Outdoor and early-evening mosquito biting evades bed nets and indoor spraying

A growing proportion of malaria transmission occurs outdoors or during early evening hours before people go to bed, completely bypassing the two most widely deployed vector control tools: long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS). On Bioko Island, each person received an average of 2.7 infectious bites per night outdoors, and two-thirds of mosquito bites were estimated to be unpreventable with current tools. This matters because national malaria programs have invested billions of dollars and decades of effort into LLIN and IRS programs, yet an increasing fraction of transmission is structurally invisible to these interventions. An additional 10.6 million clinical malaria cases per year are attributed to this 'residual transmission.' The problem persists because decades of insecticide pressure have created evolutionary selection for mosquitoes that bite and rest outdoors (exophilic/exophagic behavior), shifting species composition toward vectors that naturally avoid indoor contact. There are currently no approved, scalable outdoor vector control tools: spatial repellents, attractive toxic sugar baits, and outdoor larviciding are all either in trials or too expensive to deploy at national scale.