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Browsing by Author "Gross, Aaron D."

Now showing 1 - 16 of 16
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    Association of Salivary Cholinesterase With Arthropod Vectors of Disease
    Temeyer, Kevin B.; Schlechte, Kristie G.; Olafson, Pia U.; Drolet, Barbara S.; Tidwell, Jason P.; Osbrink, Weste L. A.; Showler, Allan T.; Gross, Aaron D.; de Leon, Adalberto A. Perez (2020-11)
    Acetylcholinesterase (AChE) was previously reported to be present in saliva of the southern cattle tick, Rhipicephalus (Boophilus) microplus (Canestrini), with proposed potential functions to 1) reduce acetylcholine toxicity during rapid engorgement, 2) modulate host immune responses, and 3) to influence pathogen transmission and establishment in the host. Potential modulation of host immune responses might include participation in salivary-assisted transmission and establishment of pathogens in the host as has been reported for a number of arthropod vector-borne diseases. If the hypothesis that tick salivary AChE may alter host immune responses is correct, we reasoned that similar cholinesterase activities might be present in saliva of additional arthropod vectors. Here, we report the presence of AChE-like activity in the saliva of southern cattle ticks, Rhipicephalus (Boophilus) microplus; the lone star tick, Amblyomma americanum (Linnaeus); Asian tiger mosquitoes, Aedes albopictus (Skuse); sand flies, Phlebotomus papatasi (Scopoli); and biting midges, Culicoides sonorensis Wirth and Jones. Salivary AChE-like activity was not detected for horn flies Haematobia irritans (L.), stable flies Stomoxys calcitrans (L.), and house flies Musca domestica L. Salivary cholinesterase (ChE) activities of arthropod vectors of disease-causing agents exhibited various Michaelis-Menten K-M values that were each lower than the K-M value of bovine serum AChE. A lower K-M value is indicative of higher affinity for substrate and is consistent with a hypothesized role in localized depletion of host tissue acetylcholine potentially modulating host immune responses at the arthropod bite site that may favor ectoparasite blood-feeding and alter host defensive responses against pathogen transmission and establishment.
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    Biology and Management of Small Hive Beetles (Coleoptera: Nitidulidae): A Pest of European Honey Bee (Hymenoptera: Apidae) Colonies
    Roth, Morgan A.; Wilson, James M.; Gross, Aaron D. (Oxford University Press, 2022-01-01)
    Small hive beetle (Aethina tumida Murray) control has become an issue of increasing importance for North American apiculturists throughout the past two decades. Aethina tumida was discovered in Florida in 1989, presumably transported from its native habitat of sub-Saharan Africa through the shipment of European honey bee (Apis mellifera L) queens. Estimates of damage from A. tumida were as high as $3 million annually in the United States by the year 2004, and A. tumida was found in nearly every state by 2008. When adult beetles emerge from pupation in soil surrounding the hive, they are attracted to A. mellifera hives through a variety of pheromones and volatile organic compounds from bees and hive products. Aethina tumida larvae and adults consume hive products and bee brood, generating fermenting waste (or slime), which can eventually lead to hive abandonment in cases of severe infestation. Pest management efforts for A. tumida have focused on trapping adults, applying lime, diatomaceous earth, pyrethroid soil drenches, and entomopathogenic nematodes to the soil surrounding A. mellifera hives. Understanding the biology and life history of A. tumida, along with current control methods, can aid apiculturists in making informed integrated pest management decisions. Additionally, understanding critical knowledge gaps in the current research is an important step in identifying promising future management tactics in the ongoing efforts to manage this invasive pest.
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    Biology and Management of Varroa destructor (Mesostigmata: Varroidae) in Apis mellifera (Hymenoptera: Apidae) Colonies
    Roth, Morgan A.; Wilson, James M.; Tignor, Keith R.; Gross, Aaron D. (Oxford University Press, 2020)
    Varroa mite (Varroa destructor Anderson and Trueman) infestation of European honey bee (Apis mellifera L.) colonies has been a growing cause of international concern among beekeepers throughout the last 50 yr. Varroa destructor spread from the Asian honey bee (Apis cerana Fabricius [Hymenoptera: Apidae]) to A. mellifera populations in Europe in the 1970s, and subsequently traveled to the Americas. In addition to causing damage through feeding upon lipids of larval and adult bees, V. destructor also facilitates the spread of several viruses, with deformed wing virus being most prevalent. Several sampling methods have been developed for estimating infestation levels of A. mellifera colonies, and acaricide treatments have been implemented. However, overuse of synthetic acaricides in the past has led to widespread acaricide resistant V. destructor populations. The application of Integrated Pest Management (IPM) techniques is a more recent development in V. destructor control and is suggested to be more effective than only using pesticides, thereby posing fewer threats to A. mellifera colonies. When using IPM methods, informed management decisions are made based upon sampling, and cultural and mechanical controls are implemented prior to use of acaricide treatments. If acaricides are deemed necessary, they are rotated based on their mode of action, thus avoiding V. destructor resistance development.
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    Characterizing Permethrin and Etofenprox Resistance in Two Common Laboratory Strains of Anopheles gambiae (Diptera: Culicidae)
    Gross, Aaron D.; Bloomquist, Jeffrey R. (MDPI, 2018-10-22)
    Anopheles gambiae Giles (Diptera: Culicidae) is the most prolific malaria vector in sub-Saharan Africa, where widespread insecticide resistance has been reported. An. gambiae laboratory strains are commonly used to study the basic biology of this important mosquito vector, and also in new insecticide discovery programs, where insecticide-susceptible and -resistant strains are often used to screen new molecules for potency and cross-resistance, respectively. This study investigated the toxicity of permethrin, a Type-I pyrethroid insecticide, and etofenprox, a non-ester containing pyrethroid insecticide, against An. gambiae at three life stages. This characterization was performed with susceptible (G3; MRA-112) and resistant (Akdr; MRA-1280) An. gambiae strains; the Akdr strain is known to contain the L1014F mutation in the voltage-sensitive sodium channel. Surprisingly, etofenprox displays a lower level of resistance than permethrin against all stages of mosquitoes, except in a headless larval paralysis assay designed to minimize penetration factors. In first-instar An. gambiae larvae, permethrin had significant resistance, determined by the resistance ratio (RR50 = 5), but etofenprox was not significantly different (RR50 = 3.4) from the wild-type strain. Fourth-instar larvae displayed the highest level of resistance for permethrin (RR50 = 108) and etofenprox (RR50 = 35). Permethrin (PC50 = 2 ppb) and etofenprox (PC50 = 9 ppb) resulted in headless larval paralysis (5-h), but resistance, albeit lower, was still present for permethrin (RR50 = 5) and etofenprox (RR50 = 6.9). In adult female mosquitoes, permethrin displayed higher resistance (RR50 = 14) compared to etofenprox (RR50 = 4.3). The level of etofenprox resistance was different from that previously reported for a similar Akron An. gambiae laboratory strain (MRA-913). The chemical synergists piperonyl butoxide (PBO) and diethyl maleate (DEM) were able to synergize permethrin, but not etofenprox in the resistant strain (Akdr). In conclusion, multiple mechanisms are likely involved in pyrethroid resistance, but resistance profiles are dependent upon selection. Etofenprox is an effective insecticide against An. gambiae in the lab but will likely suffer from resistance in the field.
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    Identification, Baculoviral Expression, and Biochemical Characterization of a Novel Cholinesterase of Amblyomma americanum (Acari: Ixodidae)
    Temeyer, Kevin B.; Schlechte, Kristie G.; Gross, Aaron D.; Lohmeyer, Kimberly H. (MDPI, 2023-04-22)
    A cDNA encoding a novel cholinesterase (ChE, EC 3.1.1.8) from the larvae of Amblyomma americanum (Linnaeus) was identified, sequenced, and expressed in Sf21 insect cell culture using the baculoviral expression vector pBlueBac4.5/V5-His. The open reading frame (1746 nucleotides) of the cDNA encoded 581 amino acids beginning with the initiation codon. Identical cDNA sequences were amplified from the total RNA of adult tick synganglion and salivary gland, strongly suggesting expression in both tick synganglion and saliva. The recombinant enzyme (rAaChE1) was highly sensitive to eserine and BW284c51, relatively insensitive to tetraisopropyl pyrophosphoramide (iso-OMPA) and ethopropazine, and hydrolyzed butyrylthiocholine (BuTCh) 5.7 times as fast as acetylthiocholine (ATCh) at 120 µM, with calculated KM values for acetylthiocholine (ATCh) and butyrylthiocholine of 6.39 µM and 14.18 µM, respectively. The recombinant enzyme was highly sensitive to inhibition by malaoxon, paraoxon, and coroxon in either substrate. Western blots using polyclonal rabbit antibody produced by immunization with a peptide specific for rAaChE1 exhibited reactivity in salivary and synganglial extract blots, indicating the presence of AaChE1 antigenic protein. Total cholinesterase activities of synganglial or salivary gland extracts from adult ticks exhibited biochemical properties very different from the expressed rAaACh1 enzyme, evidencing the substantial presence of additional cholinesterase activities in tick synganglion and saliva. The biological function of AaChE1 remains to be elucidated, but its presence in tick saliva is suggestive of functions in hydrolysis of cholinergic substrates present in the large blood mean and potential involvement in the modulation of host immune responses to tick feeding and introduced pathogens.
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    Insecticidal and repellent properties of novel trifluoromethylphenyl amides II
    Tsikolia, Maia; Bernier, Ulrich R.; Agramonte, Natasha M.; Estep, Alden S.; Becnel, James J.; Tabanca, Nurhayat; Linthicum, Kenneth J.; Gross, Aaron D.; Guerin, Patrick M.; Krober, Thomas; Bloomquist, Jeffrey R. (2018-10)
    This project focused on the design, synthesis, and testing of trifluoromethylphenyl amides (TFMPAs) as potential mosquitocides and repellents. Fourteen compounds were evaluated for toxicity against larvae and adults of Aedes aegypti. Several compounds were toxic against Aedes aegypti (larval, adult and feeding bioassays) and Drosophila melanogaster (glass-surface contact assay), but were much less toxic than fipronil, with toxicity ratios ranging from 100-fold in the larval assay to 100,000-fold for topical application to adult insects. In repellency bioassays to determine minimum effective dosage (MED), compound N-(2,6-dichloro-4(trifluoromethyl)phenyl)-2,2,3,3,3-pentafluoropropanamide (7b) repelled Ae. aegypti females at lower concentration, 0.017 (+/- 0.006) mu mol/cm(2), than N, N-diethyl-meta-toluamide (DEET) 0.026 (+/- 0.005) mu mol/cm(2). 2-Chloro-N-(3-(trifluoromethyl)phenyl)acetamide (6a) performed better than DEET against two species of mosquitoes: it repelled Ae. aegypti females at 0.013 (+/- 0.006) mu mol/cm(2) and Anopheles gambiae females (in a warm body repellent assay), at a standard exposure of 2 nmol/cm(2). These studies revealed novel active structures that could further lead to compounds with better repellent activity.
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    Methods for controlling two European Honey bee (Apis mellifera L.) pests:  Varroa mites (Varroa destructor, Anderson and Trueman) And Small hive beetles (Aethina tumida)
    Roth, Morgan Alicia (Virginia Tech, 2019-06-11)
    Throughout the last five decades, European Honey bee (Apis mellifera) colonies have been heavily damaged by invading Varroa mites (Varroa destructor), and, more recently, small hive beetles (Aethina tumida). These pests infest A. mellifera colonies throughout Virginia, with V. destructor feeding upon the lipids of their hosts and spreading viruses, and A. tumida feeding extensively on hive products and brood. Because V. destructor has historically demonstrated acaricide resistance, this study examined V. destructor resistance to three common acaricides (amitraz, coumaphos, and tau-fluvalinate) throughout the three geographic regions of Virginia using glass vial contact bioassays; the results showed no resistance in the sites tested. To gain better insights into A. tumida pharmacology, several known acetylcholinesterase (AChE) inhibitors and three novel insecticides (previously shown to have low mammalian toxicity) were tested against an A. tumida laboratory colony through in vivo and in vitro bioassays. The results of these bioassays indicated that coumaphos was most selective and topically effective against A. tumida, while only one experimental compound was selective against A. tumida, with 29-fold less potency than coumaphos. These results can help apiculturists in making informed pest management choices and can lead to future studies further examining V. destructor resistance and optimizing A. tumida insecticide treatments.
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    Pest management with biopesticides
    Seiber, James N.; Coats, Joel R.; Duke, Stephen O.; Gross, Aaron D. (Higher Education Press, 2018)
    Biopesticides are attracting interest as alternatives to conventional pesticides but without many of the non-target effects, promising a better record of safety and sustainability in pest control practices. In this article we summarize and discuss the current status and future promise of biopesticides, including how biopesticides use may increase the quality and safety of the food supply.
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    Plant Essential Oils Enhance Diverse Pyrethroids against Multiple Strains of Mosquitoes and Inhibit Detoxification Enzyme Processes
    Norris, Edmund J.; Johnson, Jacob B.; Gross, Aaron D.; Bartholomay, Lyric C.; Coats, Joel R. (MDPI, 2018-10-04)
    Mosquito-borne diseases account for the deaths of approximately 700,000 people annually throughout the world, with many more succumbing to the debilitating side effects associated with these etiologic disease agents. This is exacerbated in many countries where the lack of mosquito control and resources to prevent and treat mosquito-borne disease coincide. As populations of mosquito species grow more resistant to currently utilized control chemistries, the need for new and effective chemical means for vector control is more important than ever. Previous work revealed that plant essential oils enhance the toxicity of permethrin against multiple mosquito species that are of particular importance to public health. In this study, we screened permethrin and deltamethrin in combination with plant essential oils against a pyrethroid-susceptible and a pyrethroid-resistant strain of both Aedes aegypti and Anopheles gambiae. A number of plant essential oils significantly enhanced the toxicity of pyrethroids equal to or better than piperonyl butoxide, a commonly used synthetic synergist, in all strains tested. Significant synergism of pyrethroids was also observed for specific combinations of plant essential oils and pyrethroids. Moreover, plant essential oils significantly inhibited both cytochrome P450 and glutathione S-transferase activities, suggesting that the inhibition of detoxification contributes to the enhancement or synergism of plant essential oils for pyrethroids. This study highlights the potential of using diverse plant oils as insecticide additives to augment the efficacy of insecticidal formulations.
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    Plant essential oils synergize various pyrethroid insecticides and antagonize malathion in Aedes aegypti
    Norris, Edmund J.; Gross, Aaron D.; Bartholomay, Lyric C.; Coats, J. R. (Wiley, 2019-12-01)
    Pyrethroid resistance is a significant threat to agricultural, urban and public health pest control activities. Because economic incentives for the production of novel active ingredients for the control of public health pests are lacking, this field is particularly affected by the potential failure of pyrethroid-based insecticides brought about by increasing pyrethroid resistance. As a result, innovative approaches are desperately needed to overcome insecticide resistance, particularly in mosquitoes that transmit deadly and debilitating pathogens. Numerous studies have demonstrated the potential of plant essential oils to enhance the efficacy of pyrethroids. The toxicity of pyrethroids combined with plant oils is significantly greater than the baseline toxicity of either oils or pyrethroids applied alone, which suggests there are synergistic interactions between components of these mixtures. The present study examined the potential of eight plant essential oils applied in one of two concentrations (1% and 5%) to enhance the toxicity of various pyrethroids (permethrin, natural pyrethrins, deltamethrin and β-cyfluthrin). The various plant essential oils enhanced the pyrethroids to differing degrees. The levels of enhancement provided by combinations of plant essential oils and pyrethroids in comparison with pyrethroids alone were calculated and synergistic outcomes characterized. Numerous plant essential oils significantly synergized a variety of pyrethroids; type I pyrethroids were synergized to a greater degree than type II pyrethroids. Eight plant essential oils significantly enhanced 24-h mortality rates provided by permethrin and six plant essential oils enhanced 24-h mortality rates obtained with natural pyrethrins. By contrast, only three plant essential plants significantly enhanced the toxicity of deltamethrin and β-cyfluthrin. Of the plant essential oils that enhanced the toxicity of these pyrethroids, some produced varying levels of synergism and antagonism. Geranium, patchouli and Texas cedarwood oils produced the highest levels of synergism, displaying co-toxicity factors of > 100 in some combinations. To assess the levels of enhancement and synergism of other classes of insecticide, malathion was also applied in combination with the plant oils. Significant antagonism was provided by a majority of the plant essential oils applied in combination with this insecticide, which suggests that plant essential oils may act to inhibit the oxidative activation processes within exposed adult mosquitoes.
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    Quantifying changes in macroinvertebrate community composition, biomass, and emergence in response to mining-induced salinization in central Appalachian streams
    James, Aryanna Lee (Virginia Tech, 2021-06-03)
    Many ecosystems are losing biodiversity, raising concern for the services they provide. However, the extent of loss is uncertain, especially for insects that use freshwater during their life. Further study is needed to assess freshwater insect abundances and diversity. In Central Appalachian streams, macroinvertebrate diversity declines in response to mining-induced salinization and resulting changes to ecosystem processes remain largely unknown, such as how the availability and movement of macroinvertebrate biomass is altered in stream food webs. However, taxa observed are dependent upon sampling effort that could bias diversity-process interpretation. Taxon sampling curves can be used to estimate sampling effort that maximizes the probability of complete community characterization. We sampled six streams in the Central Appalachian region for benthic macroinvertebrates and explored the number of samples needed to capture taxonomic richness in salinized streams. Sampling effort did not differ between reference and salinized streams, though more uneven distributions of macroinvertebrates in salinized streams seemed to necessitate greater sampling effort relative to reference streams. We also used taxon and trait-based sampling curves to expand our understanding of biodiversity and functional responses to environmental change. Because macroinvertebrate biomass and emergence can assess the movement and changes in organic material and energy in response to a salinization gradient, we added them as additional metrics. Macroinvertebrates may have varied responses to a stressor dependent upon life stage, suggesting that assessments relying only on immatures may not fully characterize the effects of salinization. We sampled benthic macroinvertebrate biomass and emergent insect biomass from six streams in the Central Appalachian region to be representative of a salinization gradient. We predicted benthic biomass would either decrease, be maintained by greater density and biomass of salt-tolerant taxa, or increase from a salt subsidy effect, while emergent biomass would decrease disproportionately relative to benthic biomass due to late instar and pupae succumbing to stress. Our results suggest that total benthic macroinvertebrate biomass is maintained along a salinization gradient despite the loss of salt-sensitive mayflies due to compensation by salt-tolerant taxa that experience a subsidizing effect. Emergent biomass was variable among streams with peak emergence occurring in spring, with no apparent negative response to increasing conductivity. The present study can help to further develop metrics of stream ecosystem processes in response to a disturbance gradient.
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    Small hive beetle
    Roth, Morgan A.; Gross, Aaron D.; Wilson, James M. (Virginia Cooperative Extension, 2019)
    Provides details about small hive beetle biology, which is a crucial part of identification and treatment, along with popular small hive beetle control methods
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    Toxicity, mode of action, and synergist potential of flonicamid against mosquitoes
    Taylor-Wells, J.; Gross, Aaron D.; Jiang, S.; Demares, F.; Clements, J. S.; Carlier, Paul R.; Bloomquist, J. R. (2018-06)
    The present study focused on the toxicity of the aphid anti-feedant flonicamid and its main metabolite, 4-trifluoromethylnicotinamide (TFNA-AM) to Aedes aegypti and Anopheles gambiae mosquitoes. The compounds were toxic to both species via topical application, resulting in un-coordinated locomotion and leg splaying, with a favorable An. gambiae LD50 value of 35 ng/mg for TFNA-AM, but no significant lethality to Ae. aegypti at 10 μg/female. There was mild cross resistance in the Akron-kdr (Akdr) strain of An. gambiae. Both compounds were non-toxic to intact larvae (LC50 >300 ppm); however, headless Ae. aegypti larvae displayed spastic paralysis, with PC50 values of 2-4 ppm, indicating that the cuticle is a significant barrier to penetration. TFNA-AM showed low mammalian toxicity, with an LD50 of >2000 mg/kg in mice. Electrophysiological experiments showed larval Aedes muscle depolarization and Kv2 channel blocking activity that required near mM concentrations, suggesting that this potassium channel is not the main target for flonicamid nor its metabolite. However, TFNA-AM was a potent blocker of evoked body wall sensory discharge in dipteran larvae, suggesting that some component of the chordotonal organ system may be involved in its toxicity. Finally, flonicamid and TFNA-AM showed about 2-fold synergism of permethrin toxicity against An. gambiae adult females whose mechanism should become more clear once the mode of action of these compounds is better defined.
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    Varroa Mite Biology and Feeding Damage
    Roth, Morgan A.; Gross, Aaron D.; Wilson, James M. (Virginia Cooperative Extension, 2019-09-12)
    Describes Varroa Mites, their biology, and negative impacts on honey bees.
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    Varroa Mite Management Methods
    Roth, Morgan A.; Gross, Aaron D.; Wilson, James M. (Virginia Cooperative Extension, 2019-09-12)
    Describes treatment methods for combating Varroa mite infestations by following an integrated pest management plan.
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    Varroa Mite Sampling Methods
    Roth, Morgan A.; Gross, Aaron D.; Wilson, James M. (Virginia Cooperative Extension, 2019-09-12)
    Discusses methods for sampling hives for Varroa mites.