VECTOR CONTROL Efficacy of the Olyset Duo net against insecticide-resistant mosquito vectors of malaria Corine Ngufor, 1,2,3 * Raphael N’Guessan, 1,2,3 Josias Fagbohoun, 2 Damien Todjinou, 2 Abibath Odjo, 2 David Malone, 4 Hanafy Ismail, 5 Martin Akogbeto, 2 Mark Rowland 1,3 Olyset Duo is a new long-lasting insecticidal net treated with permethrin (a pyrethroid) and pyriproxyfen, an insect growth regulator that disrupts the maturation of oocytes in mosquitoes exposed to the net. We tested the Olyset Duo net against pyrethroid-resistant Anopheles gambiae mosquitoes, which transmit malaria parasites, in laboratory bioassays and in a trial in Benin using experimental huts that closely resemble local habitations. Host-seeking mosquitoes that entered to feed were free to contact the occupied nets and were collected the next morning from exit traps. Surviving blood-fed mosquitoes were observed for effects on re- production. Control nets were treated with pyrethroid only or pyriproxyfen only, and nets were tested un- washed and after 20 standardized washes. The Olyset Duo net showed improved efficacy and wash resistance relative to the pyrethroid-treated net in terms of mosquito mortality and prevention of blood feeding. The production of offspring among surviving blood-fed A. gambiae in the hut trial was reduced by the pyriproxyfen-treated net and the Olyset Duo net both before washing (90 and 71% reduction, respectively) and after washing (38 and 43% reduction, respectively). The degree of reproductive suppression in the hut trial was predicted by laboratory tunnel tests but not by cone bioassays. The overall reduction in reproductive rate of A. gambiae with the Olyset Duo net in the trial was 94% with no washing and 78% after 20 washes. The Olyset Duo net has the potential to provide community control of mosquito populations and reduce malaria transmission in areas of high insecticide resistance. INTRODUCTION Long-lasting insecticidal mosquito nets remain the most popular and widely used public health intervention for preventing malaria because they provide effective protection for individual users and are simple to deliver, even in remote communities (1). Pyrethroids have been the insecticide of choice for treating mosquito nets owing to their safety, effectiveness, rapid action, and capacity to repel mosquitoes (2). Un- fortunately, the development and rapid spread of resistance to pyre- throids in mosquito vectors of the malaria parasite threaten to undermine the effectiveness of insecticidal mosquito nets (3, 4). In areas of high resistance, pyrethroid-treated nets have shown reduced effectiveness in several small-scale trials (4, 5), and this is driving the search for new insecticides that can maintain the utility of this once- effective means of malaria prevention (1, 4). Research and development of alternative insecticides to pyrethroids for treating mosquito nets has been challenging because most nonpyr- ethroids tested lack the important property of excitorepellency, the characteristic responsible for stimulating mosquito movement away from the pyrethroid-treated surface and preventing blood feeding. To retain this attribute, the mosquito nets can be treated with a mix- ture of pyrethroid and nonpyrethroid insecticides, which maintains the personal protective effect mediated by the pyrethroid component while inducing mortality through the companion insecticide. This combined action should enable long-lasting insecticidal nets to kill mosquitoes and maintain community protection when deployed on a large scale against mosquito populations that are resistant to pyre- throids (4). Combining mixtures of insecticides on mosquito nets has the potential to delay the selection of pyrethroid resistance in areas where resistance is still rare (6, 7). Olyset Duo is a new type of mosquito net that is treated with a mix- ture of permethrin (a pyrethroid) and pyriproxyfen. Pyriproxyfen be- longs to a category of insecticides known as insect growth regulators, which prevent mosquito larvae from molting and adult insects from producing fertile eggs (8–11). A preliminary assessment of the un- washed Olyset Duo net against pyrethroid-resistant Anopheles gambiae in southern Benin demonstrated the potential of this mixture-treated, long-lasting insecticidal mosquito net to kill adult mosquitoes and ster- ilize survivors (12). A sterile survivor makes no contribution to the next generation, and mosquito populations should decrease over time through the collective sterilizing action of pyriproxyfen on nets. To ensure that new brands of mosquito nets are fit for malaria control, the World Health Organization (WHO), through the pesti- cide evaluation scheme (WHOPES), has set criteria that a new long- lasting insecticidal net must fulfill to attain recommendation for public health use. The WHO guidelines stipulate that a long-lasting insecticidal mosquito net must retain biological effectiveness after 20 standardized washes in defined laboratory bioassay tests and in experimental hut trials in malaria-endemic regions (13). The WHO Vector Control Action Group, which advises WHO on new vector control tools, goes one step further and stipulates that for use against pyrethroid-resistant vector populations, the mixture-treated, long-lasting insecticidal mos- quito net must induce mosquito mortality or provide personal protec- tion to a level significantly greater than a net treated with pyrethroid only (14). 1 London School of Hygiene and Tropical Medicine, London WC1E 7HT, U.K. 2 Centre de Recherches Entomologiques de Cotonou, Ministry of Health, Cotonou 06 BP 2604, Benin. 3 Pan African Malaria Vector Research Consortium, London WC1E 7HT, U.K. 4 Innovative Vector Control Consortium, Liverpool L3 5QA, U.K. 5 Liverpool School of Tropical Medicine, Liverpool L3 5QA, U.K. *Corresponding author. Email: corine.ngufor@lshtm.ac.uk RESEARCH ARTICLE www.ScienceTranslationalMedicine.org 14 September 2016 Vol 8 Issue 356 356ra121 1 by guest on April 23, 2020 http://stm.sciencemag.org/ Downloaded from