Optimizing biological control of the diamondback moth (Plutella xylostella): Evaluating the seasonality of its parasitoids and their impact in the Southeastern United States

Diamondback moth (DBM), Plutella xylostella, is a cosmopolitan pest of Brassicaceae crops, resulting in a global economic burden of $ 4-5 billion annually, due in part to its capacity for developing insecticide resistance. Several natural enemies of DBM attack its larval and pupal stages and alone can suppress DBM populations through high parasitism rates ( >80%). However, grower reliance on insecticides reduces beneficial natural enemies and selects for insecticide resistance. Insectary plants, such as sweet alyssum flowers, can enhance biocontrol if strategically introduced. This study investigates 1) DBM density and DBM parasitism rate correlation, 2) seasonal abundance of DBM parasitoid wasps and 3) relative contribution of parasitoid wasp species to DBM parasitism. Staggered collard plantings were maintained for over two years to collect DBM and its parasitoids in South Carolina. The collected insects were kept in lab for DBM adult or parasitoid emergence to determine the parasitism rate throughout the year. These results demonstrate when biological control is most and least impactful, and will aid future studies that utilize sweet alyssum to enhance conservation biological control. Overall, the seasonality of DBM parasitism provides baseline data to formulate an efficient, economical biocontrol program to reduce DBM pest problems, consequently decreasing the reliance on broad-spectrum pesticides and increasing farmers’ profitability in the southeastern United States.