Selection and optimization of a semi-synthetic diet for mass rearing of helicoverpa armigera in local laboratory conditions, Sri Lanka

Abstract

The effective mass rearing of Helicoverpa armigera under laboratory conditions is essential for numerous entomological research and pest management programs, such as biocontrol studies, resistance identification, toxicology bioassays, and integrated pest management strategies. This study aimed to develop and optimize a cost effective, nutritionally balanced semi-synthetic diet for rearing H. armigera larvae at the Horticultural Crops Research and Development Institute (HORDI). Initially, four semi-synthetic diets with wheat, mung, chickpea, and corn flours as the main ingredients were evaluated alongside cabbage leaves and soaked-chickpea natural diets. Growth and reproductive parameters such as larval and pupal durations, larval and pupal weights, pupation and moth emergence percentages, and moth fecundity were assessed. Results revealed that mung bean and chickpea flour diets significantly outperformed the others, resulting in shorter larval and pupal durations, higher survival rates, and greater fecundity. Although mung bean flour yielded slightly better results than the chickpea flour diet, the chickpea diet was selected as the optimal main ingredient for the semi-synthetic diet due to its lower market cost. Subsequently, the chickpea diet was modified by replacing costly laboratory-grade ingredients, such as yeast extract, sucrose, and agar, with food-grade alternatives, such as instant dry yeast, sugar, and gelatin or agar-agar, in two modified diets. Of the two modified diets, the one using agar-agar (modified diet 1) showed comparable results to the original in all measured parameters, while the gelatin-based diet (modified diet 2) showed slightly delayed development and lower moth emergence, possibly owing to its stickiness, due to instability in room temperature. The study concludes that the chickpea-based semi-synthetic diets, particularly the modified version using cost-effective alternatives and food-grade agar-agar, offer a reliable, economical, and efficient solution for mass rearing H. armigera larvae under local laboratory conditions.