Differential utilization of ash phloem by emerald ash borer larvae: ash species and larval stage effects

• 1 Two experiments were performed to determine the extent to which ash species (black, green and white) and larval developmental stage (second, third and fourth instar) affect the efficiency of phloem amino acid utilization by emerald ash borer (EAB) Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) larvae.
• 2 EAB larvae generally utilized green ash amino acids more efficiently than those of the other two species. For example, the concentrations of only six (two essential) and seven (two essential) amino acids were lower in frass from EAB that fed upon black and white ash than in the corresponding phloem, respectively. By contrast, concentrations of 16 (eight essential) amino acids were lower in the frass from EAB that fed upon green ash than in the phloem. In addition, in green ash, the frass : phloem ratios of 13 amino acids were lower than their counterparts in black and white ash.
• 3 The concentrations of non‐essential amino acids glycine and hydroxylproline were greater in frass than in phloem when EAB fed on black ash, although not when EAB fed on green or white ash.
• 4 The concentration of total phenolics (a group of putative defensive compounds to EAB, expressed as antioxidant activity of acetone extraction) was high in EAB frass but even higher in the phloem samples when the data were pooled across ash species and EAB larval stages. This suggests EAB larvae may eliminate phenolics through a combination of direct excretion and enzymatic conversion of phenolics to nonphenolics before excretion. Because the ratio of frass total phenolics to phloem total phenolics in white ash was lower than the ratios in black and green ash, the ability to destroy phenolics or convert them to nonphenolics was greater when EAB larvae fed on white ash.
• 5 Fourth‐instar EAB extracted phloem amino acids, including threonine, more efficiently than third‐instar EAB. The different larval developmental stages of EAB did not differ in their apparent ability to destroy phenolics or convert them to nonphenolics.

     

Effects of learning experience on behaviour of the generalist parasitoid Sclerodermus pupariae to novel hosts

Massicus raddei Blessig (Coleoptera: Cerambycidae), also referred to as the oak long‐horned beetle (OLB), is a non‐natural host for the generalist parasitoid Sclerodermus pupariae Yang et Yao (Hymenoptera: Bethylidae). To determine whether this generalist parasitoid might be a suitable agent for the control of OLB, the adaptive learning experience of adult female parasitoids to OLB larvae was investigated in the laboratory. A Y‐tube olfactometer bioassay was used to examine the effects of adaptive learning experience on the foraging ability of parasitoids for OLB larvae. The results indicated that parasitoids were significantly attracted by the volatiles of ash bark, Fraxinus velutina, with emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) larvae and larval frass, after exposure to ash bark mixed with EAB larval frass (learning condition A). In contrast, after exposure to oak bark, Quercus liaotungensis, mixed with OLB larval frass (learning condition C), parasitoids showed significant preference for the volatiles of oak bark with OLB larvae and larval frass. On the basis of the results of no‐choice tests, we found that parasitoids exposed to learning condition C had greater paralysis efficiency and higher OLB larvae parasitism rates than those exposed to learning condition A or no experience. Furthermore, parasitoids fed on OLB larvae in learning condition C had significantly greater paralysis efficiency and higher OLB larvae parasitism rates than other parasitoids tested. Parasitoids fed on EAB larvae in learning condition A had the lowest paralysis efficiency and OLB larvae parasitism rates among the parasitoids tested. These findings suggested that adaptive learning significantly enhanced the ability of a generalist parasitoid to utilize a novel host. This may provide a new approach to controlling non‐natural hosts using generalist parasitoids.     

Population responses of hymenopteran parasitoids to the emerald ash borer (Coleoptera: Buprestidae) in recently invaded areas in north central United States

Populations of hymenopteran parasitoids associated with larval stages of the invasive emerald ash borer (EAB) Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) were surveyed in 2009 and 2010 in the recently invaded areas in north central United States (Michigan), where two introduced EAB larval parasitoids, Tetrastichus planipennisi Yang and Spathius agrili Yang were released for classical biological control. Results from two years of field surveys showed that several hymenopteran parasitoids have become associated with EAB in Michigan. Among these parasitoids, the gregarious species T. planipennisi was the most abundant, accounting for 93% of all parasitoid individuals collected in 2009 (immediately after field release) and 58% in 2010 (a year later after field releases). Low levels (1–5%) of parasitism of EAB larvae by T. planipennisi were consistently detected at survey sites in both years. Separately, the abundance of the native parasitoid, Atanycolus spp., increased sharply, resulting in an average parasitism rate of EAB larvae from <0.5% in 2009 to 19% in 2010. Other parasitoids such as Phasgonophora sulcata Westwood, Spathius spp., Balcha indica Mani & Kaul, Eupelmus sp., and Eurytomus sp. were much less abundant than T. planipennisi and Atanycolus spp., and each caused <1% parasitism. Besides hymenopteran parasitoids, woodpeckers consumed 32–42% of the immature EAB stages present at our study sites, while undetermined biotic factors (such as microbial disease and host tree resistance) caused 10–22% mortality of observed EAB larvae. Relevance of these findings to the potential for biological control of EAB in the invaded areas of North America is discussed.     

Drought stress increased survival and development of emerald ash borer larvae on coevolved Manchurian ash and implicates phloem‐based traits in resistance

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Interactions between Spathius agrili (Hymenoptera: Braconidae) and Tetrastichus planipennisi (Hymenoptera: Eulophidae), larval parasitoids of Agrilus planipennis (Coleoptera: Buprestidae)

Three hymenopteran parasitoids native to China are being released in the United States as biological control agents for the emerald ash borer (EAB), Agrilus planipennis Fairmaire, an Asian buprestid species responsible for mortality of ash trees (Fraxinus spp.) in North America. Two of these hymenopterans, Spathius agrili Yang (Braconidae), a larval ectoparasitoid, and Tetrastichus planipennisi Yang (Eulophidae), a larval endoparasitoid, prefer late-instar EAB larvae. This overlapping host preference raises concerns that interspecific competition following field releases may compromise establishment of one or both species. In a series of laboratory and field experiments, we found S. agrili and T. planipennisi exhibited similar parasitism rates when presented alone with EAB larvae for 12–14 days. However, S. agrili was more efficient at locating and parasitizing hosts within the first 27 h, possibly explaining why S. agrili excluded T. planipennisi in the laboratory trials and nearly excluded T. planipennisi in field trials when the two species were presented together with EAB larvae. We found that S. agrili parasitized larvae previously parasitized by T. planipennisi but not the reverse. However, S. agrili offspring failed to complete development on hosts that were previously parasitized by T. planipennisi. We recommend releasing these species separately in time or space to avoid the antagonistic interactions observed in this study.     

The effect of bark thickness on host partitioning between Tetrastichus planipennisi (Hymen: Eulophidae) and Atanycolus spp. (Hymen: Braconidae), two parasitoids of emerald ash borer (Coleop: Buprestidae)

Parasitoids have recently been introduced from Asia to aid in biological control in the United States of the invasive, highly damaging, emerald ash borer, Agrilus planipennis. Three introduced parasitoids have established and field biological studies are underway to improve our understanding of niche partitioning among them. Here we report one such investigation, a field experiment conducted to determine how outer bark thickness of ash trees might affect parasitism by one introduced (Tetrastichus planipennisi) and one native parasitoid (Atanycolus spp.). We found that T. planipennisi was unable to parasitize EAB larvae in trees with outer bark thicker than 3.2 mm (>11.2-cm DBH) whereas Atanycolus spp. parasitized EAB larvae in ash trees with outer bark up to 8.8 mm thick (>57.4-cm DBH). These results suggest that establishment of, and control by T. planipennisi at release sites with only large diameter trees is less likely, and that T. planipennisi will be more effective in stands with younger trees (<12-cm DBH). Releasing T. planipennisi near the leading edge of EAB invasion may have little impact on EAB populations if many ash trees are too large. We recommend releasing T. planipennisi in stands dominated by small, early successional or regenerating ash trees. This may maximize the establishment and effectiveness of this species. This limitation of T. planipennisi for biological control of emerald ash borer suggests that other EAB parasitoids from its native range with longer ovipositors, such as Spathius galinae (Hymenoptera: Braconidae), should be sought and evaluated for possible use as EAB biocontrol agents in the US. The results of this study also suggest the importance of parasitoid guild introduction for biological control in general, and hint at possible broader implications relating to resource partitioning among native and introduced parasitoids.     

Moisture content and nutrition as selection forces for emerald ash borer larval feeding behaviour

1. The exotic phloem‐feeding emerald ash borer (EAB), Agrilus planipennis, has killed tens of millions of North American ash trees (Fraxinus) since its first detection in the U.S.A. in 2002. Ash trees are killed by larval feeding in the cambial region, which disrupts translocation of photosynthates and nutrients. 2. We observed that EAB larvae feed predominantly downwards in naturally grown green ash trees, a behaviour confirmed in greenhouse‐grown black ash seedlings. Furthermore, biomass of larvae feeding downwards was greater than that for larvae feeding upwards. 3. We sought to determine the relative importance of four selection forces (i.e. gravity, moisture content, plant defence, and nutrition) in driving this downward feeding behaviour in this study. The gravity and plant defence (i.e. polyphenols) hypotheses were ruled out because even when seedlings were grown upside down, more EAB larvae moved upwards (towards the root area), and phloem tissue below the feeding site contained higher concentrations of defensive compounds than that above the feeding site. 4. The moisture content hypothesis was supported as phloem moisture above the feeding site decreased to levels reducing survivorship and biomass but was unaffected below. The nutrition hypothesis was also supported as the levels of 11 amino acids (mostly essential amino acids) below the feeding site were greater than those above. Furthermore, growth of larvae reared on an artificial diet deficient in protein and amino acids was worse than larvae reared in diet with complete ingredient or diet deficient in either protein or amino acids. 5. We conclude that moisture content and nutrients are two selective forces for the downward feeding behaviour of EAB larvae.     

Volatile organic compounds released by maize following herbivory or insect extract application and communication between plants

To protect themselves from herbivory, plants have evolved an arsenal of physical and chemical defences and release a variety of volatile organic compounds (VOCs). By releasing these VOCs, a signalling plant can both reduce herbivory, sometimes by more than 90%, and also warn neighbouring plants about an attack. The aim of this study was to assess the influence of herbivory and insect extract application on VOC release by damaged/treated and nearby undamaged/untreated maize plants. We confirmed that European corn borer (Ostrinia nubilalis) larvae attack or larvae extract application induced maize VOC release. Greater amounts of (Z)‐3‐hexenal, (E)‐2‐hexenal, (Z)‐3‐hexen‐1‐ol, (E)‐2‐hexen‐1‐ol, β‐myrcene, (Z)‐3‐hexen‐1‐yl acetate, 1‐hexyl acetate, (Z)‐ocimene, linalool, benzyl acetate, methyl salicylate, indole, methyl anthranilate, geranyl acetate, β‐caryophyllene, (E)‐β‐farnesene and (Z)‐3‐hexenal, (Z)‐3‐hexen‐1‐ol, (Z)‐3‐hexen‐1‐yl acetate, (Z)‐ocimene, linalool, indole, methyl anthranilate, geranyl acetate, β‐caryophyllene and (E)‐β‐farnesene were released as a result of biotic stress after insect attack or insect extract application. The amounts of each VOC released were qualitatively and quantitatively distinct and dependent on time after biotic stress exposure. However, for all biotic stresses, significantly lower VOC induction was measured when leaves were damaged/treated for three days, as compared to seven days. Our work also demonstrated that undamaged/untreated neighbouring plants also release significant amounts of VOCs. This suggests that VOC emission by a damaged/treated plant stimulates VOC induction in nearby undamaged/untreated plants. However, the concentrations of all VOCs released by neighbouring undamaged/untreated maize plants were lower than those from damaged/treated plants and were negatively correlated with distance from a damaged/treated plant. Still, significant VOC induction occurred in undamaged/untreated plants even at 3 m distance from a damaged/infected plant. Our work suggests that maize plant protective defence responses (VOC emission) can be induced via application of European corn borer extracts.     

Feeding by emerald ash borer larvae induces systemic changes in black ash foliar chemistry

The exotic wood-boring pest, emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), has been threatening North American ash (Fraxinus spp.) resources, this being recognized since its first detection in Michigan, USA and Ontario, Canada in 2002. Ash trees are killed by larval feeding in the cambial region, which results in disruption of photosynthate and nutrient translocation. In this study, changes in volatile and non-volatile foliar phytochemicals of potted 2-yr-old black ash, Fraxinus nigra Marshall, seedlings were observed in response to EAB larval feeding in the main stem. EAB larval feeding affected levels of six compounds [hexanal, (E)-2-hexenal, (Z)-3-hexenyl acetate, (E)-β-ocimene, methyl salicylate, and (Z,E)-α-farnesene] with patterns of interaction depending upon compounds of interest and time of observation. Increased methyl salicylate emission suggests similarity in responses induced by EAB larval feeding and other phloem-feeding herbivores. Overall, EAB larval feeding suppressed (Z)-3-hexenyl acetate emission, elevated (E)-β-ocimene emission in the first 30 days, but emissions leveled off thereafter, and generally increased the emission of (Z,E)-α-farnesene. Levels of carbohydrates and phenolics increased overall, while levels of proteins and most amino acids decreased in response to larval feeding. Twenty-three amino acids were consistently detected in the foliage of black ash. The three most abundant amino acids were aspartic acid, glutamic acid, glutamine, while the four least abundant were α-aminobutyric acid, β-aminoisobutyric acid, methionine, and sarcosine. Most (16) foliar free amino acids and 6 of the 9 detected essential amino acids decreased with EAB larval feeding. The ecological consequences of these dynamic phytochemical changes on herbivores harbored by ash trees and potential natural enemies of these herbivores are discussed.     

Girdling increases survival and growth of emerald ash borer larvae on Manchurian ash

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Effects of water availability on emerald ash borer larval performance and phloem phenolics of Manchurian and black ash

The invasive emerald ash borer (EAB) beetle is a significant threat to the survival of North American ash. In previous work, we identified putative biochemical and molecular markers of constitutive EAB resistance in Manchurian ash, an Asian species co‐evolved with EAB. Here, we employed high‐throughput high‐performance liquid chromatography with photodiode array detection and mass spectrometry (HPLC‐PDA‐MS) to characterize the induced response of soluble phloem phenolics to EAB attack in resistant Manchurian and susceptible black ash under conditions of either normal or low water availability, and the effects of water availability on larval performance. Total larval mass per tree was lower in Manchurian than in black ash. Low water increased larval numbers and mean larval mass overall, but more so in Manchurian ash. Low water did not affect levels of phenolics in either host species, but six phenolics decreased in response to EAB. In both ashes, pinoresinol A was induced by EAB, especially in Manchurian ash. Pinoresinol A and pinoresinol B were negatively correlated with each other in both species. The higher accumulation of pinoresinol A in Manchurian ash after attack may help explain the resistance of this species to EAB, but none of the responses measured here could explain increased larval performance in trees subjected to low water availability.     

Effects of grafting on host plant resistance in ash (Fraxinus spp.) to emerald ash borer (Agrilus planipennis Fairmaire)

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High temperature tolerance and thermal plasticity in emerald ash borer Agrilus planipennis

• 1 The emerald ash borer Agrilus planipennis (Coleoptera: Buprestidae) (EAB), an invasive wood‐boring beetle, has recently caused significant losses of native ash (Fraxinus spp.) trees in North America. Movement of wood products has facilitated EAB spread, and heat sanitation of wooden materials according to International Standards for Phytosanitary Measures No. 15 (ISPM 15) is used to prevent this.
• 2 In the present study, we assessed the thermal conditions experienced during a typical heat‐treatment at a facility using protocols for pallet wood treatment under policy PI‐07, as implemented in Canada. The basal high temperature tolerance of EAB larvae and pupae was determined, and the observed heating rates were used to investigate whether the heat shock response and expression of heat shock proteins occurred in fourth‐instar larvae.
• 3 The temperature regime during heat treatment greatly exceeded the ISPM 15 requirements of 56 °C for 30 min. Emerald ash borer larvae were highly tolerant of elevated temperatures, with some instars surviving exposure to 53 °C without any heat pre‐treatments. High temperature survival was increased by either slow warming or pre‐exposure to elevated temperatures and a recovery regime that was accompanied by up‐regulated hsp70 expression under some of these conditions.
• 4 Because EAB is highly heat tolerant and exhibits a fully functional heat shock response, we conclude that greater survival than measured in vitro is possible under industry treatment conditions (with the larvae still embedded in the wood). We propose that the phenotypic plasticity of EAB may lead to high temperature tolerance very close to conditions experienced in an ISPM 15 standard treatment.

     

Physiological responses of emerald ash borer larvae to feeding on different ash species reveal putative resistance mechanisms and insect counter-adaptations

Emerald ash borer, Agrilus planipennis Fairmaire, an Asian wood-boring beetle, has devastated ash (Fraxinus spp.) trees in North American forests and landscapes since its discovery there in 2002. In this study, we collected living larvae from EAB-resistant Manchurian ash (Fraxinus mandschurica), and susceptible white (Fraxinus americana) and green (Fraxinus pennsylvanica) ash hosts, and quantified the activity and production of selected detoxification, digestive, and antioxidant enzymes. We hypothesized that differences in larval physiology could be used to infer resistance mechanisms of ash. We found no differences in cytochrome P450, glutathione-S-transferase, carboxylesterase, sulfotransferase, and tryptic BApNAase activities between larvae feeding on different hosts. Despite this, Manchurian ash-fed larvae produced a single isozyme of low electrophoretic mobility that was not produced in white or green ash-fed larvae. Additionally, larvae feeding on white and green ash produced two serine protease isozymes of high electrophoretic mobility that were not observed in Manchurian ash-fed larvae. We also found lower activity of β-glucosidase and higher activities of monoamine oxidase, ortho-quinone reductase, catalase, superoxide dismutase, and glutathione reductase in Manchurian ash-fed larvae compared to larvae that had fed on susceptible ash. A single isozyme was detected for both catalase and superoxide dismutase in all larval groups. The activities of the quinone-protective and antioxidant enzymes are consistent with the resistance phenotype of the host species, with the highest activities measured in larvae feeding on resistant Manchurian ash. We conclude that larvae feeding on Manchurian ash could be under quinone and oxidative stress, suggesting these may be potential mechanisms of resistance of Manchurian ash to EAB larvae, and that quinone-protective and antioxidant enzymes are important counter-adaptations of larvae for dealing with these resistance mechanisms.     

Impacts of the emerald ash borer (Agrilus planipennis Fairmaire) induced ash (Fraxinus spp.) mortality on forest carbon cycling and successional dynamics in the eastern United States

Invasive species are widely recognized as altering species and community dynamics, but their impacts on biogeochemical cycling and ecosystem processes are less understood. The emerald ash borer (Agrilus planipennis Fairmaire) is a phloem feeding beetle that was inadvertently introduced to the US in the 1990s and relies solely on ash trees (Fraxinus spp.) to complete its life cycle. Ash trees have a wide geographic distribution and are an important component of many different forest types in the US. The larval feeding behavior of the emerald ash borer (EAB) effectively girdles the tree’s phloem tissue resulting in tree mortality in as little as 2 years and stand mortality in as little as 5 years. Using the forest inventory and analysis database, we found that forest lands in the lower 48 states hold approximately 8.7 billion ash trees and saplings, which represent ~2.5 % of the aboveground forest carbon mass. Furthermore, we measured tree growth in 7 EAB impacted and 5 non-EAB impacted temperate forests in the Midwestern United States to quantify the impacts of EAB induced tree mortality on tree growth. We hypothesized that the initial C lost would be partly compensated for by the enhanced non-ash tree growth in EAB-impacted regions relative to non-EAB impacted regions. The EAB disturbance enhanced growth of non-ash trees in the EAB impacted region relative to the non-EAB impacted region. Results also indicate that in EAB impacted areas, growth of trees from the genera Acer and Ulmus responded most positively. Finally, we quantified annual biometric net primary productivity of the EAB impacted forests and compared these quantities to modeled growth of these forests in the absence of EAB and found that large scale ash tree mortality has reduced short term regional forest productivity. The loss of ash biometric net primary productivity is, in part compensated by enhanced growth of non-ash species. As expected, EAB disturbance severity was greater in forests with higher basal areas of ash. This study illustrates the ecosystem and regional scale impacts of invasive pest-induced disturbance on biogeochemical cycling and forest species composition.     

(R)‐(+)‐limonene,kairomone for Dastarcus helophoroides,a natural enemy of longhorned beetles

1 Chemical cues involved in host location by Dastarcus helophoroides (Fairmaire) (Coleoptera: Bothrideridae), a parasitoid of Anoplophora glabripennis Motschulsky, Monochamus alternatus Hope, Massicus raddei (Blessig), Apriona germari (Hope), Apriona swainsoni (Hope) and Batocera horsfielde (Hope) in the family Cerambycidae, were investigated in a Y‐tube olfactometer. Responses of D. helophoroides adults toward odour sources from their host (M. raddei) and host tree (Quercus mongolicus Fisch. ex. Turcz.) were tested in either no‐choice or two‐way choice tests. Wood with larval tunnels and larvae frass were attractive to D. helophoroides. Both sexes showed attraction to wood with larval tunnels. 2 Volatile chemicals emitted from wood with larval tunnels and larval frass were collected on Porapak Q and analyzed by gas chromatography‐mass spectrometry. Several compounds identified from these sources, including α‐pinene, β‐pinene, Δ‐3‐carene, limonene and β‐myrcene, were tested against D. helophoroides in the same Y‐tube olfactometer. 3 The result showed that D. helophoroides adults were attracted to (R)‐(+)‐limonene, with or without the background odour from uninfested fresh wood. This may suggest that (R)‐(+)‐limonene is an important kairomone for this parasitic beetle. 4 Dose‐dependent response of D. helophoroides adults to (R)‐(+)‐limonene indicated that D. helophoroides adults showed significant attraction to (R)‐(+)‐limonene when release rates exceeded 2.08 μg/h in Y‐tube olfactometer tests. Moreover, significantly more A. glabripennis larvae were parasitized by D. helophoroides in the presence of R‐(+)‐limonene, relative to the control in cage experiments.     

Rail transport as a vector of emerald ash borer

1. The emerald ash borer (EAB) Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) is an invasive woodboring beetle native to northeastern Asia that continues to expand its range within North America and European Russia. The insect reproduces within and kills most North American species of ash Fraxinus spp.
2. Because both the adult and larval life stages of EAB are difficult to detect prior to development of tree symptoms, much work has focused on quantifying spread and clarifying the potential movement pathways to improve early detection and monitoring strategies.
3. In the present study, we retrospectively analyzed county‐level infestations of emerald ash borer in the state of Iowa, U.S.A., subsequent to the initial detection of EAB in 2010. Visual data analysis had suggested that new infestations were not in accordance with the expected patterns of establishment along roads, near campgrounds or by large population centres.
4. We found a positive correlation between the establishment and detection of EAB in Iowa counties and the length of railroads in each county. To our knowledge, this is the first statistically significant association between rail pathways and the spread of EAB on the North American continent.

     

Decreased emergence of emerald ash borer from ash treated with methyl jasmonate is associated with induction of general defense traits and the toxic phenolic compound verbascoside

The emerald ash borer (EAB; Agrilus planipennis Fairmaire) is causing widespread mortality of ash (Fraxinus spp.) in North America. To date, no mechanisms of host resistance have been identified against this pest. Methyl jasmonate was applied to susceptible North American and resistant Asian ash species to determine if it can elicit induced responses in bark that enhance resistance to EAB. In particular, phenolic compounds, lignin, and defense-related proteins were quantified, and compounds associated with resistance were subsequently tested directly against EAB larvae in bioassays with artificial diet. MeJA application decreased adult emergence in susceptible ash species, comparable to levels achieved by insecticide application. Concentration of the phenolic compound verbascoside sharply increased after MeJA application to green and white ash. When incorporated in an artificial diet, verbascoside decreased survival and growth of EAB neonates in a dose-dependent fashion. Lignin and trypsin inhibitors were also induced by MeJA, and analogs of both compounds reduced growth of EAB larvae in artificial diets. We conclude that the application of MeJA prior to EAB attack has the ability to enhance resistance of susceptible ash trees by inducing endogenous plant defenses, and report evidence that induction of verbascoside is a mechanism of resistance to EAB.     

Differential response of male and female emerald ash borers (Col., Buprestidae) to (Z)‐3‐hexenol and manuka oil

We conducted two trapping experiments in green ash plantations in Ontario, Canada to compare the response of the emerald ash borer (EAB), Agrilus planipennis, to (Z)‐3‐hexenol (Z3‐6:OH) and manuka oil. In the first experiment, Z3‐6:OH (7.6 mg/day) in purple prism traps hung 1.5 m above ground caught significantly more EAB than the unbaited controls, with male catches significantly greater than female catches at two locations. Manuka oil (50 mg/day) attracted equal numbers of males and females but they were significantly greater than the controls at only one location. Adding (Z)‐3‐hexenal or (Z)‐3‐hexenyl acetate in binary or ternary combinations with Z3‐6:OH did not enhance trap catch. In the second experiment, Z3‐6:OH released at two rates (7.6 or 80 mg/day) in light green prism traps placed in the ash canopy also caught significantly more males than females and more males than the unbaited controls or manuka oil‐baited traps. Manuka oil had no significant effect on catches relative to the controls. Combining Z3‐6:OH with manuka oil did not enhance catches of EAB. We conclude that there was a strong male‐biased EAB response to Z3‐6:OH lures, whereas manuka oil, when effective, attracted both sexes equally. Z3‐6:OH in light green prism traps in the canopy is an effective lure for EAB, particularly for males.     

Evaluation of tree mortality and parasitoid recoveries on the contiguous western invasion front of emerald ash borer

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