DOCSLIB.ORG

An Investigation of Deet- Insensitivity in Aedes Aegypti

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
An Investigation of Deet- Insensitivity in Aedes Aegypti AN INVESTIGATION OF DEET- INSENSITIVITY IN AEDES AEGYPTI NINA STANCZYK, BSc. Thesis submitted to the University of Nottingham for the degree of Doctor of Philosophy July 2011 1 Abstract N,N-Diethyl-m-toluamide (DEET) is one of the most effective and commonly used mosquito repellents. However, during laboratory trials a small proportion of mosquitoes are still attracted by human odours despite the presence of DEET. In this study behavioural assays identified Aedes aegypti females that were insensitive to DEET. The selection of either sensitive or insensitive groups of females with males of unknown sensitivity over several generations resulted in two populations with different proportions of insensitive females. Crossing experiments showed the ‘DEET-insensitivity’ trait to be dominant. In addition to the finding of heritable DEET-insensitivity, unselected culture mosquitoes were shown to change their sensitivity to DEET after brief pre-exposure to the repellent. Female mosquitoes that were sensitive to DEET when first tested became insensitive when retested. Electroantennography showed that mosquitoes that were insensitive to DEET had a reduced response to DEET compared with mosquitoes that were sensitive to it. This was the case both for culture mosquitoes displaying insensitivity to DEET after brief pre-exposure to it, and for the sensitive and insensitive lines selected for several generations. Single sensillum recordings of the selected lines identified DEET-sensitive sensilla in the sensitive line that did not respond to DEET in the insensitive line. This study suggests that behavioural insensitivity to DEET in Ae. aegypti is a genetically determined dominant trait, which can also be temporarily induced by pre-exposure, and resides in changes in sensillum function. These results highlight the necessity for careful monitoring of DEET- insensitivity in the field, and caution when designing laboratory methods for repellency assays. 2 Acknowledgements Firstly I would like to thank my supervisors John Brookfield, James Logan and Lin Field for their sheer enthusiasm, unfailing support and sage advice through this project. I came out of every meeting with the three of them feeling inspired and excited (if also occasionally panicked), which I think is the best effect supervisors can have. I would also like to thank Rickard Ignell for his invaluable expertise and the opportunity to do single sensillum recordings at SLU in Alnarp, Sweden, and everyone in the lab there, particularly Sharon Hill for her patience in teaching me SSR and being a sympathetic ear when I got frustrated. I would like to acknowledge Sue Welham, Suzanne Clark and Elisa Loza at Rothamsted Research for statistical advice. Also Lynda Castle in VCU, for excellent diagrams, and Jean Devonshire, for the fantastic SEM pictures. A massive thank you to all of my past and present colleagues at Rothamsted who were willing to answer questions, demonstrate techniques and exchange ideas, particularly Sarah Dewhirst, Christine Woodcock and Lynda Ireland. I’ve had a brilliant time working at Rothamsted, due in no small part to the people I work with, so thanks to Mary Hamilton, Emma Weeks, John Caulfield and Ben Webster for all of those pub lunches! Thanks to James Cook for his consistent mocking throughout this project, without which my world would have been all askew. And finally, thank you to my parents for their help, support, and constant love – I dare you to try and read all of this and understand it. 3 Contents Contents Abstract ............................................................................................................................... 2 Acknowledgements ........................................................................................................... 3 Contents ............................................................................................................................... 4 Chapter 1. General Introduction 1.1 Mosquitoes as vectors of disease ............................................................................. 8 1.2 Current mosquito control ....................................................................................... 10 1.2.1 Repellents......................................................................................................... 12 1.3 Mosquito biology .................................................................................................... 15 1.3.1 Life-cycle .......................................................................................................... 15 1.3.2 Host location .................................................................................................... 17 1.3.3 Mosquito peripheral olfaction ......................................................................... 18 1.4 DEET ......................................................................................................................... 20 1.4.1 The mode of action of DEET ............................................................................. 20 1.4.2 DEET Insensitivity ............................................................................................. 22 1.5 Aims of this study .................................................................................................... 24 Chapter 2. Selection of DEET-Insensitivity and Crossing Experiments 2.1 Introduction ............................................................................................................. 25 2.2 Methods ................................................................................................................... 27 2.2.1 Predictions of genetic inheritance of DEET-insensitivity ................................. 27 2.2.2 Insects .............................................................................................................. 27 2.2.3 Repellency bioassay for selection of DEET-insensitive mosquitoes................. 28 2.2.4 60% penetrance explanations .......................................................................... 29 2.2.5 Fitness of selected lines ................................................................................... 30 2.2.6 Crossing ............................................................................................................ 30 2.2.7 Statistics ........................................................................................................... 30 2.3 Results ...................................................................................................................... 32 2.3.1 Predictions of genetic inheritance of DEET-insensitivity ................................. 32 2.3.2 Selection of DEET-insensitive mosquitoes ....................................................... 33 2.3.3 60% penetrance explanations .......................................................................... 35 4 Contents 2.3.4 Fitness of selected lines ................................................................................... 37 2.3.5 Crossing ............................................................................................................ 39 2.4 Discussion ................................................................................................................ 40 2.5 Conclusion ............................................................................................................... 44 Chapter 3. Using Electroantennography to Characterise DEET-Insensitivity 3.1 Introduction ............................................................................................................. 45 3.2 Methods ................................................................................................................... 47 3.2.1 Insects .............................................................................................................. 47 3.2.2 Preparation ...................................................................................................... 47 3.2.3 Stimulus Delivery ............................................................................................. 47 3.2.4 Treatments ....................................................................................................... 49 3.2.5 Air entrainment of pipette cartridge ............................................................... 50 3.2.6 Statistical Analyses ........................................................................................... 51 3.3 Results ...................................................................................................................... 52 3.3.1 EAG dose-response experiments ..................................................................... 52 3.3.2 EAG recordings from selected lines (generations F0-F8) .................................. 54 3.3.3 EAG with selected lines (F9) ............................................................................. 59 3.3.4 Pipette air entrainments .................................................................................. 60 3.4 Discussion ................................................................................................................ 61 3.5 Conclusion ............................................................................................................... 65 Chapter 4. Single Sensillum Recordings from DEET-Sensitive and DEET-Insensitive Individuals 4.1 Introduction ............................................................................................................. 66 4.2 Methods ..................................................................................................................
Load more

Recommended publications
  • What Is DEET (PDF)
    DEET is the active ingredient in many insect repellent products. It is WHAT used to repel biting pests such as mosquitoes and ticks, which may carry Lyme disease. Every year, approximately one-third of the U.S. IS population uses DEET, which is available in a variety of liquids, lotions, DEET sprays, and wrist bands. HOW DOES DEET WORK? DEET is designed for direct application to human skin to repel insects, rather than kill them. There are approximately 140 products containing DEET currently registered with the U.S. Environmental Protection Agency (EPA). IS DEET SAFE FOR CHILDREN? The American Academy of Pediatrics (AAP) Committee on Environmental Health has updated their recommendation for use of DEET products on children in 2003, citing: “Insect repellents containing DEET with a concentration of 10% appear to be as safe as products with a concentration of 30% when used according to the directions on the product labels.” AAP recommends that repellents with DEET should not be used www.dupagehealth.org/ftb on infants less than 2 months old. Parents should choose the type and concentration of repellent to be used by taking into account fightthebitedupage the amount of time that a child will be outdoors, exposure to mosquitoes, and the risk of mosquito-transmitted disease in the @fight_the_bite area. If you are concerned about using repellent products on children you may wish to consult a health care provider for advice or contact the ABATEMENT National Pesticide Information Center (NPIC) through their toll-free PARTNER LOGO number, 1-800-858-7378 or npic.orst.edu From http://www.cdc.gov/ncidod/dvbid/westnile/qa/insect_repellent.htm DUPAGE COUNTY HEALTH DEPARTMENT What IS DEET 1 USE DEET PRODUCTS SAFELY: WHAT Do not apply over cuts, wounds, or irritated skin.
    [Show full text]
  • West Nile Virus Insect Repellents and DEET Tips: Deciding on Their Use
    West Nile Virus Insect Repellents and DEET Tips: Deciding on Their Use Chemical repellents are effective at reducing bites from insects that can transmit disease. But their use is not without risk of health effects, especially if repellents are applied in large amounts or improperly. This information will help you decide when and if a repellent is right for you. ABOUT REPELLENTS Two active ingredients found in repellents are DEET (the label might say N,N-diethyl-m-toluamide) and permethrin. Most insect repellents contain one of these active ingredients. DEET comes in many different concentrations, with percentages as low as five percent or as high as 100 percent. In general, the higher the concentration, the higher the protection, but the risk of negative health effects goes up, too. Use the lowest concentration that you think will provide the protection you need. Products with up to 30 percent DEET will provide adequate protection under most conditions. The American Academy of Pediatrics recommends that repellents used on children two years -12 years of age contain no more than 10 percent DEET. DEET has been widely used for many years. Skin reactions (particularly at concentrations of 50 percent and above) and eye irritation are the most frequently reported health problems. Some reports of central nervous system problems, more frequently reported in children than adults, range from slurred speech and confusion to seizures and coma. Cases of serious reactions to products containing DEET have been related to misuse of the product, such as swallowing, applying over broken skin, and using for multiple days without washing skin in between.
    [Show full text]
  • DEET) on the Germination of Raphanus Sativus (Radish Plants)
    Caimin Xi and James T. Zacharia, AJAR, 2018; 3:18 Research Article AJAR (2018), 3:18 American Journal of Agricultural Research (ISSN:2475-2002) The Effect of N,N-Diethyl-3-methylbenzamide (DEET) on the Germination of Raphanus sativus (Radish Plants) Caimin Xi1 and James T. Zacharia2 1Adlai Stevenson High School, Illinois, 60069, USA 2Dar es Salaam University College of Education, P. O. Box 2329, Dar es Salaam, Tanzania ABSTRACT DEET is one of the major chemical constituents of bug repellant *Correspondence to Author: with an estimated global use of 7 million liters in 2016. While James T. Zacharia there has been research concerning the health safety of bug Dar es Salaam University College repellent, research concerning its environmental impact is very of Education, P. O. Box 2329, Dar limited. This study was designed to determine the impact bug es Salaam, Tanzania repellent on the germination of plant seeds. The build-up of bug repellent found in water and soil was simulated by exposing rad- ish seeds to various concentrations of repellent during the ger- How to cite this article: mination process. This two-phased experimental set up demon- Caimin Xi and James T. Zacharia. strated a significant correlation between higher bug repellent The Effect of N,N-Diethyl-3-methyl- concentrations and lower germination rates. Even in the group benzamide (DEET) on the Germi- containing 0.01% concentration of repellent, only 60% of seeds nation of Raphanus sativus (Radish germinated comparing to 93.3% in the control group on day 10. Plants). American Journal of Agri- The differences in germination rates was found to be statistically cultural Research, 2018,3:18.
    [Show full text]
  • General Fact Sheet Deet
    DEET GENERAL FACT SHEET What is DEET DEET is an insect repellent that is used in products to prevent bites from insects such as mosquitoes, biting flies, fleas and small flying insects. DEET is a colorless liquid that has a faint odor and does not dissolve easily in water. DEET was developed by the U.S. Army in 1946 for protection of soldiers in insect-infested areas. Insect repellents containing DEET have been used by the general public in the United States since 1957. What are some products that contain DEET DEET has been used in a number of insect repellent products including liquid sprays, lotions, and sticks. It has been estimated that about 30% of the U.S. population uses one or more products that contain DEET every year. If any exposures occur, be sure to follow the First Aid instructions on the product label carefully. For additional treatment advice, contact the Poi- son Control Center at 1-800-222-1222. If you wish to discuss a pesticide problem, please call 1-800-858-7378. How does DEET work Scientists do not know exactly how DEET works on all insects. Some insects sense people by detecting the chemicals from our bodies and in the air that we breathe out. It has been shown that insects exposed to DEET are not able to locate a person or animal because they cannot detect them. How might I be exposed to DEET There are four ways that people can be exposed to chemicals: contacting their skin, contacting their eyes, breathing them in, or eating them.
    [Show full text]
  • Mosquito Odorant Receptor for DEET and Methyl Jasmonate
    Mosquito odorant receptor for DEET and methyl jasmonate Pingxi Xu1, Young-Moo Choo1, Alyssa De La Rosa2, and Walter S. Leal3 Department of Molecular and Cellular Biology, University of California, Davis, CA 95616 Edited by Jerrold Meinwald, Cornell University, Ithaca, NY, and approved October 3, 2014 (received for review September 8, 2014) Insect repellents are important prophylactic tools for travelers and this putative receptor along with coreceptor CquiIR8a in the populations living in endemic areas of malaria, dengue, enceph- Xenopus oocytes. CquiIR40a•CquiIR8a-expressing oocytes did alitis, and other vector-borne diseases. DEET (N,N-diethyl-3-meth- not generate detectable currents when challenged with DEET, ylbenzamide) is a 6-decade-old synthetic repellent, which is still 200 compounds in our panel, or the newly identified mosquito considered the gold standard of mosquito repellents. Mosquitoes repellents, ethyl anthranilate, butyl anthranilate, and methyl use their sense of smell to detect DEET, but there are currently two N,N-dimethylanthranilate (3). hypotheses regarding its mode of action: activation of ionotropic To rule out a possible malfunction of the coreceptor CquiIR8a, receptor IR40a vs. odorant receptor(s). Here, we demonstrate that we first recorded from a known Drosophila IR•coreceptor system DEET, picaridin, insect repellent 3535, and p-menthan-3,8-diol ac- and then mismatched receptors and coreceptors. DmelIR84a• tivate the odorant receptor CquiOR136 of the southern house mos- DmelIR8a-expressing oocytes generated robust currents (253 ± quito, Culex quinquefasciatus. Electrophysiological and behavioral 26 nA, 1 μM; 1,616 ± 294 nA, 10 μM; and 3,783 ± 159 nA, 100 μM) assays showed that CquiIR40a knockdown had no significant ef- to phenylacetaldehyde, in agreement with a previous report (6).
    [Show full text]
  • DEET) - Toxfaqs™ CAS # 134‐62‐3
    N,N-Diethyl- meta-Toluamide (DEET) - ToxFAQs™ CAS # 134‐62‐3 This fact sheet answers the most frequently asked health questions (FAQs) about N,N-diethyl-meta-toluamide (DEET). For more information, call the CDC Information Center at 1-800-232-4636. This fact sheet is one in a series of summaries about hazardous substances and their health effects. It’s important you understand this information because this substance may harm you. The effects of exposure to any hazardous substance depend on the dose, the duration, how you are exposed, personal traits and habits, and whether other chemicals are present. HIGHLIGHTS: Exposure to DEET occurs mainly by dermal contact from intentional application to the skin and clothing of consumer products containing DEET. Unintentional inhalation and oral exposure can also occur during normal use. The risk of health effects due to exposure to DEET following recommended application procedures appears to be quite low. DEET has been found in at least 2 of the 1,699 National Priorities List sites identified by the Environmental Protection Agency (EPA). • Workers involved in the manufacture of DEET or of What is DEET? commercial products containing DEET can be exposed to higher levels of this substance. DEET is the chemical N,N-diethyl-meta-toluamide. The pure chemical is a white to amber-color liquid, with a faint aromatic odor. DEET is the • Exposure can occur by using water containing DEET for active ingredient in some common repellents widely used to repel drinking or bathing or swimming in contaminated water. biting pests such as mosquitos and ticks.
    [Show full text]
  • West Nile Virus (WNV) Fact Sheet
    West Nile Virus (WNV) Fact Sheet What Is West Nile Virus? How Does West Nile Virus Spread? West Nile virus infection can cause serious disease. WNV is ▪ Infected Mosquitoes. established as a seasonal epidemic in North America that WNV is spread by the bite of an infected mosquito. flares up in the summer and continues into the fall. This Mosquitoes become infected when they feed on fact sheet contains important information that can help infected birds. Infected mosquitoes can then spread you recognize and prevent West Nile virus. WNV to humans and other animals when they bite. What Can I Do to Prevent WNV? ▪ Transfusions, Transplants, and Mother-to-Child. In a very small number of cases, WNV also has been The easiest and best way to avoid WNV is to prevent spread directly from an infected person through blood mosquito bites. transfusions, organ transplants, breastfeeding and ▪ When outdoors, use repellents containing DEET, during pregnancy from mother to baby. picaridin, IR3535, some oil of lemon eucalyptus or para- Not through touching. menthane-diol. Follow the directions on the package. ▪ WNV is not spread through casual contact such as ▪ Many mosquitoes are most active from dusk to dawn. touching or kissing a person with the virus. Be sure to use insect repellent and wear long sleeves and pants at these times or consider staying indoors How Soon Do Infected People Get Sick? during these hours. People typically develop symptoms between 3 and 14 days after they are bitten by the infected mosquito. ▪ Make sure you have good screens on your windows and doors to keep mosquitoes out.
    [Show full text]
  • Safety Data Sheet Acc
    Page 1/9 Safety Data Sheet acc. to OSHA HCS Printing date 03/24/2019 Version Number 2 Reviewed on 03/24/2019 * 1 Identification · Product identifier · Trade name: DEET · Part number: PST-298 · CAS Number: 134-62-3 · EC number: 205-149-7 · Index number: 616-018-00-2 · Application of the substance / the mixture Reagents and Standards for Analytical Chemical Laboratory Use · Details of the supplier of the safety data sheet · Manufacturer/Supplier: Agilent Technologies, Inc. 5301 Stevens Creek Blvd. Santa Clara, CA 95051 USA · Information department: Telephone: 800-227-9770 e-mail: [email protected] · Emergency telephone number: CHEMTREC®: 1-800-424-9300 2 Hazard(s) identification · Classification of the substance or mixture GHS07 Acute Tox. 4 H302 Harmful if swallowed. Skin Irrit. 2 H315 Causes skin irritation. Eye Irrit. 2A H319 Causes serious eye irritation. · Label elements · GHS label elements The substance is classified and labeled according to the Globally Harmonized System (GHS). · Hazard pictograms GHS07 · Signal word Warning · Hazard-determining components of labeling: N,N-diethyl-m-toluamide · Hazard statements Harmful if swallowed. Causes skin irritation. Causes serious eye irritation. · Precautionary statements Wash thoroughly after handling. Do not eat, drink or smoke when using this product. (Contd. on page 2) US 48.1.26 Page 2/9 Safety Data Sheet acc. to OSHA HCS Printing date 03/24/2019 Version Number 2 Reviewed on 03/24/2019 Trade name: DEET (Contd. of page 1) Wear protective gloves / eye protection / face protection. If swallowed: Call a poison center/doctor if you feel unwell. Rinse mouth.
    [Show full text]
  • Essential Oils Sensory Quality and Their Bioactivity Against the Mosquito Aedes Albopictus Received: 28 February 2018 S
    www.nature.com/scientificreports Corrected: Author Correction OPEN Essential oils sensory quality and their bioactivity against the mosquito Aedes albopictus Received: 28 February 2018 S. Bedini1, G. Flamini2, R. Ascrizzi2, F. Venturi1, G. Ferroni1, A. Bader3, J. Girardi1 & B. Conti 1 Accepted: 2 November 2018 Repellents are a main tool to prevent the outbreak of mosquito-borne diseases that represents a threat Published online: 14 December 2018 for millions of people worldwide. Plant-based products are very promising, low-toxic and eco-friendly alternative to synthetic repellents. Here, we performed an olfactory screening of the essential oils (EOs) of Artemisia verlotiorum Lamotte (Asteraceae), Lavandula dentata L. (Lamiaceae), and Ruta chalepensis L. (Rutaceae) for their possible use as ingredients in topical repellents. The EOs smell profles were then matched with their repellence against the mosquito Aedes albopictus (Skuse) (Diptera Culicidae). To obtain a more complete bioactivity description, we also tested the EOs oviposition deterrence and the larvicidal activity. The best smell profle was associated with A. verlotiorum EO, while R. chalepensis EO showed the lowest overall pleasantness. All the EOs had a signifcant activity as skin repellent against Ae. albopictus, deterred the oviposition in the feld, and exerted a clear larvicidal activity. Beside the best smell profle, A. verlotiorum EO showed also the longest lasting repellent efect, assuring the complete protection of the treated skin against Ae. albopictus for a time 60% longer than the synthetic repellent DEET. Te Asian tiger mosquito, Aedes albopictus (Skuse) (Diptera Culicidae) is ranked among the most invasive mos- quito species in the world1. Native to the tropical and subtropical areas of Southeast Asia, in recent time, Ae.
    [Show full text]
  • West Nile Virus: Basic Questions and Answers
    West Nile Virus: Basic Questions and Answers What is West Nile virus? West Nile virus was first found in the U.S. in 1999 in New York City. Since then, it has spread to most states including Michigan. West Nile virus is spread by the bite of a mosquito that has the virus. Mosquitoes get West Nile virus from biting a bird that has the virus in its blood. After 10 to 14 days, the mosquito can then give the virus to people, birds, or other animals by biting them. West Nile virus is not spread person-to-person like a cold. But, it has been spread from a pregnant mother to her baby, and through breast milk, blood transfusions and organ transplants. What are the symptoms of West Nile virus? Most people who get West Nile virus will not have any symptoms – they won’t even know they have it. Some people may get sick 3 to 14 days after a bite from a mosquito carrying the virus. A small number of people who get West Nile virus will get a mild illness with fever, head and body aches, and sometimes a skin rash and swollen glands. There are no known long-term effects from a mild illness. West Nile virus can cause severe illness known as West Nile encephalitis or meningitis. Symptoms include headache, high fever, stiff neck, disorientation, muscle weakness, coma, and convulsions. A small number of these illnesses have been deadly. But, people do not often get severe West Nile illness. Less than 1% of the people who get West Nile virus will develop a severe illness.
    [Show full text]
  • Mosquitoes Smell and Avoid the Insect Repellent DEET
    Mosquitoes smell and avoid the insect repellent DEET Zainulabeuddin Syed and Walter S. Leal* Honorary Maeda-Duffey Laboratory, Department of Entomology, University of California-Davis, 1 Shields Ave., Davis, CA 95616 Communicated by William S. Bowers, University of Arizona, Tucson, AZ, June 12, 2008 (received for review April 28, 2008) The insect repellent DEET is effective against a variety of medically ants and DEET at the sensory level clearly demonstrated that important pests, but its mode of action still draws considerable DEET attenuation of the olfactory system is a false positive because debate. The widely accepted hypothesis that DEET interferes with the of reduced amounts of stimuli released when repellent and odorant detection of lactic acid has been challenged by demonstrated DEET- are combined in the conventional stimulus delivery cartridges. induced repellency in the absence of lactic acid. The most recent Moreover, we provide convincing behavioral evidence suggesting hypothesis suggests that DEET masks or jams the olfactory system by that repellency of the Southern house mosquito is a matter of direct attenuating electrophysiological responses to 1-octen-3-ol. Our re- detection of DEET in the vapor phase. search shows that mosquitoes smell DEET directly and avoid it. We performed single-unit recordings from all functional ORNs on the Results and Discussion antenna and maxillary palps of Culex quinquefasciatus and found an Single Sensillum Recordings. Given the experimental evidence sug- ORN in a short trichoid sensillum responding to DEET in a dose- gesting that interaction with lactic acid may not be essential for dependent manner. The same ORN responded with higher sensitivity DEET repellency (4, 7), we aimed initially at revisiting the to terpenoid compounds.
    [Show full text]
  • Repellent Activities of Essential Oils and Monoterpenes Against Culex Pipiens Pallens
    Journal of the American Mosquito Control Association, 18(4):348-351,2OO2 Copyright @ 2OOZby the American Mosquito Control Association,Inc. REPELLENT ACTIVITIES OF ESSENTIAL OILS AND MONOTERPENES AGAINST CULEX PIPIENS PALLENS WON-SIK CHOI,I BYEOUNG-SOO PARK,I SAE-KWANG KU? AND SUNG-EUN LEE14 ABSTRACT. Essential oils of Eulcalyptus globulus, Lovender fficinalis, Rosemarinus fficinalis, andThymus vulgaris were examined for their repellent activities against Culex pipiens pallens. A114 essential oils effectively repelled adult mosquitoes on hairless mice. Essential oil of T. vulgaris (thyme) had potent repellent activity within the tested materials, with a protection rate of 91Vo at a concentration of 0.057o topical treatment. Thyme essential oil significantly extended the duration of protection until 3 bites by mosquitoes. With gas chromatog- raphy-mass spectrometry analysis, thyme essential oil was a rich source of 5 monoterpenes, including in de- scending order thymol, p-cymene, carvacrol, linalool, and o-terpinene. These 5 monoterpenes also were assessed to determine their repellent activities to the mosquitoes. o-Terpinene had a potent repellent activity with a protection rate of 97Eo at a concentration of 0.057o topical treatment. Additionally, carvacrol and thymol showed an equivalent level of repellency. A spray-type solution containing 2Vo a-terpinene was tested for its repellent activity against Cx. pipiens. This solution showed stronger repellent activity than the currently used repellent N,N-diethyl-z-methylbenzamide (deet). KEY WORDS Thymus vulgaris, essential oil, Culex pipiens, repellents, d-terpinene INTRODUCTION yl-thio)ethyl)guanidine (eudragit El00; a histamine The control of mosquito vectors is becoming dif- antagonist); polyvinyl-pyrrolidone (povidone); and ficult because of resistance to insecticides (Chandre polyethylene glycol 100 (PEG 100) were kindly pro- et al.
    [Show full text]