The operational sex ratio (OSR) is one of the most important ecological factors affecting the structure of mating systems and individual mating investment. Bush cricket males produce a highly costly nuptial gift during mating, so it is expected that OSR would affect this investment. In this study, we confronted the bush cricket Isophya rizeensis with three different OSR environments, measuring effects on the males' spermatophore, spermatophylax, ampulla weight, and absolute sperm transfer. As expected, male I. rizeensis showed a decrease in the transferred sperm in a female-biased environment. When mating in different OSR environments, males did not modify their behavioral strategies with respect to spermatophore transfer and copulation duration, which was largely influenced by male body size, likely due to the high costs of nuptial gifts. Although we dismiss the “longer copulation durations function as a mate assessment period” hypothesis, longer copulations positively affect spermatophore size and sperm number.