Journal of
Entomology and Nematology

  • Abbreviation: J. Entomol. Nematol.
  • Language: English
  • ISSN: 2006-9855
  • DOI: 10.5897/JEN
  • Start Year: 2009
  • Published Articles: 129

Full Length Research Paper

Effects of neem leaf extracts on Lepidopteran pest species attacking Solanum macrocarpon L. (Solanaceae) in southern Togo

Abla Déla Mondédji
  • Abla Déla Mondédji
  • Laboratoire d’Entomologie Appliquée (LEA), Département de Zoologie et de Biologie Animale, Faculté des Sciences, Université de Lomé ; 01 BP 1515 Lomé 01, Togo.
  • Google Scholar
Seth Wolali Nyamador
  • Seth Wolali Nyamador
  • Laboratoire d’Entomologie Appliquée (LEA), Département de Zoologie et de Biologie Animale, Faculté des Sciences, Université de Lomé ; 01 BP 1515 Lomé 01, Togo.
  • Google Scholar


  •  Received: 25 March 2019
  •  Accepted: 20 May 2019
  •  Published: 30 June 2019

 ABSTRACT

Lepidopteran pests cause considerable damage to Solanum macrocarpon Linnaeus (Solanaceae). Their control by the use of botanical extracts is a promising alternative to improper use of chemical insecticides. The objective of this study was to evaluate the effects of three doses of leaf extract of the neem tree, Azadirachta indica Adrien-Henri de Jussieu (Meliaceae) against Lepidopteran pest species that attack S. macrocarpon L. in southern Togo. The experimental design used for the study was randomized complete blocks with three replicates and five treatments: three doses (N1: 300, N2: 600 and N3: 900 L/ha) of neem leaf aqueous extract, a synthetic insecticide “Cydim Super” (C.S.) and a Control (C) in field. Botanical exctract and synthetic insecticide were applied after Lepidopteran pest species frequency and number collected once a week for 8 weeks. The yield data were obtained by weighing the aerial parts (leaves and stems) of S. macrocarpon harvested. Three species of Lepidoptera (Selepa docilis Butler (Noctuidae), Spoladea recurvalis Fabricius (Crambidae) and Scrobipalpa ergasima Meyrick (Gelechiidae)) were recorded. The neem leaf extract reduced frequency and numbers of all the three species found on S. macrocarpon than Control. S. recurvalis and S. ergasima were not recorded on plots treated with N3: 900 l/ha. No Lepidopteran pest species was recorded on plots treated with synthetic insecticide. S. macrocarpon yields obtained on plots treated with neem leaf extract N1, N2 and N3 were higher (5.42 ± 1.80 t/ha, 7.39 ± 1.88 t/ha  and 6.97 ± 0.96 t/ha, respectively) than that of synthetic insecticide which was 3.51 ± 0.72 t/ha.

 

Key words: Biopesticide, Lepidopteran pests, Solanum macrocarpon, southern Togo.


 INTRODUCTION

Solanum macrocarpon Linnaeus commonly known as « gboma » is an important native African vegetable, especially in West and East Africa where both the leaves and fruits are eaten for fiber and mineral nutrients. Regular    consumption       of      leaves       especially   is recommended as this vegetable contains high levels of proteins (Dougnon et al., 2012). The saponins present in the leaves also act as cholesterol-lowering agents by binding with cholesterol in the intestinal lumen (Ghule et al., 2006)  which  lowers  circulating  cholesterol. Both the
 
leaves and fruits of this vegetable, have a cholesterol lowering effect (Sodipo et al., 2012; Dougnon et al., 2014). In Togo, Kanda et al. (2014) showed that the most represented vegetable families grown by market gardeners are Solanaceae (10 species), Alliaceae (4), Amaranthaceae, Asteraceae, Cucurbitaceae, Lamiaceae and Poaceae (3 species each). Apiaceae, Brassicaceae, Fabaceae and Malvaceae are represented by two species each. All other families are represented by a single species. Among leafy vegetables, S. macrocarpum (46%), Lactuca sativa Linnaeus (39%), Corchorus olitorius Linnaeus (36%) and Hibiscus sabdariffa Linnaeus (10%) predominate.
 
However, vegetable production is constrained by the damage caused by several insect pests (Koba et al., 2007; Agboyi, 2009; Oso and Borisade, 2017). Application of synthetic insecticides remains the most common control strategy against pest damage, even though this practice causes health and environmental problems (Toé et al., 2002; PAN-Africa, 2004; PAN-UK, 2005). Insecticidal properties of neem (Azadirachta indica A. Juss, Meliaceae) have been traditionally used in cultural practices for several thousand years (Philogène et al., 2003; Philogène et al., 2008). Neem compounds cause effects ranging from repellency to toxicity against a wide spectrum of insect pests including Orthoptera, Lepidoptera, Coleoptera, Diptera and Hemiptera (Schmutterer, 1990; Isman, 2006; Siddiqui et al., 2009; Degri et al., 2013; Shannag et al., 2014; Mondédji et al., 2016). These biological properties are mediated by different groups of compounds among which limonoids and particularly azadirachtin mainly present in the neem seeds. Those compounds are considered the most active components responsible of both antifeedant and insecticidal effects (Isman, 2006). Meliaceae-based insecticides have low environmental impact because of a rapid degradation in plants and in the soil (Isman, 2006) and low effects on beneficial insects (Charleston et al., 2005a; Defago et al., 2011).
 
Neem originating from Southeast Asia grows in many countries around the world including Togo (Klu, 2008). Despite two fruiting periods per year by the neem tree, their unavailability throughout the year limits the use of seed-based preparations. Interestingly, numerous active compounds including limonoids have also been found in neem leaves (Siddiqui et al., 2000) and leaf extracts had been shown to exert insecticidal effects against several insect pest species (Brunherotto et al., 2010; Egwurube et al., 2010). The choice of neem was made from literature but more importantly from the traditional practices of local gardeners in Togo. Under this scenario, extract based on neem preparation could be an important new compound for Lepidopteran pest species management on S. macrocarpon.
 
Owing to the high insect pest damage to vegetable crop grown in Togo and the potential of neem leaf-based preparation to control insect populations,  our  hypothesis was that neem leaf extract could affect the frequency and number of three Lepidopteran pests which attack S. macrocarpon and increase the yield of the vegetable. The objective of this study was therefore to evaluate the effects of A. indica leaf extract compared to a chemical insecticide “Cydim Super 388 EC” on the frequency and the number of Lepidopteran pests attacking S. macrocarpon and on the yield of this vegetable.

 


 MATERIALS AND METHODS

Site and experimental conditions
 
The study was carried out in Lomé (southern Togo) with a tropical Guinean climate marked by two rainy seasons (April-July and September-October) separated by two dry seasons (August and November-March). Average monthly temperatures range from 25 to 29°C during the year and the average annual rainfall is around 932 mm. The mean annual relative humidity is about 82% and the photoperiod of (12: 12) h LD.
 
The study was conducted on Agronomic Experiments Station located at University of Lomé campus (6° 17'N and 1° 21'E) during the rainy season from May to July 2017. This site is dominated by a man-made savanna with exotic plant species such as A. indica, Carica papaya Linnaeus (Caricaceae), Hibiscus lunarifolius Willd. (Malvaceae), Senna siamea Lamarck Irwin Barneby (Fabaceae), Leucaena leucocephala Lamarck de Wit (Mimosaceae), Manguifera indica Linnaeus (Anacarciaceae) and annual and seasonal crops (cassava, maize, cowpea, vegetables).
 
Experimental design and agronomic practices
 
The S. macrocarpon was grown on plots using randomized balanced complete blocks. Three blocks (B1, B2 and B3) were made (Figure 1). Each block consisted of five elementary plots: one untreated elementary plot served as control (C); one plot treated with chemical insecticide named Cydim Super (C.S.) and three elementary plots treated with different doses of neem leaf extract (N1, N2 and N3). In order to avoid or minimize insecticide drift during the treatments, a distance of 1 m separated elementary plots. Each elementary plot (1.6 m × 6.8 m) carried four rows of plants with 17 S. macrocarpon plants per row. The spacing of the plants was 0.4 m within rows and 0.4 m between the rows (Figure 2). The maintenance of the plots was essentially watering, weeding and hoeing. The watering of the plots was done with pipes fitted with a finely drilled piece (head) every day. Weeding and hoeing were done with a hoe and a forked hoe respectively every two weeks.
 
 
Preparation of botanical extract
 
Fresh leaves of neem were collected on the domain of the University of Lomé. Extract was obtained by soaking 1 kg of crushed fresh leaves in 1.5 L of water overnight at 25-30°C. After maceration for 12 h under ambient conditions, the solution was filtered. The filtrate was then applied to the plots.
 
Preparation of chemical insecticide
 
The chemical insecticide was prepared by diluting 3.5 ml of Cydim Super  in  water  to  obtain  1500 ml  of  solution.  Cydim  Super is a binary insecticide composed of 400 g/L Cypermethrin and 36 g/L Dimethoate.
 
Treatment of plots
 
Application of treatments began two weeks after transplanting. The treatments were carried out using ALTIMATE PRO 16 model with maintained pressure backpack sprayer. The treatments of the elementary plots were performed once a week during six weeks period (6 applications in total). The dose of chemical insecticide applied was 1 L of Emulsifiable Concentrate per hectare. The three doses of neem leaf extract (N1: 300, N2: 600 and N3: 900 L/ha) were applied. The control plots were untreated (Table 1).
 
Evaluation of treatments effects on Lepidopteran pests of S. macrocarpon plants
 
Observations were made the day before each application of treatment in the various S. macrocarpon plots (every seven days). The evaluation of a treatment effects was based on 30 plants in the middle of each elementary plot to avoid the bias associated with the edge effect. The presence or absence of each species of Lepidopteran was recorded during each observation on plots. This made it possible to calculate the frequency of species for each treatment. Results were expressed in terms of frequency F = (Number of observations in which the species was present / Total number of observations) × 100.
 
The number of larvae of each of the Lepidopteran pests found on S. macrocarpon plants per plot for each treatment, was recorded to determine the numbers of each species by treatment.
 
Evaluation of treatments effects on S. macrocarpon yield
 
The yield data were obtained by weighing the aerial parts (leaves and stems) of the 30 plants of S. macrocarpon harvested from the two central lines of each plot two weeks after the last application of treatment. Yields were then estimated per hectare.
 
Statistical analysis
 
Statistical analysis was performed using SPSS version 20.0. The comparisons of mean frequencies, numbers and  yield  were made using analysis of variance (ANOVA) followed by a Student Newman Keuls (SNK) comparison tests when ANOVA was significant at the 5% level. For yield, data were submitted to LSD comparison tests at the 5% level.
 


 RESULTS

Selepa docilis Butler (Noctuidae), Spoladea recurvalis F. (Pyralidae) and Scrobipalpa ergasima Meyrick (Gelechiidae)  were the Lepidopteran pests recorded on S. macrocarpon.
 
Effects of neem leaf extracts on the frequency of Lepidopteran pests of S. macrocarpon plants
 
Figure  3  shows  that  the  mean  frequency  of   different species of Lepidopteran was from 0 to 66.67% all treatments combined. The low dose of neem extract (N1) did not reduce the frequency of S. docilis (66.67%) compared to that obtained on the control (C) (55.56 ± 19.25%). However, the frequencies were lower (33.33 ± 16.67% and 25.0 ± 8.33%) on plots treated with the medium (N2) and the high (N3) doses of neem extract respectively. S. recurvalis was less frequent than S. docilis in general. Its frequency was 33.34 ± 28.87% on the control (C) and 16.67% at the level of plots treated with the low (N1) and the medium (N2) doses of neem extract. S. recurvalis was not present on plots treated with the high dose of neem extract (N3). S. ergasima was present only on the control (C). Its frequency was 41.67 ± 8.33. The three species of Lepidopteran were absent on the plots treated with the synthetic insecticide (C.S.).  The neem extract and especially the high dose allowed to obtain a low frequency or outright absence of the three species of Lepidopteran (F(14, 44) = 14.096; P = 0).
 
Effects of neem leaf extracts on the number of Lepidopteran pests of S. macrocarpon
 
Figure 4 shows that the mean number of S. docilis was 5.15 ± 1.57 larvae (caterpillars) / plant on Control plots (C). The numbers of S. docilis were 4.80 ± 1.80; 0.67 ± 0.33 and 0.44 ± 0.33 larvae / plant on the plots treated with low (N1), medium (N2) and high (N3) doses of neem leaf extract, respectively. Those of S. recurvalis were 0.29 ± 0.13 larvae / plant on Control plots (C); 0.11 and 0.16 ± 0.05 larvae / plant on the plots treated with low (N1) and medium (N2) doses of neem extract, respectively. No larva of S. recurvalis was found on plots treated with high dose of neem extract (N3). The number of S. ergasima was 0.41 ± 0.27 larvae / plant only on Control (C). No larva of S. docilis, S. recurvalis or S. ergasima was found on plots treated with synthetic insecticide (C.S.). Medium (N2) and high (N3) doses of neem leaf extract significantly control the number of different Lepidopteran pests species larvae on S. macrocarpon plant compared to Control (C) (F(14 ; 44) = 21.829;   P = 0).  But  synthetic  insecticide  Cydim  Super (C.S.) has better control the number of Lepidopteran pest species larvae on S. macrocarpon than the neem leaf extracts.
 
Effects of treatments on the yield of S. macrocarpon
 
The mean yield of S. macrocarpon leaves and stems varied according to treatment. The mean yield of Control plots was (5.33 ± 1.78 t/ha). Those of plots treated with synthetic insecticide (C.S.), the low (N1), medium (N2) and high (N3) doses of neem leaf extract were 3.51 ± 0.72 t/ha; 5.42 ± 1.80 t/ha; 7.39 ± 1.88 t/ha  and 6.97 ± 0.96 t/ha,  respectivly (F(4 ; 14) = 3.111; P = 0.066) (Figure 5). A comparison of the mean yield obtained on plots treated with synthetic insecticide (C.S.) with yields obtained on the plots treated with the medium (N2) and high (N3) doses of neem extract using LSD test, showed significant differences (P = 0.01 and P = 0.019, respectively).
 
 

 


 DISCUSSION

In this study, three species of Lepidopteran pests S. docilis Butler, S. recurvalis F. and S. ergasima Meyrick were recorded   on  S.  macrocarpon  in  the  field.  Those Lepidopteran pests have been encountered or recorded among important insect pests that caused damage to egg plants Solanum spp or other african indigenous vegetables like Amaranthus spp (Koba et al., 2007; Omburo, 2016; Oso and Borisade, 2017). Among the three species, S. docilis was the most representative in terms of frequency and numbers followed by S. recurvalis and then S. ergasima.
 
The different treatments and doses of neem leaf extract influenced the frequency and numbers of the three Lepidopteran pests on the vegetable crop. The Control plots were more attacked by these different kinds of Lepidopteran pests throughout the study period compared to the plots that were treated with the different doses of neem leaf extract and the synthetic insecticide. Research results showed the vulnerability of Control plots to insect pests (Horna and Gruère, 2006). The neem leaf extract tested was a total extract which contained the following families of compound: athraquinones, tannins, triterpenes, coumarins and flavonoids (Lagnika, unpubl.). Some of these chemical substances present in the neem leaf extract might have prevented the insects from feeding on the leaves. The neem tree (A. indica A. Juss) is known to be an important source of triterpenoids (Afshan,  2002;   Siddiqui   et   al.,   2004).   According  to Gisbert et al. (2006), neem plants also contain salannin which makes the plant unpalatable and therefore, discourages being fed on by insects. The presence of triterpenoids and salannin in the neem leaf extract might have acted as an antifeedant and therefore repelled the insects from feeding on the leaves of S. macrocarpon treated with the extracts. Neem seeds oil extracts, water and ethanolic neem leaf extracts are known to inhibit the growth of various insects species (Charleston et al., 2005b; Aggarwal and Brar, 2006; Egwurube et al., 2010; Shannag et al., 2014; Mondédji et al., 2015). Amtul (2014) reported that A. indica derived compounds inhibit digestive alpha-amylase in insect pests. Thus, A. indica extracts are potential bio-pesticides in insect pest management.
 
The effect of different treatments and doses of neem leaf extract also influenced the yield of the S. macrocarpon. The plants sprayed with the neem leaf extract grew taller than those sprayed with synthetic insecticide Cydim Super. This indicated that the yield was affected by the active ingredient in the neem leaf extract called meliantriol which prevented insect infestation of the plant and allowed S. macrocarpon plants to grow in height and to produce more leaves. The mean weight values of plants sprayed with  the  medium  and  the hight doses of the extract were higher than those plants sprayed with the synthetic insecticide. There was a significant difference among the treatments (P ˂ 0.05) with LSD test post hoc between yields obtained on plots treated with the synthetic insecticide and those treated with the medium and the hight doses of neem leaves extract. Agbenin et al. (2005) reported that azadirachtin and/or neem extracts enhanced plant growth, and increased the yield in different crops including garden egg. The S. docilis is a defoliating caterpillar that gnaws at the leaf blades, leaving only the vein. The larvae of S. recurvalis skeletonize the leaves before rolling them to provide shelter during pupation. Flower bud S. ergasima caterpillar occurs on leaves, flowers and fruit of crop plants. It damages flowers and young fruits of eggplants. Thus, despite their fairly frequency and higher numbers on control plots, these Lepidopteran did not reduce yields on the latter. However, they could reduce the market value of the vegetable because of the galleries left on S. macrocarpon leaves reduced to veins by S. docilis, and the presence of S. recurvalis and S. ergasima larvae in S. macrocarpon leaves folded by them.

 


 CONCLUSION

Three Lepidopteran pest species (S. docilis, S. recurvalis and S. ergasima) were found on S. macrocarpon. Treatments have effects on the three Lepidopteran pests. Neem extract in general and the high dose in particular  reduced the frequency and the number of the Lepidopteran larvae on S. macrocarpon. The effectiveness of different doses of neem leaf extract revealed that the high dose of neem leaf extract was better than other doses of the extract. Although neem extract failed to kill  all the Lepidopteran pests found on S. macrocarpon like synthetic insecticide, the use of neem leaf extract is an eco-friendly management method. The neem extract produced better yield than synthetic insecticide.


 CONFLICT OF INTERESTS

The authors have not declared any conflict of interests.

 


 ACKNOWLEDGEMENT

The authors are grateful to Mr Roger for his technical support in carrying out this work. 



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