Factors influencing abundance of hymenopteran parasitoids of Metisa plana in good agriculture practice (GAP) and non-gap oil palm

Abstract

The bagworm species Metisa plana (Lepidoptera: Psychidae) is a major oil palm pest in Peninsular Malaysia. Despite several control techniques being available, infestation remains a significant problem. Parasitoids are the most common natural enemies found in oil palm plantations, and their abundance is related to the host population (M. plana) and food availability. However, no detailed information on parasitoid ecology has been studied specifically in the oil palm ecosystem. Therefore, in this study, four main objectives listed: 1) to compare the abundance of hymenopteran parasitoids of Metisa plana from Good Agriculture Practice (GAP) and non-GAP plantations; 2) to investigate the relationship of weather parameters (rainfall, temperature, relative humidity and SPEI value) to the diversity of hymenopteran parasitoids; 3) to determine the occurrence of hymenopteran parasitoids based on the presence of beneficial plants and weeds; and 4) to conduct metagenomics analysis on the diet of Dolichogenidea metesae, a dominant species of M. plana’s parasitoid. The parasitoid samplings were conducted at six oil palm plantations throughout Peninsular Malaysia consisting of three GAP and three non-GAP oil palm plantations. A total of 1199 hymenopteran parasitoid specimens belonging to 16 species under eight families were successfully collected by using active and passive sampling for 12 months. Based on the Shannon–Wiener diversity index (H’), the diversity of the parasitoids was significantly higher (t = 3.840, p < 0.05) in the GAP plantations than in the non-GAP plantations. Additionally, Principal Component Analysis (PCA) showed that majority of parasitoids were associated with GAP oil palm plantations. Interestingly, the analysis indicated a strong negative correlation between the hyperparasitoids and the primary parasitoids (R= - 0.807, R2= 0.6509, p < 0.05) collected from the GAP plantation. In terms of weather parameters, rainfall frequency and rainfall volume had a strong positive relationship with parasitoid abundance (r > 0.70, p < 0.05) in the GAP plantation. The Welch’s ANOVA analysis revealed that parasitoids' abundance was significantly higher during moderately wet seasons than during dry season. In addition, the number of parasitoids in plantations with beneficial plants was significantly higher than that in plantations without beneficial plants (p <0.05), and the study also revealed that plantations with Antigonon leptopus have a higher diversity of parasitoids than other beneficial plant species. Results also showed that plantation with medium and high percentage of ground cover had significantly higher parasitoids than less percentage ground cover. Based on metagenomic analysis of trnL, there were no significant differences in the D. metesae diets between the GAP and non-GAP oil palm plantations (p = 0.683), and the results also showed that Antigonon leptopus, Paraprenanthes oligolepis, Asystasiella neesiana, wild banana (Musa itinerans), and coconut (Cocos nucifera) were the dominant food plant species consumed by the adults of D. metesae. These findings are valuable information to be utilized for greater success in Integrated Pest Management (IPM) strategies to control the oil palm pest M. plana.