Tobacco hornworms (Manduca sexta) are among very destructive insects that feed mainly on plants in Solanaceae plants. The larva stage is the most destructive, feeding on leaves and fruits, and as few as one to three insects can cause 100% loss. Damage caused by hornworms to the stem creates an environment for pathogens to grow, which ultimately kills the entire plant. Synthetic pesticides have been most effective in controlling insect pests but are harmful to the environment and humans. Plant-based biopesticides that are biodegradable, affordable, and eco-friendly may be a sustainable option to mitigate the problem. Several plants have been used as insecticides and have successfully controlled several insects. Due to the increasing demand for safe and biodegradable insecticides, there is a growing interest in sustainable pest control measures, and therefore there is a need to increase the number of plant sources to reduce the gap between demand and supply. Industrial hemp is among potential plants with phytocompounds that can be used as an anti-feeding agent against insects. However, little is known about the ability of the hemp phytocompound as an anti-feeding agent against tobacco hornworms. This study aimed to determine the antifeeding properties of industrial hemp extract against tobacco hornworms in vitro. The ethanolic hemp extracts were prepared at 50, 25, 12.5, 6.25, 3.125, and 1.56 mg/ml. Extracts were incorporated into the artificial diet, fourth instar larvae were introduced into the diet and raised in the growth chamber at 27±2°C, 60±10% RH and photoperiod 12:12 hour light/dark for four days. The relative growth rate differed significantly between concentrations. The growth rate was -0.05 g/g/day at 50 mg/ml, indicating insect body shrinkage, and 0.11g/g/day at 25 mg/ml, indicating slow growth compared to the negative control, which increased by 0.19g/g/day. The highest concentration (50mg/ml) inhibited larvae growth by 100%, similar to Malathion, which was used as a positive control in the study, 25mg/ml inhibited growth by 71%, 12.5mg/ml by 59%, 6.25mg/ml by 51%. Furthermore, an antifeedant index of 68% at 50mg/ml and 62% at 25mg/ml was reported. The findings indicate that industrial hemp extract is a strong antifeedant against tobacco hornworms and, therefore, a strong source of insecticide to control the insect, and thus, a potential contribution to sustainable agriculture.
