Agroecology is now widely recognised as a viable and sustainable agricultural production method, offering an alternative to intensive agriculture
[1]
. The fundamental principles of agroecology focus on crop protection, with an emphasis on preventive measures such as stopping the use of pesticides, implementing prophylactic measures, managing soil health and diversifying vegetation. This approach aims to bring about positive and sustainable changes in agri-food systems, with the ultimate goal of eliminating pesticides and solving the major agronomic, food, socio-economic, environmental and health challenges of the 21st century
[2]
. Agro-ecological crop protection is an ambitious scientific field, requiring a transition towards an integrative approach that goes beyond the traditional model of intensive agriculture
[3]
. This is the context for this study, which aims to develop a set of technologies for the creation of a biopesticide against the oriental fruit fly, Bactrocera dorsalis, which is particularly harmful to mango cultivation, which is widespread in West Africa. Fruit flies belonging to the Tephritidae family have been a factor in major crop losses in the horticultural sector in many countries where they are present
[4]
. The fruit and vegetable industry in West Africa is growing rapidly and is a major driver of job creation and poverty reduction. This industry offers many employment opportunities in rural areas during the dry season and generates substantial income, particularly for young people and women who market the produce
[5]
. Mango, particularly the Mangifera indica L. variety, is a major export fruit crop in West Africa, especially Senegal. In Senegal, mango is particularly threatened by B. dorsalis, which is the main threat to this fruit crop. Essential to the livelihoods of many producers. In addition to this species, mangoes are also attacked by various other types of fruit fly
[6]
[7]
. As such, this investigation could form the basis of an agroecological fruit fly management strategy. In general, it contributes to improving the technological package for agro-ecological control of these pests and reducing mango production losses. The aim of this work is to assess the attractiveness of M. leucadendra plant extracts (essential oil, hydrolatee, powder and paste) on fruit fly populations. It also aims to determine the duration of efficacy of these by-products derived from the forest tree Meulaleuca leucadendra.
2. Materials and Methods2.1. Equipment
The first trial developed from 11/06/2022 to 7/10/2022 in Notto Gouye Diama using 6 McPhail traps including DDVP (Dichlorvos) an organophosphate insecticide known for its broad effectiveness against pests. This first trial included empty McPhail trap without lure (T0), and other 5 McPhail traps bearing lures like 3 ml oil essential of Melaleuca leucadendra (T1), 10 g of leaf powder of M. leucadendra (T2), 20 g of leaf powder of M. leucadendra (T3), 30 g of leaf powder of M. leucadendra (T4) and Methyl eugenol commercial tablet as positive control (T5). The 6 treaments of this trial (T0, T1, T2, T3, T4 and T5) were replicated in four randomised blocks.
The second trial was set up in Sinthiou Dara. The trapping equipment consisted of modified 10-litres empty bottles, which were used as traps because of their accessibility and availability. Extracted from the leaves, the essential oil has a chemical composition of 99.5% methyl eugenol. The essential oil used was obtained by hydrodistillation of these leaves and it was analyzed by GC/FID and GC/MS
[8]
. The work done by Sambou
[9]
has shown that the 0.5 ml and 1ml of essential oil of M. leucadendra give satisfactory results in terms of attractiveness to fruit fly. Similarly, Mendy and Diallo
[8]
have shown that 3 ml of this oil per trap could be an optimal dose for attractiveness to B. dorsalis. The powder is obtained by grinding the leaves using a mill. Following previous work in the dissertation, a weight of 2 g was used, giving considerable results
[9]
. Leaves of Ocimum americanum, used for several years to control B. dorsalis, contain 77% methyl eugenol in their essential oil, as revealed by our study
[9]
. Melaleuca leucadendra used in Senegal to fight soil salinity was reported as a plant which is rich in methyleugenol
[8]
, a compound known for its effectiveness in controlling B. dorsalis for this trial, a weight of 20 g/trap was used. Hydrolatee is a residual aromatic water obtained after separating the product of distillation, which is the essential oil. It is much less concentrated in active ingredients. A dose of 500 ml/trap was used. The paste is made up of Melaleuca leucadendra leaf powder (20 g) and water (
Figure 1
).
<xref ref-type="bibr" rid="scirp.146660-"></xref>Figure 1. Essential oil, powder, hydrolatee and trap with hydrolatee.
2.2. Experimental Set-Up
In this randomised set-up, orchards of at least 150 m × 150 m are used. 3 water bottle traps were used for each treatment. The distance between the traps was 100 m to limit cross-actions between the products. The products will be renewed every month for 3 months. The protocol for studying the attractiveness of Melaleuca leucadendra plant products, including Essential Oil (3 ml/trap), Leaf Powder (20 g/trap), Hydrolatee (500 ml/trap) and Leaf Powder Paste (20 g powder + water/trap) was implemented on Saturday 08/07/2023 at Sinthiou Dara in the Niayes area. The orchards were grouped into blocks with different characteristics (
Table 1
). Each of these four products was considered as a treatment in a one-hectare block arrangement. A random system was placed in 7 orchards of at least 1 ha where 4 traps were placed at a distance of 100 m each in the form of a square or diamond. Twelve replications were set up with 4 traps Essential Oil (3 ml/trap), Powder (20 g/trap), Hydrolatee (500 ml/trap) and Paste (20 g powder + water). (
Figure 2
).
The chemical composition of the essential oil of M. leucadendra was supplied by the laboratory appointed for this purpose. The number of flies caught per trap per day (FTD) was weekly registrated at the same specific time. The flies collected are identified and counted by species. The data collected will be subjected to analyses of variance and Fisher’s test or Friedman test for paired samples, will be used for comparisons of catch averages using R software and Xlstat.
3. Results3.1. Specific Richness of Tephritidae Caught in Sinthiou Dara and Notto Gouye Diama
The trial installed in Notto Gouye Diama from 11/06/2022 to 07/10/2022 recorded 162,397 flies and Bactrocera dorsalis was overwhelmingly dominant, accounting for more than 99% of the total (
Table 2
). Among the ceratites, Ceratitis cosyra was the most significant species with 827 individuals.
The trial installed at the Sinthiou Dara site during the period 08/07/2023 to 29/09/2023 enabled us to capture 1,030,210 fruit flies in total. These flies belonged to different species, including a single species of the genus Bactrocera and 2 species of the genus Ceratitis. These were Bactrocera dorsalis, Ceratitis bremii and C. cosyra.
Table 2
below shows the numbers of flies caught per species.
<xref ref-type="bibr" rid="scirp.146660-"></xref>Table 2. Breakdown of numbers by species of Tephritidae caught.
Species
Sinthiou Dara
Notto Gouye Diama
Bactrocera dorsalis
99.95%
99.49%
Ceratitis bremii
0.04%
0%
Ceratitis cosyra
0.01%
0.51%
3.2. Attractiveness of Melaleuca leucadendra Extracts versus Synthetic Methyl Eugenol in Notto Gouye Diama
The first trial included empty McPhail trap without lure (T0), and other 5 McPhail traps bearing lures like 3 ml oil essential of Melaleuca leucadendra (T1), 10 g of leaf powder of M. leucadendra (T2), 20 g of leaf powder of M. leucadendra (T3), 30 g of leaf powder of M. leucadendra (T4) and Methyl eugenol commercial tablet as positive control (T5). The number of males caught was significantly different between treatments (P < 0.005) and was statistically higher in traps baited with essential oil 46 flies/trap/day followed by synthetic methyl eugenol 31 flies/trap/day then leaf powder 20 g and 30 g which had 14 flies/trap/day and 10 g which had 9 flies/trap/day (
Figure 3
).
<xref ref-type="bibr" rid="scirp.146660-"></xref>Figure 3. Fly catches using the plant extract attractants in Notto Gouye Diama.
The dynamics of trap captures by these compared attractants were fellowed from 11/06/2022 to 07/10/2022 at Notto Gouye Diama. The Friedman’s test attested a significant difference between the fluit fly yielded by the different attractants with Q(Observed value) = 75.99; Q(Critical value) = 11.07; DF = 5; p-value(Two-tailed) < 0.0001. The Multiple pairwise comparisons using Nemenyi’s procedure/Two-tailed test presented the rank mentionned with the different letters as shown in
Figure 4
and
Table 3
.
<xref ref-type="bibr" rid="scirp.146660-"></xref>Figure 4. Dynamics of Bactrocera dorsalis attracted by Melaleuca leucadendra extracts in Notto Gouye Diama.
<xref ref-type="bibr" rid="scirp.146660-"></xref>Table 3. P-values from Nemenyi’s procedure/two-tailed test.
T0
T1
T2
T3
T4
T5
T0
1
T1
<0.0001
1
T2
0.504
<0.0001
1
T3
0.001
0.002
0.197
1
T4
0.000
0.005
0.131
1.000
1
T5
<0.0001
0.238
0.002
0.626
0.742
1
3.3. Fruit Fly Captures Dynamics in Sinthiou Dara
The essential oil, hydrolatee, powder and paste are extracts from the Melaleuca leucadendra plant. Their attractiveness, presented in
Figure 5
, shows a significant difference between the different treatments (
Figure 5
and
Table 4
). The hydrolatee was the most attractive with a peak of 906 flies/day/trap, followed by the essential oil at 251 flies/day/trap, then the powder at 108 flies/day/trap and
<xref ref-type="bibr" rid="scirp.146660-"></xref>Table 4. Matrix of p-values from pairwise multiple comparisons of attractants using the Nemenyi procedure/two-tailed test.
HE
HYD500ML
P20G
PASTE
HE
1
HYD500ML
0.485
1
P20G
0.229
0.005
1
PATE
0.000
<0.0001
0.168
1
<xref ref-type="bibr" rid="scirp.146660-"></xref>Figure 5. Dynamics of Bactrocera dorsalis attracted by Melaleuca leucadendra extracts including Hydrolatee.
finally the paste at 47 flies/day/trap. The dynamics of infestations revealed a significant variation in the daily catch index as a function of time and the attractant used, with a Friedman test concluding with values of Q(Observed value) = 32.70; Q(Critical value) = 7.81; DDL = 3 with a p-value(two-tailed) < 0.0001.
3.4. Variability of Catches between Orchards in Sinthiou Dara
Regression of the catch variable on the Orchard and Attractiveness factors revealed a very strong correlation with r = 0.953. However, the orchards monitored showed relatively similar catch levels. However, the attractants used in each orchard had different catch rates depending on their type. In fact, there was no difference in catches between orchards for values of ddl = 3; SCE = 376913.32; F = 0.705 and Pr > F = 0.556 (
Figure 6
).
<xref ref-type="bibr" rid="scirp.146660-"></xref>Figure 6. Variation of trap captures by treatment and orchard.
4. Discussion
The number of Bactrocera dorsalis captured in the Niayes area is greater than that of Ceratitis. This could be explained by the pheromone used, which is specific to Bactrocera dorsalis—essential oil, hydrolatee, powder and paste of Melaleuca leucadendra containing methyl eugenol. Males of Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) are strongly attracted to Methyl Eugenol (ME) (1,2-dimethoxy-4-(2-propenyl) benzene), a phenylpropanoid compound present in many plant species. Feeding ME is known to enhance the competitiveness of B. dorsalis males during mating
[10]
. A number of specimens belonging to different species of Ceratitis bremii and C. cosyra were collected in methyl eugenol traps. These results do not corroborate those of Ndiaye et al.
[11]
-
[13]
who obtained a greater diversity of flies in the Niayes area Bactrocera dorsalis, Ceratitis bremii, C. capitata, C. cosyra, C. ditissima and C. silvestrii. In addition to these species, Dieng et al.
[6]
[7]
mentioned the presence of C. ditissima, Dacus longistilus and Zeugodacus cucurbitae in the Niayes. However, these earlier studies used more attractants such as methyl eugenol, terpinyl acetate, Cuelure and trimedlure, whereas our work used only derivatives of the Melaleuca leucadendra plant containing only methyl eugenol. This could explain the low specific diversity of Tephritidae captured.
Two derivatives (powder and essential oil) of the Melaleuca leucadendra plant were compared with synthetic methyl eugenol, with the essential oil predominating, followed by synthetic methyl eugenol and then leaf powder. Intakes of Melaleuca leucadendra powder increased in proportion to the quantity used, and persisted for 4 weeks. The phenolic compounds contained in this powder explain its attraction for B. dorsalis. The release of attractive substances from Melaleuca leucadendra powder is similar to that of the methyl eugenol tablet. However, these substances appear to be released more rapidly than in the case of the methyl derivative, resulting in a more rapid reduction in the catch with the powder. This difference is not significant compared to catches made with quantities of 20 g to 30 g. The results obtained with Melaleuca leucadendra leaf powder confirm those of Ndiaye et al.
[11]
regarding the attraction of B. dorsalis males to nutmeg powder. Analysis of weekly catches according to attractants reveals a highly significant difference between catches made with powder, essential oil and synthetic methyl eugenol. However, there was a difference in the persistence of the attractants, with Melaleuca leucadendra powder lasting 4 weeks and nutmeg powder lasting only 15 days. Similar results to those obtained in Senegal were observed in Côte d’Ivoire, where Ocimum basilicum, an aromatic plant containing methyl eugenol in its leaves, proved to be an attractant for Bactrocera dorsalis. In this study, a basil powder formulation gave a persistence of 28 days at a weight of 10 g
[14]
. The effectiveness of different baits such as hydrolatee, essential oil, powder and paste revealed significant variations in their attractiveness. In particular, hydrolatee showed twice the attractiveness of essential oil, five times that of powder, and ten times that of paste, with a persistence of one week. These results corroborate the findings of previous studies
[14]
, where basil macerate was observed to be capable of attracting and capturing B. dorsalis, as was methyl eugenol in mango orchards, at a rate of 250 ml with a persistence of one week. Waters of distillation and must extracts of M. bracteata and Ocimum sp. also retained their effectiveness for a week in the orchards, at a rate of 4 ml. It should be noted that the essential oil of Ocimum sp. contains 73.5% methyl eugenol, while the distillation water of Ocimum sp. contains only 0.43%
[9]
[15]
. This variation in methyl eugenol concentration influenced the duration of trapping efficiency, as indicated by A. Kardinan et al.
[16]
. Methyl eugenol mixed with distilled water and must extract evaporates easily due to their aqueous base. In addition, it is noted that methyl eugenol is not affected by photolysis of the UV spectrum in the atmosphere, due to the absence of absorption in the environmental UV spectrum
[17]
. Regarding biodegradation, empirical data from a study on methyl eugenol showed an ultimate biodegradation of around 90% over 28 days using an activated sludge inoculum
[18]
. However, differences in results were observed in terms of attractiveness between Senegal and Indonesia. In guava and carambola orchards, the essential oils of M. bracteata and Ocimum sp. trapped significantly more fruit flies than the distillation water and must extracts of the two plants
[19]
. And in terms of persistence, studies conducted by A. Kardinan et al.
[16]
showed a persistence of 5 weeks in mango orchards with the essential oil of Ocimum sp. whereas the essential oil of Melaleuca leucadendra had a persistence of 4 weeks in mango orchards. Works carried out by Vayssières, Korie, and Ayegnon
[20]
showed that the fluctuation of the B. dorsalis population between orchards is due to the presence of wild hosts near the orchard and/or dispersed in the savannah.
5. Conclusion
The study carried out in the Niayes area revealed that M. leucadendra oil attracts Bactrocera dorsalis, Ceratitis bremii and Ceratitis cosyra species, with Bactrocera dorsalis predominating. Essential oil of Melaleuca leucadendra ensures its attractiveness such as its derivatives (hydrolatee, powder and paste) with the revelation of the hydrolatee. The essential oil and powder have a persistence of 4 weeks in orchards. Their attractive performance shows that they can replace synthetic methyl eugenol in the formulation of a bio-para-pheromone.
Acknowledgements
Acknowledgments are addressed to thank the SyRIMAO/ECOWAS Project for its support specially the team coordinating Nata Traoré, Antonio Sinzogan and Kemo Badji and all the staff.
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