Abstract
This work has objectives to study the chemical composition of volatile extracts obtained from leaves of Polyalthia longifolia and Clausena anisata and to evaluate their ovicide and larvicide effects by fumigation against Sitotroga cerealella, as alternative to the pesticides of synthesis. The analyses of the extracts by GC-MS showed that the essential oil of P. longifolia contains 57 compounds representing 86.1% of oil and 26 compounds corresponding to 97.3% of the essential oil of C. anisata. The main compounds identified for the extract of P. longifolia are the β-Caryophyllene (24.5%), Allo-Aromadendrene (13.5%), the α-Zingiberene (9.4%), the α-Humulene (8.5%) and the α-Selinene (2.6%). The extract of C. anisata mainly composed of methyl chavicol (69.9%) is characterized by the presence of oxygenated monoterpens (1.4%), hydrogenated monoterpens (7.8%), hydrogenated sesquiterpens (16.2%), oxygenated sesquiterpens (1.7%) and of aromatic compounds (69.9%). The biological test results showed that the treatments by fumigation done with the essential oils reduce meaningfully (p<0.001) the bursting of the ovums on the paddy rice. The essential oil of C. anisata has completely inhibited the viability of the larvas and the emergence of adult butterflies from the dose 0.5 µl mL-1 contrary to P. longifolia that recorded respectively 10.0±0.3% and 50.0±0.2% at the strong dose 3 µl mL-1. The study has, otherwise, shown that the essential oils delayed the cycle of development “ovums to adult” of S. cerealella (29.0±0.4 to 35.4±0.5 days) in relation to the witness (25±0.1 days). The essential oil of C. anisata proved to be more poisonous for the juvenile stages of S. cerealella. These results provide the scientific basis for potential alternatives to the synthetic fumigants in subsistence and commercial agriculture.
Highlights
Rice has always been a basis common food in many countries in Africa
The results of the chemical analysis by gas chromatography and gas chromatography coupled with the mass Spectrometry (GC/MS) of the essential oil extracted of the leaves Clausena anisata harvested in Pahou (Benin) are shown in the Table 1 and 2
The species met in Cameroon seems completely different since Ngassoum et al (2004) showed that the majority compounds of the essential oil of the leaves of this plant are dominated by acyclic terpenic structures like the (Z)tagetenone (26.8%), the (E)-tagetenone (19.2%), the (E)neralidol (11.5%), accompanied by the D germacrene (9.2%)
Summary
Rice has always been a basis common food in many countries in Africa. It is the food source and its growth is the fastest through the continent (AfricaRice, 2012). These methods present several limits among which the adaptation of the insects and the resistant stump selection (Benhalima et al, 2004), the food poisonings compromising the human health, the pollution of the environment and the ecological messes (Regnault-Roger, 2002) Considering these ominous effects of the different methods of struggle in particular the one of the use of the chemical substances on the human health, other believable alternatives presenting less negative impacts on the environment and the human health deserve to be explored (Gueye et al, 2011). The essential oils of the leaves of Polyalthia longifolia and Clausena anisata have been studied for their ovicide and larvicide effects on Sitotroga cerealella
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