EGG-LAYING SUPPRESSION IN DROSOPHILA-MELANOGASTER (DIPTERA, DROSOPHILIDAE) AND DACUS (BACTROCERA) OLEAE (DIPTERA, TEPHRITIDAE) BY PHLOROGLUCINOL, A PEROXIDASE INHIBITOR

Eggshell peroxidase (ESP) is responsible for the hardening process in several Diptera, including Drosophila melanogaster Meigen and Bactroce ra oleae Gmelin. Its action can be inhibited by phloroglucinol, a natu ral phenolic substance, during the formation of the egg-shell. We used phloroglucinol, in the diet of adults of D. melanogaster and B. oleae , at concentrations of 1 mM, 10 mM, 25 mM, 50 mM, 100 mM and 400 mM to study its effect on egg laying. In both insects, 1 mM had no effect. At concentrations above 10 mM, egg laying of D. melanogaster was gradu ally affected leading to the deposition of empty shells and chorion-le ss eggs, while in B. oleae, it was gradually suppressed and only amorp hous masses were laid. The effect of phloroglucinol at the tested conc entrations was reversible. It is concluded that phloroglucinol added a t appropriate, non-lethal concentrations, affected egg-laying of D. me lanogaster and B. oleae in different ways, related to differences in t he ovipositor diameter relative to egg size. In B. oleae, it is relati vely narrow, causing breakage of the phloroglucinol-induced non-elasti c egg-shell, since covalent crosslinking of the chorion proteins is pr evented. In D. melanogaster, chorion-less eggs and separate chorions a re laid, due to egg dechorionation. A possible field application of th ese results is discussed.