Spatiotemporal dynamics of a palm weevils' outbreak and susceptibility of peach palm (Bactris gasipaes Kunth) landraces in a germplasm bank in southwestern Colombia

Abstract

The palm weevils Rhynchophorus palmarum and Dynamis borassi are prominent pest species in peach palms and coconut in Colombia. Nevertheless, knowledge of the population dynamics of these weevil species in the neotropical region is still scarce. In this study, we systematically sampled these weevils over 2 years using pheromone traps (1 trap ha⁻¹) in an experimental peach palm plantation under heavy weevil infestation in southwestern Colombia. Additionally, we censused the palms in a portion of the plantation (a peach palm germplasm bank) before and after the weevil monitoring. We analysed the data to elucidate sex-specific temporal and spatial patterns of both R. palmarum and D. borassi in a 19.13 ha area. Furthermore, we sought to detect peach palm landraces within the germplasm bank susceptible and resistant/tolerant to the weevil attack. During periods when insect populations were high, we observed that R. palmarum consistently outnumbered D. borassi. Specifically, we found that R. palmarum reached up to 80 insects trap⁻¹ month⁻¹, while D. borassi only reached around 30 insects trap⁻¹ month⁻¹ during the peak months. However, both species exhibited synchronous population peaks, which were not related to rainfall or temperature but rather to the phenological stage of the peach palm. Furthermore, the weevils had a highly aggregated spatial pattern; insect catchments were more prolific in areas where the landraces Nariño and Risaralda were sown. Moreover, the census evidenced that these two landraces were the most affected. Contrarily, weevil capture was overall low around the Guaviare landrace, this was the only landrace that exhibited an increase in stipes between census years. Our results highlight that complementary control strategies are needed to counteract sudden weevil population outbreaks, as pheromone traps are a good tool for monitoring but not for effective control. Furthermore, more importantly, a peach palm breeding programme based on the identified genotypes should be the basis for the integrated pest management of palm weevils.