Biorationals and synthetic insecticides for controlling fall armyworm and their influence on the abundance and diversity of parasitoids.

Abstract

Spodoptera frugiperda (fall armyworm, FAW) is a significant economic pest of maize in Uganda. Many Ugandan maize farmers employ synthetic insecticides as their main form of control despite the negative impacts of these chemicals. We tested the effectiveness of Beauveria bassiana; General Biopesticide Cocktail (mixture of B. bassiana, M. anisopliae, Isaria fumosoroseus, Lecanicillium lecani and Purporeocillium lilacanus three strains of Metarhizium anisopliae, Nimbecidine® (azadirachtin 0.03%EC), and Roket® (cypermethrin 4% and profenofos 40%); and Amdocs® (emamectin benzoate 2% and abamectin 1%) on fall armyworm and parasitoids, respectively, in 2020 and 2021. The treatments with the greatest decrease in leaf damage and infestation were Amdocs® and Roket®, followed by Nimbecidine®. The biopesticides were not always more effective than the untreated control, though; their efficacy was often lower than that of the synthetic and botanical pesticides. We recovered one egg parasitoid, Telenomus remus, and seven egg and egg-larval parasitoids (Coccygidium luteum, Coccygidium sp., Cotesia icipe, Chelonus sp., Micranisa sp., Charops cf. diversipes, and an unidentified Tachinidae). Among these, C. cf diversipes, Chelonus sp., C. luteum, C. icipe and the Tachinidae were the most abundant. Parasitism was low, averaging 10% for egg masses and 5.3% for larvae. Application of synthetic pesticides and Nimbecidine® often resulted in higher yield when compared with the untreated control. In general, a low population of parasitoids was observed. Although the parasitoid population reduced in plots treated with Amdocs® and Roket®, the percentage of parasitism of FAW was not affected. In some instances, higher yields were realized in untreated control when compared with the treated plots. Pest management practices more compatible with biological control need to be considered for the management of fall armyworm.