# Chemical Composition and Insecticidal and Repellent Effect of Essential Oils of TwoPremna Species against Sitotroga cerealella

Authors: Elvis Adjalian; Philippe Sessou; Théophile Odjo; Gilles Figueredo; Dansou Kossou; Félicien Avlessi; Chantal Menut; Dominique Sohounhloué
Journal: Journal of Insects
 (2015)

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## Abstract

This work aims to study for the first time the chemical composition and evaluate insecticidal and repellent effects of essential oils ofPremna angolensis and Premna quadrifolia leaves, against Sitotroga cerealella, an insect pest of rice stocks as alternatives to synthetic pesticides. The GC-MS analysis showed that essential oil of P. angolensis contains 29 compounds representing 96.1% of the oil and 42 compounds corresponding to 91% for the essential oil of P. quadrifolia. The main constituents regardless of the species were β-caryophyllene (13.1%), (E)-β-caryophyllene (13.5%), octen-3-ol (3.2%–28%), phytol (3.7%–4.9%), β-elemene (1.4%–21%), globulol (11.2%), germacrene-D (8.9%), α-humulene (2.9%–6.4%), α-pinene (5%), sabinene (3.7%), δ-cadinene (0.4%–3.3%), and linalool (3.3%). The results of laboratory tests showed that both essential oils have insecticidal and repellent effects on S. cerealella. Presenting the results, the damage caused by the adults and larvae of S. cerealella was evaluated by calculating the percentage of grains attacked and weight loss thereof. The results suggest that volatile extracts of P. angolensis and P. quadrifolia can be used as alternatives to synthetic chemicals in paddy protection against S. cerealella.


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## Body

## 1. Introduction

The genusPremna L. (Verbenaceae) contains about 200 species worldwide, which are distributed mainly in tropical and subtropical parts of Asia, Africa, Australia, and the Pacific Islands [1, 2]. Previous studies on chemical constituents of the genusPremna led to the isolation of triterpenes, diterpenes, and sesquiterpenes [3], some of them exhibiting significant antibacterial activities [4]. When antiparasitic activity of new Caledonian medicinal plants includingPremna serratifoliaL. was evaluated, it was observed thatP. serratifolia was active againstLeishmania donovani with IC50 values between 0.5 and 5 μg·mL−1 [5]. In addition, some preparations of plants of the genusPremna have been used in the treatment of liver disorders and antioxidant as well as for their immune modulatory effects [6] in the traditional Indian system of medicine. ThePremna genus can be used in treating various ailments like rheumatism, asthma, dropsy, cough, fever, boils, and scrofulous disease. Traditionally in tropical Africa and Benin in particular, people with low purchasing power very often use odors produced by aromatic plants collected locally for the control of insects. This is the case ofPremna angolensis Gürke andPremna quadrifolia Schum. & Thonn., leaves of which are burned and used by producers, as a fumigant in the attics of cereals against pests. In this study, extracts from leaves of both speciesP. angolensis andP. quadrifolia harvested in Benin were analyzed by gas chromatography-mass spectrometry (GC/MS) for the first time. The insecticidal and repellent activities were tested on the Angoumois grain mothSitotroga cerealella (L.) (Lepidoptera: Gelechiidae) in rice storage.


## 2. Material and Methods

### 2.1. Plant Material and Distillation of the Volatile Constituents

Leaves ofP. angolensis andP. quadrifolia were collected from the municipality of Comé by the authors and certified at the National Herbarium of Abomey-Calavi University. The collected plant materials were stored in the laboratory between 18 and 20°C in the shade of the sunlight throughout the period of extraction. The essential oils were obtained by hydrodistillation of the leaves (450 g) for five hours using a Clevenger-type extractor according to British Pharmacopoeia method [7]. They were then dried over anhydrous sodium sulfate and analyzed by GC/MS.


### 2.2. Test Organisms

Individuals ofS. cerealella used for mass rearing for this study come from the reserve WARDA (Benin). Rearing conditions were T=29±2°C, RH=70±10%.


### 2.3. Analysis of the Volatile Constituents

#### 2.3.1. GC/MS

The essential oils were analysed on a Hewlett-Packard gas chromatograph Model 7890, coupled to a Hewlett-Packard MS Model 5875, equipped with a DB5 MS column (30 m× 0.25 mm; 0.25 μm), programming from 50°C (5 min) to 300°C at 5°C/min, 5 min hold. Helium was used as carrier gas (1.0 mL min−1); injection was made in split mode (1 : 30); injector and detector of temperature were at 250 and 280°C, respectively. The MS working in electron impact mode was at 70 eV; electron multiplier was 2500 eV; ion source temperature was 180°C; mass spectra data were acquired in the scan mode inm/z range 33–450.


#### 2.3.2. GC/FID

The essential oils were analyzed on a Hewlett-Packard gas chromatograph Model 6890, equipped with a DB5 MS column (30 m× 0.25 mm; 0.25 μm), programming from 50°C (5 min) to 300°C at 5°C/min, 5 min hold. Hydrogen was used as carrier gas (1.0 mL min−1); injection was in split mode (1 : 60); injector and detector temperature were 280 and 300°C, respectively. The essential oil was diluted in hexane: 1/30. The compounds assayed by GC in the different essential oils were identified by comparing their retention indices with those of reference compounds in the literature and confirmed by GC-MS by comparison of their mass spectra with those of reference substances [8–10].


### 2.4. Test

All tests were performed at a temperature of29±2°C and natural photoperiod with relative humidity 70±10%.


### 2.5. Contact Toxicity Tests with Essential Oils

Bioassays were performed using the method described by Noudogbessi et al. [11]. The temperature of the test medium ranged from 25°C to 31°C and relative humidity was 80%. Five concentrations (0, 3, 5, 10, and 15 μL mL−1) depending on the selected chemical profile of each essential oil in absolute ethanol solution were tested. The plant material, paddy rice grains of the variety “IR841,” was treated with each essential oil. After 24 h, 5 males and 10 females ofS.cerealella, aged 0 to 24 h, were deposited on the treated plant material. Overall, 5 doses × 3 repeats × 2 types of oil = 30 experimental units (containers) were implemented. The control sample treated only with ethanol was also infested byS. cerealella. Adult mortality was monitored 96 h after exposure to the essential oils. Then the insects were separated from the grains. The emergence of new insects was then observed at intervals of 24 h in the experimental units to the 50th day after infestation. Assessment concerned the rate of infested grains and weight loss of grains of rice.To assess theS. cerealella damage on the rice seeds after treatment, the substrate grains were collected, counted, and weighed. The rate of weight loss of dry material of the grains was determined according to MCP (Method of Counting and Weighing) and MSVW (Method of Standard Volumetric Weight) [12]. Two criteria of assessment of the damage are commonly used: the percentage of attack of grains (A%) and percentage of weight loss (B%) [13], respectively, calculated by the equations:(1)A%=NaNa+Ns×100,B%=PsNa-PaNsPsNa+Ns×100,where Na is number of attacked grains, Ns is number of healthy grains, Pa is weight of damaged grains, and Ps is weight of healthy grains.


### 2.6. Repellency Tests

The repellent action of the plants was tested in an olfactometer (Figure1), consisting of a 75 cm glass tube of 4 cm in diameter, with a 29 mm hole in the middle. At either end of the tube, a small jar was placed containing either 10.0 g containing paddy rice treated with only ethanol or 10.0 g of paddy rice seeds mixed with a solution of essential oil at concentrations 0.1%, 0.5%, and 1%. The hole in the middle was covered with gauze, whereas the ends of the tube were closed by putting a plastic petri dish against them. Air was gently (ca I mls) sucked away from the centre of the tube to prevent the accumulation of plant odor in the tube.Figure 1
Olfactometer set-up. An individual female Angoumois grain moth was introduced in the center of the tube. Her position was recorded after 15 min since introduction. Treated and control paddy rice were positioned at either end of the tube.Ten femaleS.cerealella aged 24 h to 48 h were released one after the other in the middle of the tube through the hole. Insect behavior was observed and the position was recorded for 15 min. Both volatile extracts were tested once before the second round. Insects were considered to have made a choice when entered in one of the jars containing rice grains or those who have reached the last twenty-five centimeters of the tube. For those who chose the middle of the tube, they have finally made a choice. The percentage of insects rejected was calculated using the following formula:(2)Percentage  Repellency%=A-BA+B×100,where A is average number of insects present in the untreated portion (insects repelled) and B is average number of insects in the treated (not repelled insects) part.The average percentage of repulsion for the essential oil was calculated and assigned according to previous ranking [14] to one of several repulsive classes ranging from 0 to V: class 0 (Percentage Repellency (PR) < 0,1%), class I (PR = 0,1–20%), class II (PR = 20,1–40%), class III (PR = 40,1–60%), class IV (PR = 60,1–80%), and class V (PR = 80,1–100%).


### 2.7. Statistical Analysis

The results from the observations were statistically processed by Analysis of Variance (ANOVA) using SAS (Statistical Analysis System) Version 9.1. Finally, an average of the percentages of the three results of the test was made. The results of statistical tests were considered significantly different if the probability of the hypothesis was less than or equal to 5%.


## 2.1. Plant Material and Distillation of the Volatile Constituents

Leaves ofP. angolensis andP. quadrifolia were collected from the municipality of Comé by the authors and certified at the National Herbarium of Abomey-Calavi University. The collected plant materials were stored in the laboratory between 18 and 20°C in the shade of the sunlight throughout the period of extraction. The essential oils were obtained by hydrodistillation of the leaves (450 g) for five hours using a Clevenger-type extractor according to British Pharmacopoeia method [7]. They were then dried over anhydrous sodium sulfate and analyzed by GC/MS.


## 2.2. Test Organisms

Individuals ofS. cerealella used for mass rearing for this study come from the reserve WARDA (Benin). Rearing conditions were T=29±2°C, RH=70±10%.


## 2.3. Analysis of the Volatile Constituents

### 2.3.1. GC/MS

The essential oils were analysed on a Hewlett-Packard gas chromatograph Model 7890, coupled to a Hewlett-Packard MS Model 5875, equipped with a DB5 MS column (30 m× 0.25 mm; 0.25 μm), programming from 50°C (5 min) to 300°C at 5°C/min, 5 min hold. Helium was used as carrier gas (1.0 mL min−1); injection was made in split mode (1 : 30); injector and detector of temperature were at 250 and 280°C, respectively. The MS working in electron impact mode was at 70 eV; electron multiplier was 2500 eV; ion source temperature was 180°C; mass spectra data were acquired in the scan mode inm/z range 33–450.


### 2.3.2. GC/FID

The essential oils were analyzed on a Hewlett-Packard gas chromatograph Model 6890, equipped with a DB5 MS column (30 m× 0.25 mm; 0.25 μm), programming from 50°C (5 min) to 300°C at 5°C/min, 5 min hold. Hydrogen was used as carrier gas (1.0 mL min−1); injection was in split mode (1 : 60); injector and detector temperature were 280 and 300°C, respectively. The essential oil was diluted in hexane: 1/30. The compounds assayed by GC in the different essential oils were identified by comparing their retention indices with those of reference compounds in the literature and confirmed by GC-MS by comparison of their mass spectra with those of reference substances [8–10].


## 2.3.1. GC/MS

The essential oils were analysed on a Hewlett-Packard gas chromatograph Model 7890, coupled to a Hewlett-Packard MS Model 5875, equipped with a DB5 MS column (30 m× 0.25 mm; 0.25 μm), programming from 50°C (5 min) to 300°C at 5°C/min, 5 min hold. Helium was used as carrier gas (1.0 mL min−1); injection was made in split mode (1 : 30); injector and detector of temperature were at 250 and 280°C, respectively. The MS working in electron impact mode was at 70 eV; electron multiplier was 2500 eV; ion source temperature was 180°C; mass spectra data were acquired in the scan mode inm/z range 33–450.


## 2.3.2. GC/FID

The essential oils were analyzed on a Hewlett-Packard gas chromatograph Model 6890, equipped with a DB5 MS column (30 m× 0.25 mm; 0.25 μm), programming from 50°C (5 min) to 300°C at 5°C/min, 5 min hold. Hydrogen was used as carrier gas (1.0 mL min−1); injection was in split mode (1 : 60); injector and detector temperature were 280 and 300°C, respectively. The essential oil was diluted in hexane: 1/30. The compounds assayed by GC in the different essential oils were identified by comparing their retention indices with those of reference compounds in the literature and confirmed by GC-MS by comparison of their mass spectra with those of reference substances [8–10].


## 2.4. Test

All tests were performed at a temperature of29±2°C and natural photoperiod with relative humidity 70±10%.


## 2.5. Contact Toxicity Tests with Essential Oils

Bioassays were performed using the method described by Noudogbessi et al. [11]. The temperature of the test medium ranged from 25°C to 31°C and relative humidity was 80%. Five concentrations (0, 3, 5, 10, and 15 μL mL−1) depending on the selected chemical profile of each essential oil in absolute ethanol solution were tested. The plant material, paddy rice grains of the variety “IR841,” was treated with each essential oil. After 24 h, 5 males and 10 females ofS.cerealella, aged 0 to 24 h, were deposited on the treated plant material. Overall, 5 doses × 3 repeats × 2 types of oil = 30 experimental units (containers) were implemented. The control sample treated only with ethanol was also infested byS. cerealella. Adult mortality was monitored 96 h after exposure to the essential oils. Then the insects were separated from the grains. The emergence of new insects was then observed at intervals of 24 h in the experimental units to the 50th day after infestation. Assessment concerned the rate of infested grains and weight loss of grains of rice.To assess theS. cerealella damage on the rice seeds after treatment, the substrate grains were collected, counted, and weighed. The rate of weight loss of dry material of the grains was determined according to MCP (Method of Counting and Weighing) and MSVW (Method of Standard Volumetric Weight) [12]. Two criteria of assessment of the damage are commonly used: the percentage of attack of grains (A%) and percentage of weight loss (B%) [13], respectively, calculated by the equations:(1)A%=NaNa+Ns×100,B%=PsNa-PaNsPsNa+Ns×100,where Na is number of attacked grains, Ns is number of healthy grains, Pa is weight of damaged grains, and Ps is weight of healthy grains.


## 2.6. Repellency Tests

The repellent action of the plants was tested in an olfactometer (Figure1), consisting of a 75 cm glass tube of 4 cm in diameter, with a 29 mm hole in the middle. At either end of the tube, a small jar was placed containing either 10.0 g containing paddy rice treated with only ethanol or 10.0 g of paddy rice seeds mixed with a solution of essential oil at concentrations 0.1%, 0.5%, and 1%. The hole in the middle was covered with gauze, whereas the ends of the tube were closed by putting a plastic petri dish against them. Air was gently (ca I mls) sucked away from the centre of the tube to prevent the accumulation of plant odor in the tube.Figure 1
Olfactometer set-up. An individual female Angoumois grain moth was introduced in the center of the tube. Her position was recorded after 15 min since introduction. Treated and control paddy rice were positioned at either end of the tube.Ten femaleS.cerealella aged 24 h to 48 h were released one after the other in the middle of the tube through the hole. Insect behavior was observed and the position was recorded for 15 min. Both volatile extracts were tested once before the second round. Insects were considered to have made a choice when entered in one of the jars containing rice grains or those who have reached the last twenty-five centimeters of the tube. For those who chose the middle of the tube, they have finally made a choice. The percentage of insects rejected was calculated using the following formula:(2)Percentage  Repellency%=A-BA+B×100,where A is average number of insects present in the untreated portion (insects repelled) and B is average number of insects in the treated (not repelled insects) part.The average percentage of repulsion for the essential oil was calculated and assigned according to previous ranking [14] to one of several repulsive classes ranging from 0 to V: class 0 (Percentage Repellency (PR) < 0,1%), class I (PR = 0,1–20%), class II (PR = 20,1–40%), class III (PR = 40,1–60%), class IV (PR = 60,1–80%), and class V (PR = 80,1–100%).


## 2.7. Statistical Analysis

The results from the observations were statistically processed by Analysis of Variance (ANOVA) using SAS (Statistical Analysis System) Version 9.1. Finally, an average of the percentages of the three results of the test was made. The results of statistical tests were considered significantly different if the probability of the hypothesis was less than or equal to 5%.


## 3. Results

Chromatographic analysis of the essential oil extracted from leaves ofP. angolensis detected 29 compounds representing 96.1% of the weight of the essential oil (Table 1). However sesquiterpenes hydrogenated (26.6%) and oxygen (20%) were predominant. As forP. quadrifolia, 43 compounds were identified representing 91% of the essential oil. It was dominated by the hydrocarbon sesquiterpenes (65.5%) (Table 1). The predominant compounds of the two essential oils, regardless of species and their origin, were β-caryophyllene (13.1%), (E)-β-caryophyllene (13.5%), octen-3-ol (3.2%–28%), phytol (3.7%–4.9%), β-elemene (1.4%–21%), globulol (11.2%), germacrene-D (8.9%), α-humulene (2.9%–6.4%), α-pinene (5%), sabinene (3.7%), δ-cadinene (0.4%–3.3%), and Linalool (3.3%).Table 1
Yield and chemical composition of essential oil ofP. angolensis and P. quadrifolialeaves.
N
°
Name of the compound
RI
Premna angolensis
Premna quadrifolia
(%)
(%)
1
(Z)-3-Hexen-1-ol
850
1.0
—
2
α-Pinene
933
5.0
—
3
Sabinene
965
—
3.7
4
β-Pinene
970
—
0.6
5
Octen-3-ol
973
28.0
3.2
7
Octan-3-one
977
2.7
—
8
Myrcene
987
0.3
—
9
Octan-3-ol
991
1.4
—
10
α-Phellandrene
996
—
1.0
11
Limonene
1022
—
1.9
12
β-Phellandrene
1023
—
0.6
13
p-Cymene
1024
0.5
0.8
14
Eucalyptol
1025
—
t
15
Limonene
1027
1.4
—
16
(E)-β-Ocimene
1039
—
0.1
17
γ-Terpinene
1051
—
0.1
18
(Z)-Sabinene hydrate
1064
—
0.1
19
Linalool
1096
3.3
—
20
Triacetonamine
1108
—
2.8
21
Terpinen-4-ol
1174
2.5
0.5
22
Naphthalene
1178
—
0.9
23
α-Terpineol
1188
—
0.1
24
Methyl salicylate
1194
2.2
—
25
Nerol
1221
t
—
26
Ethyl salicylate
1266
t
—
27
α-Cubebene
1339
—
0.2
28
α-Ylangene
1362
—
0.1
29
α-Copaene
1369
—
1.7
30
β-Elemene
1374
1.4
21
31
(E)-β-Damascenone
1384
1.2
—
32
α-Gurjunene
1400
—
2.0
33
β-Caryophyllene
1414
—
13.1
34
γ-Elemene
1421
—
1.1
35
(E)-β-Caryophyllene
1424
13.5
—
36
(E)-α-Bergamotene
1424
—
0.8
37
Aromadendrene
1443
0.6
—
38
(Z)-β-Farnesene
1443
—
0.2
39
Alloaromadendrene
1454
—
0.4
40
α-Humulene
1458
6.4
2.9
41
Selina-4,11-diene
1466
—
1.1
42
Germacrene-D
1475
—
8.9
43
β-Selinene
1486
0.6
1.6
44
γ-Patchoulene
1490
2.8
—
45
α-Bulnesene
1490
—
1.8
46
α-Farnesene
1494
—
0.8
47
δ-cadinene
1499
0.9
—
48
β-Bisabolene
1499
—
1.9
49
Germacrene A
1501
—
0.2
50
γ-Cadinene
1506
—
0.9
51
(Z)-Calamenene
1512
—
0.4
52
δ-Cadinene
1525
0.4
3.3
53
Germacrene B
1553
—
1.1
54
(E)-Nerolidol
1562
0.7
—
55
Epiglobulol
1565
2.2
—
56
Spathulenol
1571
—
0.2
57
Caryophyllene oxide
1577
—
1.3
58
Globulol
1590
11.2
—
59
Humulene epoxide II
1616
0.9
—
60
Epi-α-muurolol
1649
—
1.2
61
Selin-11-en-4-α-ol
1653
—
1.5
62
α-Cadinol
1658
1.0
—
63
Intermedeol
1673
0.3
—
64
Phytol
2048
3.7
4.9
Total (%)
96.1
91%
Yield (%)
0.056
0.102
Hydrogenated monoterpenes (%)
8.6
8.9
Oxygenated monoterpenes (%)
9.2
4.3
Hydrogenated sesquiterpenes (%)
26.6
65.5
Oxygenated sesquiterpenes (%)
20
9.1
Oxygenated aliphatic compounds (%)
31.7
3.2
t (traces) = 0.1%; RI: retention index.The results of the estimation of the influence of different concentrations (0 to 15μL mL−1) of the two essential oils on adult mortality ofS. cerealella, the emergence of young insects, the rate of grains attacked, and loss corresponding weights are shown in Tables 2 and 3. Mortality rates of insects in Table 2 were obtained 4 days after treatment of the grains of paddy rice which ranged between 0 and concentrations 15 μL mL−1. At a concentration of 3 μL·mL−1P. angolensis essential oil showed over 90% mortality through its contact activity on the adults ofS. cerealella. The number of grains damaged and the loss of the weight of rice decrease when the dose of essential oil increases. The insecticidal effect ofP. quadrifolia essential oil was less noticed compared to the essential oil ofP. angolensis, with significant difference (P<0.001). In the controls sample, we noticed that the number of adults ofS. cerealella increased rapidly and reached the rate of 89.62±0.01 withP. quadrifolia and 85.71±0.03 withP. angolensis.Table 2
Rate ofS. cerealelladeath, of emergence, of number of rice attacked (A), and of weight loss (B) provoked by P. angolensis essential oil in contact method.
Dose (μL mL−1)
Mortality
Emerged
A (%)
B (%)
0
18.78 ± 0.07b
85.71 ± 0.03a
25.19 ± 2.41b
22.726 ± 1.955b
3
90.12 ± 0.30a
1.07 ± 0.06b
0.37 ± 0.01c
0.003 ± 0.048c
5
94.26 ± 0.17a
0.40 ± 0.11c
0.32 ± 0.020c
0.046 ± 0.028c
10
100 ± 0.00a
0.33 ± 0.05cd
0.26 ± 0.02c
0.003 ± 0.024c
15
100 ± 0.00a
0.13 ± 0.10d
0.15 ± 0.02c
0.000 ± 0.020c
Probability
<0.001∗∗∗
<0.001∗∗∗
<0.001∗∗∗
<0.001∗∗∗
CV (%)
13.75
10.58
18.76
16.85
0: ethanol treatment (control);∗∗∗very highly significant difference (0.1%).
The averages followed by the same letter were not significantly different at the beginning of 5%.Table 3
Rate ofS. cerealelladeath, of emergence, of number of rice attacked (A), and of weight loss (B) provoked by P. quadrifolia essential oil in contact method.
Dose (μL mL−1)
Mortality
Emerged
A (%)
B (%)
0
10.82 ± 0.17d
89.62 ± 0.01a
25.44 ± 0.93b
24.31 ± 0.28b
3
57.96 ± 0.05c
2.10 ± 0.04b
0.61 ± 0.05c
0.01 ± 0.00c
5
70.38 ± 0.00bc
1.62 ± 0.08b
0.48 ± 0.05c
0.05 ± 0.02c
10
76.75 ± 0.12ab
1.28 ± 0.05b
0.35 ± 0.04c
0.04 ± 0.03c
15
88.85 ± 0.17a
0.13 ± 0.10c
0.07 ± 0.01c
0.04 ± 0.01c
Probability
<0.001∗∗∗
<0.001∗∗∗
<0.001∗∗∗
<0.001∗∗∗
CV (%)
14.21
7.51
7.90
6.02
0: ethanol treatment (control);∗∗∗very highly significant difference (0.1%).
The averages followed by the same letter were not significantly different at the beginning of 5%.Repellent Effect of Essential Oils Tested. The percentages of repulsion for the different doses of the essential oil of the leaves ofP.quadrifolia andP.angolensis are summarized in Table 4. The different doses of essential oils (0.1%, 0.5%, and 1%) caused 67.11% to 96.84% repellency forP.angolensis and 65.55% to 91.55% forP.quadrifolia. This clearly shows that the percentage of repulsion increases with the dose.Table 4
Percentage (%) of the repellence with olfactometer of the essential oil of the leaves ofP. angolensis and P. quadrifolia on adult Sitotroga cerealella.
Dose (%)
Repellency rate (%) (±SD)
P. angolensis
P. quadrifolia
0.1
67.11 ± 10.95
65.55 ± 12.86
0.5
88 ± 10.95
83.55 ± 9.24
1
96 ± 8.94
91.55 ± 11.58
Mean (±SD)
83.70
±
1.16
80.22
±
13.31
Repellence class
V
IV


## 4. Discussion

The output value of the essential oil from the leaves ofP. quadrifolia was relatively better (0.102%  ±  0.005) than that ofP. angolensis (0.056%  ±  0.004). No data have been reported in the literature on the essential oils of those two species. Essential oilsP. quadrifolia andP. angolensis showed different chemical compositions. They were potentially rich in sesquiterpenoid compounds. During this study, insecticidal and repellent activity of both oils againstS. cerealella was valued according to the treatment and the dose of applied oil. Previous studies on other species ofPremna showed that their chemical compositions were rich in caryophyllene, β-cadinene, α-selinene, and phytol [15, 16]. The insecticide nature of essential oils ofP. angolensis andP. quadrifolia manifested by contact adult insectsS. cerealella may be linked to the main volatile compounds extracted reportedly acting alone or in synergy with other minor constituents. In fact, the essential oil of the leaves ofP. angolensis contains monoterpenes and oxygenated hydrocarbon such as α-pinene and Oct-1-en-3-ol and Linalool which insecticidal properties have been demonstrated againstTribolium confusum,Tribolium castaneum,Sitophilus zeamais,Callosobruchus maculatus, andRhyzopertha dominica [11, 17].The repulsion rates evaluated ofP. angolensis essential oil showed a greater repellent activity against adults of Angoumois grain moth thanP. quadrifolia essential oil belonging, respectively, to the repulsive V and IV class, according to MC-Donald and Guyr [14] ranking. This can be explained by the strong offensive odor of both oil and confirm the use of the leaves by farmers in protecting their grain in some parts of Benin. Insect repellent effect of the extract ofP. angolensis volatile proved more interesting than that ofP. quadrifolia despite having a very low yield of essential oil.The use of essential oils in the preservation of cereals is increasingly recognized [18]. Essential oils are nowadays known as neurotoxins acutely interfering with octopaminergic transmitters in Arthropods [19]. Different doses of oils caused highly significant mortality (P<0.001) in comparison with the mortality rates in the controls. Paddy rice is the most common form of conservation; onlyS. cerealella species is likely to multiply in the paddy rice which confirms the results of previous work [20]. Increasing doses of oil also reduced significantly the emergence of adults 50 days after infestation rates. Such a reduction in emergence rates results from the manifestation of ovicidal or larvicidal volatile extracts, which have destroyed the development of some eggs or larvae probably due to sesquiterpenoid compounds or oxygenated aliphatic and synergy with minor compounds.



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*Source: 319045-2015-07-27.xml*