Dr. Paul Leisnham has spent much of his career studying invasive, medically important mosquitoes in the United States. He has a long-term interest in their population dynamics, competition between invaders and natives, spatial patterns of invasion, and the influence of climate change on all of these interactions. And with good reason, as Dr. Leisnham explained, mosquitoes are well-documented vectors for a number of different diseases, including West Nile Virus, which hit peak frequencies in the U.S. in 2003 and more recently in 2012.
Dr. Leisnham went on to describe that many of the diseases vectored by mosquitoes have no vaccine, making the presence of adults a greater health risk. For this reason, effective management happens by targeting the aquatic larvae, rather than the terrestrial adults. Mosquito larvae utilize a number of different habitats, ranging from ponds and wetlands to birdbaths and discarded tires filled with water. Dr. Leisnham argues that these small containers may actually be one of the most important sources of mosquitoes found in urban and suburban areas.
or this reason, Dr. Leisnham became interested in the role of residents in managing local populations of mosquitoes. With so many potential habitats for larvae in the backyard of an average Washington D.C. resident, Dr. Leisnham posited that resident source reduction would be critical for successful management of mosquito populations.
That left him with important questions about the attitudes and knowledge of Washington D.C. residents towards mosquitoes and their management in urban settings. Working with former master’s student Zara Dowling, Dr. Leisnham designed a survey to address the following questions: 1) Can residents reduce mosquito populations? 2) Is mosquito reduction related to the attitude of the residents? and 3) Do the residents’ level of knowledge change their attitude toward reduction?
A survey of 240 households in the D.C. area was conducted by Dr. Leisnham’s lab to address these questions. The results showed that younger, higher income residents had the most general knowledge about mosquitoes, while older, male residents knew the most about mosquitoes’ larval habitat. By comparison, lower income women were the most motivated to control mosquito populations. The data also indicated that, although resident source reduction may be important, the efforts of knowledgeable residents may be rendered ineffective by residents who are not removing container habitats from their property.
Based on these results, Dr. Leisnham then designed the Tip N Trash Program, with the goal of evaluating the success of passive educational materials for effecting resident source reduction. With the help of students, Dr. Leisnham designed and circulated educational materials, including magnets and flyers, to the same 240 households used in the survey the year before.
Preliminary results from this research suggest that passive educational materials have limited success. So far, Dr. Leisnham has identified an overall improvement in knowledge and attitude of residents that corresponds with education, but this has not yet translated into source reduction. Surveys of mosquito populations in this year also indicated that residents may be missing key containers where mosquitoes breed, negating the effects of source reduction.
Since beginning this line of inquiry, Dr. Leisnham has become increasingly interested in the sociological implications of his research. He plans to continue his investigation into the role of residents in mosquito management and the effectiveness of different educational tools for engaging citizen participation. He also wants to further understand the macro- and micro-scale patterns of larval mosquito occurrence that may explain overall trends in population abundance. Dr. Leisnham’s research has important implications for human health and for understanding population dynamics of invasive species; you can keep track of his research to learn more!
1. Dowling, Z.*, P. Armbruster, S. LaDeau, and P.T Leisnham. 2013. Socioeconomic status affects mosquito (Diptera: Culicidae) larval habitat with implications for vector control. Journal of Medical Entomology. In Press.
2. Smith, C. D.*, A. H. Baldwin, J. Sullivan, and P. T. Leisnham. 2013. Effects of elevated atmospheric CO2 on competition between the mosquitoes Aedes albopictus and Ae. triseriatus through changes in litter quality and production. Journal of Medical Entomology 50: 521-532; DOI: http://dx.doi.org/10.1603/ME12149.
Elanor Spadafora is a fourth year PhD student studying the influence of vegetation on predaceous diving beetle communities (Coleoptera: Dytiscidae) in restored and historic wetlands on the Delmarva Peninsula. She uses functional traits and behavioral studies to understand how these beetles interact with aquatic macrophytes and how this may influence trophic structure.
Dr. William Reid’s presentation about pesticide resistance in the common house fly, Musca domestica, was another interesting talk in a colloquium series in which intrigue is entirely expected. But Dr. Reid’s presentation caught my attention particularly because of its focus on the mechanisms underlying an insect’s resistance to a commonly used synthetic pesticide that I’ve become increasingly more familiar with over the past couple of years: permethrin. I serve as a staff entomologist with a pest management company and as such I’m well aware that permethrin is not only widely used in structural pest management but also in agricultural and military applications and human and veterinary medicine.
Dr. Reid explained that though permethrin is widely used, and resistance to it has already mounted in several pest organisms, little is known of how the genes involved in metabolic resistance are regulated. Studies seem to suggest that insecticide resistance is mediated through a complex interplay of regulatory factors and is conferred via multiple gene up-regulation but no regulatory factors related to insecticide resistance had been identified until the research conducted by Dr. Reid and several other researchers at Auburn University. By working with a multiple pesticide resistant strain of house fly (ALHF) and two susceptible strains, aabys and CS, they were able to present compelling evidence that both interactions between autosomes and interactions within an autosome are important for the expression of genes that detoxify and subsequently confer resistance to permethrin.
The house fly has five autosomes (non-sex chromosomes), each of which contain genes involved in metabolic detoxification of pesticides and also genes that regulate the expression of pesticide resistance genes. Each of the five autosomes was individually substituted in the ALHF type (the highly insecticide resistant strain) with autosomes from CS or aabys (the pesticide susceptible strains). The individual contributions of each autosome were estimated by characterizing the changes in the gene expression levels of insecticide resistance genes as measured by the dose of the pesticide required to kill the fly. The substitution of certain autosomes could confer anything from two to over a thousand times resistance to permethrin or detract from an existing resistance to a significant degree. These findings suggest that insecticide resistance is mediated largely through interactions within an autosome and interactions between autosomes in addition to resistance conferred by the up-regulation of genes.
Dr. Reid’s research represents a much needed step forward in our understanding of the interplay of insect genetics and chemical suppression of insect populations. His work is part of an ongoing, concerted effort to understand the gene regulation and cellular signaling events that underpin insecticide resistance in insects; an effort that may lead to a better understanding of how insecticide cross-resistance develops and possibly novel ways to avoid it in the future.
Samuel Ramsey is a 2nd year PhD student in the Shrewsbury lab currently studying competition in egg parasitoids of the brown marmorated stink bug.
Recent ENTM publications
“The more you fly, the sooner you die”
Synopsis for Dr. Michelle Elekonich’s colloquium talk, “It’s not the age, it’s the mileage: honey bee behavior, stress, and aging
The second colloquium talk of the semester brought us into the world of insect physiology, as Dr. Michelle Elekonich presented research carried out by her lab on the influence of behavior on the aging process in honeybees. Much of the work presented in the talk centered around the role of reactive oxygen species (ROS) on the degradation of cellular machinery, leading to an eventual decline in function, and ultimately death. ROS are produced through metabolic reactions, with production increasing with higher metabolic output. The thrust of these findings, as they are applied to honeybees, were summarized during the talk with the colorful slogan, “the more you fly, the sooner you die.” Undoubtedly, many in the audience were mentally applying findings from these studies of senescence in bees to schemes for extending their own longevity. However, before committing to a long life of sloth and açaí berries, it is worth looking more in depth at these studies of ROS and its effects in honeybees.
ROS, such as superoxide and hydroxyl radicals are produced as intermediate steps during metabolic reactions, and can degrade important molecules within the cell, such as DNA and lipids. ROS are normally kept from damaging cellular structures by enzymes with antioxidant functions, such as catalase, as well dietary antioxidants, such as ascorbic acid (vitamin C). However, different factors can impede cells from quenching all ROS that are produced, such as oxidative stress from ionizing radiation, or extremely high metabolic levels that overwhelm antioxidant functions within the cell. There have been many studies implicating ROS in advancing aging processes at the cellular level in many different animal systems, including insects. One of the unique properties of studying this process in honeybees is the flexibility of the lifespan of the bees, which is mediated by behavioral activities, and not limited to a pre-determined death. For the most part, adult honeybees are not reproductive, so there is no single event where biological imperatives are met, and cellular functions can just shut down. Therefore natural selection is likely acting to increase the longevity of these non-reproductive bees in the face of great oxidative stress from extremely high metabolic rates.
Except for the queen, female honeybees within a hive go through different life stages, beginning their adult lives tending to duties within the hive, and culminating in foraging activities outside of the hive. As bees transition from peaceful indoor work to intense daily foraging for nectar and pollen, they are subject to a dramatic increase in cellular metabolism and stress. Dr. Elekonich’s lab performed experiments measuring the antioxidant levels in foraging bees before and after daily foraging activities, and found that only young bees show increases in antioxidant levels in response to higher metabolism, while older bees do not (Williams et al. 2008). These findings indicate that as foraging bees age, their production of antioxidant enzymes becomes reduced, and with it the ability to handle ROS production from flight activity. This likely increases oxidative damage to flight muscles and increases rates of senescence. This hypothesis was further supported by experiments testing the flying abilities of different aged bees by observing them hovering within low-density atmospheres (Vance et al. 2009). Flight is increasingly difficult for insects in gasses of lower densities. To achieve this, honeybees were flown in different atmospheres, where the nitrogen content of normal air was replaced incrementally with helium. Using high-speed photography, the mechanics of flight could be observed and quantified. The results of this experiment show the wing beats of older forager bees have reduced amplitude relative to normal aged foragers. In nature, this could result in bees not making the flight back to the hive, or being susceptible to predators. Some of the measured reduction in antioxidant response of forager bees may be attributed to patterns of gene expression that change as bees transition from nurses to foragers (Margotta et al. 2013). By manipulating the age at which bees transition from nurse to forager, Dr. Elekonich’s lab was able to show that it is the transition from nurse to forager that induces the greatest change in gene expression patterns, rather than age.
The cumulative picture that is painted from these studies is that foraging bees are worked to death, as the metabolic demands of prolonged flight take their toll on the flight muscles. By contrast, remaining in the hive as a nurse precludes the bees from behaviors that are inherently bad for their bodies. It would be wonderful to be able to apply these results directly to humans, and one could imagine that health initiatives would change dramatically. Reduce your metabolic output for a long and healthy life: avoid the gym at all costs. Use the elevator, stairs are for emergencies only. Reinstate required afternoon naptime. Robots would do all of our yard work, while we sip ginseng tea in padded armchairs and type review articles with ergonomic keyboards. No more field work. Alas, these studies should not be used to justify immobility, as the metabolic processes producing oxidative stresses in foraging bees occur at orders of magnitude higher than anything humans are capable of producing. The closest we could come to drawing parallels to human behavior would be that it is probably a bad idea to try to sprint a marathon every day for the rest of your life. Aside from that, these studies offer new insight into the role of behavior on the onset of senescence in insects, at least.
Margotta, J. W., G. E. Mancinelli, A. A. Benito, A. Ammons, S. P. Roberts, M. M. Elekonich, 2013. Effects of flight on gene expression and aging in the honey
bee brain and flight muscle. Insects. 4: 9-30.
Vance, J. T., J. B. Williams, M. M. Elekonich and S. P. Roberts, 2009. The effects of age and behavioral development on honey bee (Apis mellifera) flight performance. The Journal of Experimental Biology. 212: 2604-2611.
Williams, J. B., S. P. Roberts, M. M. Elekonich, 2008. Age and natural metabolically intensive behavior affect oxidative stress and antioxidant mechanisms. Experimental Gerontology. 43: 538–549.
Alan Leslie is a Ph.D. candidate in the Lamp Lab, studying aquatic macroinvertebrates and their effects in regulating ecosystem functions. His research project is focused on determining the effect that burrowing aquatic invertebrates have on nutrient transport in agricultural drainage networks.