Field Report
Entomological field techniques
for mosquito and sand fly
collection
By
Prakash Dhakal
Public Health Microbiol...
Abstract:
Entomological field visit was done. Relationship between vector and causative
agents of some diseases was studie...
become larger after each moult.
During the larval and pupal stage,
mosquitoes remain in the water. Both
these stages are a...
temperature. Their number increase
during warm and humid climates.
Life cycle of mosquito is completed
in water and soil w...
mixed and animal dwellings spending
15 minutes in each house by one
collector using aspirators and flash-
lights.
2. Outdo...
Adult emergence trap was observed
and its usage was learned. It consists
of two compartments. The lower
compartment accomo...
3. Zaim M, Ershadi MR,
Manouchehri AV, Hamdi MR, 1986, ,
" The use of CDC light traps and
other procedures for sampling ma...
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Entomological field techniques for mosquito and sand fly collection: a field report

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Entomological field techniques for mosquito and sand fly collection: a field report

  1. 1. Field Report Entomological field techniques for mosquito and sand fly collection By Prakash Dhakal Public Health Microbiology Central Department of Microbiology Tribhuvan University Kirtipur Nepal
  2. 2. Abstract: Entomological field visit was done. Relationship between vector and causative agents of some diseases was studied. Different entomological methods for collecting mosquitoes and sand flies were observed and handled. Mouth aspirator, BG Sentinel trap, CDC light trap, adult emergence trap and ovitrap were observed and handled. Keywords: Mosquito, Sand fly, equipments, Mouth aspirator, BG sentinel trap, CDC light trap, Adult emergence trap Introduction: Mosquitoes and sand flies are important insect pests and control efforts can be justified when they represent a significant “nuisance” or threat to public health. Mosquitoes are considered a nuisance because they can 1) decrease the quality of life of local residents by annoying and bother people (including adverse reactions to their bites) in and around their homes or in recreational areas or 2) by reducing property values, slowing economic development of an area, reducing tourism, or adversely affecting livestock production in localities that produce large adult populations1 . Different mosquito and sandflies are found to transmit different diseases. Mosquitoes Culex tritaeniorhynchus and Culex gelidae transmit Japanese Encephalitis. Aedes spp. transmits Dengue, Yellow fever and Chikengunya. Anopheles spp. transmits malaria. Sandflies (Phlebotomus spp.) transmit leishmaniasis and sandfly fever. A control of these diseases can only be done by a control in the vector population. Mosquitoes and sand flies both are holometabola insects. Mosquitoes pass through the egg, larval, pupal and adult stages during their life cycle. There are four larval instars. All stages except the egg stage are mobile. Female mosquitoes may lay their eggs either on moist soil or on the surface of water. The 1st-instar larva is very small. As the larvae pass through their four instars, they
  3. 3. become larger after each moult. During the larval and pupal stage, mosquitoes remain in the water. Both these stages are adapted for swimming. The larvae swim as they go to and from feeding to other activities, like swimming to the surface to obtain air. Many people call them 'wrigglers' because of the way in which they swim. The larvae of most species can be seen resting at the surface, hanging from the surface film by their respiratory siphon. The pupal stage looks like an inverted comma. Some people think the pupae look like miniature tadpoles. They use their flattened, paddle-like 'tails' to propel themselves through the water. They do not feed during this transitional stage of development, as they transform from larvae to adults. When mature, the skin of the pupa splits open along its back and the fresh, adult mosquito slowly emerges into the air. After resting on the surface of the water for a few minutes, the adult mosquito usually moves to a sheltered spot close by to allow its outer skeleton and wings to harden. Soon after emergence, mating takes place. Mating usually occurs in mating swarms, typically within 3 to 5 days after the adults emerge. Females are attracted to the mating swarm and soon fertilized. Females mate once, remain fertilized for life and are the only sex to seek blood from hosts. The life cycle of sandflies also includes four stages: egg, larva (4 instars), pupa and adult. The eggs are elongated oval-shaped, pale at first and darkening on exposure to air with a single black “eye spot”. The larvae emerge through a J-shaped fissure and are legless and whitish with a dark head capsule. Those of the first instar can be distinguished by the presence of two caudal bristles, all subsequent instars bearing four. Fourth instar larvae also have a prominent sclerite on the dorsum of the penultimate segment. The pupae are golden brown and are affixed to the surface of the substrate in which they developed by the final larval exuvium. Shortly before emergence the wings and eyes turn black. Male sand flies emerge about 24 h before females, allowing their external genitalia time to rotate 180° to the correct position for mating before females have emerged. Although there have been no studies of sand fly development time in nature, the time from oviposition to adult emergence at ambient temperature is around 4-6 weeks. The population of mosquitoes and sandflies is affected by humidity and
  4. 4. temperature. Their number increase during warm and humid climates. Life cycle of mosquito is completed in water and soil while that of sandflies is completed in moist soil. Control at larval and pupal stage of mosquitoes is feasible while it is not so for sandflies. Larvicides are not very effective for sandflies because of their unlocalised presence in soil. Efforts for vector control are made worldwide. Epidemiology and Disease Control Division of the Ministry of Health and Population of Government of Nepal plans and monitors control of vector of malaria, Japanese encephalitis, kala-azar, etc. Accuracy in mosquito population levels has long been major component of control efforts. Early attempts measuring mosquito populations consisted of counting, capturing and identifying the species attracted humans. Although new techniques provided useful overview of the mosquitoes causing nuisance the residents of given area. Different entomological field techniques used for vector sampling so that a study about vector can be done and planning and monitoring of plan can be done. Objective: To operate different equipments in the field for collecting mosquito and sand fly Swayambhu—Sitapaila area of Kathmandu, Nepal. Methodology: The current study was carried on 17th May 2013 at Swayambhu -Sitapaila area of Kathmandu metropolitan city. Different equipments for sampling of mosquitoes and sandflies were handled. The methodology employed was direct handling and usage of different equipments. These investigations provide information on vector species, their distribution, density, bionomics and susceptibility/resistance to insecticides for vector control. Results and Discussions: Different tools and equipments used in vectors collection were observed and used. The equipments used were aspirator, BG sentinel trap, CDC light trap, ovitrap and adult emergence trap. 1. Indoor hand collection: Indoor hand collections were carried out inside different shelters in human,
  5. 5. mixed and animal dwellings spending 15 minutes in each house by one collector using aspirators and flash- lights. 2. Outdoor hand collection Outdoor collections was similarly attempted outside the house from outside walls, under leaves, vegetation and bushes around cattle sheds and piggeries, and in and around outdoor stored materials spending 30 minutes using aspirators and flash-lights. Mouth aspirator was used for collecting indoor and mosquitoes. It can also be used for collecting sandflies. It consists of mouth piece and rubber tubing. Rubber tubing was placed near a resting mosquito and air was sucked up from mouth piece. This created a negative pressure inside the rubber tube and the mosquito was pulled in. Man hour density of mosquitoes was calculated using the formula for indoor hand collected mosquitoes and sand flies: Man-hour density= (No. of mosquitoes collected/duration in minutes)X 60 minutes Calculation for outdoor hand collected mosquitoes and sand flies: Number of mosquitoes collected per artificial shelter (No. of mosquitoes collected/No. of artificial shelters searched) BG sentinel trap is designed especially for Aedes spp1 . The equipment was set up and connected to electric source. The luring substance in the equipment, octenol, and carbondioxide attract mosquitoes. Negative pressure created by rotating fan inside the trap doesn't allow the mosquitoes to escape. Basically, Aedes mosquitoes are collected in the trap. However, Culex spp are also collected due to their abundant number. CDC (Centre for Disease Control) Light trap is used for sampling Anopheles as well as Culex mosquitoes along with sandfly(Phlebotomus argentipus), causative agent of Leishmaniasis2, 3. CDC light trap consists of light and carbondioxide to attract mosquitoes. It has a fan rotating inside the trap which maintains a negative pressure not letting trapped mosquitoes to escape. It is run for 12 hours from 6 a.m. to 6 p.m.
  6. 6. Adult emergence trap was observed and its usage was learned. It consists of two compartments. The lower compartment accomodates water containing larval stages of mosquitoes. The upper compartment also known as collection cup holds the mosquitoes that emerge from larvae. It has been used to study Culex mosquitoes in urban catch basins5 An ovitrap is a device which consists of a black cylinder with a piece of cardboard. This device is used to control the Aedes mosquito population and as well all other mosquito populations. It can monitor, control and detect Aedes mosquito populations thus acting as an early warning signal to preempt any impending dengue outbreaks.6 The black ovitrap attracts female mosquitoes to lay their eggs. When the eggs hatch and develop into adults, they cannot fly out of the device and die inside the trap. The extensive use of the ovitrap in a community can be used in Aedes population control and effectively reduce the Aedes population in that area. It has been used in countries like Singapore, United States and Hong Kong since the 1970s. Ovitrap index = Number of positive ovitrap × 100 Total ovitraps placed Conclusions: Different equipments ranging from simple to sophisticated equipments for mosquito and sandfly sampling are used. They help in studying relationship between vector and disease, planning and monitoring control measures for vector. References: 1. Ellis R, 2004, Municipal Mosquito control Guidelines, Health Canada, Centre for Infectious Disease Prevention and Control, pg.1-3 2. Maciel-de-Freitas R, Eiras AE, Lourenço-de-Oliveira R, 2006 , , "Field evaluation of effectiveness of the BG-Sentinel, a new trap for capturing adult Aedes aegypti (Diptera: Culicidae)", Journal of the American Mosquito Control, May;101(3):321-5, PMID: 16862330
  7. 7. 3. Zaim M, Ershadi MR, Manouchehri AV, Hamdi MR, 1986, , " The use of CDC light traps and other procedures for sampling malaria vectors in southern Iran", Journal of the American Mosquito Control, Dec;2(4):511-5 PMID: 3507528 4. Dinesh DS, DAS P, Picado A, Davies C, Speybroeck N, Boelaert M, Coosemans M, 2008, "The efficacy of indoor CDC light traps for collecting the sandfly Phlebotomus argentipes, vector of Leishmania donovani", Medical and Veterinary Entomology, Jun;22(2):120-3. doi: 10.1111/j.1365- 2915.2008.00724.x.,PMID: 18498610 5. Hamer GL, Kelly PH, Focks DA, Goldberg TL, Walkers ED, 2011, , " Evaluation of a novel emergence trap to study Culex mosquitoes in urban catch basins", Journal of the American Mosquito Control, Jun;27(2):142-7 PMID:21805846 6. Jakob WL, Bevier GA (1969). "Application of ovitraps in the US Aedes aegypti eradication program". Mosq News 29: 55–62. ISSN 0027- 142X. Advisor ------------------------------------ Dr. Ishan Gautam Lecturer, Tribhuvan Universisty

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