Studies on the behaviour of peridomestic and endophagic M form Anopheles gambiae from a rice growing area of Ghana J.D. Charlwood 1,2 *, E.V.E. Tomás 2 , P. Salgueiro 3 , A. Egyir-Yawson 4 , R.J. Pitts 5 and J. Pinto 3 1 DBL Centre for Health Research & Development, 57 Thorvaldensvej, Fredriksberg 1871, Denmark: 2 MOZDAN, PO Box 8, Morrumbene, Inhambane Province, Mozambique: 3 Centro de Malária e outra Doenças Tropicais, Rua da Junqueira 100, Lisbon 1300, Portugal: 4 Biotechnology and Nuclear Agriculture Research Institute, Ghana Atomic Energy Commission, Kwabenya, Accra, Ghana: 5 Vanderbilt University, Department of Biological Sciences, Nashville, Tennessee, USA Abstract The ‘paddy paradox’, the occurrence of large populations of vectors but low amounts of malaria transmission where irrigated rice is grown, was investigated in a village in Ghana where M form Anopheles gambiae are common. Peridomestic and indoor host-seeking mosquitoes were collected in tent traps and light traps over 21 consecutive nights at the start of the rainy season in June 2009 when the population increased exponentially from less than 100 per night to over 1000. Infection rates in the overall mosquito population were 0.3% and in the estimated parous population were 1.9%. Numbers of An. gambiae in the tent trap peaked between midnight and 02:40 am. The majority of insects were taking their first blood meal, as virgins or shortly after mating. More than expected were collected in the light trap during a rainstorm at the start of the rains but overall numbers were not affected. Fewer than expected were collected after a subsequent storm. Recruitment to the adult population decreased over the following days. It is hypothesised that the ‘paddy paradox’ is due to young pre-gravid insects dispersing more widely than gravid ones, not necessarily to low survival in the mosquito. Keywords: Anopheles gambiae, rainfall, behaviour, ‘paddy-paradox’, tent trap (Accepted 21 February 2011) Introduction In order to properly understand the epidemiology of malaria, information on the ecology and bionomics of the local vector population is required. Information on factors such as population density, survival rate, infection rate, blood-feeding frequency, time and location of biting, as well as host preference, all affect the ability of a mosquito population to transmit malaria. In West Africa, the most important vectors are the M and S forms of Anopheles gambiae. These are ‘incipient’ species in which hybrids are fertile and can be readily produced in the laboratory. Where they occur in sympatry in the wild, however, they often show low rates of hybridization. (Diabate et al., 2009). To paraphrase Voltaire, ‘If Anopheles gambiae did not exist, man would have created him’. Humans created the larval ecological niche, puddles in exposed forest, exploited by An. gambiae. We have also provided shelter and food for the adults since we first arrived on the planet but especially since the beginning of agriculture when the species went through a *Author for correspondence E-mail: jdcharlwood@gmail.com Bulletin of Entomological Research (2011) 101, 533–539 doi:10.1017/S0007485311000125 © Cambridge University Press 2011 First published online 15 March 2011