Evaluation of Insecticidal Potential of Capsicum chinense Jacq. and Aframomum melegueta K. Schum. Against Trogoderma granarium Everts (Coleoptera: Dermestidae) in Groundnut

Musa A K, and Adeyemi A A

Department of Crop Protection, University of Ilorin, P.M.B. 1515, Ilorin, Nigeria

Evaluation of Insecticidal Potential of Capsicum chinense Jacq. and Aframomum melegueta K. Schum. Against Trogoderma granarium Everts (Coleoptera: Dermestidae) in Groundnut

Musa A K, and Adeyemi A A

Department of Crop Protection, University of Ilorin, P.M.B. 1515, Ilorin, Nigeria

The insecticidal potential of seed powders of Capsicum chinense Jacq. (Solanaceae) and Aframomum melegueta K. Schum. (Zingiberaceae) was tested against Trogoderma granarium (Coleoptera: Dermestidae) in the laboratory at (28±2)℃ and 70%± 5% relative humidity. The seed powders were tested at the rates of 0.0%, 0.5%, 1.0% and 1.5% (w/w) of groundnut seeds replicated three times. At the highest rate of treatment, C. chinense caused 56.7% and 76.8% larval mortality at 3 and 7 days post treatment (DPT) respectively while A. melegueta exerted 53.4% and 73.8% larval mortality at 3 and 7 DPT, respectively. Results showed that insecticidal potential of the seed powders against adult mortality of T. granarium and seed damage followed similar trend. The various rates of C. chinense seed powder performed better than A. melegueta seed powder in causing larval and adult mortality and in reducing seed damage. The activity of the seed powders on mortality of the insect, seed weight loss and seed damage were exposure time and rate dependent. A significant reduction (p＜0.05) in seed weight loss and seed damage was recorded among the treatments and maximum reduction was observed in the seeds treated with the highest rate of C. chinense seed powder. Percentage seed damage significantly (p＜0.05) decreased with increase in the rate of treatment while the highest seed weight loss and seed damage were obtained in the control. The study showed that C. chinense seed powder had higher activity against the test insect pest than A. melegueta seed powder. The two seed powders had high bio-activity against the insect and therefore could be used in formulating environment friendly plant-derived insecticide.

botanicals, dermestid beetle, seed damage, seed protection

Introduction

More than three-quarter of the human population in Nigeria depend on groundnut for culinary oil, cake for livestock, food and income. Groundnut is an important leguminous crop that accounts for about 35% of the total plant protein intake of average person in the country. Khapra beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae), is a major insect pest infesting stored groundnut seeds particularly in the northern part of the country where the crop is grown. Gihanem and Shamma (2007) reported that the insect is common in geographical areas characterized by high temperature and low humidity. Several insect species in the same family attack animal and animal products including Dermestes maculatus, D. frischii D. ater and Necrobia rufipes (Don-Pedro, 1989). It is surprising therefore that the insect species is polyphagous. Literatures show that a number of insect and mite species infest stored products (Rajendran and Srianjini, 2008) and pest control becomes an indispensablepractice for sustainable agriculture. The repeated use of synthetic fumigants against Trogoderma granarium for several decades has caused upsurge in insect pests with serious attack on natural enemies and their environment (Subramanyam and Hagstrum, 1995; White and Leesch, 1995). In addition, wrong pesticides are often sold to farmers and fatalities often occur (Adesiyun, 2009). Besides, the high costs of these chemicals have brought about an interest in biopesticides as alternatives to the highly toxic synthetic pesticides as alternatives to the high toxic synthetic pesticides (Oke et al., 2010). The need to curb excessive use of synthetic pesticides has caused a shift to an empirical investigation on existing natural materials that are biodegradable and environmentally friendly. In a bid to contribute to existing literature on this, we evaluated the insecticidal potential of Capsicum chinense and Aframomum melegueta seed powders against T. granarium infestation in stored groundnut.

Materials and Methods

Insect culture

A colony of Trogoderma granarium was established in the laboratory from a batch of infested groundnut seeds obtained from the insectary of the Nigerian Stored Products Research Institute, Ilorin, Nigeria. Subcultures of the insect were maintained on susceptible groundnut seeds in three Kilner jars covered with muslin to allow aeration. Insect culture was carried out at ambient laboratory temperature of (26-29)℃and relative humidity of 67%-71%. The tiny freshly emerged adults (about two-day-old) and 4th larvae instar were collected into separate vials by sieving the stock culture on the day of the experiment (Musa et al., 2010).

Preparation of groundnut seeds

The groundnut seeds (variety SAMNUT 7) were winnowed, sorted and wrapped in a polythene bag before they were disinfested in a freezer for 7 days and air-dried for 3 days. The moisture content of the seeds was determined by the producer of AOAC (1990).

Preparation of plat powders

Fruits of two common spices in Nigeria, Capsicum chinense and Aframomum elegueta, were purchased from Oja Oba market, Ilorin were dehulled while the seeds were sun-dried for 3 days and milled into fine powder using electric blender. The powders were stored separately in their respective glass vials until required for using.

Experimental procedure

100 g of groundnut seeds in separate containers (9 cm diameter) were treated with C. chinense and A. melegueta seed powders at varying rates of 0.5%, 1.0% and 1.5% (w/w). The treated seeds were separately infested with 10 adults and 4th larval instar of T. granarium with the aid of a pooter (an aspirator). The treatments were replicated three times including an untreated control for each powder for comparison. All the experimental units were covered with muslin to allow aeration. The dermestid beetles were examined at 1, 3 and 7 days after treatment (DAT) for larval and adult mortality expressed as percentage. The difference in the initial and final seed weight was expressed as percentage seed weight loss at 30, 60 and 90 DAT (Ojo et al., 2013). Counts of numbers of seeds with holes or tunnels were taken as index of damage caused by the larvae and adults of the insect (Jia et al., 2008).

Data analysis

Data collected were subjected to analysis of the variance (ANOVA) and significant differences were found, treatment means were separated using Least Significant Deference at p=0.05.

Results

Contact action of C. chinense seed powder against larval and adult T. granarium is presented in Table 1.C. chinense seed powder applied at the highest rate 1.5% (w/w) caused 16.7% larval mortality which was significantly higher (p＜0.05) than the mortality in the lowest rate of 0.5% (w/w) having 3.3% larval mortality at 1 day post treatment (DPT). At 3 DPT, the highest rate of treatment caused 56.7% larval mortality which differed significantly (p＜0.05) from 30.0% recorded for the lowest rate of treatment. At 7 DPT, the highest rate treatment caused the highest larval mortality of 76.8%, whereas 1.0% caused larval mortality of 69.9%, thereby showing no significant difference (p＞0.05) between the two rates of treatment. However, different rates of treatment caused significantly higher larval mortality compared with the control seeds which had no mortality from 1 to 7 DPT. It was observed that larval mortality in the highest rate of treatment 5-fold that in the lowest rate at 1 DPT. Larval mortality was significantly higher in the highest rate of seed powder treatment (1.5%) than the lowest rate of treatment (0.5%), but no significant difference was observed between 0.5% and 1.0% rates of treatment (Table 1). The contact action of C. chinense seed powder applied at the highest rate of treatment caused 80.1% adult mortality of T. granarium which was significantly higher (p＜0.05) than the mortality at 3 DPT. That is, adult mortality in the highest rate of treatment was double that in the lowest rate of treatment at 3 DPT. The lowest rate of treatment caused 100.0% adult mortality was at 7 DPT which compared favourably with higher rate of treatment. All the rates of C. chinense seed powder treatments significantly caused adult mortality of T. granarium from 1 to 7 DPT compared with the control seeds which had no mortality.

Contact action of A. melegueta seed powders against larval and adult T. granarium is presented in Table 2. A. melegueta seed powder applied at the highest rate caused 13.3% larval mortality which was significantly higher (p=0.05) than the mortality in the lowest rate with 3.3% larval mortality at 1 DPT. At 3 DPT, the highest rate of treatment caused 53.4% larval mortality which differed significantly (p＜0.05) from value for the lowest rate of treatment (20.1%). The highest rate of treatment (1.5%) caused the highest larval mortality of 73.8%, while 1.0% caused the highest larval mortality of 66.9% showing favourable comparison between the two rates of treatments at 7 DPT. The contact action of A. melegueta seed powder applied at 1.0% and 1.5% rates of treatments caused the same adult mortality of 53.4% which was significantly higher (p＜0.05) than the mortality of 40.0% in 0.5% rate of treatments at 3 DPT. At 1 DPT, different rates of treatments caused the same adult mortality of 20.01% which differed significantly (p＜0.05) from the control seeds which had no mortality. At 7 DPT, all the rates of the seed powders caused 100% adult mortality showing that treatment of groundnut seeds with the lowest rate of C. chinense seed powder compared favourably with A. melegueta seed powder applied at the highest rate.

Table 1 Evaluation of Capsicum chinense seed powder in control of larval and adult Trogoderma granarium

Table 2 Evaluation of Aframomum melegueta seed powder in control of larval and adult Trogoderma granarium

The mean seed weight loss caused by both larval and adult T. granarium in groundnut seeds treated with C. chinense seed powder is given in Table 3. Treatment applied at the highest rate of 1.5% (w/w) accounted for 0.80%, 1.09% and 1.82% seed weight loss by the larval at 30, 60 and 90 DPT, respectively. These values of seed weight loss were higher than 0.03%, 0.05% and 0.07% seed weight loss caused by adults at the same rate of treatment at 30, 60 and 90 DPT, respectively. There was 51.2%, 62.0% and 57.4% significant reduction (p＜0.05) in mean seed weight loss caused by larvae in the highest rate of treatment when compared to the lowest rate of treatment at 30, 60 and 90 DPT, respectively. Similarly, there was significant reduction of 25%, 37.5% and 41.7% in the mean seed weight loss caused by adults at the highest rate of treatment, when compared to the lowest rate of treatment at 30, 60 and 90 DPT, respectively. All the treatments were significantly different from the control seeds.

Table 3 Evaluation of different rates of Capsicum chinense seed powder on groundnut seeds weight loss after Trogoderma granarium larval infestation

The mean seed weight loss by both larval and adult T. granarium in seeds treated with A. melegueta seed powder is given in Table 4. Treatment applied at the highest rate of 1.5% (w/w) accounted for 0.87%, 1.16% and 1.28% mean seed weight loss by the larvae at 30, 60 and 90 DPT, respectively. These values of seed weight loss were higher than 0.02%, 0.04% and 0.06% mean seed weight loss caused by adults at the same rate of the treatment at 30, 60 and 90 DPT, respectively. There were 57.4%, 62.2% and 68.4% significant reduction (p＜0.05) in mean seed weight loss caused by larvae at the highest rate of treatment when compared to the lowest rate of treatment at 30, 60 and 90 DPT, respectively. Similarly, there was significant reduction of 50.0%, 42.9% and 40.0% in the mean seed weight loss caused by adults at the highest rate of treatment when compared to the lowest rate of the treatment at 30, 60 and 90 DPT, respectively. All the treatments were significantly different from the control seeds. Mean seed weight loss caused by the larvae ofT. granarium was significantly lower in the highest rate of C. chinense seed powder than the lowest rate of at 30, 60 and 90 DPT. Mean seed weight loss caused by adult T. granarium was significantly affected by C. chinense seed powder as treated seeds had lower seed weight loss than the control seeds 30 and 60 DPT. However, C. chinense seed powder had no effects on mean seed weight loss caused by adult T. granarium as there was no significant difference observed at 90 DPT.

Table 4 Evaluation of different rates of Aframomum melegueta seed powder on groundnut seeds weight loss after Trogoderma granarium larval infestation

Damage caused by larvae and adults of T. granarium on groundnut seeds treated with C. chinense and A. melegueta seed powders is shown in Table 5. Significant differences were also detected among different rates of treatments in mean number of seeds perforated by larvae. Seeds which had the highest seed powder treatment had no damage while seeds which had the least seed powder treatment had the highest number of seeds damaged by the insect. Damage caused by T. granarium larvae increased gradually with decrease in rate of treatment of the seed powders. Across treatments, damage was consistently and significantly (p＜0.05) more severe in the control seeds than in the treated seeds.

Capsicum chinense seed powder was found to be more effective in reducing the number of seeds perforated by T. granarium than A. melegueta seeds powder.

Table 5 Damage caused by larvae and adults of Trogoderma granarium on groundnut seeds treated with Capsicum chinense and Aframomum melegueta seed powders

Damage of groundnut seeds caused by T. granarium larvae was 6.65% and 11.65% at 1.0% and 0.5% rates of C. chinense seed powder treatment, respectively. This showed an average of about 41.0% reduction in seed damage caused by the larvae in groundnut seeds treated with 1.0% rate of C. chinense seed powder. Seed damage caused by T. granarium adults was 1.65% at both rates of treatment which was considerably lower than what obtained in groundnut seeds infested with larvae during the same exposure time. Damage of groundnut seeds caused by T. granarium larvae was 11.65% and 15.00% at 1.0% and 0.5% rates of A. melegueta seed powder treatment, respectively. This showed an average of about 22.4% reduction inseed damage caused by the larvae in groundnut seed treatment with 1.0% rate of A. melegueta seed powder. Seed damage caused by T. granarium adults was 1.65% and 3.35% at 1.0 and 0.5% rates of A. melegueta seed treatments showing about 51.0% reduction in seed damage in 1.0% rate of treatment compared with the lowest rate of the treatment during the same exposure time of 90 DPT. There was no seed damage in the highest rate of C. chinense and A. melegueta seed powder treatments and all the rates of treatments were significantly different from the control seeds.

Discussion

The use of plant materials as seed protectants against insect pests are known in Nigeria. Pepper fruits and seeds were applied by spraying in powder and liquid forms on plant and animal products to enhance preservation and prevent wastage. Researchers found the use of plant materials as a topical approach towards finding a sustainable substitute to the application of toxic pesticides. This study showed the insecticidal potential of C. chinense and A. melegueta seed powders against T. granarium under artificial infestation of groundnut. The various rates of C. chinense seed powder performed better than A. melegueta seed powder in causing larval and adult mortality at 3 and 7 DPT. The observed mortality might be due to oleoresin component of the seed powder of C. chinense (Relly et al., 2001).

The high mortality reached by these seed powders could be due to cumulative effects of exposure time and concentration thereby affecting the normal behaviour of the insects which subsequently led to their death. It was observed that the seed powders had significant effects on the mortality of larvae and adults of T. granarium. Capsicum sp. may have been potent because of its strong taste which might have exerted a lethal effect against the insect following topical application. The seed powders probably possess behaviour-modifying properties which could be used to control T. granarium. In a related experiment, Oigiangbe et al. (2010) attributed the insecticidal action of cultivars of Capsicum spp. to the inability of the insect to moult in the presence of the plant materials. The three major compounds identified in A. melegueta, (S)-2-heptanol, (S)-2-heptyl acetate and (R)-linalool (Ukeh et al., 2009) may have provided scientific basis for the potential for its use in storedproduct protection at small scale farmer level. In a related investigation, Okpako et al. (2013) reported that A. melegueta aqueous seed extract had insecticidal action against insects of okra.

C. chinense and A. melegueta seed powders significantly reduced the weight loss and damage of treated groundnut seeds. C. chinense seed powder applied at 1.0% rate of treatment gave an average of 41.0% reduction in seed damage caused by the larvae, while A. melegueta seed powder applied at the same rate of treatment gave an average of 22.4% reduction in seed damage caused by the larvae. This finding was suggestion of the greater potential of C. chinense than A. melegueta seed powder against the insect. The adults were particularly important in reproductive ability of the insect while the larvae were observed to have been greatly responsible for the damage. The seed powders protected the groundnut throughout the storage period at the highest rate of the treatment. Oni (2014) noted that the protection of agricultural produce required more attention as it was required for their production because of various losses that occurred after harvest. Dubey et al. (2008) reported 5%-10% losses of stored grains in the temperate countries and 20%-30% in the tropical zones due to insect attack alone. Seed powders of C. chinense and A. melegueta significantly increased larval and adult mortality of T. granarium. Reduced seed weight loss and seed damaged by the larvae and adults of the insect. It is evident that seed powders of C. chinense and A. melegueta constitute potential protectants against T. granariun infestation. Results obtained from this study showed that C. chinense and A. melegueta seed powders had great significant insecticidal effects on larvae and adults of T. granarium when compared withthe control seeds especially at the highest rate. Oni (2014) reported that extracts of cayenne pepper, sweet pepper and long-cayene pepper showed fumigant effect on different stages of Sitophilus zeamais.

Conclusions and Recommendation

The findings of the study revealed that C. chinense and A. melegueta seed powders tested were effective in causing insecticidal action against T. granarium and maintaining the appearance of seeds by reducing the destructive behaviour of the insect. This study had revealed the potential of C. chinense and A. melegueta seed powders for use as protectants of groundnut seeds against T. granarium infestation during storage with the former being more potent. This study drew further attention to the concern raised that plant powders had to be applied in large quantities to be effective against insect pests. To minimize severe damage caused by T. granarium, the traditional use of the seed powders could be encouraged against the insect pest. In Nigeria, these plant species were available, affordable and edible and thus pose no detrimental effects on the environment and life of the user.

Determination and analysis of the relationship between feedstuffs and milk samples showed that Pb, Cd and As were very low in milk and their milk contents did not affect by feedstuff intake. Beneficial elements of Mg, Ca, Fe and Zn contents in milk could be affected by feedstuffs, Ca and Zn were affected mainly by forage feed, whereas Mg was affected mainly by concentrate feed.

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Received 21 May 2015

Musa A K, E-mail: akmusa2013@gmail.com