Fly into the light: eliminating Drosophila melanogaster with chlorophyllin-based Photodynamic Inactivation.

Abstract

Fruit flies spoil crops in agricultural settings. As conventional pesticides may generate negative off-target effects on humans or the environment, existing treatment methods need eco-friendly and safe alternatives. Photodynamic Inactivation (PDI) is based on the photosensitizer-mediated and light-induced overproduction of reactive oxygen species in targets. We here explore the potential of PDI for the control of fruit fly pests. Drosophila melanogaster serves as well-established model organism in this study. Two distinct experimental approaches are presented: the feed assay, in which fruit flies are provided with sodium magnesiumchlorophyllin (Chl, approved as food additive E140) along with sucrose (3%) as their food, and the spray assay, where the photosensitizer is sprayed onto the insects. We show that PDI based on Chl can induce moribundity rates of Drosophila melanogaster of more than 99% with 5mM Chl and LED illumination (395nm, 8h incubation in the dark, radiant exposure 78.9J/cm2) with the feed assay. If the radiant exposure is doubled to 157.8J/cm2, 88% of insects are killed by PDI based on 1mM Chl. The photoactive compound is also effective if presented on strawberries without addition of sucrose with somewhat lower moribundity (71% at 5mM Chl). Spraying Chl onto insects is less effective than feeding the photosensitizer: 5mM Chl resulted in 79.5% moribundity (drug to light interval 8h, radiant exposure 78.9J/cm2), but if 5h of sun light (532J/cm2) and overnight (14h) dark incubation is used for activation of Chl, more than 95% of insects are killed. As conclusion, Chl serves as effective photoinsecticide against Drosophila melanogaster if a drug to light interval of 8h is maintained. Feeding the photoactive compound together with sucrose is more effective than spraying it onto insects and increasing the radiant exposure allows for lowering the photosensitizer concentration. Photodynamic Inactivation might therefore represent an eco-friendly addition to the farmers armamentarium against (semi-transparent) insects.