A number of insects are associated with gut microorganisms, wherein symbionts play pivotal metabolic roles such as nutrient supplementation, diet degradation, and pesticide detoxification. Despite the ecological and evolutionary importance of gut microbial communities in insects, their diversity and dynamics need to be better investigated in many insect species. The green plant bug Apolygus spinolae, a notorious grapevine pest in Japan, damages grape shoots and severely reduces grape berry yield and quality. The plant bug possesses a simple tubular gut housing ~ 104 bacteria. Here we investigated geographic, seasonal, and growth-related dynamics of gut microbiota by high-throughput sequencing in the grapevine pest. In Japanese populations of the plant bug, gut bacterial community was dynamically altered depending on geographic region, season, and developmental stage, in which particularly Serratia, Lactococcus and Caballeronia were abundantly detected. In one vineyard population, Spiroplasma was prevalent. Among the gut bacterial microorganisms, Serratia was consistently and abundantly detected, but significantly affected by seasonal change. In addition, Caballeronia, known as a specific symbiont of stinkbugs, was abundantly detected, especially in insects collected in late summer. The increase of Caballeronia was negatively correlated with Serratia, strongly suggesting an antagonistic interaction between gut bacterial members in A. spinolae.