Economic impact and yield loss assessment due to cabbage butterfly (Pieris brassicae nepalensis Doubleday) infestation in Brassica crops

Abstract:

Economic injury caused by crop pests encompasses not only direct yield reductions but also a complex cascade of quality degradation, increased management expenditures, and market disruption effects that collectively determine the true economic burden on agricultural production systems. This research was conducted at the Chiang Mai Academy of Agricultural Sciences, Thailand, during two consecutive Brassica growing seasons (2022-2023) to quantify the economic impact of Pieris brassicae nepalensis Doubleday infestation across five infestation severity levels on cabbage (Brassica oleracea var. capitata) and to develop yield loss prediction models for informing management decision-making. Artificial infestation experiments were established in a randomized complete block design with five infestation levels (0, 5-10, 11-20, 21-40, and >40 larvae per plant) and four replications. Results demonstrated a curvilinear relationship between larval density and yield loss (r² = 0.96, P < 0.001), with losses ranging from 14.6% at low infestation levels to 82.6% under severe infestation conditions. Total economic losses at severe infestation levels reached USD 5,120 per hectare, comprising direct yield loss (42.8%), quality degradation (24.6%), management costs (16.2%), post-harvest losses (10.4%), and market price depression (6.0%). The economic injury level was estimated at 4.2 larvae per plant, and the economic threshold was established at 2.8 larvae per plant. These findings provide quantitative decision-making tools for optimizing the timing and intensity of management interventions against cabbage butterfly in commercial Brassica production systems.