The molecular mechanisms underlying diversity in animal behavior are not well understood. A major experimental challenge is determining the contribution of genetic variants that affect neuronal gene expression to differences in behavioral traits. In Caenorhabditis elegans, the neuroendocrine transforming growth factor-β ligand, DAF-7, regulates diverse behavioral responses to bacterial food and pathogens. The dynamic neuron-specific expression of daf-7 is modulated by environmental and endogenous bacteria-derived cues. Here, we investigated natural variation in the expression of daf-7 from the ASJ pair of chemosensory neurons. We identified common genetic variants in gap-2, encoding a Ras guanosine triphosphatase (GTPase)-activating protein homologous to mammalian synaptic Ras GTPase-activating protein, which modify daf-7 expression cell nonautonomously and promote exploratory foraging behavior in a partially DAF-7-dependent manner. Our data connect natural variation in neuron-specific gene expression to differences in behavior and suggest that genetic variation in neuroendocrine signaling pathways mediating host-microbe interactions may give rise to diversity in animal behavior.