Comparative field performance of pupal and adult releases of Trichogramma pretiosum Riley, 1879 (Hymenoptera: Trichogrammatidae) for control of Spodoptera frugiperda (J.E. Smith, 1797) (Lepidoptera: Noctuidae) in maize

Abstract

The fall armyworm, Spodoptera frugiperda (J.E. Smith, 1797) (Lepidoptera: Noctuidae), is an important pest of maize, particularly during the early vegetative stages of the crop. The egg parasitoid Trichogramma pretiosum Riley, 1879 (Hymenoptera: Trichogrammatidae) is used for its biological control, but information comparing different field release forms remains limited. This study compared pupal and adult releases of T. pretiosum at two release rates for suppression of S. frugiperda damage in second-crop maize under field conditions. The experiment was conducted in Ribeirão Preto, São Paulo State, Brazil, in a randomized block design with five treatments and six replicates. Treatments consisted of three consecutive weekly releases of 100,000 or 200,000 pupae or adults ha⁻¹ and an untreated control. Leaf damage was assessed weekly on ten plants per plot using a 0–9 visual scale. The overall treatment effect was significant (P = 0.00071), and all T. pretiosum treatments had significantly lower overall damage than the untreated control. Mean damage scores were 5.30 in the control and 3.79, 3.55, 3.85, and 3.98 for adult releases at 100,000 and 200,000 ha⁻¹ and pupal releases at 100,000 and 200,000 ha⁻¹, respectively, corresponding to reductions of 25.0–33.1% relative to the control. No overall significant differences were detected between pupal and adult release forms or between the two release rates. These results demonstrate that inundative releases of T. pretiosum can reduce S. frugiperda injury in maize, while indicating that, under the conditions of this study, pupal and adult releases provided comparable levels of damage suppression.