Optimized temperature enhancing the performance of Trichogramma egg parasitoids against yardlong bean pod borer

Abstract

Background : Climate change is leading to unpredictable weather patterns globally, which in turn affects food security in numerous countries, especially the developing nations. Identifying specific temperature thresholds facilitating the efficient parasitization of Trichogramma species group could offer an effective biological approach to pest control resilient to climate variations. So, the paramount focus of biocontrol research involves optimizing thermal conditions to enhance the efficacy of Trichogramma egg parasitoids against any select lepidopteran pest. Methods : This study followed a factorial CRD comprising five varied temperatures 15°C, 20°C, 25°C, 30°C, and 35°C and five Trichogramma egg parasitoids T. chilonis , T. evanescens , T. pretiosum , T. japonicum , and T. bactri to explore their best combination in managing the destructive foe of yardlong bean ( Maruca vitrata – yardlong bean pod borer, YBPB). Results : Temperature had a significant effect on the biological characteristics of Trichogramma species, wherein 25°C appeared as ideal for maximum parasitism and emergence rate. Of the parasitoids, T. chilonis and T. evanescens exhibited maximum biological activities such as parasitism, fecundity, larval emergence and longevity on host YBPB at 25°C though no significant difference was noticed between 25°C and 30°C for most of the variables. Conversely, the extreme temperatures of 15°C and 35°C diminished the biological activities of all the egg parasitoids, underscoring their thermal sensitivity. The three polynomial regression analyses yielded a parabolic curve showing the vertex peak of biological behavior at 25–30°C with 84–98% goodness of data fit. A three-variable contour map demonstrated a significant positive correlation among egg parasitization, adult emergence, and larval emergence. Multivariate PCA analysis isolated imago, larvae emergence, and parasitization as key variables accounting for maximum variation. The dendrogram grouped the temperatures into three clades: 25°C in one, 15°C and 35°C in another, and 20 and 30°C in a separate clade. Conclusions : The study findings thus transformed these bioagents into highly efficient management tools, specifically calibrated to the temperatures required to mitigate the enormous damage inflicted by the economically detrimental YBPB, and eventually helped develop a promising, sustainable, and environmentally benign IPM.