Action des huiles lourdes de graines de trois plantes spontanées du Sahara Algérien sur quelques paramètres biologiques du Criquet pèlerin

Abstract

Our study’s objective is to test the lethal and sub-lethal effects of heavy seed oils from three spontaneous plants from the Algerian Sahara, which are Peganum harmala L. (Zygophyllaceae) and Cleome arabica L. (Capparidaceae) and Datura stramonium L. ( Solanaceae) against L5 larvae and imagos of Schistocerca gregaria Forsk. (Orthoptera-Acrididae). The treatment technique consists of injecting a dose of pure seed oil into the insect's esophagus using a micropipette. The seed oil doses injected into L5 larvae and imagoes of S. gregaria are 60 µl/individual and 120 µl/individual, respectively. The doses injected into L5 larvae and imagoes of S. gregaria are 60 µl/individual and 120 µl/individual, respectively. Forced buccal injection of heavy vegetable oils in treated L5 larvae and imagoes of S. gregaria showed various toxicological symptoms, i.e. movement disorders, diarrhea, reduction in food intake, weight loss, digestive disorders, retardation and difficulties in molting and in the extreme cases, death. S. gregaria L5 larvae treated with P. harmala seed oil showed a mortality rate of 50% after 12 days. In addition, L5 larvae treated with C. arabica seed oil had a mortality rate of 63.63% after 16 days of treatment. Whereas we obtained with D.stramonium seed oil a mortality rate of 100% after only 7 days of treatment. It seems that the most toxic seed oil on the L5 larvae of S.gregaria is that of D.stramonium followed by the oil of C.arabica and finally that of P.harmala. In addition, imagos of S. gregaria treated with P. harmala and C. arabica seed oils showed mortality rates of 50% and 45.45% respectively after 29 days. Whereas, imagoes treated with D.stramonium seed oil reached 100% mortality rate after 13 days. Similarly, D.stramonium seed oil is also found to be more toxic to S.gregaria imagos than P.harmala and C.arabica seed oils. In addition, it appeared that imagos are more sensitive to the lethal action caused by the seed oil of P.harmala compared to the seed oil of C.arabica. The evaluation of lethal time 50 (TL50), showed that the shortest TL50 are recorded in L5 larvae treated with D.stramonium seed oil, it is 3.54 days in male L5 larvae and 5.97 days in female L5 larvae, followed by male L5 larvae treated with C. arabica seed oil with 7.6 days, then that of male L5 larvae treated with P. harmala with 8.47, then that of female L5 larvae treated with P.harmala and C.arabica seed oil with 9.5 days and 11.09 days respectively. Moreover, in S. gregaria imagos the shortest TL50 are recorded in imagos treated with D. stramonium seed oil, with 5.62 days in males and 5.74 days in females, then that female and male imagos treated with P.harmala seed oil with 22.52 days and 23.48 days respectively. The highest TL50 are recorded in imagos treated with C. arabica seed oil, with 24.54 days in male imagos, and finally that of female imagos with 27.23 days. At the same time, it seems that the lethal action of D.stramonium seed oil is faster compared to the two seed oils of P.harmala and C.arabica in this locust. The deterrent effects of the tested seed oils on the appetite and digestion of this locust are reflected in the weight losses recorded in the L5 larvae and treated imagoes of S. gregaria. S.gregaria L5 larvae treated with P.harmala and C.arabica seed oils show a low weight gain of around 15.64±31.35% and 14.28±38.74% respectively. While, L5 larvae treated with D.stramonium seed oil show a drop in weight of -17.55±36.97%. In addition, a reduction in weight gain was observed in imagos of S. gregaria treated with C. arabica and P. harmala seed oils, which are respectively of the order of 21.28 ± 22.65% and 15.51±31.35%, while the imagos of S. gregaria treated with D. stramonium seed oil recorded a drop in weight gain of the order of -22.44 ± 25.02%. The three heavy vegetable oils tested have toxic effects on L5 larvae and imagos of S. gregaria, the toxic effects vary with the injected seed oil, the treatment dose, the sex and the development stage of the insect.