Abstract:
Effectivenes of hexane, acetone and ethanol crude extracts from 4 plants including, star anise (Illicium verum), clove (Syzygium aromaticum), sweet fennel (Foeniculum vulgare) and lemon grass (Cymbopogon citratus) against stored product insect pests namely, corn weevil (Sitophilus zeamais) cowpea weevil (Callosobruchus maculatus) and southern cowpea weevil (Callosobruchus chinensis) was eveluated in laboratory by contact method. Innitial concentration of different extracts used was 157.2 µg/cm2 and insect mortality was observed at 24 hours. The result showed that hexane extract from star anise and clove performed high toxicity against those 3 insect pests. Following test of hexane crude extracts from both star anise and clove to all insect pests were made in order to obtain the toxicity levels at 24, 48 and 72 hours. It was found that hexane extract from star anise had the highest efficiency in killing corn weevil that showed the LC50 values of 131.5, 117.3 and 112.8 µg/cm2 at 24, 48 and 72 hours, respectively. While hexane extract from clove was extremely effective in killing cowpea weevil and southern cowpea weevil. Remarkably, it caused 100% insect mortality at the concentration of 31.4 and 27.5 µg/cm2 WIThin 48 hours. The result of repellent test revealed that hexane extracts of star anise and clove were able to repel those 3 insect pests with more than 80 %RI (Repellent Index) at 6 hours. Toxicity test of hexane extracts from star anise and cloves to corn weevil, cowpea weevil and southern cowpea weevil was further investigated by the method of seed coating. It was found that hexane extract of star anise was moderately and extremely toxic to corn weevil and southern cowpea weevil when at 5% concentration caused 52.7 and 100% mortality, respectively, followed by 3% concentration where the mortality percentage of 43 and 37.8% respectively was obtained. While hexane extract from clove was the most effective compound to kill cowpea weevil, therefor at 5% concentration presented the percentage of mortality as high as 100%, followed by 3% concentration which gave the percentage mortality up to 99%. As for the coated seeds with insecticides, it could kill all 3 insect pests with more than 90% throughout storage period of 6 months. The insecticidal test of those hexane plant extract in term of inhibition rate of progeny emerging was further investigated by seed coating method. It was found that hexane extracts from star anise and clove at 1% concentration could inhibit the emerging of those insect progenies up to 80% throughout 6 months. Additionally, the influence of hexane extracts from star anise and clove on seed germination was also invitigated. The corn and mung bean seeds were coated with those herbal extracts and stored at different conditions. It was found that the corn seed coated with hexane extract from clove at 1% concentration and kept at temperature of 4 and 25 degrees Celsius throughout the storage period of 6 months had the germination percentage up to 73.5 and 70.5% respectively. When the corn seed uncoated with this extract showed the germination percentage up to 95.0 and 97.5%, respectively. However, there were statistically significant differences between treatments of coated and non-coated seed. Amazing result found in mung bean seed, when star anise extract at 1% concentration kept at 4 and 25 degrees Celsius throughout the storage period of 6 months had very high germination percentages of 99.0 and 97.5% respectively, whereas, non-coated seed presented the germination percentage up to 100.0%, at both storage conditions under the temperature of 4 and 25 degrees Celsius, with no statistical differences among them.