Abstract: 【Aim】 Mate choice is a central process of sexual selection, and whenever fluctuations in the cost of reproduction and variance in mate quality occur, the traditional sex roles may also vary. In order to testify the thought that males can also be choosy like the females under certain circumstances, we studied male and female mating success in relation to adult body size as an indicator of fitness in Menochilus sexmaculatus (Fabricius) (Coleoptera: Coccinellidae). 【Methods】 Small and large adults of both sexes were selected randomly from the stock culture and subjected to male and female mate choice trials. The offspring of successful pairs were also tested for their mating success by placing them in mate choice trials too. 【Results】 Mate choice experiments revealed the presence of size dependent mating success in both male and female mating trials. Males discriminated between the females on the basis of their quality, i.e., body size which is an indicator of fecundity function. In female mating trials also large males achieved higher mating success than small males. Large females produced more eggs than did small females regardless of paternal size, and body size, however, did not influence egg viability. The offspring of large parents developed faster and lived longer than those of small parents, but did not display any advantage in terms of sexual desirability or competitiveness as mates when they were put in mate choice with the offspring from stock culture. 【Conclusion】 This study revealed the presence of mutual mate choice in this insect with size being the trait of interest.

Key words: Menochilus sexmaculatus, fitness, mate choice, mating success, reproductive output, sexual competitiveness