Malaria Vector control CHIMIA 2016, 70, No. 10 721

doi:10.2533/chimia.2016.721 Chimia 70 (2016) 721–729 © Swiss Chemical Society Evaluation of Commercial Agrochemicals as New Tools for Malaria Vector Control

Mark Hoppé*a, Ottmar F. Hueterb, Andy Bywaterc, Philip Weged, and Peter Maienfisch*e

Abstract: Malaria is a vector-borne and life-threatening disease caused by parasites that are transmitted to people through the bites of infected female Anopheles mosquitoes. The vector control market represents a small fraction of the crop protection market and is estimated to be valued at up to $500 million at the active ingredient level. Insecticide resistance towards the current WHOPES-approved products urgently requires the development of new tools to protect communities against the transmission of malaria. The evaluation of commercial products for malaria vector control is a viable and cost effective strategy to identify new malaria vector control products. Several examples of such spin-offs from crop protection are already evidencing the success of this strategy, namely pirimiphos-methyl for indoor residual sprays and spinosad, , novaluron, and pyriproxifen for mosquito larvae control, a supplementary technology for control of malaria vectors. In our study the adulticidal activities of 81 insecticides representing 23 insecticidal modes of action classes, 34 fungicides from 6 fungicidal mode of action classes and 15 herbicides from 2 herbicidal modes of action classes were tested in a newly developed screening system. WHOPES approved insecticides for malaria vector control consistently caused 80–100% mortality of adult Anopheles stephensi at application rates between 0.2 and 20 mg active ingradient (AI) litre–1. Chlorfenapyr, , and showed the expected good activity. Four new insecticides and three fungicides with promising activity against adult mosquitoes were identified, namely the insecticides , , thiocyclam and metaflumizone and the fungicides diflumetorin, picoxystrobin, and fluazinam. Some of these compounds certainly deserve to be further evaluated for malaria vector control. This is the first report describing good activity of commercial fungicides against malaria vectors. Keywords: Adult mosquito screening · Aedes · Agrochemicals · Anopheles · Malaria · Vector control

1. Introduction and organochlorines), as indoor residual cost for a new active ingredient over the sprays (IRS).[3.4] It is noteworthy that all last two decades and has negatively im- The conventional chemical-based these products represent only two distinct pacted interest in minor markets such as crop-protection agrochemical market is modes of actions: inhibition of acetylcho- vector control.[7] currently valued at $51.655 billion and the line esterase ( and carba- Today, an R&D investment of approx- non-crop agrochemical market only $6.322 mates) and disruption of the voltage-gated imately $280 million is necessary to bring billion.[1] The vector control insecticide sodium channels (organochlorines and py- a new crop protection product to market.[8] market represents a small fraction of the rethroids). Resistance towards the current The required R&D investments to develop non-crop market and valued at up to $500 solutions is increasing and already pre- an insecticide specifically for the malaria million at the active ingredient level.[2] sents a major problem. New chemistries vector control market, assuming a broad In the vector control insecticide market targeting new sites of action are urgently range of adulticidal applications and glob- only six insecticides, all , are needed to enable rotation of products with al registration, is estimated to be $70–150 recommended for use in insecticide treated different modes of action to manage resist- million,[9] which is only marginally lower nets (ITNs) and thirteen insecticides, be- ance and to secure the best possible pro- than for a broad spectrum crop protection longing to only four chemical classes (py- tection of people at risk from vector-borne compound, however, the sales potential is rethroids, organophosphates, disease. markedly less. Furthermore, the time taken Considerable change has occurred in to perform the necessary research and de- the agrochemical industry since the time velopment work to introduce a new prod- when pyrethroids, such as [5,6] in uct onto the market would not differ sig- 1987, were introduced as new tools into the nificantly from the 10–12 years required d *Correspondence: Prof. Dr. P. Maienfisch , [8] Dr. M. Hoppéa vector control market. Consolidation with- for the agricultural sector. It is therefore E-mail: [email protected], in the industry has resulted in a significant not unsurprising that to date all the active [email protected] reduction in the number of research-driven ingredients used for malaria vector control Syngenta Crop Protection AG agrochemical companies. Additionally, the market are spin-offs from agricultural us- aInsecticide Research Biology, Stein Research Centre, Schaffhauserstrasse, CH-4332 Stein, Switzerland focus of the leading companies has been es, and that vector control R&D is not a bInsecticide Research Chemistry, Stein Research Cen- triggered by growers’ needs in the main high priority for major agrochemical com- tre, Schaffhauserstrasse, CH-4332 Stein, Switzerland market regions of Latin America, Asia, US panies. cLawn & Garden R&D, Schwarzwaldallee 215, CH-4002 Basel, Switzerland and Europe and research was concentrated Many of the novel insecticides recent- dChemical Research Biology, Jealott’s Hill Inter- on delivery of broad-spectrum blockbust- ly introduced to the market have been de- national Research Centre, Bracknell, Berkshire, er compounds, as well as novel seeds and signed to have good plant-systemic prop- RG42 6EY, UK traits. This development has also been in- erties. The physical-chemical properties eCrop Protection Research, Schwarzwaldallee 215, CH-4002 Basel, Switzerland fluenced by the steady increase in the R&D required for this are high water solubility 722 CHIMIA 2016, 70, No. 10 Malaria Vector control

and low logP. Conversely ITN and IRS thrin, , etofenprox and perme- 129 insecticides in order to identify those products require a high degree of tarsal thrin; DDT (sodium channel modulator); having the best chance to potentially de- contact activity which is typically associ- the organophosphates (acetylcholinester- liver a new larvicide and/or adulticide for ated with compounds with entirely differ- ase inhibitors) , and mosquito control. Several interesting can- ent physical-chemical properties – notably pirimiphos-methyl; and the carbamates didates were discussed, however, it was high logP – such as are found in the py- (acetylcholinesterase inhibitors) bendio- also concluded that a full risk assessment rethroid insecticides.[10] Furthermore, if a carb and .[13–15] New tools for ma- study was required for a final judgement. compound is to be considered for inclusion laria vector control are urgently required to Furthermore, crop protection companies within an ITN, it must also be thermally complement the current arsenal of vector such as BASF, Bayer, Sumitomo, Syngenta stable at the temperatures required to melt control products for resistance manage- and others have performed their own stud- and extrude the polymer. ment and to effectively protect people from ies to evaluate the potential of their com- Our research has found that contact risks of vector borne diseases. mercial insecticides for additional uses in activity and rapid knockdown is relatively Several research groups and crop pro- vector control over the last two decades rare amongst insecticide chemistries. For tection companies have sought to evaluate (see also Table 1 below). example, the current leading class of insec- commercial insecticides for mosquito con- The strategy for repurposing active ticides, the , are highly sys- trol over the last few years. In 2006, Scott ingredients with unique formulations has temic which facilitates use patterns such et al.[16] reported on the toxicity of a small already resulted in the development of se- as soil and seed treatment applications, but series of novel insecticides against Aedes ries of compounds for malaria vector con- these chemicals often lack significant con- aegypti and concluded that chlorfenapyr, trol such as pirimiphos-methyl (organo- tact activity and are therefore less suitable , indoxacarb, and imida- phosphate, acetylcholinesterase inhibitor) for malaria vector control.[11] Furthermore, cloprid warranted further evaluations as lar- for IRS;[15] and spinosad (fermentation the implications for disease transmission of vicides; diafenthiuron and chlorfenapyr for product, nicotinic acetylcholine receptor slower acting classes such as pyrazolines control of adult mosquitoes; and pyriprox- allosteric modulator), diflubenzuron (ben- and pyrroles must be considered.[12] The yfen as potential mosquito growth regula- zoylurea, chitin biosynthesis inhibitor), requirement for an enduring effect from an tor. In 2008 Pridgeon et al.[17] assessed the novaluron (benzoylurea, chitin biosynthe- IRS treatment is also at odds with many of relative potency of 19 pesticides against sis inhibitor) and pyriproxifen (juvenile the contemporary insecticidal chemistries adult mosquitoes including Anopheles hormone mimic, ) which have been optimized to reduce lon- quadrimaculatus and found fipronil to for mosquito larvae control,[19] a supple- gevity for environmental reasons. have higher activity than , and mentary technology to control malaria Despite this, some commercial crop abamectin, , , carba- vectors.[20] However, this strategy has not protection products might be suitable for ryl, spinosad and chlorfenapyr to be only yet resulted in a new compound for ITN. repurposing as new malaria vector con- slightly less potent than permethrin against In addition, a series of commercial insec- trol solutions. This strategy would benefit Anopheles quadrimaculatus. Furthermore ticides are currently under WHOPES tech- from the already established knowledge their study revealed that different species nical evaluation for malaria vector control base, e.g. the registration dossier in rele- of mosquitoes had different susceptibility (Table 1, Fig. 1).[21] This list includes the vant areas such as chemistry, production, to pesticides. Recently Devillers et al.[18] insecticides chlorfenapyr,[22–25] clothiani- and product safety which ultimately would applied the SIRIS multicriteria analysis to din,[26,27] and pyriproxifen.[28–31] result in strongly reduced R&D costs and registration timelines.

2. Evaluation of Commercial Agrochemicals for Control of Adult Malaria Vectors

Currently only 13 insecticides, belong- Chlorfenapyr Pyriproxifen ing to four chemical classes and represent- American Cyanamid (now BASF) Takeda (now Sumitomoand Bayer) Sumitomo ing only two distinct modes of actions, Chemical class: Phenylpyrrol Chemical class: Chemical class: Juvenile hormone analogue are WHOPES approved for malaria adult MOA: Uncoupler of oxidative MOA: Modulator of nAChR MOA: Insect growth regulator phosphorylation vector control. These are the pyrethroids (mode of action: sodium channel modula- Fig. 1. Structures of new commercial insecticides currently under WHOPES evaluation for malaria tors) lambda-, alpha-cyperme- vector control.

Table 1: New commercial insecticides currently under WHOPES evaluation for malaria vector control

Product Active Ingredient (AI) Company Application Current phase Ref. SumiShield WG Clothianidin Sumitomo Chemical IRS 1[25], [27] Mixture of deltamethrin 1[26] Fludora Fusion WP-SB Bayer CS IRS and clothianidin Mixture of alpha- Interceptor G2 LN BASF ITN 2[21] and chlorfenapyr SumiLarv Pyriproxifen Sumitomo Chemical Larvicide 2-3 [27], [30] Mixture of permethrin Olyset Duo Sumitomo Chemical ITN 3[27] and pyriproxifen Malaria Vector control CHIMIA 2016, 70, No. 10 723

3. ACTELLIC® 300CS (Pirimiphos- Fig. 2. Pirimiphos- methyl) for Control of - methyl: The active resistant Mosquitoes ingredient of ACTELLIC 300CS – At Syngenta the repurposing of com- a new malaria vector control tool for IRS mercial insecticides for control of adult application. malaria vectors has delivered ACTELLIC 300CS, a new solution for long-lasting control of pyrethroid resistant mosquitoes 48 h after application were further tested of ≤200 mg AI litre–1. The results of our after indoor residual spraying (IRS), and against a pyrethroid susceptible strain of secondary screening against a pyrethroid has demonstrated the attractiveness of this Anopheles stephensi for adult knockdown tolerant strain of Anopheles stephensi is strategy. activity and mortality 24 and 48 h after shown in Table 5. A total of 9 compounds ACTELLIC 300CS is a new malaria application at concentrations of 200, 20, 2 – 6 insecticides (Fig. 4) and 3 fungicides vector control tool for IRS application.[32] and 0.2 mg AI litre–1. (Fig. 5) displayed activity comparable to It is based on the active ingredient (AI) the WHOPES approved insecticides for pirimiphos-methyl (Fig. 2) and shows malaria vector control. high insecticidal efficacy and long resid- 5. Bioassays against Adult Aedes ual activity against pyrethroid-resistant aegypti and Anopheles stephensi 6.1 WHOPES Approved Insecticides mosquitoes.[33,34] Pirimiphos-methyl is an for Malaria Vector Control insecticide introduced The compounds were applied to the The pyrethroids etofenprox, deltame- to the crop protection market by Syngenta base of wells as solutions in ethanol. After thrin, lambda-cyhalothrin and al- in 1970, where it was originally used as the ethanol had evaporated five adult fe- pha-cypermethrin consistently caused broad-spectrum insecticide in a wide range male mosquitoes, three to five days old 80–100% mortality between 0.2 and 2 mg of crop and non-crop applications. and non-blood fed, were placed in a treat- AI litre–1 and knockdown activity at ap- The project to evaluate the potential of ed well, then a retaining lid was used to proximately 2 mg AI litre–1 against Aedes pirimiphos-methyl for the control of adult prevent escape. Lids of the tissue culture aegypti and Anopheles stephensi (Table vectors via IRS and to develop a specif- plates were modified to hold small sections 5). Overall, lambda-cyhalothrin showed ic formulation for this use started in 2008 of cotton wool over each well in order to the greatest potency, whereas permethrin with funding from the Innovative Vector allow air exchange. The infested plates was somewhat weaker than the other py- Control Consortium (IVCC) and was suc- (Fig. 3) were held with the base at an angle rethroids. Adult mortality and knockdown cessfully completed by the end of 2012. of 60 degrees to the horizontal in a con- activity of the and Modern micro-encapsulation technology trolled environment chamber at 26 °C and the organophosphates fenitrothion and was used to develop ACTELLIC 300CS, 60% relative humidity. The mosquitoes pirimiphos-methyl were also in the range a formulation capable of providing at least were assessed for knockdown one hour of 0.2 and 2 mg AI litre–1. Only DDT with after introduction. Then, a small quantity an LC of 20 mg AI litre–1 was somewhat 9 months’ control on surfaces encountered 80 in African habitations. By comparison, of 10% sucrose solution was provided as weaker in our assays. From these data we a source of food and water. Mortality was concluded that compounds with LC val- current alternatives to pyrethroids typi- 80 cally last only for three months after ap- assessed 24 and 48 h after introduction ues of ≤20 mg AI litre–1 deserve further plication, resulting in additional costs and and recorded as LC values indicating the evaluation as potential candidates for IRS 80 complexity for malaria programs. lowest concentration where at least 80% of or ITN applications in malaria vector con- the mosquitos were dead. A mosquito was trol. Selection criteria to be considered in recorded as ‘dead’ if it was unable to right such an evaluation include the ease of for- 4. Evaluation of Commercial itself when knocked onto its back or side. mulation and polymer coating or incorpo- Agrochemicals for Control of Adult ration, activity and durability of the treated Malaria Vectors polymer or the IRS formulation, potential for cross-resistance, cost efficiency, toxic- In our study to evaluate the potential ity, and ecotoxicity. of commercial agrochemicals for malar- ia vectors control we included 81 insec- 6.2 Other Insecticides ticides (including 9 WHOPES approved Products belonging to twelve mode of insecticides for reference) representing action classes displayed activity at 200 mg 23 insecticidal mode of action classes.[34] AI litre–1 in the primary test against Aedes Furthermore, we have tested 34 fungicides aegypti (Table 2). No active compounds from 6 fungicidal mode of action classes[35] were identified amongst juvenile hormone and 15 herbicides from 2 herbicidal mode mimics, TRPV channel modulators, mite of action classes.[36] These fungicides and growth inhibitors, inhibitors of chitin bi- herbicides were included because their osynthesis type 0, moulting disruptors, modes of action are also of relevance to Fig. 3. Syngenta 12-well microtitre plate adult ecdysone receptor agonists, mitochondrial insect control and could be of interest in mosquito screening assay. complex I inhibitors, mitochondrial com- vector control. plex II inhibitors, mitochondrial complex For the evaluation of the selected agro- III inhibitors, ACCase inhibitors, as well chemicals a tiered screening approach 6. Results and Discussion as among the tested compounds with un- was applied. The adulticidal activity of all known modes of action. These findings compounds was initially accessed against In our primary test 37 insecticides confirmed that mainly compounds affect- an insecticide susceptible strain of Aedes (Table 2), 7 fungicides (Table 3) and 1 her- ing the insect nervous system offer the aegypti. Compounds that caused mortali- bicide (Table 4) were found to be active greatest potential to deliver adult control ty at a concentration of ≤200 mg AI litre–1 against Aedes aegypti at a concentrations of mosquitoes. 724 CHIMIA 2016, 70, No. 10 Malaria Vector control

GABA-gated chloride channel block- ers: Endosulfan and fipronil (Fig. 4) were highly potent against mosquitoes, but both lacked knockdown activity against Anopheles stephensi. Fipronil was exten- sively evaluated for mosquito control, but has not yet entered the market, most prob- ably due to stewardship issues around its Carbosulfan Endosulfan Fipronil use in or on a bed net. The close analogue Origin:FMC Origin:Höchst(now Bayer) Origin:Rhone-Poulenc (now BASF) ethiprole showed much weaker activity Chemical class: Carbamate Chemical class: Organochlorine Chemical class: Phenylpyrazole a) LC An.stephensia):20 a) than fipronil. The organochlorine endo- LC80 An.stephensi :<0.2 80 LC80 An.stephensi :2 Knockdownactivityb) No knockdownactivityb) No knockdownactivityb) sulfan was biologically active, but showed MoA: AChE inhibitor MoA: GABA-gated chloride MoA: GABA-gated chloride channel blocker channel blocker cross-resistance to , and this re- sistance mechanism is widespread in field mosquito populations. Furthermore, it has been classified as a persistent organ- ic pollutant (POP) under the Stockholm Convention and should therefore not be considered for use in vector control. nAChR competitive modulators: The Acetamiprid Thiamethoxam Chlorfenapyr neonicotionoids are currently the most Origin:Nippon Soda Origin:Ciba(now Syngenta) Origin:AmericanCyanamid (now BASF) successful class of insecticides in crop Chemical class: Neonicotinoid Chemical class: Neonicotinoid Chemical class: Pyrrol protection. Their physical-chemical prop- a) a) a) LC80 An.stephensi :20 LC80 An.stephensi :20 LC80 An.stephensi :2 No knockdownactivityb) No knockdownactivityb) No knockdownactivityb) erties, which confer plant systemicity, are MoA: Modulator of nAChR MoA: Modulator of nAChR MoA: Uncoupler of oxidative not ideal for adult vector control. Despite phosphorylation this two neonicotionoids, namely acetam- iprid and thiamethoxam, displayed good activity (LC = 20 mg AI litre–1) against 80 Anopheles stephensi (Fig. 4). Imidacloprid and were only weakly active, and the most recent market products, sul- foxaflor, flupyradifurone and the develop- ment product triflumezopyrim were not Thiocyclamhydrogenoxalate Metaflumizone active at 200 mg AI litre–1 in our assays. Origin:Sandoz(now Arystaand Nippon Kayaku) Origin:Nihon Nohyaku(licensed to BASF forsomecountries) Chemical class: Nereistoxinanalogue Chemical class: Hydazinecarboxamide All tested neonicotinoids lacked knock- a) a) LC80 An.stephensi :20 LC80 An.stephensi :20 down activity. Knockdownactivityb) No knockdownactivityb) nAChR allosteric modulators: The MoA: BlockerofnAChR MoA: Blockerofvoltage-dependent Na channel fermentation product spinosad and its Fig. 4. Most active insecticides for the control of adult Anopheles stephensi beyond the WHOPES semi-synthetic analogue spinetoram dis- approved compounds. a) LC in mg AI litre–1 against Anopheles stephensi after 48 h – lowest played only weak activity against adult 80 measured concentration at which at least 80% of the mosquitoes were killed. b) Knockdown mosquitoes. Their strength is more on lar- against Anopheles stephensi determined after 1 h; concentration ≤ 200 mg AI litre-1 at which at vicidal activity. least 80% of the mosquitoes showed knocked-down. nAChR channel blockers: Thiocyclam (Fig. 4), an analogue of the natural toxin , showed knockdown activi- ty and mortality at 20 AI mg litre–1 and reached the performance level of DDT. In our study thiocyclam was one of the most efficacious commercial insecticides not yet used in malaria vector control. However, it Diflumetorim Picoxystrobin Fluazinam is questionable if the thermal stability of Origin:Ube (now SDSBiotech) Origin:Zenca (now E.I. Du Pont de Nemours) Origin:IshiharaSangyo Kaisha this compound would be sufficient for in- Chemical class: Pyrimidine Chemical class: Strobilurin Chemical class: Pyridine clusion within an ITN. Its analogue cartap a) a) a) LC80 An.stephensi :20 LC80 An.stephensi :20 LC80 An.stephensi :20 Knockdownactivityb) Knockdownactivityb) Knockdownactivityb) was only weakly active. MoA: Mitochondrialcomplex I MoA: Mitochondrialcomplex III MoA: Uncoupler of oxidative GluCl allosteric modulators: In our electron transportinhibitor electron transportinhibitor phosphorylation test system the fermentation product abamectin and its semi-synthetic analogue Fig. 5. Most active fungicides for the control of adult Anopheles stephensi. a) LC in mg AI litre–1 80 emamectin benzoate were clearly less against Anopheles stephensi after 48 h – lowest measured concentration at which at least 80% of the mosquitoes were killed. b) Knockdown against Anopheles stephensi determined after 1h; active than permethrin and other concentration ≤ 200 mg AI litre–1 at which at least 80% of the mosquitoes showed knocked-down. WHOPES approved products. Based on our results the potential of these com- pounds for adult vector control is esti- AChE inhibitors: In our testing system considerations do not suggest further eval- mated to be low. the carbamate carbosulfan (Fig. 4) was uation of carbosulfan for malaria vector Uncouplers of oxidative phosphoryla- found to be as potent as the WHOPES ap- control. and were tion: Chlorfenapyr (Fig. 4) was active at 20 proved organophosphates and carbamates, ≥100 times less active than the WHOPES mg litre–1 and 2 mg litre–1 24 and 48 h after but cross-resistance and product safety approved AChE inhibitors. infestation, respectively, however, it did Malaria Vector control CHIMIA 2016, 70, No. 10 725

Table 2. Activity of commercial insecticides against Aedes aegypti

Mode of actiona IRAC Cmdps active against LC a,b Cmpds not active against Aedes 80 class Aedes aegypti at LC < 200b aegypti LC ≥ 200b 80 80 Acetylcholinesterase (AChE) inhibitors 1Bendiocarb c) 2 Carbosulfan 2 Formetanate 200 Pirimicarb 200 Fenitrothion c) < 0.2 Pirimiphos-methyl c) 2 GABA-gated chloride channel blockers 2Endosulfan < 0.2 Fipronil < 0.2 Ethiprole 2 Sodium channel modulators 3 lambda-Cyhalothrin c) < 0.2 alpha-Cypermethrin c) 2 Deltamethrin c) < 0.2 Etofenprox c) 2 Permethrin c) 2 DDT c) 20 Nicotinic acetylcholine receptor 4Acetamiprid 200 Clothianidin, (nAChR) competitive modulators Imidacloprid 20 Nitenpyram 200 Thiamethoxam 200 Flupyradifurone 200 200 Triflumezopyrim 200 Nicotinic acetylcholine receptor 5Spinosad 200 (nAChR) allosteric modulators Spinetoram 20 Glutamate-gated chloride channel 6Abamectin 20 - (GluCl) allosteric modulators Emamectin benzoate 20 Juvenile hormone mimics 7– –, Chordotonal organ TRPV channel 9, 29 ––Pymetrozine, Pyrifluquinazon, modulators Flonicamid Mite growth inhibitors 10 ––Clofentezine, Hexythiazox, Etoxazole Inhibitors of mitochondrial ATP 12 Diafenthiuron 200 Fenbutatin oxide, Propargite, synthase Azocyclotin 200 Cyhexatin 200 Uncouplers of oxidative phosphorylation 13 Chlorfenapyr 20 Nicotinic acetylcholine receptor 14 Thiocyclam hydrogenoxalate 20 (nAChR) channel blockers Cartap 200 Inhibitors of chitin biosynthesis, type 015– –Chlorfluazuron, Diflubenzuron, Flucycloxuron, , Noviflumuron, Teflubenzuron, Triflumuron Inhibitors of chitin biosynthesis, type 116Buprofezin 20 – Moulting disruptors 17 ––Cyromazine Ecdysone receptor agonists 18 ––Chromafenozide, Halofenozide, Methoxyfenozide, Mitochondrial complex III electron 20 ––Acequinocyl, Fluacrypyrim, transport inhibitors Bifenazate Mitochondrial complex I electron 21 ––Fenazaquin, Fenpyroximate, transport inhibitors Pyridaben, Pyrimidifen, Tolfenpyrad Voltage-dependent sodium channel 22 Indoxacarb (racemic) 200 blockers Metaflumizone 200 Inhibitors of acetyl CoA carboxylase 23 ––Spirodiclofen, Spiromesifen, (ACCase) Spirotetramat Mitochondrial complex II electron trans- 25 ––Cyflumetofen, Cyenopyrafen, port inhibitors Pyflubumide receptor modulators 28 200 200 Unknown UN –Bromopropylate, , Pyridalyl aFor details on the mode of action classes and the products see ref, [35]; bLC : Lowest applied dosage in mg AI litre–1 which provides >80% mortality 80 after 48 h. Concentrations tested: 200, 20, 2 and 0.2 mg AI litre–1; cWHOPES approved chemicals for bed net or indoor residual sprays for malaria vector control. 726 CHIMIA 2016, 70, No. 10 Malaria Vector control

Table 3. Activity of commercial fungicides against Aedes aegypti

Mode of actiona FRAC Cmdps active against Aedes LC a,b Cmpds not active against 80 code aegypti at LC < 200b Aedes aegypti LC ≥ 200b 80 80 Mitochondrial complex I electron transport C1 Diflumetorim 200 inhibitors Mitochondrial complex II electron C2 Penthiopyrad 200 Bixafen, Boscalid, Carboxin, transport inhibitors (SDHI) Fluopyram, Flutolanil, Fluxa- pyroxad, Furametpyr, Mepronil, Penflufen, Mitochondrial complex III electron C3 Kresoxim-methyl 20 Azoxystrobin, Coumoxystrobin, transport inhibitors at Qo site Flufenoxystrobin 20 Dimoxystrobin, Enoxastrobin, Orysastrobin 20 Fenaminstrobin, Fluoxastrobin, Picoxystrobin 200 Mandestrobin, Metominostrobin, Pyraclostrobin, Pyrametostrobin, Pyraoxystrobin, Triclopyricarb, Trifloxystrobin, Famoxadone, Fenamidone, Pyribencarb Mitochondrial complex III electron C4 --Cyazofamid transport inhibitors at Qi site Uncouplers of oxidative phosphorylation C5 Fluazinam 200 Mitochondrial complex III electron C8 --Ametoctradin transport inhibitors at Qo site, stigmatellin binding sub-site aFor details on the mode of action classes and the products see ref. [36]; bLC : Lowest applied dosage in mg AI litre–1 which provides >80% mortality 80 after 48 h. Concentrations tested: 200, 20, 2 and 0.2 mg AI litre–1.

Table 4. Activity of commercial herbicides against Aedes aegypti

Mode of actiona HRAC Cmdps active against Aedes LC a Cmpds not active against Aedes 80 class aegypti at LC < 200b aegypti LC ≥ 200b 80 80 Inhibitors of acetyl CoA carboxylase A- -Fluazifop (ACCase) Inhibition of protoporphyrinogen oxidase EHalosafen 200 Acifluorfen (acid), Bifenox, (PPO) Butafenacil, Flumiclorac-pentyl, Flumioxazin, Fomesafen, Lactofen, Oxadiazon, Oxyfluorfen, Pentoxazone, Pyraflufen-ethyl, Saflufenacil, Sulfentrazone aFor details on the mode of action classes and the products see ref. [37]; bLC : Lowest applied dosage in mg AI litre–1 which provides >80% mortality 80 after 48 h. Concentrations tested: 200, 20, 2 and 0.2 mg AI litre–1. not show adult knockdown activity. The sidered to offer an attractive potential for any activity against Aedes aegypti at 20 compound is currently under evaluation as vector control. mg AI litre–1 (Table 2). This confirms the a solo formulation for IRS and in mixture value of evaluating commercial fungicides with alpha-cypermethrin for LLIN appli- 6.3 Fungicides or fungicidal chemical classes possessing cation by BASF (Table 1). Products belonging to four modes of a mode of action relevant in the field of Voltage-dependent sodium channel action classes displayed activity at 200 mg insect control. blockers: Metaflumizone (Table 4) is slow litre–1 in the primary test against Aedes ae- Mitochondrial complex II electron acting and shows moderate activity 24 h gypti (Table 3). No active compounds were transport inhibitors (SDHI): Among the after infestation. Indoxacarb was only ac- identified amongst mitochondrial complex SDHI inhibitors tested only penthiopyrad tive against Aedes aegypti, but not against III electron transport inhibitors acting at showed some weak activity against adult Anopheles stephensi 24 h after infestation. the Qi site or the Qo site (stigmatellin bind- mosquitoes. It can be concluded that this Compounds from the mode of action ing sub-site). class of compounds is of very low potential classes, mitochondrial ATP synthase in- Mitochondrial complex I electron for malaria vector control. hibitors (difenthiuron, azocyclotin, cyhex- transport inhibitors: Diflumetorin (Fig. 5), Mitochondrial complex III electron atin), chitin biosynthesis inhibitors type the only fungicidal compound tested from transport inhibitors at Qo site: 20 com- 1 () and ryanodine receptor this mode of action class, was active at 20 mercial products were tested among which modulators (chlorantraniliprole, cyan- mg AI litre–1, whereas all the insecticides the strobilurin kresoxim-methyl, was traniliprole) showed only weak activity tested with this mode of action, namely found to possess weak activity, and picox- and did not display knockdown activities. fenazaquin, fenpyroximate, pyridaben, ystrobin (Fig. 5), was the most efficacious Therefore, none of these products is con- pyrimidifen and tolfenpyrad did not show compound controlling adult Anopheles Malaria Vector control CHIMIA 2016, 70, No. 10 727

Table 5. Activity of agrochemicals against Aedes aegypti and Anopheles stephensi Compound Aedes aegypti Anopheles stephensi KD LC LC LC LC 80 80 80 80 80 Adult Adult mortality, Adult Adult mortality, Adult mortality, knockdowna 24 hb knockdowna 24 hb 48 hc Bendiocarbe) 222≤ 0.2 ≤ 0.2 Carbosulfan 222≤ 0.2 ≤ 0.2 Formetanate > 200 200 > 200 200 200 Pirimicarb > 200 200 200 20 20 Fenitrothione) 2 ≤ 0.2 ≤ 0.2 ≤ 0.2 ≤ 0.2 Pirimiphos-methyle) > 200 22≤ 0.2 ≤ 0.2 Endosulfan ≤ 0.2 ≤ 0.2 > 200 20 20 Fipronil > 200 ≤ 0.2 > 200 22 Ethiprole >200 2>200 > 200 200 lambda-Cyhalothrine) 2 ≤ 0.2 2 ≤ 0.2 ≤ 0.2 alpha-Cypermethrine) 2220 22 Deltamethrine) 2 ≤ 0.2 222 Etofenproxe) 20 2222 Permethrine) 20 2 20 20 20 DDTe) 20 20 20 20 20 Acetamiprid > 200 200 > 200 20 20 Imidacloprid > 200 200 > 200 > 200 200 Nitenpyram > 200 200 > 200 200 200 Thiamethoxam > 200 200 > 200 200 20 Flupyradifurone > 200 200 > 200 > 200 > 200 Sulfoxaflor > 200 > 200 > 200 > 200 > 200 Triflumezopyrim > 200 > 200 > 200 > 200 > 200 Spinosad > 200 200 > 200 200 200 Spinetoram > 200 200 > 200 200 200 Abamectin > 200 200 > 200 200 20 Emamectin benzoate > 200 200 > 200 > 200 200 Diafenthiuron > 200 > 200 > 200 200 200 Azocyclotin > 200 200 > 200 > 200 200 Cyhexatin > 200 200 > 200 200 200 Chlorfenapyr > 200 20 > 200 20 2 Thiocyclam hydrogenoxalate 200 20 20 20 20 Cartap 200 200 > 200 200 200 Buprofezin > 200 20 > 200 > 200 > 200 Indoxacarb (racemic) > 200 > 200 > 200 > 200 > 200 Metaflumizone > 200 > 200 > 200 > 200 20 Chlorantraniliprole > 200 200 > 200 > 200 > 200 Cyantraniliprole > 200 > 200 > 200 200 200 Diflumetorim 20 200 20 20 20 Penthiopyrad > 200 > 200 > 200 > 200 > 200 Kresoxim-methyl 200 200 > 200 200 200 Flufenoxystrobin > 200 > 200 > 200 > 200 > 200 Orysastrobin > 200 20 > 200 > 200 > 200 Picoxystrobin > 200 200 200 20 20 Fluazinam > 200 > 200 200 20 20 Halosafen > 200 > 200 > 200 > 200 > 200 aKD : Lowest applied dosage in mg AI litre–1 which provides > 80% knock-down effects after 1 h. Concentrations tested: 200, 20, 2 and 0.2 mg AI 80 litre–1; bLC : Lowest applied dosage in mg AI litre–1 which provides > 80% mortality after 24 h. Concentrations tested: 200, 20, 2 and 0.2 mg AI litre–1; 80 cLC : Lowest applied dosage in mg AI litre–1 which provides > 80% mortality after 48 h. Concentrations tested: 200, 20, 2 and 0.2 mg AI litre–1;dAdult 80 mortality against Aedes aegypti after 48 h is shown in Tables 1–3; eWHOPES approved chemicals for bed net or indoor residual sprays for malaria vector control. 728 CHIMIA 2016, 70, No. 10 Malaria Vector control

stephensi at 20 mg AI litre–1. This is the for IRS or ITNs applications in malaria Downs, L. Furlan, D. W. Gibbons, C. Giorio, first report on the valuable activity of stro- vector control. V. Girolami, D. Goulson, D. P. Kreutzweiser, C. Krupke, M. Liess, E. Long, M. McField, P. bilurin fungicides for vector control. The insecticides carbosulfan, endosul- Mineau, E. A. D. Mitchell, C. A. Morrissey, D. Uncouplers of oxidative phosphoryl- fan, fipronil, acetamiprid thiamethoxam, A. Noome, L. Pisa, J. Settele, J. D. Stark, A. ation: Surprisingly, the fungicide fluazi- chlorfenapyr, thiocyclam, and metaflu- Tapparo, H. van Dyck, J. van Praagh, J. P. van nam was almost as active as chlorfenapyr, mizone reached this level of potency. der Sluijs, P. R. Whitehorn, M. Wiemers, Envir. a commercial insecticide known to act as Among these compounds carbosulfan, Sci. Pollution Res. 2015, 22, 5. [12] K. Wellinga, A, C. Grosscurt, P. J. van Hes, J. uncoupler of oxidative phosphorylation. endosulfan and fipronil are not considered Agric. Food Chem. 1977, 25, 987. Chlorfenapyr is currently under evalua- to be valuable candidates due to cross-re- [13] WHOPES. WHO recommended insecticide tion for ITN use (Table 1). These results sistance and product safety considerations. products for treatment of mosquito nets for suggest that the potential of fluazinam for Chlorfenapyr is currently under evaluation malaria vector control, 2016, http://www. who.int/whopes/Insecticides_ITN_Malaria_ malaria vector control should be further in a mixture with alpha-cypermethrin for Feb2016.pdf?ua=1, updated: 5 February 2016. evaluated. ITN by BASF. The neonicotinoids aceta- [14] WHOPES. WHO recommended long-lasting miprid and thiamethoxan, the nAChR insecticidal nets, 2016, http://www.who.int/ 6.4 Herbicides channel blocker thiocyclam and sodium whopes/Long-lasting_insecticidal_nets_ 15 commercial herbicides, 1 ACC in- channel blocker metaflumizone are newly April_2016.pdf?ua=1, updated 1 April 2016. [15] WHOPES. WHO recommended insecticides hibitor and 14 PPO inhibitors were tested. identified compounds with interesting po- for indoor residual spraying against malaria Only one compound, the PPO inhibitor ha- tential for malaria vector control that de- vectors, 2015, http://www.who.int/whopes/ losafen showed some weak activity against serve further evaluation. Insecticides_IRS_2_March_2015.pdf?ua=1, Aedes aegypti. The fungicides diflumetorin (com- updated: 2 March 2015. [16] A. Paul, L. C. Harrington, J. G. Scott, J. Med. plex I inhibitor), picoxystrobin (complex Entomology 2006, 43, 55. III inhibitor), and fluazinam (uncoupler) [17] J. W. Pridgeon, R. M. Pereira, J. J. Becnel, S. A. were found to control Aedes aegypti and Allan, G. G. Clark, J. Med. Entomology 2008, 7. Summary and Conclusions Anopheles stephensi at an application rate 45, 82. of 20 mg AI litre–1. These compounds and [18] J. Devillers, L. Lagadic, O. Yamada, F. Darriet, R. Delorme, X. Deparis, J-P. Jaeg, C. Lagneau, The vector control insecticide market the corresponding fungicidal chemical B. Lapied, F. Quiniou, A. Yebakima, ‘Juvenile represents a small fraction of the crop pro- classes are certainly worth further evalua- Hormones and Juvenoids’, Ed. J. Devillers, tection market and is estimated to be worth tion for use in malaria vector control. 2013, p. 347. up to $500 million at the active ingredient [19] WHOPES-recommended compounds and Acknowledgments formulations for control of mosquito larvae, level. Currently only 13 insecticides, be- 2016, http://www.who.int/whopes/Mosquito_ longing to four chemical classes and rep- The authors would like to thank Mr Israel larvicides_March_2016.pdf?ua=1, updated 18 resenting only two distinct modes of ac- Tsegaye Beyene and Ms Nicoleta Daems for March 2016. tions, are WHOPES approved for malaria their valuable assistance in undertaking the bi- [20] WHO, ‘Larval Source Management - A adult vector control. Resistance towards oassays presented in this paper. We also thank supplementary measure for malaria vector the Innovative Vector Control Consortium, control’, 2013, http://apps.who.int/iris/ the current solutions is increasing and especially Prof. Dr. Trevor Perrior, Dr. Colin bitstream/10665/85379/1/9789241505604_ already presents a major problem. New Ruscoe, Dr. Robert Sloss and Dr. Sarah Rees eng.pdf chemistries targeting new sites of action for fruitful discussions and a great collabora- [21] WHOPES, Pecticide products under WHOPES are urgently needed to enable rotation of tion over the past few years. laboratory and field testing and evaluation, 2016, http://www.who.int/whopes/Products_ products with different modes of action to Under_WHOPES_Evaluation_March_2016. manage resistance and to secure the best Received: August 19, 2016 pdf?ua=1 possible protection of people at risk from [22] BASF SE Professional & Specialty Solutions, vector borne diseases. 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