Urban Area Mosquito Control: Results of Two Experiments

Dr. Grayson C. BrownPublic Health Entomology Laboratory

Department of EntomologyUniversity of KentuckyLexington, KY 40546

Residual Adulticides for Residential Mosquito Suppression

Most homeowners are skeptical that PMPs can provide real mosquito control at the spatial scale of an

individual back yard

Performance data with modern pyrethroids has been lacking in actual suburban

environments.

We studied this technique

Study involved two principal experiments

Will summarize results here

More detail in the May, 2005 and August, 2006 issues of PCT magazine.

Study conducted at 24 residences in Lexington, KY

Median assessed value: $185,750

2004 Lexington, KY median value: $143,100

Average age: 43.4 years

Average lot size: 0.31 A

Treatments applied with a backpack mist blower

Applications made by a certified PMP (Charlie Asbury or Scott Quinton both from All-Rite Pest Control, Lexington)

Objective is to treat mosquito adults’ daytime resting sites

Treat vegetation near home perimeter

Treat vegetation in the yard

Treat vegetation on the perimeter

First Experiment Treatment Specifications

Treatment Water Placebo

Demand®CSSyngenta

TalstarOne™FMC

A. I. Water Lambda-cyhalothrin Bifenthrin

App. Rate --- 0.8 fl. Oz/ gallon 1.0 fl. Oz/gallon

Flow Rate: 14 oz/min (“3”)

Droplet size: 50µ VMD

Avg of 21 minutes a Home

Avg of 6.5 Gallons/Home, or ca. 3.3 gal/1,000 sq. ft treated

Mosquito Monitoring

• Sampled mosquitoes in backyards weekly for 10 weeks (-2…8)

• All sampling after 6 pm

• Mosquito Surveillance– CDC Traps– Human Landing Rate– Gravid Traps– Ovitrap– Sweepnet

Two Mosquito Genera Dominate in Most Kentucky SuburbsAedes Culex

Cause majority of bites to humans

Hide in bushes during day

Many species are primarily nuisance

Mainly bites birds

Hide in tree canopies during day

Primary vectors of WNV, et al.

Human Landing Rate

0

2

4

6

8

-2 -1 0 1 2 3 4 5 6 7 8

Weeks Post Treatment

Mos

quito

Bite

s/10

min

Demand CS TalstarOne Water Placebo

85% reduction after 1 week

73% reduction over 6 weeks

98% Aedes

98% Aedes species

Homeowner experienceHomeowners kept a “diary”

• 1 = We did not notice any mosquitoes.

• 2 = We noticed or were bitten by mosquitoes, but not enough to use repellents or avoid being outdoors.

• 3 = At least some of us were bothered enough by mosquitoes to use repellents or avoid being outdoors.

• 4 = Mosquitoes were very noticeable and were a definite annoyance for most of the week.

• 5 = Mosquitoes were very bad the entire week.

• NA = I was out of town.”

Homeowner ExperienceAverage Homeowner diary rating

1

2

3

-2 -1 0 1 2 3 4 5 6 7 8

Weeks Post Treatment

Ave

rage

Dia

ry R

atin

g

Demand CS TalstarOne Water Placebo

Avoided outdoors

Did NOT avoid outdoors

Gravid Traps

0

15

30

45

60

-1 0 1 2 3 4 5 6 7 8

Weeks Post Treatment

Mos

quito

es/T

rap/

Nig

ht

Demand CS TalstarOne Water Placebo

No Effect

96% Culex (A Principal WNV vector)

96% Culex

Conclusions from this Expt• Mosquito bites were

reduced by 75 – 85% for 6 weeks.

• Degree of control was noticeable by homeowners.

• Nuisance species were controlled but some primary disease vectors were not.

Why the difference between Aedes & Culex?

Insecticide layer & Aedes resting sites

Culex resting sites

8 – 10 feet

Next Questions

• If product could get into the tree canopy, could the Culex disease vectors be controlled in the spatial scale of the residential backyard?

• How sensitive is the method with respect to thoroughness of the coverage?

Launching insecticide into the trees will create chemical trespass problems

Would the treatment be effective against Culex if we could get it up there?

Treated tree lines with Demand

Eight Blocks, each had 100’ lengths with 100’ untreated borders

Used Demand at max label rate and compared to a water control

Height maxed at 25 – 30’

Sampled mosquitoes near ground and at 25’ above ground

Lifted the trap into the tree canopy

Putting it in the canopy locates it close to the Culex mosquitoes

In addition, another CDC trap was mounted at the standard height near the ground

Finally, a Gravid Trap (not shown) was also placed on the ground – These trap females that have already had a blood meal and are looking for a place to lay eggs.

20 –

25

feet

Results?

Canopy: 89% Reduction,

98% Culex

Ground: 58% Reduction,

94% Aedes

Then tried this technique at 24 residential properties in Lexington

Tested 2 techniques against water: Quick/Fast vs. Thorough (including tree canopies).

Treatment Specs Compared Application Technique With Demand CS

Treatment Rate Product Cost Time

Water 0 0 10 min

Quick/Cheap 3.2 g/home $5 - 10 10 min

Slow/Thorough 6.5 g/home $10 – 20 20 min

Results – Mosquito reduction compared with control (2wk post treatment)

Quick Thorough, includes tree spraying

Aedes (Responsible for most bites)

33% 82%

Culex (Primary WNV vector) 0% 85%

Method

Mosquito

CDC Ground Trap Catch

0

20

40

60

80

100

1 2 3 4

Weeks Post Treatment

% S

upre

ssio

n

Thorough Quick

Culex were suppressed in both tree traps and gravid traps

0

100

200

300

400

Cul

ex/tr

ap/n

iight

Tree GravidTrap Type

ControlQuickThorough

Homeowner Opinion After One Month

0

20

40

60

80

100

% S

atis

fact

ion

Throrough Quick Water

Do you believe that the treatment reduced mosquito populations to your satisfaction?

Homeowners spent more time in their backyards

0

20

40

60

80

100

% m

ore

time

spen

t in

back

yard

Thorough Quick WaterPlacebo

75%

27%

Survey taken 4 weeks post treatment

75%

Conclusions

• Culex can be suppressed if the product can get into the tree canopy.

• Thorough coverage with significant volume is critical to suppression of all mosquito species.

• In this study, homeowner satisfaction was NOT a good indicator of mosquito suppression.

Lessons

• Understanding vector behavior is crucial to the success of barrier applications.

• In many situations, “mosquitoes” are a mixture of many species, each with its own behavioral characteristics.

• A treatment that reduces mosquito bites will not necessarily reduce disease risk.