Ashot Khrimian | USDA Agricultural Research Service (original) (raw)

Papers by Ashot Khrimian

Synthetic Communications, Dec 1, 1988

A kinetic resolution of racemic ally1 propargyl alcohols by enantioselective epoxidation is descr... more A kinetic resolution of racemic ally1 propargyl alcohols by enantioselective epoxidation is described. The Sharpless asymmetric epoxidation method of allylic alcohols is an indispensable tool for the synthesis of optically active molecules because of its simplicity, predictability and high chemical as well as optical yield. Sharpless and his coworkers have studied' the kinetic resolution of racemic secondary allylic alcohols. The Sharpless resolution of secondary allylic alcohols, kinetically favours the 5' enantiomer of the racemic mixture to form the epoxide, while the 'R' enantiomer

Biological Control, Oct 1, 2021

Abstract The brown marmorated stink bug, Halyomorpha halys, is an alien pest native to East Asia,... more Abstract The brown marmorated stink bug, Halyomorpha halys, is an alien pest native to East Asia, which in the past two decades has invaded USA, Europe and other countries around the globe, causing severe economic losses and public nuisance. The Asian egg-parasitoid Trissolcus japonicus is the most promising agent currently under study for the classical biological control of H. halys. The foraging behavior of this wasp was investigated in response to chemical traces - ‘footprints’ - deposited by its host H. halys and by a suboptimal predatory host species, the spined soldier bug, Podisus maculiventris. Motion tracking software (Ethovision) was employed to record and analyze the behavior of T. japonicus on stink bug-contaminated and on control substrates. Wasps exhibited a ‘motivated searching’ behavior (i.e. longer residence time, slower walking velocity, higher angular velocity and coverage of greater distances) in response to footprints originating from females and from males of both species compared to blank controls. However, this searching behavior was significantly more intense on H. halys footprints, compared to those of P. maculiventris. Moreover, T. japonicus significantly intensified its searching on footprints of all mobile nymphal instars of H. halys, but not on those of P. maculiventris nymphs. Additionally, the longevity of H. halys female trails was assessed, and footprints remained bioactive, eliciting a consistent searching behavior in the wasp for 72 hours after initial deposition. A series of GC-MS chemical analyses revealed components of these trails, with n-tridecane and (E)-2-decenal found to be the most abundant, and probably the key components of the kairomone utilized by the wasp for short range host location. Solutions of the synthetic compounds were tested both together and singly. The blend of n-tridecane and (E)-2-decenal (4: 1) significantly prolonged the residence time of T. japonicus, as did n-tridecane alone. These results are discussed in the context of host preference and classical biological control.

Journal of Chemical Ecology, Sep 29, 2018

Insects use a wide range of structurally diverse pheromones for intra-specific communication. Com... more Insects use a wide range of structurally diverse pheromones for intra-specific communication. Compounds in the class of terpenes are emitted as sex, aggregation, alarm, or trail pheromones. Despite the common occurrence of terpene pheromones in different insect lineages, their origin from dietary host plant precursors or de novo biosynthetic pathways often remains unknown. Several stink bugs (Hemiptera: Pentatomidae) release bisabolene-type sesquiterpenes for aggregation and mating. Here we provide evidence for de novo biosynthesis of the sex pheromone trans−/cis-(Z)-α-bisabolene epoxide of the Southern green stink bug, Nezara viridula. We show that an enzyme (NvTPS) related to isoprenyl diphosphate synthases (IDSs) of the core terpene metabolic pathway functions as a terpene synthase (TPS), which converts the general intermediate (E,E)-farnesyl diphosphate (FPP) to the putative pheromone precursor (+)-(S,Z)-α-bisabolene in vitro and in protein lysates. A second identified IDS-type protein (NvFPPS) makes the TPS substrate (E,E)-FPP and functions as a bona fide FPP synthase. NvTPS is highly expressed in male epidermal tissue associated with the cuticle of ventral sternites, which is in agreement with the male specific release of the pheromone from glandular cells in this tissue. Our study supports findings of the function of similar TPS enzymes in the biosynthesis of aggregation pheromones from the pine engraver beetle Ips pini, the striped flea beetle Phyllotreta striolata, and the harlequin bug Murgantia histrionica, and hence provides growing evidence for the evolution of terpene de novo biosynthesis by IDS-type TPS families in insects.

Ethyl cis-5-iodo-trans-2-methyl-1-cyclcohexane-1-carboxylate (ceralure B1) is a potent attractant... more Ethyl cis-5-iodo-trans-2-methyl-1-cyclcohexane-1-carboxylate (ceralure B1) is a potent attractant for the Mediterranean fruit fly, Ceratitis capitata (Wiedemann). We developed a new synthesis of ceralure B1 that provided better yields than the existing methods. Commercially available trans-6-methyl-3-cyclohexane-1-carboxylic acid (Siglure acid) was converted in two steps to trans-2-methyl-6-oxabicyclo[3.2.1]octan-7-one, which was transformed with trichloromethylsilane to a mixture of cis-5-iodo-trans-2-methyl-1-cyclcohexane-1-carboxylic acid and trans-5-iodo-trans-2-methyl-1-cyclcohexane-1-carboxylic acid. In the key step, the undesired trans,trans acid was converted back to the precursor lactone and recycled. The new approach seems suitable for scale-up and commercialization. Field studies have revealed that racemic ceralure B1 exceeded the attractiveness of standard trimedlure by two to five times, whereas optically active (-)-ceralure B1 was only 30-40 % more active than the racemate.

Journal of Economic Entomology, Jul 27, 2015

Euschistus servus (Say), Nezara viridula (L.), and Chinavia hilaris (Say) (Hemiptera: Pentatomida... more Euschistus servus (Say), Nezara viridula (L.), and Chinavia hilaris (Say) (Hemiptera: Pentatomidae) are economic pests of cotton in the coastal plain of the southeastern United States. The objective of this 2-yr study was to determine the ability of trap cropping systems, pheromone-baited stink bug traps, and a synthetic physical barrier at the peanut-to-cotton interface to manage stink bugs in cotton. The physical barrier was the most effective management tactic. Stink bug density in cotton was lowest for this treatment. In 2010, boll injury was lower for the physical barrier compared to the other treatments except for soybean with stink bug traps. In 2011, boll injury was lower for this treatment compared to the control. Soybean was an effective trap crop, reducing both stink bug density in cotton and boll injury regardless if used alone or in combination with either stink bug traps or buckwheat. Incorporation of buckwheat in soybean enhanced parasitism of E. servus egg masses by Telenomus podisi Ashmead in cotton. The insertion of eyelets in the lid of the insect-collecting device of a stink bug trap allowed adult stink bug parasitoids, but not E. servus, to escape. Stand-alone stink bug traps were not very effective in deterring colonization of cotton by stink bugs or reducing boll injury. The paucity of effective alternative control measures available for stink bug management justifies further full-scale evaluations into these management tactics for control of these pests in crops. KEY WORDS pheromone-baited stink bug trap, trap cropping system, physical barrier, nectar provision Stink bugs (Hemiptera: Pentatomidae) are economic pests in many agricultural crops (McPherson and McPherson 2000). In the coastal plain of the southeastern United States, cotton, Gossypium hirsutum L., is a mid-to-late-season host crop for stink bugs (Bundy and McPherson 2000). Barbour et al. (1990) reported that the green stink bug, Chinavia hilaris (Say), formerly Acrosternum hilare (Say) (Schwertner and Grazia 2007, Rider 2009), was the predominant stink bug pest in cotton in North Carolina. Turnipseed et al. (1995) and Bundy and McPherson (2000) noted in their studies that the southern green stink bug, Nezara viridula (L.), and the brown stink bug, Euschistus servus (Say), were major pests of cotton in South Carolina and Georgia, respectively. Generally, a farmscape is composed of fields of different crops whose edges interface with each other.

Journal of Chemical Ecology, Mar 21, 2012

An unsaturated hydroxy-ester pheromone was isolated from the headspace and feces of male Diaprepe... more An unsaturated hydroxy-ester pheromone was isolated from the headspace and feces of male Diaprepes abbreviatus, identified, and synthesized. The pheromone, methyl (E)-3-(2-hydroxyethyl)-4-methyl-2-pentenoate, was discovered by gas chromatography-coupled electroantennogram detection (GC-EAD), and identified by gas chromatographymass spectrometry (GC-MS) and nuclear magnetic resonance spectroscopy (NMR). The synthesis yielded an 86:14 mixture of methyl (E)-3-(2-hydroxyethyl)-4-methyl-2-pentenoate (active) and methyl (Z)-3-(2-hydroxyethyl)-4-methyl-2-pentenoate (inactive), along with a lactone breakdown product. The activity of the synthetic E-isomer was confirmed by GC-EAD, GC-MS, NMR, and bioassays. No antennal response was observed to the Z-isomer or the lactone. In a two-choice olfactometer bioassay, female D. abbreviatus moved upwind towards the synthetic pheromone or natural pheromone more often compared with clean air. Males showed no clear preference for the synthetic pheromone. This pheromone, alone or in combination with plant volatiles, may play a role in the location of males by female D. abbreviatus.

Pest Management Science, Sep 21, 2018

BACKGROUND: Introduction of Halyomorpha halys (Stål) in the USA has disrupted many established in... more BACKGROUND: Introduction of Halyomorpha halys (Stål) in the USA has disrupted many established integrated pest management programs for specialty crops, especially apple. While current management heavily relies on insecticides, one potential alternative tactic is attract-and-kill (AK), whereby large numbers of H. halys are attracted to and retained in a circumscribed area using attractive semiochemicals and removed from the foraging population with an insecticide. The goal of this study was to evaluate if AK implementation in commercial apple orchards can result in levels of H. halys damage that are equal to or less than those from grower standard management programs. RESULTS: Over 2 years at farms in five Mid-Atlantic USA states, we found that the use of AK resulted in 2-7 times less damage compared with grower standard plots, depending on year and period. At selected trees on which AK was implemented, over 10,000 H. halys individuals were killed in two growing seasons, and the use of AK reduced the crop area treated with insecticide against H. halys by 97%. Using AK had no impact on the natural enemy or secondary pest community over the same period. CONCLUSIONS: Overall, the use of AK was effective at managing low to moderate H. halys populations in apple orchards, but must be optimized to increase economic feasibility for grower adoption.

Journal of Natural Products, Jul 10, 2020

Sesquipiperitol is a sesquiterpene alcohol, some stereoisomers of which were found in several pla... more Sesquipiperitol is a sesquiterpene alcohol, some stereoisomers of which were found in several plant species. The biological role of these compounds in plants and their absolute configurations have not been reported. Recently, we found that 1S,6S,7R stereoisomer of sesquipiperitol was a key precursor in the biosynthesis of the harlequin bug, Murgantia histrionica, pheromone, which consists of two stereoisomeric zingiberenol oxides. In addition, the Tibraca limbativentris stink bug was shown to produce two sesquipiperitol stereoisomers as minor components in their male-produced sex pheromone, the main constituents of which were zingiberenols. To determine absolute configurations of plant-and stink-bugproduced sesquipiperitols, we undertook syntheses of all stereoisomers of this sesquiterpene alcohol. The syntheses were based on 1,10-bisaboladien-3-ols (aka zingiberenols) with known configurations at C-6 and C-7, the oxidation of which provided sesquipiperitone precursors with retention of configurations of these stereogenic centers. The foremost challenge of the synthetic endeavor was the assignment of absolute configurations of secondary carbinol centers, which was resolved by NMR analyses of corresponding Mosher's esters. Thus, the availability of all eight diastereomers allowed us to assign sesquipiperitols from Fitzroya cupressoides and Argyranthemum adauctum spp. jacobaeifolium plants 1S,6S,7R (16) and 1R,6R,7S (14) configurations, respectively. A chiral-phase gaschromatographic method was developed to determine 1S,6S,7R and 1R,6S,7R (15) configurations of T. limbativentris sesquipiperitol pheromone components.

Journal of Chemical Ecology, May 29, 2023

Entomologia Generalis, 2019

The diversity of herbivorous insects may arise from colonization and subsequent specialization on... more The diversity of herbivorous insects may arise from colonization and subsequent specialization on different host plants. Such specialization requires changes in several insect traits, which may lead to host race formation if they reduce gene flow among populations that feed on different plants. Behavioural changes may play a relevant role in host race formation, for example if different races evolve distinct sexual communication signals or adult phenology. Previous research has revealed differences in larval phenology in different host-associated populations of the browntail moth, Euproctis chrysorrhoea (Lepidoptera: Erebidae). Here, sex pheromones among populations of this species are compared, and pheromone trapping data obtained is used in the field to build a phenological model that tests whether populations that feed on different plants differ in their adult flight period. The chemical and electrophysiological analyses revealed that two E. chrysorrhoea populations (on Prunus and on Arbutus unedo) use the same sex pheromone component for mate finding. Our trapping data, however, showed that males fly on average 25 days earlier in populations whose larvae feed on A. unedo compared to those whose larvae feed on Quercus species. Although the shifted phenology described here may underlie host-plant specialization in E. chrysorrhoea, and adults of this species are short-lived, the use of a common sexual pheromone and a large overlap in flight periods suggest that host race formation via allochronic isolation is unlikely in this moth.

Journal of Economic Entomology, 2019

The brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) is attracted t... more The brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) is attracted to its male-produced aggregation pheromone, a ~3.5:1 mixture of (3S,6S,7R,10S)- and (3R,6S,7R,10S)-10,11-epoxy-1-bisabolen-3-ol (SSRS and RSRS respectively), and also to the pheromone of its Asian sympatric species Plautia stali Scott (Hemiptera: Pentatomidae), methyl (2E,4E,6Z)-2,4,6-decatrienoate (MDT). A stereoisomeric mixture of (7R) 10,11-epoxy-1-bisabolen-3-ols (= mixed murgantiols) is used together in commercialized products with MDT because the latter is a synergist for H. halys attraction to mixed murgantiols. However, the optimal ratio for MDT combination with mixed murgantiols, and the sensitivity of bug captures to variation in ratio of the two pheromone components, have not been tested to date. Using black pyramid traps at two sites (in Maryland and West Virginia, United States), different ratios of mixed murgantiols to MDT were tested over two entire seasons. Also, captures ...

Synthetic Communications, 1988

Florida Entomologist, 2009

BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access t... more BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

Environmental Entomology, 2010

Detecting infestations of stink bugs (Heteroptera: Pentatomidae) using pheromones remains problem... more Detecting infestations of stink bugs (Heteroptera: Pentatomidae) using pheromones remains problematic, particularly so in the United States for the exotic stink bug, Nezara viridula L., and our native stink bug, Acrosternum hilare (Say). Therefore, we conducted a 2-yr on-farm study to examine the attractiveness and possible cross-attraction of the reported pheromones for N. viridula and A. hilare and those previously discovered for Euschistus servus (Say) and Plautia stali Scott to N. viridula, A. hilare, and E. servus. The attractiveness of selected pentatomid pheromones to tachinid parasitoids of stink bugs was also examined. We showed for the Þrst time under Þeld conditions that N. viridula can be trapped with its reported pheromone, a 3:1 transto cis-(Z)-␣-bisabolene epoxide blend. In fact, attraction of N. viridula increased with higher pheromone doses. Traps baited with a 5:95 transto cis-(Z)-␣-bisabolene epoxide blend, the reported male-produced A. hilare attractant pheromone, failed to attract signiÞcantly more A. hilare than did unbaited control traps. Instead A.

2016 International Congress of Entomology, 2016

Semiochemicals are central to success of the Pentatomoidea, as the name "stink bug" implies. Pent... more Semiochemicals are central to success of the Pentatomoidea, as the name "stink bug" implies. Pentatomoid semiochemistry includes sex, aggregation, and alarm pheromones; allomones; kairomones used by parasitoids and predators of stink bugs; and tritrophic interactions. Of the ~45 pentatomoid species with identified pheromones, all are male-produced; approximately half are sex pheromones (attracting females only), and half are aggregation pheromones (attracting both sexes and, where tested, nymphs). The pheromone chemical structures are very diverse, ranging from acyclic straight-chain and terpenoid molecules with typically one functional group, to cyclic sesquiterpenoids with up to 4 chiral centers, posing significant analytical and synthetic challenges. Most stink bug pheromones probably consist of 2 or more components: of 32 species with clearly defined pheromones, 14 have multiple components; 7 species apparently have a single component; the remaining 11 may be single or multiple, requiring further stereochemical analysis, synthesis, and/or behavioral bioassays. Detailed studies of pheromone emissions indicate complex variation by individual, age, population density, time of day, and other environmental stimuli. The cross-attraction of several species to pheromones of other species occurs for both adults and nymphs. In some cases, it represents known or probable overlap in pheromone chemistry; in other cases, it does not, for reasons that are not yet clear. Pentatomoid pheromones can potentially be exploited for detection or monitoring, and in attractand-kill or other pest control tactics, but are currently used almost exclusively for monitoring a few important species. We assess the requirements and prospects for expanded use in future pest management.

Journal of Entomological Science, Oct 1, 1998

Experiments were conducted using tritiated European corn borer, Ostrinia nubilalis (Hübner), pher... more Experiments were conducted using tritiated European corn borer, Ostrinia nubilalis (Hübner), pheromone, (Z)-[11,12-3H2]-11-tetradecen-1-ol acetate, a tritiated fluorinated analog of the European corn borer pheromone, 2-fluoro-(Z)-[11,12-3H2]-11-tetradecen-1-ol acetate, and methyl-4-bromocrotonate (MBC) to determine if pheromone catabolism proceeds on the moth&amp;#39;s antennae via the β-oxidation pathway of fatty acid degradation. When antennae were treated with tritiated natural pheromone plus MBC (a precursor of the known β-oxidation inhibitor, 4-bromocrotonic acid), catabolism of the pheromone was significantly inhibited. When the 2-fluoro pheromone analog was applied alone to antennae, it was hydrolyzed to the corresponding alcohol but was not degraded. MBC had no effect on catabolism of the 2-fluoro analog, and 2-fluoro substitution inhibited entrance of the compound into β-oxidation. These results demonstrate that β-oxidation is the primary oxidative pathway by which pheromone is degraded on the antennae of European corn borer moths.

Journal of Medical Entomology, 2006