Insecticidal activity of Ricinus communis L. seed extract against Spodoptera frugiperda J.E. Smith under laboratory and field conditions

Abstract

Insecticidal activity of the aqueous extract of the castor seed (Ricinus communis L.) against the Fall Armyworm (FAW), Spodoptera  frugiperda (Lepidoptera: Noctuidae), one of the worst pests of maize crop, was assessed under laboratory and field conditions. In  laboratory, the larvicidal activity of three concentrations of the extract that are 150 g/l, 200 g/l and 250 g/l and their effects on the  development of FAW were evaluated through direct exposure and ingestion tests. The field experiment consisted of a randomized block  design with two extract concentrations – 200 g/l and 250 g/l – and negative control consisted of untreated plots and positive control plots were treated with Emacot (Emamectin benzoate). Results of the laboratory experiments revealed considerable larvicidal activity of the  extract through the ingestion test, inducing the larvae mortality of 75.8%, 60.3% and 46.5% for the extract concentrations of 250 g/l, 200  g/l and 150 g/l respectively, whereas positive (Emacot) and negative controls (emulsified water) recorded 100% and 3.3% of the larvae  mortality, respectively. The field results showed 10% and 11% of infested plants in plots treated with 200 and 250 g/l, respectively,  whereas Emacot-treated plots recorded 9.5% of infested plants. Untreated plots recorded the highest infested plants of 22.5%. The two- castor seed extract concentrations 200 g/l and 250 g/l reduced about 50% of maize plant infestation by FAW, thus could be a good  candidate as alternative to chemical pesticides in controlling the pest.