Pyriproxyfen as a mosquito control tool.

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Pyriproxyfen as a mosquito control tool. DWFP
2005-2007
Greg Devine (Rothamsted, UK) Jeff Stancil, Victor
Lopez, Helvio Astete, John Ramirez, Karin
Escobedo, David Florin (NMRCD Peru) Amy Morrison
(UC Davis, USA) Elvira Zamora, Ernesto Curto,
Gloria Diaz, Wagner Orellana, Elvis Sandoval
(DISA and DIGESA Peru) Stephen Yanoviak
(University of Arkansas, USA)
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Project aims

• DWFP project 2005-2007 Evaluation of Aedes
  aegypti control using pyriproxyfen in Iquitos,
  Peru
• 1. Compare efficacy and longevity among approved
  larvicides (pyriproxyfen, temephos, methoprene
  and Bti).
• With two best-performing formulations, undertake
  full field trials on effects of targeted
  larvicides on larval and adult indices.
• Field trials - effect of broadcasting
  pyriproxyfen in addition to targeted focal
  treatment.
• Examine potential for horizontal transfer by
  exposed adults.
• Examine ecotoxicological effects on non-targets
  in a tropical field environment.
• Some of that DWFP work (2005-2006) already
  reported on
• Devine GJ, Morrison A, Florin D, Lopez V, Astete
  H, Ramirez J, Yanoviak S (2007). Control fo
  Culicines and Anophelines using pyriproxyfen
  field scale evaluations. American Society of
  Tropical Medicine and Hygiene. 56th Annual
  Meeting, Nov 4th 8th Philadelphia 2007
  presentation.
• Devine GJ Cabezas, C Lopez, V Escobedo, K
  Stancil, J Astete, H Morrison, A Alvarez, C
  Zamora, E Vidal, C Yanoviak, S Ramirez, JE
  (2006) The use of pyriproxyfen as a control agent
  for Aedes aegypti in Peru. American Journal of
  Tropical Medicine and Hygiene 75 (5) 200-200,
  Suppl. S presentation. 
• Devine GJ, Zamora-Perea E, Orellana-Rios W,
  Sihuincha M, Vidal-Ore C, Morrison A, Stancil J
  D,. The use of pyriproxyfen for the control of
  Aedes aegypti in Iquitos, Peru. American Society
  of Tropical Medicine and Hygiene. 54th Annual
  Meeting, Dec 11-15th Washington DC 2005
  presentation.

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Pyriproxyfen the most effective of the WHO
approved larvicides against Aedes aegypti
75-fold
750 -fold
16500 -fold
0.0375 g a.i 3,750,000 litres.
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Semi-field trials comparisons of approved
larvicides in 50 litre drums.
Sixty 50 litre drums placed in 10 households.
Four treatments control tested. To give an
approximation of domestic water use, 15 litres
removed every three days, and refilled to 50
litres level every 9 days. Outdoor drums also
diluted by rainfall.
Each month, all larvae and pupae removed from
drums. Each day, all pupae removed from drums.
IDd to species and returned to laboratory for
maintenance until dead or emerged as adults.
Study ran for 7 months. 92-98 of all pupae
collected from control drums emerged successfully
(month 5, n382, month 7 n168). Formulations
and rates for pyriproxyfen and methoprene
suggested and approved by manufacturers.
pyriproxyfen temephos methoprene Bti
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Field trials effects of targeted larviciding,
and of pyriproxyfen broadcast treatments (in
collaboration with UC Davis WHO trial).
The UC Davis / NMRCD group has geo-referenced
30,000 houses in 100s of city blocks. They can
manage full entomological surveys in ca. 1500
houses per month. Our DWFP project used UC Davis
experience to carry out its comparative trials.
GIS map Amy Morrison, UC Davis
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Field trials involving ca 2000 households methods
ID and characterisation of all positive
containers. Collection of all larvae and pupae.
Collection and ID of adult mosquitoes.
Return all pupae to lab, maintain until all dead
or emerged as adults and ID.
Focal treatments larvicides applied in
pre-weighed bags in specific subsets of
containers. Broadcast applications granules
dispensed from belly grinders in gardens and
yards.
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Field trials questions asked
1. The greatest constraint to larvicide efficacy
against Aedes in Iquitos is the diversity of
unmanaged breeding sites, and the rate at which
new sites appear. What are the consequences of
increasing the frequency of application
(treatments 1 and 2 tri-monthly and bimonthly
applications of temephos)? 2. The aim of vector
control is to reduce populations below disease
threshold levels. Can we show reductions in
adult mosquito abundance reflect different
strategies for targeting larvicides (treatments
3 and 4 focal treatment with pyriproxyfen of
containers responsible for 58 and 92 of pupal
production)? 3. Can we assure the local health
authority that pyriproxyfen is at least as
effective as the current strategy used by the
local health authority (treatment 4 92 strategy
is similar to standard DISA practice)? 4. Can
we maximise the impact of pyriproxyfen, whilst
reducing cost and increasing ease of application
by treating gardens and yards (treatment 5 92
strategy broadcast element involves treating
all potential outdoor breeding sites using a
granule applicator)? NB. For the 58 and 92
strategies involving pyriproxyfen, all sites are
revisited every 2 months, but only NEW
containers, NOT previously treated with
pyriproxyfen (i.e. no gauze bags obvious) are
treated. After 6 months, all containers are
re-treated. Surveys all houses fully surveyed
every two months (all wet containers checked,
measured, larvae counted, pupae returned to lab,
adults collected with backpack aspirators). These
are standard surveys developed by UC Davis.
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Field trial results 50 city blocks, ca. 2000
households (post treatment indices
pretreatment indices, transformed data)
pupae n ca. 5000
Overall, ca. 99 of all pupae recovered from
pyriproxyfen treated containers died.



58 pyriproxyfen
92 pyriproxyfen
temephos trimonthly (DISA)
temephos bimonthly (DISA)
92 pyriproxyfen broadcast

• This trial was conducted during a period of
  rapidly increasing indices across the city. Bars
  above the line mean that Aedes indices are
  increasing despite treatment. Bars below the line
  mean that Aedes indices are decreasing. Note that
  there is no untreated control. The comparison
  is with the usual temephos tri-monthly practice.
• Larviciding does impact indices, even when
  breeding sites are myriad (contrary to some
  opinion).
• Increasing frequency of application, increases
  control.
• Coverage has to maximal to exert an effect.
• Pyriproxyfen is at least as good as temephos,
  observations continue.

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Pyriproxyfen is effective in rural environments
and has a favourable environmental profile
studies in 10 disused tropical ponds at 50
ppb. Emergence traps More than 97 of insects
(n10,523) collected were dipterans. The vast
majority were chironomids. Only 70 mosquitoes
were collected in total An. darlingi (1) Cx.
(Mel) spp (34) An. triannulatus (26), other
Anophelines (9) but NO mosquitoes were recovered
from any treated pond until the 10th
week. Larval sampling 1897 mosquito larvae and
pupae were recovered in total from all ponds 55
Culex, 38 Anophelines, 2 An. darlingi. These
were maintained in the lab until death or
emergence. Mortality was high (ca. 30) but, in
comparison, 80 of mosquitoes from treated ponds
failed to develop to the adult stage.
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Ecotoxicology Pyriproxyfen applied in disused
ponds 50ppb Abundance and diversity in
non-target arthropods
Sweep-netting No differences in abundance,
diversity of proportion juveniles adults for
non-target orders (e.g. for hemiptera and
coleoptera) (35,538 insects collected)
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Photographs of aquatic larvae, nymphs and adults
taken from trial ponds, 2006
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Pyriproxyfen horizontal transfer by exposed
adult mosquitoes. Dissemination traps to
artificial breeding sites in local cemetery
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Pyriproxyfen horizontal transfer by exposed
adult mosquitoes. Dissemination traps to
artificial breeding sites in local cemetery
Control period 40 days (with no pyriproxyfen
added to dissemination traps). Treatment period
40 days (with dissemination traps dusted with
pyriproxyfen). Artificial breeding sites (36)
seeded with 25 2/3rd instar laboratory-reared
larvae 900 larvae / test Every day, all pupae
removed from all artificial breeding sites and
returned to lab for monitoring.
Total of 10,800 larvae placed in field
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Conclusions Pyriproxyfen as a mosquito control
tool
Pyriproxyfen is effective at tiny doses for
several months. Pyriproxyfen is more persistent
than other larvicides Pyriproxyfen temephos
methoprene Bti. Under semi-field conditions, it
is effective for ca 5 months. Larviciding with
pyriproxyfen under field conditions does have an
impact on adult indices, even when breeding sites
are myriad. In the field, natural populations of
mosquitoes can transfer lethal doses of
pyriproxyfen to breeding sites. It remains to be
tested in a domestic environment (useful for
myriad, cryptic breeding sites exposure to
pyriproxyfen also effectively sterilises
females) At recommended doses (50 ppb)
pyriproxyfen has profound effects on mosquitoes
and other small bodied diptera, but no
discernible impact on many non-target arthropod
orders (Coleoptera, Hemiptera, Ephemeroptera,
Odonata, Trichoptera).
Recommendation
Pyriproxyfen has been approved for use in
drinking water by the WHO, has a very low
mammalian and environmental toxicity, is
effective at a fraction of the dose of other
larvicides, and is longer-lived. It also has some
interesting characteristics in terms of its
capacity for horizontal transfer. These
characteristics have implications for the
logistics of its use in the field by the
military. The granular formulation (Sumilarv
0.5G) is particularly useful and should be
registered for mosquito control in the wider
environment in the USA.
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Many thanks for the enthusiasm and expertise of
the NMRCD Iquitos technical team..
..the UC Davis Proyecto Dengue team
..the Beneficencia Publica for allowing us access
to the cemetery for several months ..and the
people of Iquitos and surrounds for allowing us
to enter their homes and paddle in their ponds.
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