Many ecological studies of tropical insects are based on small sample sizes or lack sampling scheme rigor, which prevents testing ecological hypotheses and comparing samples from different sites and times. Here we present the results of quantitative trapping of bark and ambrosia beetles over 2 yr at two localities in northern Thailand separated by 5 km, 1,100 m in altitude, and in different forest types. Beetles were collected using a spatially and temporally standardized sampling scheme, followed by a quantitative analysis of community composition and its responses to environmental variables and trapping techniques. In total, 118 species were collected, but the species accumulation curves show little sign of leveling off. Based on slightly different species accumulation rates, the more humid site has a little higher species richness. Species composition was significantly different between the sites, which was not a result of undersampling of rare species. α diversity at each site contributes to the regional diversity more than the turnover of species between the sites (β diversity). Mean annual temperature and humidity have larger effects on the community species composition than seasonal fluctuations of temperature and humidity at each site—beetles do choose their environment but are aseasonal. The site with greater humidity supported significantly more species living in a symbiosis with fungi (ambrosia beetles), whereas the drier and more disturbed site hosted a greater number of circumtropical colonizer species. Each of the different types of trap had a bias for certain taxonomic groups. The results show that even modest samples, if properly structured and analyzed, can answer many ecological questions and can serve in biodiversity comparisons on broad scales.