Evaluating the population dynamics of a maize weevil under varying initial population sizes

Abstract

Maize is the most widely cultivated crop worldwide, and weevils, Sitophilus zeamais. Boisduval 1835 (Coleoptera: Curculionidae), are recognized as a major pest of stored maize. In this study, we investigated the population dynamics of weevils under varying initial population sizes. We used three initial population sizes (64, 128, and 256 individuals), each with identical maize availability (70 g), and replicated each initial population size three times. Populations were counted weekly over 12 weeks. Sigmoidal growth models, including three-phase, logistic, Gompertz, and Baranyi models, were fitted to each population. Model selection was conducted using the Akaike Information Criterion. Additionally, we assessed the influence of initial population size on population growth parameters: λ (lambda), μ (mu), and carrying capacity (K), using a one-way ANOVA. The Gompertz model best fit nearly all populations. Lambda (λ) varied significantly among initial population sizes, with the smallest populations showing the shortest lambda duration (approximately 4.247 weeks) and the largest populations exhibiting the longest duration (approximately 5.525 weeks). No significant differences were found in μ (mean μ = 0.197) or carrying capacity (K = 2.619, approximately 416 individuals) across initial population sizes. These findings underscore the role of density dependence in weevil populations, with a notable lag phase effect. Furthermore, the lack of impact of initial population size on μ indicates that small initial populations can achieve carrying capacity at the same rate as larger populations. This study offers valuable insights for weevil pest management in maize production.