Temperature modulates feeding attributes, biochemical assimilation of macronutrients and rate of development in larvae of Parthenium beetles

The present study assessed the feeding efficiency, macronutrient assimilation, and larval development of the Parthenium beetle, Zygogramma bicolorata Pallister, a biocontrol agent for the invasive Parthenium weed, under varying temperature conditions. We hypothesized that deviations from the optimal temperature (~25°C) would impair larval feeding efficiency due to temperature-induced stress. Our results revealed that both larval consumption and growth rates declined at temperatures below (15°C, 20°C) and above (30°C) the optimal temperature (25°C). In contrast, food conversion efficiency improved as temperatures increased from 15°C to 30°C. Protein assimilation by larvae decreased across the temperature range, while glucose assimilation increased. Triglyceride assimilation initially decreased from 15°C to 20°C/25°C but increased from 20°C/25°C to 30°C. As temperatures increased from 15°C to 30°C, both the body size and developmental durations of larvae decreased. These findings suggest that Z. bicolorata larvae adopt different survival strategies depending on temperature conditions. At suboptimal temperatures, larvae grow larger, assimilate more proteins and triglycerides, but consume and utilize food more slowly. Conversely, at supraoptimal temperatures, larvae exhibit reduced body size and food consumption rates, but their food utilization efficiency improves, leading to faster development. Therefore, both low and high temperatures could limit the biocontrol efficiency of Z. bicolorata larvae in the Indian subcontinent.

本研究探究了不同温度条件下，作为入侵性银胶菊（Parthenium weed）生防因子的银胶菊叶甲（Zygogramma bicolorata Pallister）的取食效率、宏量营养素同化能力及幼虫发育情况。本研究提出假设：偏离适宜温度（约25℃）将因温度胁迫降低幼虫取食效率。研究结果显示，在适宜温度（25℃）以下的15℃、20℃以及高于该温度的30℃环境中，幼虫取食量与生长速率均出现下降。与之相对，食物转化效率随温度从15℃升至30℃持续提升。幼虫对蛋白质的同化作用在整个温度梯度范围内均呈下降趋势，而对葡萄糖的同化作用则逐步升高。甘油三酯的同化率先在15℃至20℃/25℃区间内下降，随后在20℃/25℃至30℃区间内回升。随着温度从15℃升高至30℃，幼虫的体型大小与发育时长均有所缩短。上述结果表明，银胶菊叶甲幼虫会根据温度环境采取差异化的生存策略：在亚适宜温度环境下，幼虫体型更大，对蛋白质与甘油三酯的同化量更高，但取食及食物利用的速率更慢；反之，在超适宜温度环境下，幼虫体型更小、取食速率更低，但食物利用效率提升，发育速度加快。因此，在印度次大陆区域，低温与高温均可能限制银胶菊叶甲幼虫的生防效能。