Morphometric analysis of Parthenium beetle, Zygogramma bicolorata (Pallister) under thermal-stress conditions

Abstract

This study highlights the effects of thermal stress on the morphology of the Parthenium beetle, Zygogramma bicolorata Pallister. Our findings indicate that temperature significantly influences the body biomass of adults, with optimal (25 ± 2 °C) conditions resulting in the highest biomass. Body size and antennal length were reduced under both cold (15 ± 2 °C) and hot (35 ± 2 °C) conditions, with greater variability recorded at cold temperatures. Moreover, cold stress increased melanization and induced developmental abnormalities, such as fused flagellomeres in the antennae. The abundance of sensilla varied significantly across temperature treatments, except for sensilla chaetica types I and II. Antennal segments also exhibited temperature-dependent variations in length. Eight types of sensilla were identified, with sensilla trichodea I and sensilla coeloconica being more abundant under thermal extremes, potentially influencing host and mate detection. Sensilla chaetica were the most widespread and robust, displaying variability in both length and abundance. Structural differences were observed between sensilla trichodea and sensilla basiconica, particularly in terms of curvature and socket embedding. Overall, the results suggest that thermal stress affects both morphological and sensory traits in Z. bicolorata, which may in turn, impact their survival and reproductive success. © African Association of Insect Scientists 2025.