticide tolerance in southern pine beetle associated with an efficient conversion of carbaryl into metabolites, and a rapid rate of ex‐ cretion [27-29]. Therefore, despite important environmental differences between the south‐ ern and western U.S., carbaryl is regarded as ineffective for preventing southern pine beetle

**Spruce beetle.** Most research suggests that three field seasons of protection can be expected with a single application of carbaryl. In south-central Alaska, [31] reported that 1.0% and 2.0% Sevin® SL protected white spruce, *Picea glauca* (Moench) Voss, and Lutz spruce, *P*. *glau‐ ca* X *lutzii* Little, from attack by spruce beetle for three field seasons, despite early work indi‐ cating carbaryl was ineffective in topical assays [32]. One and 2.0% Sevimol® were effective for protecting Engelmann spruce, *P. engelmannii* Parry ex. Engelm., from spruce beetle attack for two field seasons in Utah [33], which agrees with results from [9] for 2.0% Sevin® SL. However, the two latter studies were concluded after two field seasons. In the case of [9], all

**Red turpentine beetle.** Red turpentine beetle, *D*. *valens* LeConte, usually colonizes the basal portions of stressed, weakened, or dead and dying trees. Therefore, the species is not consid‐ ered an important source of tree mortality in the western U.S., and limited work has occur‐ red regarding the development of tree protection tools. [34] reported that 2.0% Sevin® XLR and 4.0% Sevimol® 4 were effective for protecting ponderosa pine in California. Several for‐ Pyrethroids are synthesized from petroleum-based chemicals and related to the potent in‐ secticidal properties of flowering plants in the genus *Chrysanthemum*. They are axonic poi‐ sons and cause paralysis by keeping the sodium channels open in the neuronal membranes [37]. First generation pyrethroids were developed in the 1960s, but are unstable in sunlight. By the mid-1970s, a second generation was developed (e.g., permethrin, cypermethrin and deltamethrin) that were more resistant to photodegradation, but have substantially higher mammalian toxicities. Third generation pyrethroids (e.g., bifenthrin, cyfluthrin and lambdacyhalothrin) have even greater photostability and insecticidal activity compared to previous generations. Pyrethroids are one of the least acutely toxic insecticides to mammals, essential‐ ly nontoxic to birds, but are highly toxic to fish, amphibians and honey bees [38]. Today, permethrin (e.g., Astro® and Dragnet®, among others) and bifenthrin (e.g., Onyx™) are com‐ monly used to protect trees from bark beetle attack, and following carbaryl are the most-ex‐ tensively studied active ingredients registered for use.

**Mountain and western pine beetles.** Several active ingredients and formulations of pyreth‐ roids have been evaluated as preventative treatments, and most research indicates at least one field season of protection can be expected with a single application. [8] evaluated 0.1%, 0.2% and 0.4% permethrin (Pounce®) for protecting ponderosa pine from mortality due to western pine beetle attack, and reported that 0.2% and 0.4% provided control for four months. Permethrin plus-C (Masterline®), a unique formulation containing methyl cellulose (i.e., "plus-C") thought to increase efficacy and stability by reducing photo-, chemical- and biological-degradation of the permethrin molecule, exhibits efficacy similar to that of other formulations of permethrin [12]. [39] examined several rates of esfenvalerate (Asana® XL) and cyfluthrin (Tempo® 20 WP) as preventative treatments. In California, 0.025% and 0.05% Asana® XL protected ponderosa pine for western pine beetle attack for one field season, but not a second. In Montana, 0.006% and 0.012% Asana® XL were ineffective for protecting lodgepole pine from mountain pine beetle, but 0.025% was effective for one field season. Tempo® 20 WP applied at 0.025% provided protection of ponderosa pine from western pine beetle for one field season in Idaho, but not California [39]. Surprisingly, 0.025%, 0.05% and 0.1% Tempo® 20 WP were effective for protecting lodgepole pine from mountain pine beetle attack for two field seasons [39]. [9] evaluated 0.03%, 0.06% and 0.12% bifenthrin (Onyx™) reporting at minimum one field season of protection for mountain pine beetle in lodgepole pine and two field seasons of protection for western pine beetle in ponderosa pine. This study and related research led to the registration of 0.06% Onyx™ as a preventative spray in the mid-2000s. [40] reported 0.06% Onyx™ failed to provide three field seasons of protection for western pine beetle in ponderosa pine, confirming Onyx™ is only effective for two field seasons in that system.

secticides directly into the lower bole. Early work indicated that several methods, active ingredients and formulations were ineffective [e.g., 13,42-44]. In recent years, the efficacy of phloem-mobile active ingredients injected with pressurized systems (e.g., Sidewinder® Tree Injector, Tree I.V. micro infusion® and Wedgle® Direct-Inject™) capable of maintain‐ ing >275 kPA have been evaluated for engraver beetles, mountain pine beetle, southern pine beetle, spruce beetle, and western pine beetle (Fig. 5). These systems push adequate volumes of product (i.e., generally less than several hundred ml for even large trees) in‐ to the small vesicles of the sapwood [45]. Applications take <15 minutes per tree under most circumstances. Following injection, the product is transported throughout the tree to the target tissue (i.e., the phloem where bark beetle feeding occurs). Injections can be applied at any time of year when the tree is actively translocating, but time is needed to allow for full distribution of the active ingredient within the tree prior to the tree being attacked by bark beetles. Under optimal conditions (e.g., adequate soil moisture, moder‐ ate temperatures and good overall tree health) this takes ~4 weeks [46], but may take much longer, particularly in high-elevation forests. Tree injections represent essentially closed systems that eliminate drift, and reduce non-target effects and applicator expo‐ sure, but efficacy is often less than that observed for bole sprays in high-elevation forests [40]. Significant advancements in the development of this technology have been made in recent years, but tree injections are still rarely used in comparison to bole sprays in the western U.S. With the advent of designer formulations of insecticides specific for tree in‐ jection, we suspect that tree injections will become a more common tool for protecting trees from bark beetle attack in the near future, particularly in areas where bole sprays

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are not practical (e.g., along property lines or within no-spray buffers).

**Figure 5.** Experimental injections of emamectin benzoate for protecting trees from western pine beetle attack in Cala‐ veras County, California, U.S. (left), and mountain pine beetle attack in the Uinta-Wasatch-Cache National Forest, Utah, U.S. (right). Photos: C.J. Fettig, Pacific Southwest Research Station, USDA Forest Service (left) and D.M. Grosman,

Texas A&M Forest Service (right).

**Southern pine beetle.** While limited research has occurred, permethrin (Astro®) appears to have longer residual activity than bifenthrin (Onyx™) at least in small-bolt assays [11].

**Spruce beetle.** Most research suggests that at least one field season of protection can be ex‐ pected. [9] reported 0.03%, 0.06% and 0.12% bifenthrin (Onyx™) would likely provide pro‐ tection for two field seasons in Utah. However, 0.025% cyfluthrin (Tempo® 2) and 0.025% and 0.05% esfenvalerate (Asana® XL) only provided one field season of protection in Utah [33]. Protection of Lutz spruce in Alaska is possible for two field seasons with a single appli‐ cation of 0.25% permethrin (formulation unreported) [41].

**Red turpentine beetle.** [35] reported 0.5% permethrin (Dragnet®) was effective for protect‐ ing Monterey pine, and that it had longer residual activity than carbaryl. [34] reported 0.1%, 0.2% and 0.4% permethrin (formulation unreported) were ineffective for protecting ponder‐ osa pine from red turpentine beetle.

**Engraver beetles.** Most research suggests that at least one field season of protection can be expected with a single application; however, [9] reported 0.03%, 0.06% and 0.12% bifenthrin (Onyx™) protected single-leaf pinyon from pinyon ips for two field seasons in Nevada. A similar study on the Southern Ute Reservation in Colorado found 0.12% Onyx™ protected pinyon pine for one field season, but bark beetle pressure was insufficient the second year of the study to make conclusions regarding efficacy at that rate. Both 0.03% and 0.06% Onyx™ were ineffective [9]. [13] reported that 0.19% permethrin plus-C (Masterline®) and 0.06% bi‐ fenthrin (Onyx™) were effective for protecting ponderosa pine bolts from engraver beetle at‐ tack in Arizona. [36] reported 0.06% bifenthrin (Onyx™) significantly reduced colonization of trees by bark and woodboring beetles, including sixspined ips, in the southeastern U.S.
