Research Report

Evaluation of the insecticidal effects of Hyptis suaveolens (L.) for the management of Callosobruchus maculatus (F.) on two varieties of cowpea, Vigna unguiculata walp  

Raphael Abiodun Adebayo , M. E. Eyo
Federal University of Technology, Akure, PMB 704, Akure, Nigeria
Author    Correspondence author
International Journal of Horticulture, 2014, Vol. 4, No. 17   doi: 10.5376/ijh.2014.04.0017
Received: 25 Jul., 2014    Accepted: 15 Sep., 2014    Published: 27 Oct., 2014
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Adebayo and Eyo, 2014, Evaluation of the insecticidal effects of Hyptis suaveolens (L.) for the management of Callosobruchus maculatus (F.) on two varieties of cowpea, Vigna unguiculata walp, International Journal of Horticulture, 2014, Vol.4, No.17 1-6 (doi: 10.5376/ijh.2014.04.0017)


Studies were conducted at the laboratory of the department of Crop, Soil and Pest Management, the Federal University of Technology Akure, Ondo State, Nigeria to test the insecticidal effects of powder from the leaf of Hyptis suaveolens (L.) for the management of Callosobruchus maculatus (F.) on Oloyin and Ife brown varieties of cowpea, Vigna unguiculata Walp. Five levels of the powder,0.00, 0.05g, 0.1g, 0.2g and 0.3g per 20g of cowpea varieties were evaluated against Callosoruchus maculatus under laboratory conditions of 25-28oC, 65-75% RH). Mortality of C. maculatus was assessed at 24hours, 48hours and 72hours after treatment application. Data were taken on oviposition, seeds with and without eggs, seeds with and without holes, adult emergence, seed weight loss and germination tests. The results from the study revealed that the percentage mortality increased significantly with concentrations. Highest number of C. maculatus died in seeds treated with 0.3g of the powder. Reduced values were obtained on treated seeds compared to the untreated and were significantly different at p<0.05. Treated seeds had fewer eggs laid, reduced emerged adults and seeds with eggs. Similar result was also observed for seeds with and without holes. Untreated seeds germinated better than the treated seeds and showed statistical differences. Significantly higher weight loss was recorded in the untreated seeds compared with the seeds treated with 0.3g of hyptis powder. The results obtained in this study showed that the tested powder exerts protectant effects on the cowpea seeds and that the powder of Hyptis suaveolens is a potential bioinsecticide in the management C. maculatus. Therefore it is recommended that higher rates of the powder and other components such as oil, water extract and ash of the plant should be investigated.

Hyptis suaveolens; Callosobruchus maculatus; Vigna unguiculata; Management

Cowpea beetle, Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae) is a cosmopolitan insect pest of cowpea. It is a field -to-store pest as its infestation of cowpea often begins in the field as the mature pods dry (Huignard et al.,1985; Sathyaseelan et al., 2008) and when such seeds are harvested and stored, the pest population increases rapidly and results in total destruction within a short duration of 3-4 months (Rahman and Talukder, 2006). It multiplies very rapidly in storage and has caused 8.5% loss in pulses during postharvest handling and storage in India (Ouedraogo et al., 1996). Insect infestation is a major contributor of quality deterioration of durables (cereals, pulses, and tubers) stored in warm and humid climates. Considerably physical and nutritional losses sustained in these countries are due to infestation of stored food products by weevils, bruchids and other insects (Narong, 2003). Apart from the detrimental economic impact, these losses pose a major threat to food security. Currently, insect control in stored products relies primarily upon the use of gaseous synthetic fumigants and residual insecticides (Isman, 2005). Synthetic chemical insecticides have proved very effective in the control of the beetle. However, the problems associated with chemical insecticides such as health hazards, insect resistance, pest resurgence, residual toxicity, widespread environmental hazards and increasing costs of application have directed the need for effective, biodegradable pesticides (Talukder and Howe, 2000; Elhag, 2000). Ofuya (2003) reported that when these chemicals are used improperly they pose risk to man and environment. He also argued that this is most common among uneducated rural farmers in Africa. Plant derived materials for the protection of field crops and stored commodities have a long history of use against insect attack (Golob and Webley, 1980). They have been reported to be safe and promising in the protection of crops (Jilani et al.,1988).
Several products from the plant kingdom have been evaluated and noted for their effectiveness in the management of insect pests (Oni, 2014). Lale (2001) also suggested that plant derived insecticides could be a better replacement for the synthetic insecticides in stored products protection. Vegetable oils, essential oils, crude extracts, powders and other products from plant have been tested against C. maculatus (Lale, 1995; Boeke et al., 2001). Effective control of the cowpea seed beetle in storage with powder of parts of many indigenous plants when applied at 2% of the weight of stored beans has been well documented (Adedire and Lajide, 2001; Ofuya and Salami, 2002). Botanical insecticides are naturally occurring insecticides that are derived from plants, they possess repellent and or deterrent properties and are environment friendly (Isman 2000; Ayvas et al., 2009). Therefore, in this study insecticidal effects of powder from the leaf of H. suaveolens (L.) was evaluated for the management of C. maculatus (F.) on Oloyin and Ife brown varieties of cowpea, V. unguiculata Walp.
The effects of the powder on adult mortality revealed that significantly more adult died with higher doses of the powder. The powder exerts insecticidal effect on the C. maculatus over the 3days of exposure. Treated seeds of oloyin cowpea had higher number of C. maculatus killed compared with the untreated and was significantly different at p<0.05 (Table 1). Result obtained for mortality on ife-brown cowpea in Table 2, was similar to that in Table 1. Seeds treated with 0.3g of the powder consistently had highest number of killed adults which was different statistically from those of the untreated seeds (p<0.05). This revealed insecticidal properties of the powder of hyptis on the exposed adults. Table 3 showed the effects of the powder on the bionomics of the beetle insect. Treatment significantly reduced oviposition and adult emergence both of which were significantly different (p<0.05) from the untreated seeds. Least number of eggs was laid and fewer adults emerged from the seeds treated with the powder at 0.3g. Highest number of seeds with eggs was obtained from the untreated seeds and was statistically different from those of the treated at p<0.05. Similar observation was also made for the number of seeds without eggs.

Table 1 Mortality of Callosobruchus maculatus on Oloyin after 24, 48 and 72hours after treatment application

Table 2 Mortality of Callosobruchus maculatus on Ife-brown at 24, 48 and 72hours after treatment application

Table 3 Effects of Hyptis suaveolens on oviposition, adult emergence of Callosobruchus maculatus, seeds with and without eggs on Oloyin cowpea seeds

The results obtained for the ife-brown cowpea seeds treated with the powder were similar to the result for oloyin cowpea in Table 3. All the parameters measured differ significantly at p<0.05. Significantly reduced oviposition, number of emerged adults and seeds with eggs were recorded on seeds treated with 0.3g of the powder. Though, no significant difference exist among the treatments for the number of seeds without eggs differences exist between the treated and untreated which was significant at p<0.05 (Table 4).

Table 4 Effects of Hyptis suaveolens on oviposition, adult emergence of Callosobruchus maculatus, seeds with and without eggs on Ife-brown cowpea seeds

Results on holed and unholed seeds, germination test and weight loss were significantly different at p<0.05. Fewer seeds were holed when treated with 0.3g of the powder and was significantly different from the untreated seeds. The result of germination test showed that oloyin cowpea treated with the powder germinated well but the untreated seeds had significantly higher number of geminated seeds (Table 5). Weight loss was significantly reduced in treated seeds while highest value was recorded from the untreated seeds and was significantly different at p<0.05. In Table 6 similar patterns was observed for all the measured parameters on ife-brown cowpea as in the Table 5. However, the result on the germination test revealed a reduced germination for the seeds treated with the powder at the rates of 0.2g and 0.3g. Similarly highest number of seeds germinated from the untreated seeds and was significant (p<0.05) from the others except for the seeds treated with 0.05g of the hyptis powder.

Table 5 Mean number of seeds with and without holes, germination tests and weight loss of Oloyin cowpea seeds treated with leaf powder of Hyptis suaveolens

Table 6 Mean number of seeds with and without holes, germination tests and weight loss of Ife-brown cowpea seeds treated with leaf powder of Hyptis suaveolens

Resultant negative effects of synthetic chemicals used in the protection of crops and crop products have been noted by scientists and have directed research toward identifying effective, environment friendly and biodegradable pesticides (Talukder and Howe, 2000; Elhag, 2000; Ofuya, 2003). Products such as ashes, sand and powder from leaves of some plants have been investigated for effective management of stored crop insect pests (Lajide et al., 1998; Adebayo and Ibikunle, 2014). Oil and powder obtained from several plants have been reported to provide sustained protection for the stored grains (Lale and Ajayi, 1996; Ogunwolu and Odunlami, 1996; Oni, 2014).
The powder of hyptis effected insecticidal properties by killing adult C. maculatus over the period of exposure thus seems to possess protectant ability. The ability of the plant powder to cause mortality of adult beetle on grains can be attributed to contact toxicity of the powder on the beetle. The effectiveness of some plant powders in controlling beetlesby causing adult mortality of the insects had been reported by Lajide et al. (1998). The result of this study was in agreement with the work of Lajide et al. (1998). Similarly effects of plant materials as crop seeds protectants have also been observed in the treatment of cowpea and maize weevils where adult insects were killed through contact toxicity (Ofuya and Dawodu, 2002; Asawalam et al.,2007).
Lale and Abudulrahman (1999) reported that the powders of some plants are effective in reducing egg-laying and adult emergence of the bruchid. In this study powder of Hyptis suaveolens showed to be potent or effective at reducing oviposition and adult emergence of C. maculatus especially when treated with higher dose of the powder. Eggs were laid on cowpea seeds but their hatchability was reduced as earlier reported by Lale and Mustapha (2000). Previous work on components of some bioactive plant species showed that they caused mortality, oviposition deterrence and or ovicidal action resulting in reduced progeny production of stored product insects (Aswalam, 2007; Oni, 2014). However the powder in this present study might have invoked ovicidal action rather than oviposition deterrence. As result of reduced oviposition and consequent few adults emergence loss in weight due to adult activity was least in the treated seeds (Idoko and Adebayo, 2011).
In this study germinability of seeds of Ifebrown was negatively affected and was contrary to the previous works of (Murdock and Shade, 1991; More et al., 1996) who reported that germination of cowpea seeds was not adversely affected. The result of germination test recorded for oloyin and ifebrown cowpea does not warrant rejection of the positive findings from this study.
Conclusion and recommendation
Results from this study have proved that tested rates of hyptis leaf powder were potent against bruchid beetles. Its protectant properties were observed from the mortality caused and reduction in oviposition, adult emergence and weight loss occasioned by the beetle’s infestation.
Although, results from the study did show insecticidal activities of Hyptis suaveolens powder, it is recommended that higher rates and other components of the plant should be further investigated for effective management of Callosobruchus maculatus (F.).
Materials and Methods
Study sites
The experiment was carried out at the entomology laboratory of the Department of Crop, Soil and Pest Management, Federal University of Technology Akure (FUTA), Ondo State, Nigeria. All studies were conducted under the laboratory conditions at 25-28oC and 65-75% R.H.
Collection of materials
Fresh unifested Oloyin beans were obtained from Oja-Oba and Ife-brown was obtained from Ondo State ADP. The leaves of H. suaveolens were collected from a nearby field at the Teaching and Research Farm, FUTA by Mr. G. F. Hassan, a technologist in the pathology laboratory of the department.
Preparation of plant materials
The plant materials were air dried for two weeks in a well-ventilated place. The powder was obtained by blending the dried leaves using a warring blender at the laboratory of the department of Crop, Soil and Pest Management. The blended material was sieved with 200mm aperture metal sieve to obtain a fine powder which was kept in an air-tight container and stored until it was used (Egwuyenga,1997).
Insect culture
Cowpea seeds infested by C. maculatus were collected from Oja-Oba, Akure and brought to the laboratory. The infested seeds were set aside in a plastic container (4.2 x 9.0cm) and covered with muslin cloth till the emergence of adult. Healthy adults that emerged from the initial culture were transferred to another plastic container (4.2 x 9.0cm) and provided with clean uninfested cowpea seeds for oviposition and maintained in the laboratory. Prior to insect infestation the beans were sterilized in Gallenkamp oven to avoid contamination and overlapping of generations (Allotey and Azalekor, 2000). The container was undisturbed until the emergence of adults. Freshly emerged subsequent generations were used for the experiments.
Assessment of insecticidal properties of powder of Hyptis suaveolens (l.)
Ten freshly emerged adults of C. maculatus were introduced into the white disposable plastic container (4.2 x 9.0cm) already containing 20g of cowpea treated with 0.05g, 0.1g, 0.2g, 0.3g and 0g (control) of H. suaveolens. Mortality of the cowpea beetles were made at 24hours, 48hours and 72hours. Percentage adult’s mortality was corrected using Abbot (1925) formula.
After seven days of oviposition, numbers of egg laid on treated seed were recorded; number of seeds with eggs and without eggs was also counted. The experiment was laid out in a Completely Randomized Design with each treatment replicated three times. After the data on oviposition parameter have been taken, experimental set-up was kept undisturbed till the emergence of adults. The numbers of adults that emerged from the seeds 21days after infestation with C. maculatus were recorded. Data were also obtained on seeds with holes, weight loss after adult emergence. Germination tests were also carried out on the seeds treated with various concentrations of H. suaveolens after a month of storage. The germination test was done by arranging ten seeds in a petridish (8.5 x 1.2cm) lined with moistened facial tissue paper. Counting was done after 5days of planting.
Data analysis
Data on number of egg laid, number of seeds with eggs and without eggs, number of seeds with holes and without holes, adult emergence were square root transformed while data on germination test was arcsine transformed before subjecting to the analysis of variance (ANOVA) using SPSS statistical package version 15.0. Means were separated using Duncan multiple range test at 95% level of significance.
The authors are thankful to Mr. Mr. G. F. Hassan, a technologist in the department for the provision of the hyptis leaf. They also appreciate Mrs. Adekanle for her advice and technical support during the study.
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