Abstract
Surface contact toxicity of clove, Syzygium aromaticum L. Merr. & Perry, and rosemary, Rosmarinus officinalis L., oils were investigated against the American cockroach, Periplaneta americana (L.), in the laboratory. Both clove and rosemary oils showed variable mortality percentages according to concentration, exposure time and stage of the insect. Clove oil exhibited stronger toxic effects than rosemary oil. First instar nymphs were more sensitive than the fourth instars followed by adults. Clove oil induced highly significant contact toxic effects against P. americana nymphs and adults after 4, 24 and 48 h exposure. First and fourth instar nymphs were more sensitive to clove oil (LC50 values of 0.0001 and 0.0077 µl/cm2, respectively) than rosemary oil (LC50 values of 1.92 and 2.25 µl/cm2) after 24 h, respectively. Regarding adults, the effect of both oils was very weak after 48 h exposure. Adults of P. americana were the least sensitive to clove and rosemary oils, recording LC50 values 1.5375 and 6.09 µl/cm2, respectively. In continuous exposure tests, LT50 values correlated negatively with concentrations. Clove oil had lower LT50 values than rosemary oil. For clove oil the lowest LT50 values ranged between 14.10 and 4.85 h in case of the first instar at low concentration level of 0.0005–0.0020 µl/cm2 and 20.00 to 5.00 h for adults at high concentration level of 2.0–3.0 µl/cm2. While the LT50 was high for the fourth instar nymphs and ranged from 43.67 to 26.68 h at moderate concentrations, 0.002–0.010 µl/cm2, respectively. For rosemary oil the highest LT50 values were 115.03-97.00 h for adults followed by 32.76-8.86 h for the fourth instar nymphs and 25.45-5.62 h for first instars at the same concentrations level, 2–4 µl/cm2, respectively. Clove and rosemary oils may be used as promising botanical insecticides against P. americana.