Cost estimation model for small-scale rearing systems of natural enemy insects: Propagation for controlling <i>Spodoptera frugiperda</i> (Lepidoptera: Noctuidae) in Thailand

Abstract Since 2018, the fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) has posed a significant threat to maize production in Thailand, prompting the government to recommend the use of natural enemy insects (NE) for biological control. However, previous studies on NE propagation costs, which are vital for widespread adoption, have often relied on single-scale estimates and have lacked comprehensive cost classifications. This study estimated the propagation costs of four NE species used to control S. frugiperda in Thailand— Trichogramma pretiosum (Riley) (Hymenoptera: Trichogrammatidae), Eocanthecona furcellata (Wolff) (Hemiptera: Pentatomidae), Sycanus versicolor (Dohrn) (Hemiptera: Reduviidae), and Proreus simulans (Stål) (Dermaptera: Chelisochidae)—based on rearing costs incurred at a government research institute. A small-scale production cost model was developed by considering factors such as the populations of NE, hosts, and prey, and the associated input quantities and costs. The model accounts for economies of scale and estimates both the current and potential costs at the maximum scale manageable by a single worker. At this optimal scale, the average costs were 15 USD/ha for T. pretiosum , 57 USD/ha for E. furcellata , 276 USD/ha for S. versicolor , and 237 USD/ha for P. simulans . Per-hectare costs decline with larger production scales, highlighting the importance of labor-saving innovation. Economic simulations suggest that small-scale T. pretiosum production could be profitable if maize producers accept slightly higher costs than those of conventional pesticides and if adequate distribution networks are in place.