AbstractSpodoptera frugiperda(J. E. Smith) (Lepidoptera: Noctuidae), or the fall armyworm, is a voracious, polyphagous insect that forms large populations and has a high spread rate. This species is considered an extremely dangerous plague; one of the most destructive in the American continent. One of the main insects, found in Costa Rica that damages fig crops is S. frugiperda.This research was aimed to develop a prediction larval-stage model of S. frugiperda and determine the effectiveness of Apantelessp. as a parasitoid. Both organisms were collected in fig plantations. To achieve this, eggs were collected and then breeding stocks were established. Stocks were bred for 38 days at 24°C and 70% relative humidity, identifying the lepidopteran as S. frugiperdaby a taxonomist. We determined significant differences between the larval stages according to size, and established a quadratic prediction model. Also, we determined a Spearman correlation of 0.627 between the number of eggs laid per couple and the number of eggs hatched. Finally, Apantelessp. (Hymenoptera: Braconidae) was identified as a parasitoid to the fall armyworm in fig.