Entomotoxic efficacy of cayenne pepper, sweet pepper and long cayenne pepper oil extracts against Sitophilus zeamais infesting maize grain  

Mercy O 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
Molecular Entomology, 2014, Vol. 5, No. 5   doi: 10.5376/me.2014.05.0005
Received: 09 Apr., 2014    Accepted: 23 Apr., 2014    Published: 09 Jul., 2014
© 2014 BioPublisher Publishing Platform
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.
Abstract
The study was conducted to evaluate the efficacy of cayenne pepper, long cayenne pepper and sweet pepper as protectant of maize grain against Sitophilus zeamais. The oils were extracted with n-hexane and used for the treatment of maize grains at dosage of 0.5, 1.0, 2.0, 5.0 and 10.0ml. The experiment was divided into three parts, those that were infested immediately after treatment (initial), and those that were stored for three and six months before been infested with S. zeamais. At the initial storage, oil of cayenne and long-cayenne pepper achieved 100% insect mortality within 96h and also prevented the damage and weight loss of the treated grains at all dosages. The effect of these oils were significantly (p<0.05) different from sweet pepper which only achieved 60% insect mortality after 110h at 10.0ml dosage. The efficacy of the oil extracts of these peppers was greatly reduced as the period of storage of treated grains was increasing. The extract of sweet pepper was unable to achieve complete mortality of S. zeamais  after 110h of exposure, yielding less than 60% mortality. After six months of storage, only the extract of cayenne pepper was able to achieve above 50% mortality at 10ml dosage. However, at all dosages, the oils did not affect the viability of the treated grains. These oils could be integrated into pest management strategy as they may increase the marketability of botanical base insecticides. Moreso, they are been eaten by consumers on daily basis.
Keywords
Capsicum spp; cayenne pepper; Sitophilus zeamais; maize grains; protectant; oil extracts

Introduction
Maize (Zea mays) is an important agricultural produce in the group of cereals. It occupied the first position among the cereal grains produced in the world (Ashamo and Odeyemi, 2001) and it serves as one of the major source of energy for both man and animals because of its high content of digestible carbohydrate (Ling and Edmeades, 1997; Ofuya, 2003; Ashamo, 2007). Despite the importance of this valuable grain among Nigerians, its production and storage has been threatened by many insect pests including Rhizopertha dominica, Sitophilus zeamais, S. oryzae, S. granarious and many others (Ashamo, 2007). Because of field to store notorious activities of S. zeamais, it has remained the major pest of maize and its infestation do not only brought about diminution in both quantity and quality of this crop but also led to the declination of market price of this imperative cereal (Oni et al., 2011; Akinneye and Ogungbite, 2013).
Since early 1940s, synthetic chemical insecticides have been overwhelmingly relied upon as means of controlling many of these infamy stored product insect pests in order to safe guard farm produces including maize from attacks and to improve food security. Despite the success of synthetic chemical insecticides in the control of store product insect pests, the problems allied with their use have called for urgent alternative of insect control (Oni and Ileke, 2008; Ileke and Oni, 2011; Akinneye and Ogungbite, 2013; Ashamo et al., 2013; Ogungbite and Oyeniyi, 2014). In order to obviate the use of these perilous synthetic chemical insecticides, the world entomologist have focused on plants derivatives as a new boulevard of insects control as many of them are medicinal, readily biodegradable and less toxic to mammals. Plants oils contain myriad of secondary metabolites that are believed to have toxic effects against insect pests (Zibaee, 2011).
Hitherto, even though botanical oils have proven their efficacy against wide range of insect pests, their insecticidal activities are yet to be comparable to many synthetic chemical insecticides and have commanded less than 1% of the insecticides market of the globe which could be due to adverse effect associated with them, for example change in taste (Begum et al., 2013). For that reason, there is still need to search for other plants species which could effectively vie with chemical insecticides and be more acceptable to local farmers and consumers. Moreso, tropical zones of the world including Nigeria are well endowed with medicinal botanicals which could have insecticidal properties. Capsicum spp. is one of these plants with high medicinal value and high daily consumption but despite its popularity throughout the world, the insecticidal prospective of its oils have not been investigated (Oni, 2011). Therefore, bearing in mind the importance of crop protection as well as safeness of the materials used for their protection, this present work investigated the effectiveness of cayenne pepper, sweet pepper and long cayenne pepper as protectant of maize grain against S. zeamais infestation. Moreso, dust of dried peppers have been used by West African farmers for decades even before the commercial success of synthetic chemical insecticides (Akinkurolere, 2007).
1 Results
1.1 Toxicity of extracts of Capsicum spp. cultivars on mortality S. zeamais after initial, three and six months of storage
The percentage mortality of S. zeamais expose to different dosages of Capsicum spp. after initial, three and six months of storage was presented in Table 1. Percentage mortality of S. zeamais was recorded on maize grains treated with oil extracts of different cultivars of Capsicum spp. at 96 and 110h post treatment after initial (immediately after treatments), three and six months of storage. Mortality of S. zeamais varied with cultivar of Capsicum spp. used, dosages of oil extracts and period of exposure. Insect mortality increased with increase in extract dosages and period of exposure regardless the cultivar of Capsicum spp. used. All the dosages of cayenne and long-cayenne pepper were able to achieve complete beetle mortality within 96h of exposure after initial and 3months of storage except 0.5ml dosage of long-cayenne pepper which only achieved 91.25% mortality but its effect was not significantly (p>0.05) different from other dosages of the two cultivars. After six months of storage, only the extract cayenne pepper at 10.0ml dosage was able to achieve above 50% mortality of S. zeamais after 110h of exposure and its effect was significantly (p<0.05) different from the extracts of other plants which achieved low or no mortality after this storage period. Regardless the dosages of the extracts, the oil extract of sweet pepper achieved the lowest beetle mortality throughout the period of exposure except after six months of storage where long-cayenne pepper could not also achieve any insect mortality except at 10.0ml dosage where it achieved 18.75% mortality. However, the effectiveness of all the cultivars of capsicum spp. decreases as the period of storage after treatment increases.
1.2 Effect of oil extract of cultivars of Capsicum spp. on adult emergence of S. zeamais on treated maize grain after initial, three and six months storage
Table 2 presented the effect of oils of Capsicum spp. on adult emergence of S. zeamais on treated maize grain after initial, three and six months. All the oil extracts of capsicum significantly reduced the emergence of the adult beetle when compared to the control. At the initial storage of stored grains, only the oil extract of cayenne pepper at 5.0ml was able to prevent the adult emergence and its effect was significantly (p<0.05) different from all other Capsicum spp. regardless of their dosages. However, none of the pepper cultivar was able to prevent the emergence of the adult beetle in spite of the dosage of their oils after three and six months of storage of treated grains. It was also noted that oil from sweet pepper at 0.5ml dosage was less effective than the two remaining cultivars as it recorded highest number of adult emergence of 32.00, 36.00 and 71.50 at initial storage, after three and six months of storage respectively. The longer the period of storage the higher the number of adults that emerges in each treated maize grains.

Table 1 Percentage mortality of S. zeamais on maize grain treated with oil extracts of different pepper after three and six post-treatments
Pepper cultivars
Dosage (ml)
%Mortality ± SE in hours
Initial
After 3months
After 6 months
96
110
96
110
96
110
Cayenne
 
 
 
0.5
1.0
2.0
5.0
10.0
100.00±0.00f
100.00±0.00f
100.00±0.00f
100.00±0.00f
100.00±0.00f
100.00±0.00e
100.00±0.00e
100.00±0.00e
100.00±0.00e
100.00±0.00e
100.00±0.00e
100.00±0.00e
100.00±0.00e
100.00±0.00e
100.00±0.00e
100.00±0.00e
100.00±0.00e
100.00±0.00e
100.00±0.00e
100.00±0.00e
5.00±2.04a
12.50±1.44b
12.50±3.23b
17.50±1.44b
23.75±1.25e
15.00±5.40b
25.00±2.04bc
33.75±1.25cd
43.75±1.25d
53.75±2.39e
Long-Cayenne
 
 
0.5
1.0
2.0
5.0
10.0
100.00±0.00f
100.00±0.00f
100.00±0.00f
100.00±0.00f
100.00±0.00f
100.00±0.00e
100.00±0.00e
100.00±0.00e
100.00±0.00e
100.00±0.00e
91.25±5.150e 100.0±0.00e
100.0±0.00e
100.0±0.00e
100.0±0.00e
100.00±0.00e
100.00±0.00e
100.00±0.00e
100.00±0.00e
100.00±0.00e
0.00±0.00a
0.00±0.00a
0.00±0.00a
0.00±0.00a
0.00±0.00a
0.00±0.00a
0.00±0.00a
0.00±0.00a
0.00±0.00a
18.75±6.75b
Sweet
0.5
1.0
2.0
5.0
10.0
16.25±2.39b
21.25± 2.39bc
27.50±1.44cd
35.00±2.04d
45.00±4.56e
40.00± 2.04b
42.50± 3.23b
47.50± 1.44bc
53.75± 2.39cd
60.00±4.56d
11.25 ±2.39b
16.25 ±2.39b
35.00±5.40c
32.50±3.23c
40.00±4.56d
32.50±1.44b
38.75±2.39bc
47.50±4.33cd
51.25±4.27d
55.00±4.62d
0.00±0.00a
0.00±0.00a
0.00±0.00a
0.00±0.00a
0.00±0.00a
0.00±0.00a
0.00±0.00a
0.00±0.00a
0.00±0.00a
0.00±0.00a
Control
0.0
0.00±0.00a
0.00±0.00a
0.00±0.00a
0.00±0.00a
0.00±0.00a
0.00±0.00a
 
Note: Each value is mean ± S.E of four replicates and means within the same column followed by the same letter(s) are not significantly (p>0.05) different from each other using Turkey’s test.

Table 2 Adult emergence of S. zeamais in maize seeds treated with different pepper extracts.
Pepper cultivars
Dosage (ml)
% adult emergence in Months
Initial
3
6
Cayenne
 
 
 
 
 
Long- Cayenne
 
 
 
 
 
Sweet Pepper
0.5
1.0
2.0
5.0
10.0
0.0
0.5
1.0
2.0
5.0
10.0
0.0
0.5
1.0
2.0
5.0
10.0
9.75±1.03bcd
9.25±0.75bcd
8.00±0.91bc
0.00±0.00a
0.00±0.00a
73.75±1.79j
14.0±1.08 def
11.5±1.04cde
7.75±1.03bc
7.50±0.65bc
4.25±0.95ab
73.75±1.79j
32.00±1.58h
25.75±1.03g
18.00±1.35f
16.00±0.93ef
12.75±0.85cdef
17.25 ±1.79efg
12.00±1.87bcde
9.25 ±1.65abc
6.75 ±0.95b
4.25 ±0.75a
73.25±1.25k
22.25±1.03gh
20.75±0.85fgh
16.00±1.08defg
11.75±0.85bcde
9.50±0.65abcd
72.75±1.25k
36.00±1.83j
31.50±1.19ij
25.00±1.68hi
18.25±1.03efg
15.25±1.38cdef
59.75±6.90fg
41.5±1.50bc
4.25±1.75bc
32.50±1.85b
17.25±0.48a
75.50±1.32ij
60.0±0.00fg
58.0±0.41efg
53.0±2.83def
48.50±1.50cde
43.5±1.32bcd
75.25±1.49ij
71.5±0.65hij
71.25±0.75hij
68.75±0.48ghij
64.25±0.63hij
61.0±2.38fgh
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