mosquitoes in oklahoma dr. russell wright, prof. emeritus

Mosquitoes in OklahomaMosquitoes in Oklahoma

Dr. Russell Wright, Prof. Emeritus

General Biology of MosquitoesGeneral Biology of Mosquitoes

• Insects that belong to Order DIPTERA which includes all the flies.

• Have four life stages:– Egg -- laid on surface or edge of water.

– Larvae -- live only in water.

– Pupae -- live only in water.

– Adults

EggsEggs

• Laid on singly on surface or edge of water.

• Some species lay eggs in rafts on surface of water.

• Some sp. hatch 24-36 hrs.• Some hatch after one, two

or three years. • Over wintering stage for

some species

LarvaeLarvae

• Four stages: 1st, 2nd, 3rd, 4th instars.

• Called “wrigglers”, very active, come to surface for air.

• Total length 6-12 days. Some species even weeks.

PupaePupae

• Stage that changes from larvae to adult.

• Called “tumblers” very active, come to surface for air.

• Stage lasts from 3-6 days.

Adult (Male)Adult (Male)

• Emerges first

• Feeds on nectar sources for energy.

• Mates within 3 to 7 days and dies

Adult (Females)Adult (Females)

• Emerges and feeds on nectar.

• Mates, usually only once.

• Searches for blood meal.

• Needs blood meal to develop eggs.

• 1-5 blood meals over life of 7 to 28 days.

Mosquito Life Mosquito Life CycleCycle

Mosquito Species Present Mosquito Species Present in Oklahoma:in Oklahoma:

• Approximately 60 known species in Oklahoma. Over 230 species in U.S.

• Usually only 6-8 species will be a nuisance pest in any given area.

Genus and species

• Every species is more different from each other genetically than you and I are from any other human on earth.

• So I will need to use at least Genus names, sometimes species as I refer to biology.

• Think of these names as the folks you know as Jane, Linda, Ann , Tom. Dick, Harry etc.

• However if you think of any of your friends by these names, don’t tell them I told you to do so.

Classification Based on Classification Based on Larval HabitatLarval Habitat

• Flood Water Mosquitoes

• Permanent Water Mosquitoes– Permanent Pool Group– Transient Water Group

• Container Mosquitoes

Larval HabitatLarval Habitat

• Important to know which mosquitoes cause problems and when.

• Identify larval habitats based on adults present.

• Most effective to find and map larval habitats and eliminate or treat in this stage.

Flood Water MosquitoesFlood Water Mosquitoes

• Mosquitoes in Genera Aedes, Ochlerotatus, and Psorophora

• Some species from these three genera are the most important pest species.

• Bite humans, livestock, pets. And can have very large populations in spring and early summer.

• Do not believe that most vector WNV

• Eggs are laid on the soil surface at the edge of standing pools of water that are left from heavy rains or floods.– Often woodland pools; roadside ditches or

low areas along creeks rivers that collect flood water.

• Eggs hatch when flooded by run off from heavy rains or flood water.

Flood Water Mosquitoes (cont.)Flood Water Mosquitoes (cont.)

• Eggs are over wintering stage. In most cases must spend winter in egg case, called diapause stage.

• Can survive in egg stage for several years until flooded.

• However, can have different hatches within several days if increased water levels hatch new eggs.

Flood Water Mosquitoes (cont.)Flood Water Mosquitoes (cont.)

• Adult populations peak in late April, May, and June, some species hatch with late summer fall rains .

• Adults die quickly during hot weather.• Any flooded pools usually dry up too fast to

support larvae in hot weather.• Females most active around sunset or in

shady areas when disturbed.

Flood Water Mosquitoes (cont.)Flood Water Mosquitoes (cont.)

Floodwater Pool – Aedes vexans

Floodwater Pool – Aedes vexans

Permanent Water MosquitoesPermanent Water MosquitoesPermanent Pool GroupPermanent Pool Group

• Genera Anopheles, Coquillettida, Mansonia some Culex sp.

• Found in quiet bodies of freshwater with sunlight, much surface vegetation and very little wave action.

• Shallow edges of ponds, some lakes backwaters of rivers even slow moving streams.

• Never in main lake or pond areas with much wave action.

• Anopheles lay eggs singly on surface of water, each egg with a float.

• Eggs hatch in 24-36 hrs. Many generations a year tend to peak mid late summer

• Adults over winter triggered by photoperiod.

• Deep south perhaps cycle can go all year, slower in winter.

Permanent Pool Group (cont.)Permanent Pool Group (cont.)

• Genera Coquillettidia and Mansonia • Mansonia mosquitoes lay eggs in groups attached to

plant stems underwater; Coquillettidia in rafts on water surface.

• Larvae insert breathing siphon into plant and takes oxygen directly from plant tissues. Cattail marshes and similar type water.

• Appear to have one prolonged generation per year and at least in south over winter in larval stage.

• Not much of a nuisance pest.

Permanent Pool Group (cont.)Permanent Pool Group (cont.)

Permanent Water MosquitoesPermanent Water MosquitoesTransient Water GroupTransient Water Group

• Genera Culex and Culiseta • Canals, long standing ground pools or roadside

ditches, catch basins, storm sewers , clogged sewers long standing irrigation pools, water often becomes very foul polluted for some species others need fairly clean water.

• These mosquitoes lay eggs in rafts on the surface of the water.

• Eggs hatch within 24-36 hours.

Transient Water Group (cont.)Transient Water Group (cont.)

• These mosquitoes normally over winter in the adult stage.

• Adults emerging in late summer or fall do not search for a blood meal, but mate and female searches for sheltered areas to spend winter.– Caves, burrows, sewers, basements etc.

• Populations low in spring peak in mid to late summer. Vary some with species.

CulexCulex spp. Laying Eggs spp. Laying Eggs

• Populations of these mosquitoes low in spring.

• Takes awhile to build large populations.

• Peak abundance July-October.

• Many species prefer birds as hosts.

• Are often best vectors of viruses.

• Bite more readily at night.

Transient Water Group (cont.)Transient Water Group (cont.)

Transient Water Mosquito HabitatTransient Water Mosquito Habitat

Container Mosquitoes

• Certain species in 5-6 Genera• In nature larvae live in tree holes, rock

pools even leaf axils.• Many species now associated with man

made containers or materials that hold water.– Tires, cans, buckets , birdbaths, gutters, pet

water dishes, plant container bottoms that catch water, even cans, paper cups etc.

Typical Container Mosquito HabitatTypical Container Mosquito Habitat

Asian Tiger MosquitoAsian Tiger Mosquito

• Aedes albopictus

• Larvae in containers of any size.

Aedes albopictus Eggs in Container

• Efficient container breeder utilizing available sources.

• Eggs laid on surface of water, on sides of container, and on stick.

• Immediate egg hatch of some eggs, delayed hatch for others.

Asian Tiger MosquitoAsian Tiger Mosquito

• First found in OK 1990-91, Tulsa, SE Counties.

• By 2000 was found in all counties we surveyed.

• Most important pest in most areas.

• Bites in mid to late afternoon.

• Abundant from mid June through Sept.

Distribution of Asian Tiger Distribution of Asian Tiger Mosquito in OklahomaMosquito in Oklahoma

1990-91

Thru 2000

Mosquito Species of Greatest Mosquito Species of Greatest ConcernConcern

• Belong to Genus Culex

• Include C. pipiens/quinquefasciatus, southern house mosquito most likely vector

• C. restuans, C. salinarius, C. tarsalis.

• Note: all are permanent water mosquitoes, populations peak in summer through fall at same time virus activity peaks

• All prefer to feed on birds.

Possible WNV Vector SpeciesPossible WNV Vector Speciesin Oklahoma in Oklahoma

• Bridge vectors to humans & horses.• Culex tarsalis – Cx. salinarius

Permanent transient water but not very stagnant

• Aedes vexans –floodwater; spring through mid summer

• Aedes albopictus• Ochlerotatus triseriatus. Oc.

hendersoni– Container or tree hole species

SurveillanceSurveillance

• Knowledge of the mosquito species in a given area and relative abundance is necessary in planning control measures.

• Some species do not vector WNV, control not as important.

• Accurate records must be kept of surveillance locations.

• Species I.D. is essential.

LarvicidingLarviciding• Controlling mosquito larvae most effective

control measure because life stage is confined to aquatic habitat.

• Water management by drainage or source reduction.

• Larvicides can be used if drainage not available or adequate.

• Not as practical in Oklahoma until we have identified larval sites.