Cayenne Pepper, Sweet Pepper and Long-cayenne Pepper Oil Extracted with Different Solvents as Fumigant Entomocide against Sitophilus zeamais Infestation  

Mercy Olayinka Oni
Department of Crop, Soil and Pest Management, School of Agriculture and Agricultural Technology, Federal University of Technology, P.M.B 704 Akure, Nigeria
Author    Correspondence author
International Journal of Horticulture, 2014, Vol. 4, No. 9   doi: 10.5376/ijh.2014.04.0009
Received: 08 Apr., 2014    Accepted: 15 Apr., 2014    Published: 22 Apr., 2014
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This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Oni, 2014, Cayenne Pepper, Sweet Pepper and Long-cayenne Pepper Oil Extracted with Different Solvents as Fumigant Entomocide against Sitophilus zeamais Infestation, International Journal of Horticulture, 2014, Vol.4, No.9 44-49 (doi: 10.5376/ijh.2014.04.0009)

Abstract

N-hexane, ethanol and acetone extracts of cayenne pepper, sweet pepper and long cayenne pepper were used as fumigant under laboratory at ambient temperature of (28±2)˚C and (75±5)% relative humidity against infestation of Sitophilus zeamais on stored maize. The fumigant toxicity of the extracts were tested at dosage of 0.5 ml, 1.0 ml, 2.0 ml, 5.0 ml and 10.0 ml and their effect was observed on the adult mortality and emergence as well as the ability of the insects to cause seed damage and weight loss. Regardless of the solvent used for the extraction of the peppers, cayenne pepper extract significantly effect high weevil mortality than other extracts. The n-hexane extract of this pepper was the only extract that achieved 100% mortality even at lowest dosage (0.5 ml) and it’s effect was significantly (p<0.05) different from other extracts. None of the extract was able to prevent adult emergence, seed damage and seed weight loss; nevertheless, their effect was significantly different from the controls. The ability of cultivars of Capsicum spp. against S. zeamais was rated as cayenne pepper>long cayenne pepper>sweet pepper while they were rated based on the solvent used for their extraction as n-hexane extract>ethanol extract>acetone extract. Therefore, the n-hexane extract of the three peppers could be introduced into pest management techniques since Capsicum spp. used showed high insecticidal effect and they were medicinal in nature. Nevertheless, n-hexane extract of cayenne pepper was recommended as fumigant for effective control of S. zeamais in storage.

Keywords
Capsicum spp. Sitophilus zeamais; Adult emergence; Seed weight loss; Seed damage

Agriculture is the backbone of development of any nation. It plays a vital role in the survival of the world ever-increasing population. However, the protection of agricultural produce requires more attention as it is required for their production because of various losses that occur after harvest. Post-harvest losses are directly proportional to the backwardness of a nation as food insecurity will increase (Ashfaq et al., 2003). Insect attack alone have been noted to be one of the major threat that is enfeebling the food security of the world especially in the developing countries where most of their farmers are illiterate and government intervention is low. For example, Dubey et al. (2008) noted that 5%~10% losses of stored grains in the temperate countries and 20%~30% in the tropical zones are due to insect attack alone.

Maize grain been one of the major staple food of the world from which carbohydrate, protein, fats, vitamin B and minerals can be derived has been attack by wide range of insects pest including coleopteran and lepidopteran (Ashamo, 2007; Oni 2011; Akinneye and Ogungbite, 2013; Ileke and Ogungbite, 2014). Taylor (1971) reported that Sitophilus zeamais infestation is about 8%~10% before harvest and continues until about 30%~50% of the grain is damaged after six months in storage. For years, the control of this insect pest and other store product insect pests has profoundly relied on the use of synthetic chemical insecticides which are associated with many cons that is encumbering their use nowadays. The public awareness of the cons of synthetic chemical insecticides has called for search of other alternatives that could contend with chemical insecticides in action.
Plant kingdom have been relied upon as new thoroughfare of controlling stored products insect pests as many of them contain myriad of secondary compounds that could have toxic effect against insects (Zibaee, 2011). Moreover, in spite of effectiveness of many well-known botanical insecticides used as protectants of stored grains, they have some effects that are thwarting their acceptability among consumers. Such effects include change in colour and taste of the protected grains as well as unpleasant odour pose by these botanicals (Begum et al., 2013). Therefore, an acceptable method of application of botanical pesticides is of great deal to the entomologist and pest managers of the world. For this reason, this research investigated the entomocidal efficacy of fumigant of cayenne pepper, sweet pepper and long-cayenne pepper oil extracted with different solvents against Sitophilus zeamais infestation.
Result
Fumigant effect of oils of cultivars of Capsicum spp. extracted with different solvent on the S. zeamais mortality, adult emergence as well as the ability of the insect to cause seed weight loss and damage.
The fumigant effect of oils of cultivars of Capsicum spp. extracted with different solvent on the S. zeamais mortality, adult emergence as well as the ability of the insect to cause seed weight loss and damage was presented in Table 1-Table 5. Insect mortality, adult emergence as well as ability of the insects to cause damage and weight loss of treated maize grains varied with cultivars of Capsicum spp. and the solvent used for the extraction of the oils. The fumigant effects of the oils were significantly increasing as the dosage of the oils was increasing. None of the extracts was able to achieve 100% beetle mortality except the n-hexane extract of cayenne pepper which was also the only extract that prevented the adult emergence, seed weight loss and seed damage. The acetone oil extracts of all the three cultivars of Capsicum spp. showed the lowest effect on the mortality and emergence of the adult weevil as well as the ability of the weevil to cause seed damage and weight loss. Also, the extracts of sweet pepper showed lowest effects among the three cultivars of Capsicum spp. regardless of the solvent used for their extraction and their effect was significantly (p<0.05) different from other cultivars of Capsicum spp. At 0.5, 1.0 and 2.0 dosage of sweet pepper extracts regardless of the solvent used for their extraction were not significantly (p>0.05) different from the controls in term of weevil mortality while at 5.0 only the acetone extract of this cultivar was not significantly (p>0.05) different from the controls. However, all the extracts of Capsicum spp. was significantly (p<0.05) different from the controls in term of adult emergence, seed damage and weight loss. The effectiveness of the extracts cayenne pepper, sweet pepper and long cayenne pepper regardless of the solvent used for their extraction could be rated as follow, cayenne pepper>long cayenne pepper>sweet pepper while their effect could also be rated in term of the solvent use for their extraction as follow, acetone extract of the peppers<ethanol extract of the peppers<n-hexane extract of the peppers. N-hexane extract of cayenne pepper showed the greatest insecticidal effect among the pepper and was more consistence in it action than others regardless of the dosage used.


Table 1 Effect of oil of three cultivars of capsicum spp. extracted with different solvents on S. zeamais and it infestation at 0.5 ml dosage



Table 2 Effect of oil of three cultivars of capsicum spp. extracted with different solvents on S. zeamais and it infestation at 1.0 ml dosage



Table 3 Effect of oil of three cultivars of capsicum spp. extracted with different solvents on S. zeamais and it infestation at 2.0 ml dosage



Table 4 Effect of oil of three cultivars of capsicum spp. extracted with different solvents on S. zeamais and it infestation at 5.0 ml dosage



Table 5 Effect of oil of three cultivars of capsicum spp. extracted with different solvents on S. zeamais and it infestation at 10.0 ml dosage


Discussion
Use of plant materials has remained the major weapons among the tropical zones farmers even before the discovery and commercial success of nowadays synthetic chemical insecticides. However, consumers seem to reject many food commodities treated with these botanical materials especially their extracts which are believed to be more effective than their powders. This is because of the unpleasant effect such as obnoxious odour, change in taste and change in colour pose by these extracts (Begum et al., 2013). Therefore, acceptable method of application such fumigation is required. Nevertheless, Okosun and Adedire (2010) noted that ability of a botanical extract to contain its active compounds depends on the types of solvent used for their extraction.
The result obtain from this work showed that all the extracts of the three Capsicum spp. tested showed a greater significant fumigant effect on the different life stages of S. zeamais when compared to the controls especially at the higher dosages. However, n-hexane extracts of these pepper cultivars showed more insecticidal bustle than ethanol and acetone extracts of these cultivars. The high adult insect mortality recorded by these extracts could be due to the ability of the fumes of the oils to block the breathing organelle (spiracle) of the insect and thereby led to suffocation and subsequent death of the insects. However, none of the oil extracts used as fumigant was able to prevent the emergence of the adult weevil, seed damage and weight loss regardless of the dosage used and solvent used for their extraction. The fumigants (oil extracts) nevertheless have a greater insecticidal effect on the emergence of the adult weevil and ability of the weevil to cause seed damage and weight loss with the acetone extract of the Capsicum spp. showing the lowest effect. This is agreement with the work of Ofuya and Olowo (2006) in which the extract of some medicinal plants used as fumigant were found to significantly reduced adult emergence of Calllosobruchus maculatus on cowpea. The ability of cultivars of Capsicum spp. used as fumigant could be due to the death of the insect larvae which may occur due to inability of the larvae to fully cast off their exoskeleton which remained linked to the posterior part of their abdomen as suggested by Oigiangbe et al. (2010). This work also showed that the fume of cayenne pepper, sweet pepper and long cayenne pepper have effect on the post embryonic survival of the S. zeamais as they reduced the adult emergence of the insect at different dosages. Yang et al. (2006) opined that the secondary metabolites found in plants have growth disruptive effect on insects and therefore affect their life cycle. These secondary metabolites in plants were also found to affect the survival rate of insects. Therefore, the phytochemicals such as flavonoid, alkaloid and saponin (Lee et al., 1995) which are reported to present in these Capsicum spp. could responsible for their insecticidal effect on both adult mortality and emergence. The insecticidal effects of these oil fumigants could be correlated with the type of solvent used for their extraction since different solvents have different ability of extracting the active compounds in plants (Okosun and Adedire, 2010; Patra et al., 2012).
Therefore, the ability of n-hexane extract of Capsicum spp. to show efficacy on adult emergence of S. zeamais than ethanol and acetone extract of the peppers may be due to the high extraction capacity of the solvents. The findings of Patra et al. (2012) and Zeeshan et al. (2012) in which methanolic extracts of some plants were found to be effective against Staphylococcus epidermidis than other extracts was in agreement with this work.
The fumigants of these oils of cultivars of Capsicum spp. significantly reduced the weight loss and damage of treated seeds.This reduction in weight loss may be due to the inability of the larvae of the weevil to feed on the treated maize grains. Similar observation has been reported by Jayakumar et al. (2003) on cowpea seeds treated with plant materials. Cayenne pepper, sweet pepper and long cayenne pepper could serve as alternative to the use of synthetic chemical insecticides moreso they are highly medicinal and being used on daily bases throughout the world. However, the n-hexane extract of cayenne pepper could be more preferable as fumigant since it shows more insecticidal effect than other extracts.
Materials and Methods
Insect culture
The culture of S. zeamais was obtained from an infested maize grain at Entomology Research laboratory of the Crop, Soil and Pest Management Department, Federal University of Technology, Akure, Nigeria. This was reared on non-infested clean maize grains obtained from Agricultural Development Project (ADP) Akure, Nigeria. The experiment was setup in the laboratory at temperature of 28±2oC and relative humidity of 75%±5%.
Collection of plant materials and maize seeds
The three varieties of pepper used were bought from Oba market in Akure, Ondo State, Nigeria. Collected pepper varieties were taken to botanist in the Department of Crop, Soil and Pest Management. The T-swan variety of maize grains used for the experiment was obtained from the Agricultural Development Project (ADP), Akure, Nigeria. The seeds were cleaned of foreign matter and disinfested by keeping in freezer at -5oC for 7 days. They were then allowed to air-drying order to avoid mouldeness of the grains.
Preparation of plant extracts
The pepper cultivars (cayenne pepper, sweet pepper and long-cayenne pepper) used was collected fresh and sun dried. The peppers were ground into fine powder with electric blender and the powders were further sieved to pass through 1mm2 perforations before being stored in separate glass containers with tight lids for subsequent use. To extract the oils of these peppers, twenty grammes of each pulverized pepper varieties was put in a muslin cloth and transferred into the thimble and extracted separately with hexane, ethanol and acetone in a soxhlet apparatus. The extraction was carried out for 3-4hr depending on the pepper varieties. The extraction was terminated when the solvent in the thimble becomes clear. Then, the thimble was removed from the unit and the solvent recovered by distilling in the soxhlet extractor. The resulting extracts contain both the solvent and the oil. The solvent was separated from the oil using rotary evaporator. The extracted oils were exposed to air to remove all the traces of volatile solvents as the will help to avoid false concentrations.

From this main stock solution, different dosages of 0.5 ml, 1.0 ml, 2.0 ml, 5.0 ml and 10.0 ml of each pepper varieties were made.
Fumigant toxicity of oil extracts
Twenty grammes of maize grains were weighed into muslin cloth and were infested with twenty unsexed 0~24 hr old adult S. zeamais before being tied. The infested maize grains were hung to the top of 250 ml plastic containers containing the pepper extracts at dosage of 0.5 ml, 1.0 ml, 2.0 ml, 5.0 ml and 10.0 ml. The oil extracts were placed at the bottom of the plastic containers and it was ensured that the oils were not in contact with the maize grains hung at the top of the containers. Two control experiments were set up, one container with solvent alone and another with neither solvent nor extract (untreated control). The experiments were arranged in a complete randomized design and each treatment was replicated four times. Adult mortality was observed after of exposure. Both dead and live insects were removed on the seventh day and experiments were left for 42days to allow for emergence of F1 generation and the number of adult emerged was counted. The percentage weight loss and damage of the stored grains were calculated using the formulae given below.
 
 


 
Statistical analysis
All the data obtained were subjected to analysis of variance (ANOVA) and where significant differences existed, means were separated with Turkey’s test using SPSS Version 20.
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