Chemical composition, toxic and development- and reproduction-inhibiting effects of some essential oils against Tetranychus urticae Koch (Acarina: Tetranychidae) as fumigants

The two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), is one of the most serious pests of many crops both indoors and outdoors in south-western Turkey (Antalya). In the present study, essential oils (EOs) from five medicinal and aromatic plants [Mentha pulegium L. (Labiatae), Foenicultan vulgare Mill. (Umbelliferae), Pistacia terebinthus L., Schinus molle L. (Anacardiaceae) and Vitex agnus-castus L. (Verbenaceae)] were tested for their fumigant toxic and development- and reproduction-inhibiting effects against the pest under in vivo conditions. In the fumigant toxicity assays, newly emerged (0-24 h) adult females and larvae and 0-24-h-old eggs of the mite were exposed to four different concentrations of each EO for 12 h in separate desiccators (10 L) used as test chambers. In the development- and reproduction-inhibiting assays, newly emerged (0-24 h) female deutonymphs of the mite were separately exposed to a lower concentration (0.5 mu L/L for M. pulegium, 2 mu L/L for F. vulgare, 2.5 mu L/L for P. terebinthus and 10 mu L/L for V. agnus-castus and S. molle) of each EO in desiccators for 12 h, and then, 20 survivors from each EO were individually maintained on cotton leaf discs to obtain data on some parameters (adult emergence rate, number of eggs per female, egg-hatching rate, etc.) until there are no living individuals. The results from the study indicated that all the EOs had fumigant effect against the mite in varying degrees. M. pulegium was found to be the most toxic oil against all the biological stages tested (LC50 = 0.60 mu L/L air for eggs, 0.60 mu L/L air for larvae and 0.49 mu L/L air for adult females), followed by F. vulgare (LC50 = 2.67 mu L/L air for eggs and adult females, and 2.56 mu L/L air for larvae). M. pulegium EO also had the highest development- and reproduction-inhibiting effect on the pest. Fecundity was reduced by 55.9% and egg hatching was inhibited by 29.9% in survivors of deutonymphs of T. urticae fumigated with M. pulegium EO at 0.5 mu L/L air for 12 h. In the phytotoxicity assays with tomato, cucumber, Phaseolus and eggplant seedlings, scattered necrotic spots and slight chlorosis only on the young foliage of cucumber seedlings exposed to M. pulegium EO at the highest concentration for 12 h were visual symptoms of phytotoxicity. Overall results indicate that M. pulegium EO can be used in the management of T. urticae in greenhouses as a fumigant for both toxic and development- and reproduction-inhibiting effects.