The essential oil characteristics obtained by the hydro-distillation of plant used extract of Eucalyptus from the region of Tissemsilet is light (colorless) with a strong and clear odor. Eucalyptol (1.8-cinceole) is the major constituent of the 70-80% of oil, with compounds witch are terpene (
Bruneton, 1993). The yield of essential oil extracted after hydro distillation was found to be 1.05%.
Bruneton (1993) reported the content of Eucalyptus oil is between 0.5 and 3.5%.
Our objective was to determine the insecticidal effect of
E. globulus essential oils on
S. granarius and
S. oryzae. The criterion of oil efficiency is mortality, according to the following formula:
Regarding the first method which is ingestion, the insect was nourish by grains brushed with different doses.
After two hours of treatment the mortality rate of
S. oryzae was 0% for the first two doses while for the third dose it was 66%. After four hours, the mortality rate for the dose D3 has increased to 20%. After eight hours, the mortality rate reached 50% for the dose D3, 26.6% for (D2) and 10% (D1).
So the LD
50 (lethal dose for 50% of the population) was recorded after ingestion of grains (Fig 1). All mortality was recorded after 24 hours of treatment for a dose of 20μl of oil by ingestion while for the second species
S. granarius the mortality rate required longer than the previous species, it took 8 hours of treatment to reach 6.6% for D1 et D3 doses.
After one day, the highest mortality rate was 63.3% to increase on the second and third day to reach 90 and 100% for the dose (D3) (Fig 1).
After eight (8) hours of treatment the mortality rate reached 6.66% for the doses (D2) and (D3). It was only in the third day that mortality rates started to reach 16.6% for (D1) and 30% eatch for (D2) and (D3). On the fourth and fifth day mortality rates increased significantly to over 50% and reached 83.3%. More than 90% mortality on the sixth day is recorded for the different doses.
On the eighth day the mortality was 100% for the (D2) and (D3) with regard to the second method (Fig 2). The doses of the inhalation treatment were higher D1, D2, D3 respectively 30.40 and 50 microliters. The mortality rate of
S. oryzae after using eucalyptus oil as a biopesticide by this method causes 10% mortality.
After eight (08) hours the rate increased to 36.6% for (D3). In twenty-four hours, the mortality rate increased to 63.3% for (D3) exceeding the DL50, 26.6 for (D2) and 20% for (D1). On the second day and the third day the mortality rate continued to increase for all the three doses to reach 86.6 and 90%. On the fourth and fifth day the mortalities exceeded 90% (Fig 3). While for
S. granarius the mortalities recorded after the use of inalation begins to increase only after 3 days of treatment to reach only 20% with the D3 it took 5 days of treatment to arrive the LD50.
No mortality was recorded for the three different doses during two, four and eight hours of treatment. It was only after the first and second days, low mortality could be recorded especially for D2 and D3. On the third day the mortality rate was 20% for D3, 26.6% for D2, for D1 the rate was lower with 3.33%. On the fourth day the mortality rate reached 26.6% for D3, 40% for D2 and 16.6% for D1 at the fifth day the mortality rate (50%) for the dose D2, 40% for D3 and 23.3% for D1. After eighth and tenth day, the mortality rate reached 73.3% and gradually increased to 80% on the fifteenth (Fig 4).
Bekhechi et al., (2008) reported the insecticidal effect of Eucalyptus and the results of the present study showed the effect of this oil on the mortality for both the species of Sitophilus. The mortality rate of
S. oryzae was observed to be high in a very short time compared to
S. granarius with ingestion treatment. The absence of mortality in the control showed that our test was reliable for the studying the insecticidal effect of the essential oils tested.
With regard to the method of ingestion,
S. granarius recorded a mortality rate of 3.33% after four (04) hours of treatment and a rate of 6.66% and 6.66% after twenty four (24) hours. On the fourth and fifth day, mortality rates increased to 53% and 83.3%, respectively. After eight (08) days, the mortality rate was 100%.
While for
S. oryzae, the oil took effect earlier than that for the other species since after only two (02) hours the mortality rate reached 6.66% and 50% after eight (08) hours and after only (02) two days the mortality are 90% and reached 100% on the third day. The mortality rate of
S. granrius is lower than that of
S. oryzae. As these two species are different morphologically and in the duration of the development cycle (the time to have a generation).
So, the efficiency of the oil on S.
oryzae is better than on
S. granaius, since after 48 hours of use of the oil against
S. oryzae, its mortality rate increased to 90% whereas after the same period the mortality of the latter did not exceed 20%. For the inhalation method, the mortality rate for
S. orysae are remarkable with values reaching 10% after two (02) hours of treatment, 36.6% after eight hours, 63.3% (a significant value) after one (01) day and exceeded 90% on the fourth and fifth day.
S. granarius, recorded 3.33% and 10% mortality after one and two days respectively. The mortality rate reached 40% on the fourth 50% on the fifth day. Eighty per cent mortality could be achieved only after 15 days of treatment It.
The method of inhalation required a larger amount of oil and more time compared to the method of ingestion. The doses used were higher and the effectiveness of the oil on
S. oryzae was more marked than that on
S. granarius.
S. oryzae proved to be more sensitive to oil than
S. granarius, which was more tolerant resistant.