REPORTS Cite as: S. N. Emami et al., Science 10.1126/science.aah4563 (2017). Earlier studies have shown that mosquito vectors are more attracted to hosts infected with malaria than to healthy hosts, including humans, mice and birds (1–4). The Plasmo- dium parasites infecting these animals differ, and the vector species attracted and transmitting the disease include Anopheles and Culex mosquitoes. The increase in attraction coincides, at least in part, with changes in odor profiles of the respective hosts carrying malaria (5–7). Behavioral alter- ations are also conferred by other Apicomplexan parasites such as Toxoplasma gondii, which increases its transmis- sion between infected prey and predator hosts (8, 9). The molecular mechanisms remain unknown. HMBPP is a precursor in the 2-C-methyl-D-erythritol 4- phosphate (MEP) pathway for the synthesis of isopentenyl pyrophosphate (IPP) and its isoform, dimethylallyl pyro- phosphate (DMAPP), are building blocks for isoprenoids. All higher eukaryotes, including humans and mosquitoes, use the mevalonate pathway for IPP and DMAPP synthesis. By contrast, most eubacteria and apicomplexan parasites, in- cluding Plasmodium falciparum (10) use the alternative MEP pathway. HMBPP is an activator of human Vγ9Vδ2 T- cells and triggers innate immune responses in Anopheles gambiae s.l. (10, 11). We observed a propensity of female mosquitoes to land and feed on membrane feeders containing HMBPP- supplemented red blood cells (hmbRBCs) compared with control red blood cells (RBCs) (Fig. 1A). In a dual choice at- traction bioassay, 95% of the host-seeking mosquitoes chose hmbRBCs over RBCs, indicating the involvement of volatile factors derived from hmbRBCs. HMBPP-supplemented se- rum or glucose solution (5%) containing para-aminobenzoic acid (PABA 0.05%) did not, however, increase mosquito at- traction, which suggests that the attraction is an RBC de- pendent effect (Fig. 1A). The diol, (2E)-2-methylbut-2-ene- 1,4-diol, a putative volatile form of HMBPP, had no effect on the attraction of mosquitoes to RBCs, indicating that the phosphate groups are required for the activity of HMBPP (fig. S1). We compared RBC feeding rates with hmbRBCs, P. falci- parum asexual trophozoite-, and gametocyte-infected RBCs (tiRBCs and giRBCs, respectively). The proportion of fe- males that fed more than doubled when hmbRBCs, tiRBCs or giRBCs were provided (Fig. 1B). We next investigated whether the amount of HMBPP released in the medium of giRBCs was sufficient to stimulate mosquito blood feeding. The proportion of mosquitoes feeding on RBCs supplement- ed with HMBPP or supernatants from giRBCs, respectively, were compared over a wide range of concentrations (Fig. 1, C and D). This confirmed that 10 μM HMBPP, used in Fig. 1, A and B, corresponded to the concentration present in the undiluted supernatant from giRBCs, and also that substan- tially lower doses were sufficient to trigger enhanced mos- quito feeding (Fig. 1C). Moreover, treatment of tiRBCs with a fosmidomycin derivative to block HMBPP synthesis (12) reduced feeding to control levels, despite supplementation with the downstream metabolite IPP (Fig. 1D, triangle). A key malaria metabolite modulates vector blood seeking, feeding, and susceptibility to infection S. Noushin Emami, 1 Bo G. Lindberg, 1 Susanna Hua, 1 Sharon Hill, 2 Raimondas Mozuraitis, 3,4 Philipp Lehmann, 5 Göran Birgersson, 2 Anna-Karin Borg-Karlson, 3 Rickard Ignell, 2 Ingrid Faye 1 * 1 Department of Molecular Biosciences, Wenner-Gren Institute, Stockholm University, SE 106 91 Stockholm, Sweden. 2 Unit of Chemical Ecology, Department of Plant Protection Biology, SLU, SE 230 53 Alnarp, Sweden. 3 Department of Chemistry, Organic Chemistry, Royal Institute of Technology, SE 100 44 Stockholm, Sweden. 4 Laboratory of Chemical and Behavioral Ecology, Institute of Ecology, Nature Research Centre, LT-08412 Vilnius, Lithuania. 5 Department of Zoology, Stockholm University, SE 106 91 Stockholm, Sweden. *Corresponding author. Email: ingrid.faye@su.se Malaria infection renders humans more attractive to Anopheles gambiae sensu lato mosquitoes than uninfected people. The mechanisms remain unknown. Here, we show that an isoprenoid precursor produced by Plasmodium falciparum, (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP), affects A. gambiae s.l. blood meal seeking and feeding behaviors, as well as susceptibility to infection. HMBPP acts indirectly by triggering human red blood cells to increase the release of CO 2 , aldehydes, and monoterpenes, which together enhance vector attraction, and stimulate vector feeding. When offered in a blood meal, HMBPP modulates neural, antimalarial, and oogenic gene transcription without affecting mosquito survival or fecundity, while in a P. falciparum infected blood meal, sporogony is increased. First release: 9 February 2017 www.sciencemag.org (Page numbers not final at time of first release) 1 on February 14, 2017 http://science.sciencemag.org/ Downloaded from