Acta Tropica 150 (2015) 131–135 Contents lists available at ScienceDirect Acta Tropica jo ur nal home p age: www.elsevier.com/locate/actatropica Evaluating the sterilizing effect of pyriproxyfen treated mosquito nets against Anopheles gambiae at different blood-feeding intervals Aneesa Jaffer a , Natacha Protopopoff a,b,c , Franklin W. Mosha b,c , David Malone d , Mark W. Rowland a,c , Richard M. Oxborough a,b,c,∗ a Department of Disease Control, London School of Hygiene and Tropical Medicine, London, UK b Department of Entomology and Parasitology, Kilimanjaro Christian Medical University College, Moshi, Kilimanjaro, Tanzania c Pan-African Malaria Vector Research Consortium, (PAMVERC), Moshi, Tanzania d Innovative Vector Control Consortium (IVCC), Liverpool School of Tropical Medicine, Liverpool, UK a r t i c l e i n f o Article history: Received 31 May 2015 Received in revised form 10 July 2015 Accepted 12 July 2015 Available online 19 July 2015 Keywords: Pyriproxyfen Juvenile hormone mimic LLIN Oviposition Fecundity Fertility a b s t r a c t Pyrethroid resistant malaria vectors are widespread throughout sub-Saharan Africa and new insecticides with different modes of action are urgently needed. Pyriproxyfen is a juvenile hormone mimic that reduces fecundity and fertility of adult Anopheles mosquitoes when used as a contact insecticide. A long- lasting insecticidal net incorporating pyriproxyfen is under development. As wild, host-seeking females may succeed in blood-feeding at different intervals after initial contact with mosquito nets the aim of this study was to determine the effect that age and gonotrophic status (nulliparous or parous) and the interval between initial pyriproxyfen exposure and blood-feeding has in terms of subsequent reduced fecundity and fertility. Anopheles gambiae s.s. were exposed to pyriproxyfen LLIN for three minutes in WHO cone bioas- says. Four regimens were tested with different blood-feeding intervals A-1 hour (nulliparous), B-1 hour (parous), C-24 h (nulliparous), or D-120 h (nulliparous) after pyriproxyfen exposure. Mosquito ovipo- sition rate, fecundity and fertility of eggs were recorded for several days. All four treatment regimens produced levels of mortality similar to unexposed females. The overall reduction in reproductive rate of 99.9% for regimen A relative to the untreated net was primarily due to oviposition inhibition in exposed females (97%). Pyriproxyfen was equally effective against older parous mosquitoes and when blood- feeding was 24 h after exposure. Regimen D produced a reduction in reproductive rate of 60.1% but this was of lesser magnitude than other regimens and was the only regimen that failed to reduce fertility of laid eggs, indicating the effects of pyriproxyfen exposure on reproduction are to some extent reversible as mosquitoes age. In an area of moderate to high mosquito net coverage a host-seeking mosquito is likely to contact a treated mosquito net before: (a) penetrating a holed net and blood-feeding shortly after exposure or, (b) be frustrated by intact nets before succeeding in blood-feeding on an unprotected individual the following night. Mosquito nets are an appropriate delivery system for pyriproxyfen, based on the large reductions in reproductive rate when blood-feeding between 1 h and 24 h after exposure. Combining with a pyrethroid should be an effective approach if susceptible mosquitoes are killed and resistant mosquitoes sterilized. © 2015 Elsevier B.V. All rights reserved. ∗ Corresponding author at: Department of Disease Control, London School of Hygiene and Tropical Medicine, London, UK. E-mail addresses: aneesajaffer@hotmail.com (A. Jaffer), nprotopopoff@gmail.com (N. Protopopoff), fwmosha@gmail.com (F.W. Mosha), david.malone@ivcc.com (D. Malone), mark.rowland@lshtm.ac.uk (M.W. Rowland), oxandbull@hotmail.com (R.M. Oxborough). 1. Background Pyriproxyfen is a juvenile hormone mimic which inhibits eclo- sion of agricultural, domestic, and aquatic insect pests and was first registered by the United States Environment Protection Agency (US EPA) in 1995 (EPA, 2011). Pyriproxyfen is safe to use in the context of human habitations, with an LD 50 oral toxicity in rats of >5,000 mg/kg body weight and World Health Organization (WHO) toxicological classification U (unlikely to present acute hazard in normal use) (WHO, 2002). Pyriproxyfen has been recommended by WHO Pesticide Evaluation Scheme (WHOPES) for control of http://dx.doi.org/10.1016/j.actatropica.2015.07.011 0001-706X/© 2015 Elsevier B.V. All rights reserved.