Extracts of medicinal plants as entomocide against  Sitotroga cerealella  (Olivier) infestation on paddy rice

M.O. Ashamo; O.C. Ogungbite

Extracts of medicinal plants as entomocide against Sitotroga cerealella (Olivier) infestation on paddy rice

M.O. Ashamo

, O.C. Ogungbite

Department of Biology, School of Sciences, Federal University of Technology P.M.B 704, Akure, Nigeria

Author

Correspondence author
Medicinal Plant Research, 2014, Vol. 4, No. 9 doi: 10.5376/mpr.2014.04.0009
Received: 10 Sep., 2014 Accepted: 21 Oct., 2014 Published: 20 Nov., 2014

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.

Preferred citation for this article:

Ashamo and Ogungbite, 2014, Extracts of medicinal plants as entomocide against Sitotroga cerealella (Olivier) infestation on paddy rice, Medicinal Plant Research, 2014, Vol.4, No.9 1-7 (doi: 10.5376/mpr.2014.04.0009)

Abstract

Studies on the efficacy of extracts from some plants as entomocides against Sitotroga cerealella (Olivier) infestation on paddy rice were carried out in the laboratory at ambient temperature of 28±2^oC and relative humidity of 75±5%. Ethanolic, acetone and water extracts of seeds from Aframomum melegueta K. Schumn, Eugenia aromatica L. Merril and Perry, Piper guineense Schum and Thonnand Xylopia aethiopica Dunal A. The plant materials were tested against 0-24hr old eggs of S. cerealella in paddy rice at different concentrations. Results showed that all the extracts have significant effect on the adult emergence, developmental period and longevity of the adult moth. There was no adult emergence at 4 and 6% concentrations of ethanol and acetone extracts of the plants tested. Highest adult emergence of 36.6 was obtained from the control which was significantly different (p<0.05) from others. There were some adult emergence (5.27 to 7.67) in water extracts of the plants but significantly lower than in the control. The ethanolic extract of the plants showed the greatest efficacy as they were able to prevent emergence of the adult moth at all concentrations. The efficacy of the plants could be arranged in this order ethanol extract>acetone extract>water extracts. Water absorption capacity of treated seeds was not adversely affected when compared with control but the values were higher in ethanol extracts than others.

Keywords

Entomocides; Sitotroga cerealella; Adult emergence; Life span; Water absorption capacity

Insect pests play an integral role in food insecurity of a country especially in the developing countries where losses of their agricultural produce to insect infestation alone can amount to more than 30%. Rice being one of the world staple foods has been infested by a wide range of insect pests in storage including Sitotroga cerealella (Olivier), Sitophilus oryzae L., S. granarius L., Ryzopertha dominica F., as well as Scirpophaga incertulas and Scirpophaga innotata (Ashamo and Akinnawonu, 2012; Sarwar, 2012; Ileke, 2013). These insects attack paddy rice both on the field and in storage and brought about diminution of this important crop marketability.

Over the years, the control of these infamous insect pests has overwhelmingly relied upon the use of synthetic chemical insecticides which their use have been greatly reduced because of many disadvantages associated with them. Such disadvantages include high cost of procurement, pest resurgence and resistance, poisonous residue accumulation in foods, risks of user’s contamination, effect on both human and environmental health (Sighamony, 1986; Ashamo and Akinnawonu, 2012; Akinneye and Ogungbite, 2013, Ashamo et al., 2013). The public awareness of the disadvantages of chemical insecticides has led researchers to search for alternative ways of controlling insect pests of stored products.

Plant kingdom have been relied upon to serve as new boulevard of controlling stored products insect pests as many of them are believed to have myriad of secondary compounds that could have toxic, antifeedant and growth reducing properties against insects (Zibaee, 2011). Indeed, prior to the discovery and commercial success of the synthetic chemical insecticides in the late 1930s and early 1940s, botanical insecticides have remained important weapon in the farmers armoury in managing insect pests of their farm produce (Forim et al., 2012). Hitherto, in spite of the effectiveness of many botanical insecticides, their insecticidal activities are yet to be comparable with many synthetic chemical insecticides and the ones that are believed to be comparable with chemical insecticides have not commanded more than 1% of the global insecticide market (Isman, 2000; Begum et al., 2013) because they are believed to be short lived and lose their potency over time (Oruonye and Okrikata, 2010). For these reasons, there is need to search for other plants which could comparably contend with synthetic chemical insecticides since tropical region of the world including Nigeria are well endowed with a number of plant species that could have insecticidal properties. This study therefore investigated the extracts of four medicinal plants as entomocides against the infestation of Sitotroga cerealella (Olivier) on paddy rice.

Materials and Methods

Insect culture

The starter culture of adult S. cerealellaused for this research was obtained from the existing culture of the insect in the Department of Biology Research Laboratory, Federal University of Technology, Akure, Nigeria. The moths were reared on clean uninfested paddy rice (FARO-52) collected from the Agricultural Development Project, Akure, Nigeria. The grains were kept inside 2-litre jars covered with muslin cloth to allow ventilation. The jars were kept in insect rearing cage and the culture was maintained by replacing the devoured grains with fresh uninfested grains. The research environment was maintained at 28±2^oC and 75±5% relative humidity.

Collection of plant materials

Seeds of P. guineense, E. aromatica, X. aethiopica and A. melegueta used in this study were sourced fresh from a market at Ipetu Ijesha, Osun State, Nigeria. The seeds were sun dried and were separately milled into fine powders. The powders were further sieved to pass through 1mm²mesh size and were kept inside different plastic containers with tight lids until use.

Preparation of extracts

Twenty grammes of each pulverized plant material was put in a muslin cloth and transferred into the thimble and extracted separately with ethanol and acetone in a soxhlet apparatus. The extraction was carried out for 3-4hr and the extraction was terminated when the solvent in the thimble became clear. Then, the thimble was removed from the unit and the solvent recovered by distilling in the soxhlet extractor. Rotary evaporator was used to separate the solvent from the oil after collection of the resulting extracts from the soxhlet, after which the oil was exposed to air so that traces of the volatile solvent evaporates, leaving the oil extract. Also, another set of the plant extracts was made using water as solvent. Fifteen grammes of each pulverized plant materials were separately soaked in 100ml of water inside beakers and were heated for 1h inside water bath. After heating, the extracts were allowed to cool and were separated from the particles of the plant materials by filtering the extracts through muslin cloth. After extraction, 2, 4 and 6% concentration of the extracts were made.

Collection of S. cerealella eggs

Adult male and female of 0-24hour old S. cerealella were collected from the culture jar using aspirator. Collected adult moths were transferred into an oviposition chamber in which a folded black cardboard paper was hanged to encourage oviposition by the female moths and to give contrast to the appearance of the eggs which are white and glossy. The paper was carefully removed after 24hours and was replaced with another. The eggs were carefully detached from the paper using a soft-mouthed camel hair brush first to the larger black paper and then counted.

Effect of plant extracts on adult emergence and life span of adult S. cerealella

Twenty grammes of paddy grains were placed inside plastic containers and 2ml of each concentration of 2, 4 and 6% of the plant oils extracted with different solvents were separately added. The oils were separately thoroughly mixed with the grains using glass rod in order to ensure uniform coating of the grains with the oils. The treated paddy grains were exposed to air for 30minutes to allow the escape of the volatile solvents. Twenty 0-24hr eggs of S. cerealella were introduced into those treated paddy grains at different concentrations and was left covered for 20 days to allow for adult emergence. Paddy grains treated with 0% oil extract served as control and all the treatments were replicated three times. The number of adults that emerged was counted and recorded after every 24hrs until there was no emergence after five consecutive days. The percentage adult emergence was calculated by using the formula below. The life span of the adult moth emerged from those treated grains was observed and recorded. The experiment was set up in a complete randomized design.

Effect of extracts on the water absorption capacity of the paddy grains

Twenty grammes of disinfested paddy grains were weighed into different plastic containers and were separately thoroughly mixed with 2ml of 2, 4 and 6% concentrations of the plant extracts. The grains were exposed to air to allow the volatile solvent to escape. Paddy grains treated with 0% plant extract was set as control. The experiment was set up in a completely randomized design with each treatment being replicated three times. The treated paddy grains and the control were later submerged in water for 1hr and then removed and was later submerged again for 4hrs and removed; and then finally submerged for 24hrs. The grains were dried with multiple layers of filter paper on each occasion and reweighed after each interval.

Data analysis

All the data obtained in the research were subjected to analysis of variance (ANOVA) and means were separated using New Duncan’s Multiple Range Test.

Results

Effect of plants extracts on adult emergence, developmental period and life span of the S. cerealella

The effect of plants oils extracted with different solvents was presented in Table 1-3. All the plants oils extracted with different solvents significantly reduced the adult emergence, developmental period and life span of S. cerealella when compared with the control. At all concentrations, only the oils of the plants seeds extracted with ethanol were able to prevent the adult emergence of the moth and their effect was significantly (p<0.05) different from the plants seeds extracted with acetone and water. However, the seeds of A. melegueta, E. aromatica, P. guineense and X. aethiopica extracted with acetone were also able to prevent the emergence of the adult moth at higher concentrations (4 and 6%) and their effect was significantly (p<0.05) different from those extracted with water. At all concentrations, the seed of E. aromatica extracted with water showed more effect on the emergence of the adult moth, their developmental period and life span than the water extract of A. melegueta, P. guineense and X. aethiopica. There was no significant (p>0.05) difference among the oils of plants extracted with water. Among the three solvents used for the extraction of these plants, ethanolic extracts of these plants proved to be more effective than the rest and the order of their effectiveness can be arranged as follow ethanol>acetone>water. Also, the extract of E. aromatica extracted with different solvents showed more effectiveness than other plants extracted with the same solvents.

Table 1 Effect of plant extracts at 2% concentration on adult emergence, developmental period and life span S. cerealella

Table 2 Effect of plant extracts at 4% concentration on adult emergence, developmental period and life span S. cerealella

Table 3 Effect of plant extracts at 2% concentration on adult emergence, developmental period and life span S. cerealella

Effect of oils of plants seeds on the water absorption capacity of paddy grains

Table 4 presents the effect of different plant oils on the water absorption capacity of paddy grains. The water absorption capacity of the treated seeds varied with the type of oil extracts used, the type of solvent used for extraction, the extract concentration and the period of submergence. The effect of the oils extracted with different solvents were not significantly (p>0.05) different from the control except those that were extracted with ethanol. The oils extracted with ethanol showed high water absorption capacity than other extracts and it effect was significant at all periods of observation. Moreover, the paddy grains treated with the oil of A. melegueta extracted with ethanol had high water absorption capacity than other plant oils extracted with ethanol.

Table 4 Effect of plant extracts on water absorption capacity on paddy grain

Discussion

The ability of insect pests to cause damage to stored grains does not depend on the number of eggs they laid but the ability of their eggs to hatch and develop to other destructive stages in their life cycle. Many botanical extracts have however been proven to either reduce or prevent the development of insects eggs into larva and adult stages which are believed to be the most destructive stages of insect pests. Botanical extracts are believed to contain myriad of secondary metabolites which could act as an entomocides, antifungi and antibacterial (Zibaee, 2011; Martins et al., 2012). However, the ability of these botanical extracts to fully contain their active compounds depends on the types of solvent used for their extraction (Okosun and Adedire, 2010; Patra et al., 2012; Zeeshan et al., 2012).

The result obtained in this research showed that the oils extracted from seeds of A. melegueta, E. aromatica, P. guineense and X. aethiopica have a great effect on the adult emergence, developmental period and life span of S. cerealella regardless of the type of solvent used for the extraction of these four botanicals. Moreover, the ethanolic extracts of these four botanicals proved to be more effective than acetone and water extracts of the plants as it was the only one to prevent the emergence of the adult moth at all concentrations. The acetone extract of A. melegueta and E. aromatica were also able to prevent the emergence of the adult moth at low concentration (2%) while acetone extract of P. guineense and X. aethiopica prevented the adult emergence of the insect at higher concentrations (4 and 6%). Regardless of the concentration used, water extracts of the four botanicals were unable to prevent the emergence of adult moth but they significantly reduced the adult emergence of the insect when compared with the control.

The ability of these extracts to prevent or reduce emergence of adult S. cerealella could be due to the death of the insect larval which may occur due to inability of the larval to fully cast off their exoskeleton which remained linked to the posterior part of their abdomen (Oigiangbe et al., 2010). The results of this study indicated that the extracts of these plants had obvious effect on post embryonic survival of this insect which resulted in prevention of adult emergence at different concentrations. The secondary metabolites present in these plants could be responsible for the inability of the adult insect to emerge as opined by Murdue-huntz and Nisbet (2000) as well as Yang et al. (2006) that secondary metabolites in botanicals are found to disrupt growth and reduced larva survival as well as disruption of life cycle of insects. The high efficacy of these extracts against the emergence of the adult moth may be related to the type of solvent used for their extraction because it was believed that different solvent have different capacity of extracting the active compounds in plants (Okosun and Adedire, 2010; Zeeshan et al., 2012). Therefore, the ability of ethanolic and acetone extracts of these plants to show more efficacy on adult emergence of S. cerealella than water extract could be due to the high extraction capacity of the solvents. This result was in accordance with 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. The result of this work agreed with the research of Ileke (2013) in which the extracts and powders of different plant were found to reduce adult emergence of S. cerealella infesting wheat grains.

The water extracts of these plants despite not able been to prevent the emergence of the adult moth significantly increased the developmental period and reduced the life span of the emerged insects. The water extract of E. aromatica showed greater effect on the developmental period and life span of S. cerealella than other extracts. This work agreed with the work of Ashamo and Akinnawonu (2012) in which the powders and extracts of different plant species were found to increase the developmental period of S. cerealella. The result on water absorption capacity showed that all the seeds treated with plant extracts have good water absorption capacity regardless of the type of solvent used for the extraction of the oils. Nevertheless, plant extracts extracted with ethanol have the greatest water absorption capacity of the seeds than other extracts. Therefore, with the result obtained in this research, extract of the four medicinal plants used could go a long way in the quest of providing alternative means to the use of chemical insecticides for protecting paddy grain in storage. Moreover, ethanolic extract of all the four plants could be more preferable since it presented the greatest entomocidal effect among the other extracts.

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