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

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

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

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,

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.

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

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