From Transient Knockdown to Density-Driven Collapse: A Mechanistic Comparison of Adult Mosquito Control by Space Spraying and Mass Trapping in Maldivian Islands

Space spraying and mass trapping represent distinct adult mosquito control strategies with fundamentally different population-level consequences. We developed a density-regulated population model incorporating either pulsed mortality from spraying (efficacy α = 0.2-0.6 per application) or continuous proportional removal through trapping. Parameters were derived from empirical island datasets. Spraying produced rapid but transient reductions and required high-frequency re-application (weekly to daily) to approach structural suppression when α ≤ 0.4. Consistent with model predictions, analysis of Maldivian resort practices indicated that daily spraying is common in operational settings. In contrast, trapping shifted long-term equilibrium density and induced population collapse above a model-estimated threshold density that, under the baseline parameterization used here, corresponded to approximately 8-10 traps per hectare in geographically bounded island systems. Sensitivity analyses demonstrated that qualitative outcomes were robust across plausible parameter ranges. Economic comparison indicated that spraying frequencies required to match threshold trapping substantially increased cumulative cost. In small island settings with negligible immigration, threshold-based mass trapping provides a structurally stable pathway toward sustained suppression, whereas spraying remains primarily a rapid-response tool with limited durability under moderate-efficacy conditions. When potential ecological externalities and human health considerations associated with repeated insecticide use are considered, trapping may offer additional advantages beyond purely economic comparisons.