Arun Rajamohan

@ars.usda.gov

Research Entomologist, Insect Genetics and Biochemistry, USDA-ARS-Edward T Schafer Agricultural Research Center
USDA-ARS

Arun Rajamohan


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https://researchid.co/arunrajmohan

RESEARCH, TEACHING, or OTHER INTERESTS

Agricultural and Biological Sciences, Animal Science and Zoology
31

Scopus Publications

Scopus Publications

  • Cryopreservation and other preservation approaches for animal models workshop session I: Invertebrate models in biomedical research
    Christopher Fang-Yen, Daryl M. Gohl, Jonathan D. Hibshman, Estefania Paredes, Arun Rajamohan, Ann E. Rougvie, Rebecca D. Sandlin, Nicholas M. Teets, Jeffery K. Tomberlin, Cale Whitworth, John C. Bischof, Joseph Rinehart
    Cryobiology, 2026
    The ability to preserve small invertebrate organisms indefinitely at ultracold temperatures has been an important tool for biological and biomedical research. This report provides a summary of an NIH-sponsored workshop on Cryopreservation and Other Preservation Approaches for Invertebrate Models. This workshop addressed topics related to cryopreservation and other long-term preservation methods of invertebrate models commonly used in biomedical research, including the fruit fly Drosophila melanogaster, roundworm Caenorhabditis elegans, sea urchin Paracentrotus lividus, and other invertebrate models. The session presentations focused on current approaches and limitations in preserving these organisms and lessons learned from preserving other invertebrate organisms, such as tardigrades, mosquitoes, and black soldier flies. The workshop focused first on established models, then emerging models and finally new investigator work in the area. Future priorities suggested during the workshop included standardization and dissemination of successful protocols for established models, validating new protocols for emerging models on cells or tissues of invertebrates (e.g. 15 insect species by USDA, tardigrades, and mosquitoes), and a focus on new tools and approaches.
  • High abundance of lactobacilli in the gut microbiome of honey bees during winter
    Gagandeep Brar, Lyna Ngor, Quinn S. McFrederick, Alex S. Torson, Arun Rajamohan, Joesph Rinehart, Preetpal Singh, Julia H. Bowsher
    Scientific Reports, 2025
    Honey bee gut microbiota play specific roles in promoting host growth and physiology by regulating the immune system, behavior, metabolism, and neurological processes. While the gut microbiota of honey bee queens, workers, and larvae has been extensively studied, less is known about the composition of gut microbiota in the winter worker bees. This study investigates the dynamics of the gut microbiota in overwintering adult worker bees, focusing on two commercial bee strains: Bolton™ bees and Mann Lake™ bees. These Apis mellifera strains were investigated under different storage conditions (indoor storage at 6 °C and outdoor storage in natural conditions) during the winter months (October, November, and December). Utilizing 16S rRNA gene amplicon sequencing, we characterized the microbial composition of the whole gut. We observed the Lactobacilli dominated in all the overwintering honey bee guts with a significantly higher abundance of unclassified Lactobacillus species in November, while Lactobacillus apis showed significantly higher abundance in October. Bolton bees exhibited significantly higher abundance levels of Bartonella (denoted as uncultured) and Bifidobacterium, along with an unexpected presence of Wolbachia. In contrast, Mann Lake bees demonstrated an increased abundance of Commensalibacter. Our results suggest that Shannon diversity is influenced by the month rather than by the bee strain or storage conditions. We also found significant differences in Bray Curtis diversity index by month. Overall, taxonomical abundance was not affected by whether the hives were stored outside or in constant temperature indoor storage. However, various bacterial species showed differences in abundance across different months, with slight variations observed between bee strains. Given the potential benefits of the honey bee gut microbiome for health and nutrition, our data suggests that the genus Lactobacillus may play a significant role in bee health during winter and overwintering storage.
  • Reproductive Senescence in the Pollinator, Megachile rotundata
    Jacob B. Pithan, Brooke L. Kohler, Arun Rajamohan, Kendra J. Greenlee
    Insects, 2025
    The disposable soma theory posits that organisms allocate limited resources between reproduction, maintenance, and growth, resulting in trade-offs, particularly as they age. In this study, we examined age-related reproductive senescence in Megachile rotundata, a solitary bee and important agricultural pollinator. We hypothesized that, similarly to social bees, aging females would show declines in foraging behavior and reproductive fitness. Contrary to this hypothesis, we found no evidence of reproductive senescence in M. rotundata within the timeframe observed. Instead, older females increased their foraging rate, leading to larger provisions and offspring. We also observed that older bees exhibited improved foraging efficiency, likely due to learning and muscle physiology changes. Furthermore, ovarian development showed no decline with age, indicating that reproductive capacity remains stable throughout the observed timeframe. Our results challenge conventional assumptions about reproductive senescence in solitary bees and suggest that older M. rotundata may contribute to more efficient pollination, with implications for pollinator management. This study provides new insights into the aging process in solitary bees, emphasizing the need for further research into the mechanisms behind age-related behavioral and reproductive changes.
  • Monarch butterfly conservation through male germplasm cryopreservation
    Courtney C. Grula, Arun Rajamohan, Joseph P. Rinehart
    Scientific Reports, 2024
    Monarch butterfly (Danaus plexippus L.) populations have declined in North America. The International Union for Conservation of Nature (IUCN) recently classified the species as endangered, sparking public concern and conservation efforts. Our approach to conservation is through cryopreservation of germinal cells and tissue. The goal of this study was to develop a cryopreservation protocol for monarch spermatozoa to ensure successful long-term storage. Cryopreserved sperm cells would provide a reserve of monarch germplasm, which could be utilized in the event of population loss. In this study, sperm cell bundles collected from male monarch butterflies were cryopreserved in a cryoprotective medium and stored in liquid nitrogen. To determine the post-cryopreservation sperm cell viability, a subsample of preserved sperm bundles were thawed rapidly, and their viability was qualified using a sperm live/dead stain. We are presenting a protocol to preserve and store genetic material and viable sperm bundles of the monarch butterfly. To date, this is the first report of successful cryopreservation of monarch germplasm which sets the foundation for cryostorage and could be extensible to other vulnerable lepidopterans.
  • Environmentally acquired gut-associated bacteria are not critical for growth and survival in a solitary bee, Megachile rotundata
    Gagandeep Brar, Madison Floden, Quinn McFrederick, Arun Rajamohan, George Yocum, Julia Bowsher
    Applied and Environmental Microbiology, 2024
    Social bees have been extensively studied for their gut microbial functions, but the significance of the gut microbiota in solitary bees remains less explored. Solitary bee, Megachile rotundata females provision their offspring with pollen from various plant species, harboring a diverse microbial community that colonizes larvae guts. The Apilactobacillus is the most abundant microbe, but evidence concerning the effects of Apilactobacillus and other provision microbes on growth and survival are lacking. We hypothesized that the presence of Apilactobacillus in abundance would enhance larval and prepupal development, weight, and survival, while the absence of intact microbial communities was expected to have a negative impact on bee fitness. We reared larvae on pollen provisions with naturally collected microbial communities (Natural pollen) or devoid of microbial communities (Sterile pollen). We also assessed the impact of introducing Apilactobacillus micheneri by adding it to both types of pollen provisions. Feeding larvae with sterile pollen + A. micheneri led to the highest mortality rate, followed by natural pollen + A. micheneri , and sterile pollen. Larval development was significantly delayed in groups fed with sterile pollen. Interestingly, larval and prepupal weights did not significantly differ across treatments compared to natural pollen-fed larvae. 16S rRNA gene sequencing found a dominance of Sodalis , when A. micheneri was introduced to natural pollen. The presence of Sodalis with abundant A. michene ri suggests potential crosstalk between both, shaping bee nutrition and health. Hence, this study highlights that the reliance on nonhost-specific environmental bacteria may not impact fitness of M. rotundata . IMPORTANCE This study investigates the impact of environmentally acquired gut microbes of solitary bee fitness with insights into the microbial ecology of bee and their health. While the symbiotic microbiome is well-studied in social bees, the role of environmental acquired microbiota in solitary bees remains unclear. Assessing this relationship in a solitary pollinator, the leaf-cutting bee, Megachile rotundata , we discovered that this bee species does not depend on the diverse environmental bacteria found in pollen for either its larval growth or survival. Surprisingly, high concentrations of the most abundant pollen bacteria , Apilactobacillus micheneri did not consistently benefit bee fitness, but caused larval mortality. Our findings also suggest an interaction between Apilactobacillus and the Sodalis and perhaps their role in bee nutrition. Hence, this study provides significant insights that contribute to understanding the fitness, conservation, and pollination ecology of other solitary bee species in the future.
  • Development of a degree-day model for adult emergence of the red sunflower seed weevil, Smicronyx fulvus LeConte (Coleoptera: Curculionidae)
    Shawna Pantzke, Beth Ferguson, Arun Rajamohan, Joseph P. Rinehart, Deirdre Prischmann-Voldseth, Jarrad R. Prasifka
    Journal of the Kansas Entomological Society, 2024
    The red sunflower seed weevil, Smicronyx fulvus LeConte (Coleoptera: Curculionidae), is the most destructive seed-feeding pest of sunflower in North America. The life history of S. fulvus (e.g., univoltine, overwintering within 6 cm of soil surface) suggests several strategies to limit crop damage, but insecticides remain the primary management tool. To facilitate broader management of S. fulvus, a degree-day model for adult emergence was developed and tested. Emergence of adults under controlled conditions produced a lower developmental threshold of 5 °C, ≈ 970 degree-days to first emergence, and ≈ 1160 degree-days to 50% emergence. Soil temperature data showed accumulated degree-days were similar 5 cm below turf and 10 cm beneath bare soil. Observed emergence of weevils in field plots occurred several days earlier than predicted (using 5 cm turf or 10 cm bare soil temperatures) when soil was kept free of vegetation. However, observed emergence was similar to predicted emergence when plots were shaded by spring wheat, which is representative of crops planted after sunflower for much of North America. Though access to soil (rather than ambient) temperature data is needed, this first degree-day model provides a tool to help growers avoid S. fulvus damage using early planting or early-maturing hybrids.
  • Diapause, pollen ball incidence, and overwintering energetics in the alfalfa leafcutting bee, Megachile rotundata
    Preetpal Singh, Arun Rajamohan, Sarah A. Waybright, Michael E. Dillon, Scott M. Ferrenberg, Joseph P. Rinehart, Julia H. Bowsher
    Frontiers in Bee Science, 2024
    IntroductionWarming summer temperatures have the potential to harm managed pollinators, impacting both summer performance and overwintering success. The alfalfa leafcutting bee, Megachile rotundata, is a solitary bee used for commercial pollination of alfalfa. M. rotundata undergoes facultative diapause in the prepupal stage. Prepupae that diapause early in the season are exposed to warm temperatures for a longer period of time than the individuals that start diapause closer to fall, which may reduce lipid reserves required for overwintering survival. Warm temperatures may also contribute to pollen ball incidence, which is when a provision is present but there is no sign of a larva in the brood cell. Our goal was to identify factors that regulate diapause and pollen ball incidence and examine effects of pre-wintering field conditions on post-overwintering energy reserves in M. rotundata.MethodsNest boxes were installed near Fargo, ND, Laramie, WY, and Las Cruces, NM, which exposed bees to different photoperiods and thermal regimes. Three nest boxes were placed at each site. We monitored nesting conditions and diapause and pollen ball incidence throughout the season. Lipids, sugars, and glycogen reserves were measured in adults after overwintering.Results and DiscussionOur models indicate that most of the variation in diapause incidence was explained by nest, with individuals within a nest tending to have the same diapause outcome. This suggests that the environmental conditions experienced by the mother, or genetic predisposition, influences offspring diapause. We also found evidence that high cavity temperatures can cause diapause aversion. In addition, our study is the first to link high nesting cavity temperatures to increased pollen ball incidence. Exposure to stressful temperatures during development and early diapause resulted in an increase in adult lipid reserves after overwintering. Adult sugar and glycogen reserves were not affected by exposure to warm temperatures during development and early diapause. In conclusion, maternal effects and temperature were important factors for diapause and pollen ball incidence in M. rotundata with macronutrient reserves similar for early and late season bees.
  • Thermal biology and overwintering behavior of the red sunflower seed weevil (Coleoptera: Curculionidae)
    Shawna Pantzke, Beth Ferguson, Arun Rajamohan, Joseph P Rinehart, Deirdre Prischmann-Voldseth, Jarrad R Prasifka
    Environmental Entomology, 2023
    Most natural mortality of the red sunflower seed weevil, Smicronyx fulvus LeConte (Coleoptera: Curculionidae), occurs while larvae overwinter in the soil. To test the hypothesis that S. fulvus mortality is related to low temperatures, experiments were used to (i) evaluate the temperature at which larvae freeze (= supercooling point [SCP]), (ii) assess possible vertical movement between entry into the soil in fall and adult emergence in summer, and (iii) determine if realistic soil temperatures could explain patterns of overwintering mortality. Mean SCP for groups of S. fulvus larvae differed between years and months, but only ranged from −20.93 to −22.68 °C. Most overwintering larvae were found within 6 cm of the soil surface, but larvae appeared to move 1–2 cm deeper between pairs of successive sample dates (September to January, January to April). Significant larval mortality that occurred between January and April 2021 was tentatively attributed to a period in February where daily minimum soil temperatures ranged from −8 to −12 °C. When overwintering under control conditions (constant 4 °C) was interrupted with week-long exposure to −4, −8, or −12 °C in a cold bath, significant S. fulvus mortality was seen for temperatures at or below −8 °C. Combined results suggest that mortality of overwintering S. fulvus is likely caused by continuous exposure to low temperatures that may not be cold enough to freeze larvae. Additionally, the shallow overwintering by S. fulvus supports the idea that routine farm management, including tillage and herbicide incorporation, may help limit populations of this sunflower pest.
  • Sperm can't take the heat: Short-term temperature exposures compromise fertility of male bumble bees (Bombus impatiens)
    Claire Campion, Arun Rajamohan, Michael E. Dillon
    Journal of Insect Physiology, 2023
  • Vitrification of Lepidopteran Embryos—A Simple Protocol to Cryopreserve the Embryos of the Sunflower Moth, Homoeosoma electellum
    Arun Rajamohan, Jarrad R. Prasifka, Joseph P. Rinehart
    Insects, 2022
    Embryos of the sunflower moth, Homoeosoma electellum (Hulst), were cryopreserved after modification to the method that was previously described for Pectinophora gossipiella. The workflow to develop the protocol consisted of methods to weaken the embryonic chorion followed by the application of various methods to disrupt the sub-chorionic wax layer. These steps were necessary to render the embryos permeable to water and cryoprotectants. Initially, the embryos were incubated at 21° and 24 °C, and the development of the double pigment spots/eyespot and eclosion were tracked every two hours. The embryos at 24 °C showed eyespots as early as 30 h, while in the case of the embryos that were incubated at 21 °C, there was a developmental delay of approximately 20 h. The embryos at 24 °C showed peak eclosion between 55 and 70 h, and the embryos at 21 °C eclosed between 80 and 100 h of development. Estimating this range is crucial for the purposes of stage selection and treatment initiation for cryopreservation protocol development for the embryos. The control hatch percentage at either developmental temperature was >90%, and the sodium hypochloride, 2-propanol and alkane-based treatments reduced the embryo hatchability to <10%. Hence, a modified surfactant—hypochlorite mixture—was used to destabilize the chorion and solubilize the hydrophobic lipid layers. Water permeability assessments using the dye-uptake method show that polysorbate 80 in combination with sodium hypochlorite alone is capable of permeabilizing the embryo as efficiently as sequential hypochlorite—alkane treatments, but with significantly higher hatch rates. A vitrification medium consisting of ethane diol and trehalose was used to dehydrate and load the embryos with the cryoprotective agent. The median hatch rates after vitrification were 10%, and maximum was 23%.
  • Vitrification of manually stage-selected embryos of Drosophila have significantly higher survival and emergence – Consequences for insect germplasm storage
    Korie M. DeBardlabon, Arun Rajamohan, Joseph P. Rinehart
    Cryobiology, 2022
  • Cryopreservation of seminal vesicle derived spermatozoa from Bombus impatiens and Apis mellifera – Implications for artificial insemination of bumble bees
    Claire Campion, Arun Rajamohan, Joseph P. Rinehart
    Cryobiology, 2021
  • Comparison of Fluctuating Thermal Regimes and Commercially Achievable Constant-Temperature Regimes for Short-Term Storage of the Alfalfa Leafcutting Bee (Hymenoptera: Megachilidae)
    George D Yocum, Arun Rajamohan, Joseph P Rinehart
    Journal of Economic Entomology, 2021
  • Physiological responses to cryoprotectant treatment in an early larval stage of the malaria mosquito, Anopheles gambiae
    Jacob B. Campbell, Andrew Dosch, Catherine M. Hunt, Ellen M. Dotson, Mark Q. Benedict, Arun Rajamohan, Joseph P. Rinehart
    Cryobiology, 2021
  • A non-activating diluent to prolong in vitro viability of Apis mellifera spermatozoa: Effects on cryopreservation and on egg fertilization
    Arun Rajamohan, Robert G. Danka, Brandon K. Hopkins, Joseph P. Rinehart
    Cryobiology, 2020
  • Thermoprofile Parameters Affect Survival of Megachile rotundata during Exposure to Low-Temperatures
    George D Yocum, Joseph P Rinehart, Arun Rajamohan, Julia H Bowsher, Kathleen M Yeater, Kendra J Greenlee
    Integrative and Comparative Biology, 2019
  • Environmental history impacts gene expression during diapause development in the alfalfa leafcutting bee, Megachile rotundata
    George D. Yocum, Anna K. Childers, Joseph P. Rinehart, Arun Rajamohan, Theresa L. Pitts-Singer, Kendra J. Greenlee, Julia H. Bowsher
    Journal of Experimental Biology, 2018
  • Effect of cryopreservation on the pre-hatching behavior in the Mexican fruit fly Anastrepha ludens Loew (Diptera, Tephritidae)
    Arun Rajamohan, Joseph P. Rinehart, Roger A. Leopold
    Cryobiology, 2018
  • The geometric framework for nutrition reveals interactions between protein and carbohydrate during larval growth in honey bees
    Bryan R. Helm, Garett Slater, Arun Rajamohan, George D. Yocum, Kendra J. Greenlee, Julia H. Bowsher
    Biology Open, 2017
  • Cryopreservation of embryos of the mediterranean fruit fly ceratitis capitata vienna 8 genetic sexing strain
    Antonios A. Augustinos, Arun Rajamohan, Georgios A. Kyritsis, Antigone Zacharopoulou, Ihsan ul Haq, Asya Targovska, Carlos Caceres, Kostas Bourtzis, Adly M. M. Abd-Alla
    Plos One, 2016
  • Stage selection and restricted oviposition period improves cryopreservation of dipteran embryos
    Arun Rajamohan, Joseph P. Rinehart, Roger A. Leopold
    Cryobiology, 2015
  • Cryopreservation of embryos of lucilia sericata (Diptera: Calliphoridae)
    Arun Rajamohan, Joseph P. Rinehart, Roger A. Leopold
    Journal of Medical Entomology, 2014
  • Permeability barriers to embryo cryopreservation of pectinophora gossypiella (Lepidoptera: Gelechiidae)
    Arun Rajamohan, Joseph P. Rinehart, Stephen P. Foster, Roger A. Leopold
    Journal of Economic Entomology, 2013
  • High temperature tolerance and thermal plasticity in emerald ash borer Agrilus planipennis
    Stephanie Sobek, Arun Rajamohan, Daniel Dillon, Robert C. Cumming, Brent J. Sinclair
    Agricultural and Forest Entomology, 2011
  • Quality testing of three species of tephritid fruit flies after embryo cryopreservation
    Roger A Leopold, Arun Rajamohan, Todd E Shelly, Alfred M Handler
    Annals of the Entomological Society of America, 2010
  • Synchrotron x-ray visualisation of ice formation in insects during lethal and non-lethal freezing
    Brent J. Sinclair, Allen G. Gibbs, Wah-Keat Lee, Arun Rajamohan, Stephen P. Roberts, John J. Socha
    Plos One, 2009
  • Hardening trumps acclimation in improving cold tolerance of Drosophila melanogaster larvae
    ARUN RAJAMOHAN, BRENT J. SINCLAIR
    Physiological Entomology, 2009
  • Short-term hardening effects on survival of acute and chronic cold exposure by Drosophila melanogaster larvae
    Arun Rajamohan, Brent J. Sinclair
    Journal of Insect Physiology, 2008
  • Slow or stepped rewarming after acute low-temperature exposure does not improve survival of Drosophila melanogaster larvae
    Brent J. Sinclair, Arun Rajamohan
    Canadian Entomologist, 2008
  • Cryopreservation of Mexican fruit flies by vitrification: Stage selection and avoidance of thermal stress
    A. Rajamohan, R.A. Leopold
    Cryobiology, 2007
  • Cryopreservation of Mediterranean fruit fly embryos
    Cryo Letters, 2003