Peter B. Schultz

Influence of flood-stress on ambrosia beetle host-selection and implications for their management in a changing climate

1 Xylosandrus germanus (Blandford) is a key pest of ornamental nursery trees. Ethanol is the most attractive semiochemical known for X. germanus, and its emission from trees represents a primary host‐selection cue. Ethanol production is induced by a variety of abiotic and biotic stressors, which could thereby predispose trees to attack by ethanol‐responsive ambrosia beetles. 2 To better understand X. germanus host‐selection behaviour within ornamental nurseries, a series of experiments examined the influence of flood‐stress on the attractiveness and susceptibility of flowering dogwood Cornus florida L. Under field conditions, more X. germanus were attracted to experimentally flood‐stressed dogwoods than neighbouring nonflooded controls in 2009, 2010 and 2011. Flood‐stressed dogwoods were also preferentially attacked in 2009–2011, although no attacks occurred on any of the neighbouring nonflooded trees. 3 Solid‐phase microextraction‐gas chromatography‐mass spectrometry detected ethanol in stem tissue from flooded dogwoods but not nonflooded trees. Acetaldehyde, acetic acid and ethanol were also emitted from the outer bark of flooded dogwoods but not nonflooded trees. 4 These results demonstrate that X. germanus preferentially lands on and attacks physiologically‐stressed hosts, and further support the role of ethanol in mediating this interaction. 5 Attacks by X. germanus have previously been suspected to occur on trees viewed as ‘apparently‐healthy’, although the possibility of such trees being in apparently‐stressed at the time of attack cannot be ruled out given the results obtained in the present study. Minimizing the impact of stressors known to induce the production of ethanol should be the primary foundation of a management plan for X. germanus and other ethanol‐responsive ambrosia beetles.

Species Dependent Influence of (−)-α-Pinene on Attraction of Ambrosia Beetles (Coleoptera: Curculionidae: Scolytinae) to Ethanol-Baited Traps in Nursery Agroecosystems

ABSTRACT Field-based trapping experiments were conducted in Ohio in 2003, 2004, and 2008 to determine the influence of (—)-&agr;-pinene on the attraction of exotic and native ambrosia beetles (Coleoptera: Curculionidae: Scolytinae) to ethanol-baited traps. In 2003 and 2004, we determined the effect of adding an (—)-&agr;-pinene ultrahigh release lure (UHR; 2 g/d at 20°C) to traps baited with an ethanol UHR lure (0.39 g/d). Fewer Anisandrus (Xyleborus) sayi (Hopkins) and Xyleborinus saxeseni (Ratzeburg) were collected in 2003 and 2004 from traps baited with ethanol UHR plus (—)-&agr;-pinene UHR compared with ethanol UHR. (—)-&agr;-Pinene also reduced the attraction of Xyloterinus politus (Say) to ethanol-baited traps in 2004. Total captures of Xylosandrus germanus (Blandford) in 2003 were higher in traps baited with ethanol UHR plus (—) -&agr;-pinene UHR than in traps with ethanol UHR alone but not in 2004. In 2008, captures were compared among traps baited with eight combinations of ethanol and (—)-&agr;-pinene at both UHR and low release (LR) rates. Release rates for ethanol LR and (—)-&agr;-pinene LR were 0.027 and 0.0015g/d, respectively. (—)-&agr;-Pinene UHR and (—)-&agr;-pinene LR reduced the attractiveness of ethanol UHR to A. sayi and X. saxeseni. Ethanol UHR was also more attractive than ethanol LR to A. sayi and X. germanus. These findings demonstrate traps baited with ethanol alone are more effective than ethanol plus (—) -&agr;-pinene for monitoring ambrosia beetle flight activity in ornamental nurseries. Ethanol release rate is also an important consideration for monitoring purposes.

Optimizing ethanol-baited traps for monitoring damaging ambrosia beetles (Coleoptera: Curculionidae, Scolytinae) in ornamental nurseries.

ABSTRACT The exotic ambrosia beetles Xylosandrus crassiusculus (Motschulsky) and Xylosandrus germanus (Blandford) (Coleoptera: Curculionidae: Scolytinae) are serious pests in ornamental tree nurseries. To optimize bottle-traps as a monitoring system for X. crassiusculus and X. germanus in nurseries, we tested whether increasing the rate of commercial ethanol lures improved captures or early detection of these species. Experiments were conducted in Ohio (2008 and 2009) and Virginia (2008), two states that have experienced significant damage from X. crassiusculus, X. germanus, or both. There were four treatments: no-lure (unbaited control), 1-ethanol lure, 2-ethanol lures and 1 + 1-ethanol lures (one lure in the trap and one suspended 0.5 m above the trap). Captures of X. crassiusculus and X. germanus were higher in all ethanol treatments than unbaited controls, and were generally higher in treatments with two lures versus one. There was no difference in beetle captures between the 2-lure and 1 + 1-lure treatments. First detection of X. crassiusculus and X. germanus occurred more consistently in the treatments with two lures than one lure. Xyleborinus saxesenii (Ratzeburg), Anisandrus sayi Hopkins, Hypothenemus dissimilis Zimmermann, and Hypothenemus eruditus Westwood were also more attracted to traps baited with ethanol than unbaited controls. X. saxesenii was captured in higher numbers in the treatments with two lures than one in Virginia but not in Ohio. There was no difference in captures of the other species among ethanol treatments. The current research shows that ethanol release rates influence sensitivity of traps for detecting emergence of overwintered ambrosia beetles.

Ambrosia Beetle (Coleoptera: Curculionidae) Responses to Volatile Emissions Associated with Ethanol-Injected Magnolia virginiana

ABSTRACT Xylosandrus germanus (Blandford) and other species of ambrosia beetles are key pests of ornamental nursery trees. A variety of laboratory- and field-based experiments were conducted in pursuit of improved monitoring strategies and to develop a trap tree strategy for ambrosia beetles. Traps baited with bolts prepared from Magnolia virginiana L. injected with ethanol caught five times more X. germanus than ethanol-baited traps. Basal stem injections of ethanol into M. virginiana induced more ambrosia beetle attacks than irrigating or baiting with ethanol, and no attacks occurred on water-injected trees. A positive correlation was also detected between concentration of injected ethanol and cumulative attacks. Solid phase microextraction-gas chromatography-mass spectrometry characterized bark emissions from ethanol- and water-injected M. virginiana at 1, 2, 10, and 16 d after treatment. Ethanol emission from injected trees steadily declined from 1 to 16 d after treatment, but was not emitted from water-injected trees. A variety of monoterpenes were also emitted in trace amounts from the ethanol- and water-injected trees. Antennal responses of X. germanus via gas chromatography-electroantennographic detection to volatiles from ethanol-injected M. virginiana occurred for ethanol, but not the various monoterpenes. X. germanus and other ambrosia beetles were also equally attracted to traps baited with ethanol alone compared with a synthetic mixture of ethanol plus various monoterpenes formulated to mimic ethanol-injected M. virginiana. Injecting concentrated solutions of ethanol into trees may be useful for establishing odor-based trap trees, which could aid with monitoring programs and/ or potentially deflect ambrosia beetles away from valuable nursery stock.

Non-Native Ambrosia Beetles as Opportunistic Exploiters of Living but Weakened Trees

Exotic Xylosandrus spp. ambrosia beetles established in non-native habitats have been associated with sudden and extensive attacks on a diverse range of living trees, but factors driving their shift from dying/dead hosts to living and healthy ones are not well understood. We sought to characterize the role of host physiological condition on preference and colonization by two invaders, Xylosandrus germanus and Xylosandrus crassiusculus. When given free-choice under field conditions among flooded and non-flooded deciduous tree species of varying intolerance to flooding, beetles attacked flood-intolerant tree species over more tolerant species within 3 days of initiating flood stress. In particular, flood-intolerant flowering dogwood (Cornus florida) sustained more attacks than flood-tolerant species, including silver maple (Acer saccharinum) and swamp white oak (Quercus bicolor). Ethanol, a key host-derived attractant, was detected at higher concentrations 3 days after initiating flooding within stems of flood intolerant species compared to tolerant and non-flooded species. A positive correlation was also detected between ethanol concentrations in stem tissue and cumulative ambrosia beetle attacks. When adult X. germanus and X. crassiusculus were confined with no-choice to stems of flood-stressed and non-flooded C. florida, more ejected sawdust resulting from tunneling activity was associated with the flood-stressed trees. Furthermore, living foundresses, eggs, larvae, and pupae were only detected within galleries created in stems of flood-stressed trees. Despite a capability to attack diverse tree genera, X. germanus and X. crassiusculus efficiently distinguished among varying host qualities and preferentially targeted trees based on their intolerance of flood stress. Non-flooded trees were not preferred or successfully colonized. This study demonstrates the host-selection strategy exhibited by X. germanus and X. crassiusculus in non-native habitats involves detection of stress-induced ethanol emission and early colonization of living but weakened trees.

Integrating Chemical and Biological Control of European Corn Borer in Bell Pepper

ABSTRACT Using multiple locations and a series of field trials over 2 yr, we evaluated an integrated pest management program for Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae) management in peppers involving biorational chemistries, inundative releases of Trichogramma ostriniae (Pang & Chen), and conservation of generalist predators. In small plot trials, three biorational insecticides (spinosad, indoxacarb, and methoxyfenozide) provided comparable control of O. nubilalis as two broad-spectrum conventional insecticides (acephate and lambda-cyhalothrin). However, lambda-cyhalothrin at most locations, and indoxacarb at one location, resulted in outbreaks of green peach aphids. We also observed significant effects on the generalist predator community: beneficial communities in methoxyfenozide-treated plots were most similar to untreated controls, and acephate-treated plots were the least similar. Management systems comparing untreated controls, inundative release of T. ostriniae with methoxyfenozide applied when lepidopterans exceeded thresholds, or weekly applications of acephate or lambda-cyhalothrin, showed no effects on marketable fruit or percentage of fruit damaged, but the conventional insecticide approach caused aphid flares. Inun-dative releases of T. ostriniae and biorational chemistries provide a more environmentally sound approach to managing O. nubilalis in peppers, due, in part, to conservation of generalist predators.

Ethanol Injection of Ornamental Trees Facilitates Testing Insecticide Efficacy Against Ambrosia Beetles (Coleoptera: Curculionidae: Scolytinae)

ABSTRACT Exotic ambrosia beetles are damaging pests in ornamental tree nurseries in North America. The species Xylosandrus crassiusculus (Motshulsky) and Xylosandrus germanus (Blandford) are especially problematic. Management of these pests relies on preventive treatments of insecticides. However, field tests of recommended materials on nursery trees have been limited because of unreliable attacks by ambrosia beetles on experimental trees. Ethanol-injection of trees was used to induce colonization by ambrosia beetles to evaluate insecticides and botanical formulations for preventing attacks by ambrosia beetles. Experiments were conducted in Ohio, Tennessee, and Virginia. Experimental trees injected with ethanol had more attacks by ambrosia beetles than uninjected control trees in all but one experiment. Xylosandrus crassiusculus and X. germanus colonized trees injected with ethanol. In most experiments, attack rates declined 8 d after ethanol-injection. Ethanol-injection induced sufficient pressure from ambrosia beetles to evaluate the efficacy of insecticides for preventing attacks. Trunk sprays of permethrin suppressed cumulative total attacks by ambrosia beetles in most tests. Trunk sprays of the botanical formulations Armorex and Veggie Pharm suppressed cumulative total attacks in Ohio. Armorex, Armorex + Permethrin, and Veggie Pharm + Permethrin suppressed attacks in Tennessee. The bifenthrin product Onyx suppressed establishment of X. germanus in one Ohio experiment, and cumulative total ambrosia beetle attacks in Virginia. Substrate drenches and trunk sprays of neonicotinoids, or trunk sprays of anthranilic diamides or tolfenpyrad were not effective. Ethanol-injection is effective for inducing attacks and ensuring pressure by ambrosia beetles for testing insecticide efficacy on ornamental trees.

Monitoring Attack and Flight Activity of Xylosandrus spp. (Coleoptera: Curculionidae: Scolytinae): The Influence of Temperature on Activity

ABSTBACT Wood-boring ambrosia beetles (Coleoptera: Curculionidae: Scolytinae), including Xylosandrus spp., are key pests in ornamental nurseries. Knowledge of their activity in spring is important for nursery growers to effectively time their protective sprays. We measured the reliability of ethanol-baited bottle traps for monitoring emergence of overwintered Xylosandrus spp. in ornamental nurseries. Detection of initial flight activity by traps was compared with initial attacks on ethanol-injected trap trees. To develop tools for forecasting Xylosandrus germanus (Blandford) activity, the relationships between temperature and their attack and flight activity were examined, and the bloom sequence of ornamental plants was examined as phenological indicators of X. germanus emergence in Ohio. Captures of X. germanus coincided with attacks on trap trees on seven of eight occasions over 2 yr in four nurseries. Xylosandrus crassiusculus (Motshulsky) were detected in only one nursery and captures coincided with attacks each year. There was a strong relationship between maximum daily temperatures 20 and 21°C and X. germanus attack and flight activity. No attack or flight activity were detected in a monitoring period unless there were 1 or 2 d of at least 20°C. Emergence of X. germanus always began after and within 6 d of full bloom on Cornelian cherry dogwood, and usually after and within 4 d of first bloom on Norway maple and full bloom on border forsythia. The traps or phenological indicators can be used by growers to monitor emergence of X. germanus to time their initial protective sprays. The relationship between X. germanus activity and temperature can be used by growers to make decisions on timing subsequent treatments.

Comparative Efficacy of Plant-Derived Essential Oils for Managing Ambrosia Beetles (Coleoptera: Curculionidae: Scolytinae) and Their Corresponding Mass Spectral Characterization

ABSTRACT Ambrosia beetles (Coleoptera: Curculionidae: Scolytinae) pose a significant challenge to producers of ornamental nursery stock. Conventional insecticides are commonly used for management purposes, but plant-derived essential oils also may discourage ambrosia beetles from initiating attacks. To identify promising commercially available products, field-based efficacy trials were conducted in Ohio in 2009 and 2010 with the following products: Armorex (Soil Technologies), Cinnacure (Proguard, Inc.), EcoTrol (EcoSMART Technologies, Inc.), and Veggie Pharm (Pharm Solutions, Inc.). Potted Magnolia virginiana L. were first injected with 75 ml of 5% ethanol to ensure ambrosia beetle pressure on experimental trees. Mixtures of each product (10% in water) and a water control were applied until runoff and attacks occurring under field conditions were quantified at 1, 4, 7, and 14 d after treatment (DAT). Ambrosia beetle attacks generally increased over time but at differing rates depending on the particular treatment. In 2009, Armorex and Veggie Pharm were associated with the lowest cumulative attacks 14 DAT. In 2010, Armorex and Cinnacure were associated with the fewest attacks 14 DAT. Solid phase microextraction-gas chromatography-mass spectrometry was used to characterize the volatile compounds associated with each product. Allyl isothiocyanate, a compound with known repellent and insecticidal properties, was unique and predominant in Armorex. These experiments identified commercially available botanicals containing plant essential oils with activity against ambrosia beetles, along with demonstrating the usefulness of ethanol-injection to ensure ambrosia beetle pressure under field conditions. Characterizing the constituents of efficacious botanically based products could also lead to the development of improved botanical insecticides.

Dispersal of Trichogramma ostriniae (Hymenoptera: Trichogrammatidae) in Potato Fields

ABSTRACT The dispersal ability of Trichogramma ostriniae Pang and Chen, a biological control agent of Ostrinia nubilalis Hübner, was studied in commercial potato fields on the Eastern Shore of Virginia. The purpose was to quantify dispersal of T. ostriniae after an inundative release to aid in determining the number of release points needed per unit area for effective biological control of O. nubilalis in solanaceous crops. A single release of ≈0.5 million wasps was made in two spatially separate potato fields in summer 2005 and 2006. Each release area contained 25 monitoring points at distances from 5 to 45 m from the release point bearing a yellow sticky card and O. nubilalis egg sentinels to observe for adult parasitoids and parasitism, respectively. Results showed that movement of T. ostriniae adults from the release point was rapid with individuals captured at 45 m within 1 d of emergence. High rates of parasitization (20–50%) also were observed at this distance, but the levels decreased with increasing distance from the release point. The distances that encompassed 98% recaptured T. ostriniae adults (x98) were 27.5 and 12.9 m from the release point in 2005 and 2006, respectively. The (x98) distances for parasitization of O. nubilalis were 21–26 m in 2005 and 8–10 m in 2006. However, the highest levels of parasitization in both years occurred nearest the release point. T. ostriniae showed uniform dispersal within an area of ≈0.1 ha, indicating that multiple release points should be used for effective dispersal of T. ostriniae and control of O. nubilalis in solanaceous crops. Based on the assumption that a distance of 16 m represents the radius around a release point in which T. ostriniae activity was at its maximum, we estimate that ≈12 release points/ha would be required in potato fields.