Opisina arenosella (Lepidoptera: Oecophoridae) is a major leaf-feeding pest of palm crops that has invaded several tropical and subtropical countries or regions. Habrobracon hebetor (Hymenoptera: Braconidae) is a parasitoid of O. arenosella larvae whose efficiency in controlling its hosts is inhibited by high temperatures. The body color of this wasp exhibits a plastic response to temperature (melanin fades with increasing temperature). Based on the thermal melanism hypothesis, we proposed that H. hebetor adults with lighter body color would have better biological performance at high temperatures. This paper established the link between the parasitoid’s body color phenotype and biological performance. Our results show that exposure to 32°C for more than 3 d during the pupal stage induced almost complete loss of abdominal melanin in H. hebetor adults. At the population level, when adults were held under heat stress (34°C), the percentage of abdominal melanin in the parasitoids was negatively correlated with parasitoid longevity and the number of paralyzed hosts, But, in contrast, melanization was positively correlated with parasitoid fecundity. The yellow-biotype of H. hebetor has higher host control potential in tropical regions. Related aspects of our results also improve understanding the biological significance of plastic body color in insects and provide information on host control by H. hebetor in tropical environments.