Arthropod-borne infectious diseases are responsible for nearly 1.5 million deaths annually across the globe, with malaria responsible for over 50% of these deaths. Recent efforts to enhance malaria control have focused on developing genetically modified Anopheles mosquitoes that are resistant to malaria parasite infection by manipulating proteins that are essential to the immune response. Though this approach has shown promise, the lack of efficient genetic tools in the mosquito makes it difficult to investigate innate immunity using reverse genetics. Current gene knockdown strategies based on small interfering RNAs (siRNA) are typically laborious, inefficient, and require extensive training. Here, we describe the use of morpholino anti-sense oligomers to knockdown MEK-ERK signaling in the midgut of Anopheles stephensi through a simple feeding protocol. Anti-MEK morpholino provided in a saline meal was readily ingested by female mosquitoes with minimal toxicity and resulted in knockdown of total MEK protein levels 3-4 days after morpholino feeding. Further, anti-MEK morpholino feeding attenuated inducible phosphorylation of the downstream kinase ERK and, as predicted by previous work, reduced parasite burden in mosquitoes infected with P. falciparum. To our knowledge, this is the first example of morpholino use for target protein knockdown via feeding in an insect vector. Our results suggest this method is not only efficient for studies of individual proteins, but also for studies of phenotypic control by complex cell signaling networks. As such, our protocol is an effective alternative to current methods for gene knockdown in arthropods.