Larvicidal effect of plant extracts on Tuta absoluta (Lepidoptera, Gelechiidae)
Abstract: Seven plants (Thymus vulgaris, Ricinus communis, Ononis natrix, Peganum harmala,Argania spinosa, Urtica dioïca, and Lawsonia inermis) collected in the Souss valley were testedfor their insecticidal effects on the larvae of Tuta absoluta under laboratory conditions. Aftermaceration in ethanol, extracts were obtained using a rotary evaporator. For each extract, 100%,20%, 10%, 2% and 1% concentrations were prepared for bioassays on the larvae of T. absoluta,according to the “Leaf-dip bioassay” method. The results showed that the extracts had varyinglevels of toxicity for the larvae. The extracts that produced the highest rates of mortality werethose of T. vulgaris leaves (95%) and the seeds of R. communis (58%), applied at concentrationsof 46667mg/l and 77500mg/l, respectively. The other plant extracts had a moderate larvicidaleffect. In fact, O. natrix, P. harmala, U. dioïca, L. inermis and A. spinosa, respectively, causedmortality rates of 45%, 43%, 42%, 32% and 28%. The LD90 of these extracts revealed that theethanol extract of T. vulgaris was the most toxic (LD90 = 89383mg/l).