Population Dynamics of the Cassava Shoot Fly Neosilba perezi (Diptera: Lonchaeidae) in Organic Fields of the Brazilian Cerrado

Abstract

The shoot-mining fly Neosilba perezi (Diptera: Lonchaeidae) severely limits stem cutting production in cassava, yet its population ecology in tropical dry savannas is poorly documented. We monitored two contiguous 0.20 ha organic cassava fields in the Brazilian Cerrado monthly for 17 months (March 2017 - July 2018), visually inspecting every plant at each visit (34 site-months; 85,000 shoots). Mean infestation was 13.3 %, but prevalence climbed to 45 % at the onset of the dry, cool season. A quasi-binomial generalised linear model revealed a strong quadratic response to 14-day mean temperature, with maximal infestation predicted at 28 °C, and a weaker negative association with cumulative rainfall. Field identity explained < 3 % of the deviance, indicating homogeneous pressure at the landscape scale. The resulting 28 °C / low-rainfall threshold delineates a June-August surveillance window in which early trap sampling can guide selective interventions in pesticide-restricted systems. These baseline parameters extend the biogeographical range of quantified N. perezi outbreaks and provide input for phenology models that anticipate pest pressure under future warming scenarios.