A simple artificial diet for feeding and sequestration assays for the milkweed bugs Oncopeltus fasciatus and Spilostethus saxatilis

Abstract

Insect artificial diets are not only an important tool for mass rearing, nutritional research, and maintaining laboratory colonies but also for studying insect‐plant interactions. For herbivorous insects able to sequester plant toxins, feeding and sequestration assays based on artificial diet allow for the investigation of physiological, ecological, and evolutionary questions which may be difficult to study using real plants representing complex chemical environments. We developed a simple artificial diet, consisting of sunflower meal pressed into pills, for the milkweed bugs Oncopeltus fasciatus (Dallas) and Spilostethus saxatilis (Scopoli) (Heteroptera: Lygaeidae), which are capable of sequestering cardenolides and colchicum alkaloids, respectively. We assessed insect performance, suitability of the diet for sequestration assays, and its shelf life. Compared to sunflower seeds which are widely used as a laboratory maintenance diet for milkweed bugs, no differences were found in terms of weight development, presence of deformities, speed of development, or mortality. Importantly, after feeding O. fasciatus and S. saxatilis sunflower pills enriched with crystalline ouabain (cardenolide) or colchicine (colchicum alkaloid), respectively, sequestration was observed in both species. Moreover, as a prerequisite to test ecological hypotheses, our method allows for adequate concentration control and homogenous distribution of toxins across the diet. Under relatively warm conditions (27 °C and 60% r.h.), the new diet was stable for up to 10 days when used for feeding assays with adult bugs. Therefore, studies focusing on the role of plant toxins in predator–prey interactions and plant defense, but also insecticide research could benefit from using this approach.