[Objectives]  To determine the effects of octopamine and tyramine on the offspring sex ratio of the bean flower thrip, Megalurothrips usitatus (Bagnall), an economically important pest of legumes. [Methods]  Under conditions of (26 ± 1) ℃, 60% ± 5% RH and a photoperiod of 14︰10D, 1-day-old mated, adult females were fed for 48 h on either a 10% sucrose solution (control), or a 10% sucrose solution plus either 20 mmol∙L^﹣1 octopamine, 20 mmol∙L^﹣1 tyramine, 1 mmol∙L^﹣1 phentolamine, 1 mmol∙L^﹣1 mianserin, or 1 mmol∙L^﹣1 yohimbine, which was confined between two layers of stretched parafilm, then reared individually for 10 d on a section of young cowpea (Vigna unguiculata) bean pod in a glass tube. Bean pod sections were replaced daily. Replaced bean pod sections were placed into a new glass tube until offspring emerged, after which the numbers of nymphs, and their sex were recorded. Sex ratio (defined as proportion of males) and offspring survival (%) were calculated. [Results]  Only the phentolamine treatment group had a significantly higher adult offspring sex ratio (0.47) than that of the control group (0.34). Offspring sex ratios in this treatment group were significantly higher than those of the control on the 4th, 5th day and 9th day of oviposition. Both the octopamine and phentolamine treatment groups had significantly fewer adult female offspring, as well as fewer adult offspring overall. The production of female offspring was inhibited by yohimbine. None of the treatments affected the number of male offspring or the offspring survival rate. [Conclusion]  Phentolamine inhibits the production of female offspring by mated female bean flower thrips, and thereby increases sex ratio of their offspring.