VISIBLE LIGHT-ACTIVATABLE PORPHYRIN DERIVATIVES AS LARVICIDAL AGENTS WITH A LOW ENVIRONMENTAL IMPACT: STUDIES WITH AEDES ALBOPICTUS

In several cases, natural waters exhibit high levels of microbiological pollution, while insect larvae infestation often induces appreciable damages at a sanitary, economic and social level. As a consequence, such waters have been found to promote the transmission of infectious and parasitic diseases to farmed animals and man, thereby causing serious problems in agriculture. The rapid diffusion of Aedes albopictus in many Italian towns has a great impact from the point of view of public health since this mosquito is responsible for the onset of serious diseases, since it acts as vector of viruses which are etiologic agents of Dengue and Chikungunya. At present, the control of insect vectors of infectious diseases is based on the use of chemical compounds, namely insecticides or larvicides, often generating harmful effects to the environment. The present study aims at providing a contribution to the solution of such issues through the development of innovative technologies taking advantage of the combined action of porphyrin and visible light, that could represent a novel larvicidal strategy with favourable properties. Semi-field experiments were performed in a public area of Cadoneghe Municipality (Padova, North-East Italy). Six hundred Aedes albopictus larvae at the L2 an L3 stages were divided into groups of 50 individuals and were added to 12 trays, each one containing 2 liters of water. In the night preceding exposure of the larvae-infested water to sunlight, a formulate (named C-food) associated with a novel cationic porphyrin, namely meso-tri(N-methyl-pyridyl), mono(N-dodecyl-pyridyl) porphine (C12) bound with finely ground cat food was put in the trays at the concentration of 50 μM, while in 2 control trays only C-food without C12 was given. All the trays were subsequently exposed to sunlight starting at 8 a.m.: 90% of larvae in the C12 containing trays were killed within 4 h from the beginning of the sunlight exposure; no living larvae were found after 24 h. Control larvae showed an essentially complete survival. Therefore, photosensitization by means of the selected cationic porphyrin appears to represent a possible promising approach opening new perspectives for the disinfection of polluted waters by pathogenic agents of vector-borne diseases.