OF ocP/EAcl2.5 ORGANIZATION

ONCHOCERCIASIS CONTROL PROGRAMME IN WEST AFRICA

PROGRAMME DE LUTTE CONTRE L'ONCHOCERCOSE EN AFRIQUE DE L'OUEST

EXPERT ADVISORY COMMITTEE Twelfth session

Ouaeadoueou. l0-14 June l99l

ocP/EAcl2.5 ENGLISH ONLY

ANNUAL REVTEW OF INSECTICIDES

ocP/EACr2.,

rlorld Health OrganlZatlon - Onchocerciasis Control ^Programme - Insectlctoe ^Research Unit

ANNUAL REVIEW OF TNSECTICIDES

l.

Insecttcides in ooerations ano status

of

resistance-

l.l.

Insecticide use

in

t9(D.

In

1990 630,000

liters of

insecticides were used

for the

control

of

^S.

daanosun s.

/. in the

^{Programme area,}

an

increase

of

^120,000

liters over

^the previous year (Table 1). This increase was mostly due

to the

^{prolonged use of}

B.t.H14 when the rainy season was delayed

in

May-July ¹⁹⁹⁰ (Fig. _{1). The amount}

of

^temephos used had increased as ^well,

in

^part due

to

dwindling chlorphoxim,

but also because

of

the onset of full-scale treatments in Sierra Leone, where half

of the

^temephos

and

permethrin used

in the

Western Oprational Area was

sprayed. The cycle

of

^use of the different insecticides followed the usual seasonal

pattern (Fig.2), with

a

^peak

of

permethrin, and secondarily of carbosulfan,

at

the height

of

the rainy season (September);

this

^peak was encompassed by

a

longer peak

of

temephos and chlorphoxim, while B.t.H14 was mostly used

in the

dry season. The relative importance of temephos was greater than appears rn Fig.2 if

one takes into account

its

tong carry.

l.ZStatus

of

resistance

in

lg!D.

Resistance

to

^temephos

in

1990 showed

the

same consistent patterrl as in

the ^previous years, with fixed foci

of

resrstance

of S.

sillsanun populations in the Bafing/Senegal Basin, and

of 5.

^san.:t ipaulr and .9. clannosun s. s. populations _on

the

Lower Comoe Basin.

In

the operational area

only

two tocalized episodes of resistance were found, one on the Sassandra (r^, _dann,lsun s.s., Jan. 1990) and on

(

the Baou16

(S.

sirltattun, Nov. 1990). These

foci

were eliminated

alternative insecticides. The year-round control

of rrver

^basins

by in

reverting to Guinea was

successful,

but

^prevented

the

monitoring

of

susceptibility levels

in this

^area.

Measures

will be

taken

in

1991

to

circumvene

this

^problem.

in

Sierra Leone

susceptibility

to

temephos has decreased over the last

four

^years, but ^temephos

is still

operational. Recent tests have shown low levels

of

resistance

in a

^few

localities.

Resistance

to

chlorphoxim

and

^phoxim

is still

restrrcted

ro tlre

^.S.

sancLipauli

and S.

danrtctsun ^.s.

s.

populations

of the

Lower Comoe Basin. No

resistance to either carbosulfan

or

permethrin has yet been found.

l-3- Ner operational insecticides: ^phoxim and pyraclofc.

The year 1990-1991 was marked by the introduction

of

two new operational rnsecticides, pyraclofos arrd phoxim. both organophosphate compouttds. Thus ^OCP now uses six insecticides: three organophosphates (temephos, phoxtm, pyraclofos),

one

pyrethroid (permethrin),

one

carbamate (carbosulfan)

and one

^blotoxtn

(B.t.u14) (Table 2).

The 50% EC formulation

of

^phoxim was selected

as a

replacement for chlorphoxim, which

is

not available anymore. Phor.im was recently intrbduced ^arld

is

undergoing operational evaluation. ^Phoxim will marnly be used

at

tntermediate

a

-1-

vlorld H€alth organization - onchocerci.si6 Control PrograoD€ - tnsectlciclc Rea.lrch Unit

discharges

in

areas where

there is a risk of

resrstance

of s.

sirbanun to temephos.

In the

screening process pyraclofos showed

no

spontaneous cross- resistance with either temephos

or

chlorphoxim, excellent carry properties, _and acceptable impact

on the

non-target fauna. Although expensive, pyraclofos _has now proved

to be

very efficient

in

operations

after

several cycles

of

use in

different

river

basins

of the

OCP area.

Initial

tevels

of

susceptibility to

pyraclofos were remarkably even throughout

the

OCP area, irrespective of resistance

to

temephos

or

^phoxim. Only S. dannosun s.s. populations _had shown a

slightly

lower level

of

susceptlbility.

A

long series

of l6

weekly cycles of treatment was initiated

at

the end

of

¹⁹⁹⁰ 0n the Lower Marahou6 River

in

order to assess the long-term effect

of

pyraclofos. The black

fly

populations _consisted

of

^{S. daanosun}

s,s.

which were susceptible to temephos, phoxim and pyraclofos. _At the end

of

the experiment the LC95

for

pyractofos was increased

by

a factor of

l3x' along with a slight

increase

of the

LC95

for

ternephos. Thorough investigations are underway

to

^determine the nature

of

this resistance, but

it

^is

thought that under normar conditions (use of shorter cycres, outside of the range

of

distribution

of 5.

dannosun

s.s.)

resistance

to

pyraclofos can be avoided in

the future.

l-{

^The susceptibility rrcnibring progranme and

assiated

research.

Monitoring the susceptibility

of s.

dannosun

s.l.

populations

to

insecticides

is

essential

for both

screening new insecticides

and

extending their. use ⁱⁿ

operations. This

is

why temephos can

still

be used effrcienfly 17 years after its introduction

in

the ocP. The recent development

of

data banks

of

susceptibility

tests and

cytotaxonomic identifications has increased

the

usefulness

of

the mottitoring program. Current treatnlent plans now

rely on

^precise information concerning

the

distribution

of

the species

as

well as

their

^potential

or

^actual

susceptibility

levels. The use of

cytotaxonomy

for the

identification of

susceptibility

test

material has also been extended, allowing

for

instance to

pinpoillt resistance to pyraclofos on one species

of

the

s.

tlannosun complex, even before its onset.

Resistance management is an integral part of ocp vector control operations

and

it

^relies on

a

deep knowledge

of

the mechanisms implied. Therefore

it

^has

been planned to intensify research activities, within oCp and in collaboration with external scientists, on resistance mechanisms and ^genetics.

l-5- l'lanagelrent

of

vecbr

ontrol

operatlons and lnsectcide staks.

A ^process

for

improving the management

of

vector control operations arrd

of

insecticide stocks was initiated

by

ocP and

is

now being imptemented. The

first

step involved

the

development

of a

discharge assessment and ^prediction computer program, _PERLES,

in

collaboration

with

oRSToM. pERLES

is

now

operational

in

the central part

of

the Programme area and

is

being extended in 1991

to

^Guinea and to the Eastern operational Zone. A new management computer program

for

insecticide and aerial operations data has been designed ^(BOA) and

will be operational

in

July. Thls new prograrn

is

better adapted

to thb

recent developments

of

control operations. Flnally,

the

computer progrurm (CREDO)

developed in collaboration with the Universitd du eudbec A Trois-Rlvieres

for

the

[orld ^Ho.Ith Organization - OnchGorcle.lB Control Progrme - Ineecticid. ^Reacarch Unit

optimization

of

treatment operations will also be implemented

in

^Odiennd

in

July

1991.

The quality

of

insecticide stocks

is a critical

factor

in the

success of

vector control activitles. Therefore

a

^quality assessment programme, coordinated

by IRU, has been established

to

ensure the quality

of

operational insecticides at

tlme

of

dellvery

and after fleld

storage. Measures have also been taken to mlnlmlze the lnterval between the two.

2 Rerch rllvltes

^on

ner

lnsectlddee and ner fuimulatlons.

Experlence has shown

ln

OCP that there

ls

a constant ^need

for

identifying new lnsectlcldes

or

new formulations

in order to

^improve

the

efficacy, the selectlvlty or the cost efflclency

of

vector control operations.

Zl.

^Ch€mlcal lns€cdclde.

In

1990 bioassays and

rlver trials

^resulted

in

the selection of

.a 50I

^EC

(

formulatlon

of

^phoxlm

as a

replacement

for

chlorphoxim. Apart from

this

the screenlng

of

alternative carbosulfan formulations proposed

by

FMC

is still

^under

way; the ^purpose

of

these formulatlons

ls to

^{improve the} carry, and eventually selectivity, of operational carbosulfan. The current formulation

of

pyraclofos could

be further

improved (density

and

dispersability

) ^{and new}

formulations are expected this year from Takeda.

Followlng concertation within OCP and with the Ecological Group, the ^need

of

pyrethrold compounds more selective

than

permethrin

has

been clearly

identified. This

screening

is

^performed

in close

collaboration

with

^the

Hydrobiologlcal

Unit of

^OCP, which

is

responslble

for

lmpact studies

on

non-

target fauna. Currently

3

new pyrethrolds are being screened

:

bioresmethrin (Roussel-Uclaf), OMS 3O5O

(ICI) _and

betacyfluthrin

(Bayer). In'

^addltion,

ethofenprox ^(OMS 3002, Mitsul Toatsu), submltted

initlally in

^1983,

is

being re- examined

in

vlew

of

the selectlvlty crlterlon; Mitsui Toatsu

is

expected'to submit

shortly a new, more potent, varlant of this

compound. I

Insectlcldes belonglng

to

new groups

are

under

evaluation:

OMS 3055

(aralkyl-silan group, _Hoechst) and OMS 3055 (2-aryl triazole ^group, Camco). Initial tests show little activity of these insecticides on .S. dannosua s.1., but screening

is stlll

^{pursued. Sampl6s}

of

OMS 3054 (related

to

barbituric acid, Hoechst) are expected shortly, and Amerlcan Cyanamld

ls

^expected

to

submit

an

insecticide belonglng

to a

new group,

the

^{pyrroles (not yet} registered

ln

WHOPES). These

new groups

of

lnsecticides

are

interesting because

of their lack of

^cross-

resistance wlth classical insecticides.

2, _LLtll.i

furmulaUons.

The screenlng

of

^B.t.H14 was continued

ln

1990-1991, wlth

the

hope of identifying more potent formulatlons

for

OCP operatlons. New formulations were

submitted

by

^{Solvay and} Becker Microblal Products ^(BMP). Samples from BMP

were not adequate, but ^new formulatlons from thls company are expected shortly.

Solvay

has

submltted successlve

sets of

samples,

the last

showing some

improvement compared

to

current operatlonal standards. Abbott has

set up

^a

prograrn

for

the lmprovement of their operatlonal formulatlon, whlch

is

currently used

by

OCP. They have sponsored

the

development

of a

new bloassay system

-5-

hbrlcl tl..lth orgnnlzetioo - onclroccrcialle Control Progrrn - In..ctlcido Rer.rch unlt

whlch could tremendously improve the screening

of

B.t.H14 formulations, both in number

of

bloassays performed and standardlzatlon

of

results. This system will be tested on S. daanosuo

s.J. ln

^1991.

23

Ollabordon

rtth

the lndus;tr7.

The need

for ocP to

collaborate

with the industry has

been.clearly identlfied

during the ad

lroc meeting

in

Geneva (June _t99O). The

efforts

^put forward

by

^oCP

to

develop new insecticides and resistance management schemes

are

widely acknowledged

by the

industry and form

the

basis

of a

^conflnued

collaboration.

In order to further

^promote

this

collaboration,

it has

^been

recommended

that a

brochure

be

^produced

about

IRU/OCP,

stating

the achievements,

structure and

objectives

of the unit. This

brochure

will

^be

designed

for industry

representatives

and

coltaborators

of the

^programme.

Meanwhile, specialists from Abbott, FMC, Takeda and Mitsui Toatsu are expected to

visit the program before the end

of

the ^year.

Iablo I. ANNUAL USE OF ]NSECTICIOES SY OCP tolAL lN ll{otJsANl)s (,f Lllt-lls

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J2l, JJ I t lrr r:,

299 71 33 10 I

3AO 8.r 80 I tl

271 92 65 51 ³¹

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Fig I . MONTHLY TOTAL OF INSECTICIOES USEO

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Fig 2. ^{MONTHLY rOTAL OF CUMECS TREATEO}

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