Study of the larvicidal activity of hydro-alcoholic extracts Nerium oleander L. and Ricinus communis L. on Tuta absoluta M.
The use of synthetic pesticides is now in frequent use in crop protection. But they are considered as a major problem on the environment, the flora and fauna or human health. Biopesticides of botanical origin are a good alternative to remedy this evil. Our study aimed at assessing the toxicity of hydro-methanoic, hydro-ethanoic and synergistic extracts of two toxic plants, including Nerium oleander and Ricinus communis growing spontaneously in Mostaganem area, on larvae of the tomato leafminer T. absoluta (Meyrick), which is considered as a serious pest on tomato crop in Algeria. The extraction yields (Method of Soxhlet) obtained by the two hydro-methanoic and hydro-ethanolic extracts are (26%, 18%) for N. oleander and (35%, 29%) for R. communis respectively. However, the hydro-methanoic extract remains the most effective. These extracts were tested adopting the method of toxicity by direct contact or spray". The biological tests on the larvae of T. absoluta have shown that there is a difference between the toxicity of hydro-methanoic and hydro-ethanolic extracts within the same plant. The synergistic extract caused a remarkable mortality rate that exceeded 90%. N. oleander et R. communis presented a low toxicity not exceeding 30% for the hydro-ethanolic extracts and 40% for the hydro-methanoic extracts. After 24 hours of exposure to the test, the LD50 values were very high (above 50%) for hydro-ethanolic and hydro-methanoic extracts for the two plants used. However, the LD50 values were relatively low for the synergistic extract (19%). The results showed that L2 and L1 larvae are most sensitive to all extracts used. The L3 and L4 are the most resistant, except for the synergistic extract.