In-depth investigations on diapause behaviour of Z. bicolarata revealed that the adults entered diapause at any time from August to December and that the number peaked (42.00%) during the last half of November. The percentage of adults entering diapause increased with a decrease in day length. Weight of diapausing adults was significantly higher than weight of non-diapausing adults. The percentage of adults undergoing diapause at $30^{circ}C$ was significantly lower than those undergoing diapause at 15 and $25^{circ}C$. The percentage of adults burrowing increased with increasing moisture. In silty soil and soil with high organic matter, 46.7% and 49.2% of adults entered diapause, respectively, whereas in sandy soil, only 23.5% of adults entered diapause. When newly emerged beetles were exposed to $5{mu}g$ of human insulin 30/70, a significantly lower percentage of treated adults underwent diapause compared to untreated adults under both feeding and no feeding conditions. Insulin treatment also influenced the emergence period from diapause ($93.92{pm}1.73$ days), percent emergence ($81{pm}1.54%$) and fecundity/month ($512.7{pm}25.38$ eggs) of Z. biealarata in treated adults as compared to untreated adults ($109.05{pm}2.2$, $74.00{pm}1.82$ and $438.3{pm}19.33$ eggs, respectively). However, there was no significant impact of insulin on adult longevity. These findings are of great utility in the biological suppression of Parthenium as it will enhance the effectiveness of this beetle through manipulation of diapause.