The Insecticidal Activity of Neem and Palm Kernel Oils on Bean Weevil (<i>Callosobruchus maculatus</i> F.) (Coleoptera: Chrysomelidae: Bruchinae) Infestations of Stored Cowpea (<i>Vigna unguiculata</i> L. Walp)

Gever, Esther Rita; Echezona, Bonaventure C.

doi:https://doi.org/10.1155/2023/5536943

Journal of Food Processing and Preservation

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Abstract Introduction Literature Review Materials and Methods Results Discussion Abbreviations Data Availability Conflicts of Interest Authors’ Contributions References Copyright Related Articles

Research Article | Open Access

Volume 2023 | Article ID 5536943 | https://doi.org/10.1155/2023/5536943

The Insecticidal Activity of Neem and Palm Kernel Oils on Bean Weevil (Callosobruchus maculatus F.) (Coleoptera: Chrysomelidae: Bruchinae) Infestations of Stored Cowpea (Vigna unguiculata L. Walp)

Esther Rita Gever¹and Bonaventure C. Echezona¹

Academic Editor: Alam Zeb

Received20 Apr 2023

Revised27 May 2023

Accepted13 Jun 2023

Published24 Jun 2023

Abstract

Even though it has been established that neem oil has insecticidal properties, its desirability as a plant-based insecticide is unsuitable owing to the sulfurous odour it deposits on the grain(s) that makes it bitter and impinges on its acceptability. For this reason, another oil of plant origin, palm kernel oil (PKO), was admixed with it to reduce the bitter taste and test for their bioinsecticidal potential on the insect pest of stored cowpea seeds. The general objective was to determine the combined effect of neem and palm kernel oils in controlling bean weevil infestations of stored cowpea. The results showed that the treated seeds recorded a significantly higher () mortality of adult Callosobruchus maculatus (Coleoptera: Chrysomelidae: Bruchinae), a reduction in oviposition, and a decrease in the number of emerged insects with the interval of treatment application, and the seeds that were treated had a significantly lower adult emergence hole () and a reduction in % grain damage (), and the weevil perforation index (WPI) was <100%. The findings of this study suggest that admixing neem oil and palm kernel oil has the potential insecticidal efficacy of controlling the bean weevil of stored cowpea, and based on the quantity of palm kernel oil mixed with neem oil, the seeds treated tend to have varying levels of bitterness and sulfurous odour deposit.

1. Introduction

Cowpea (Vigna unguiculata L. Walp) is an annual seed legume within the pea family Fabaceae. Another name for cowpea is “black-eyed pea” or “Southern pea.” In tropical and subtropical regions, it is considered the most important food crop grown and widely consumed [1]. It is a major, cheap, and quality protein source for urban and rural African dwellers [2, 3]. In many regions, its production is restricted by several biotic and abiotic factors in the field and the harvested seeds in storage. Insect pests are among the constraining biotic factors in storage [4]. As Dubey et al. [5] reported, in temperate zones, insect infestation accounts for 5-10% of losses of stored seeds and 20-30% in tropical zones.

In West Africa, up to 100% losses of cowpea seeds can be incurred in storage in a few months when infestation surges [6], especially by the bean weevil—Callosobruchus maculatus. Its presence limits the storage lifespan of cowpea due to the eventual damage it causes. Researchers posit that the larval stage of this weevil makes tunnels and develops within the cowpea seeds [7, 8]. This weevil brings about decreased yield and increased quantitative and qualitative losses after harvest, which manifest as seed perforation, reduction in market value, viability loss of seeds, and weight reduction [9].

Locally, crop pest management is achieved by the use of plant extracts and plant-dried powders such as wood ash, lemongrass, clove, eucalyptus (Koul et al., 2008)[10], turmeric, ginger, neem extracts (cake, oil, bark, leaves, kernel, root, and seed), scale leaves of onions, chili peppers, and garlic [11] due to their insecticidal potentials. This system is beneficial because it poses little or no threat to the environment and the health of humans.

These plant materials used as pesticides to control the insect pest cowpea have relative advantages over synthetic chemicals; they are cheap and easily obtainable. Additionally, no particular skill is required in their usage, unlike the synthetic chemicals that require specialized skills, especially concerning calibration, which may pose a serious challenge to local farmers who do not have the basic skills [12]. Researchers [13, 14] add that some of these plant materials, particularly monoterpenes, are target-specific and biodegradable, and they can be practically used as a tool in programs related to integrated pest management.

Even though it has been established that neem oil has insecticidal properties, it is expensive, not readily sourced, and it is not widely accepted as a protectant against the cowpea weevil owing to the sulfurous odour that it deposits on the grain(s) that makes it bitter and impacts on the acceptability and marketability of treated produce [15]. For this reason, this study seeks to address this problem by admixing neem oil with another readily available oil of plant origin, palm kernel oil (PKO), to reduce the bitter taste that neem oil impinges on seeds and also to determine the combined toxicity of neem and palm kernel oils (at different concentrations) on bean weevil infestations of stored cowpea.

1.1. The Objective of the Study

The general objective of this study was to determine the combined effect of neem and palm kernel oils in controlling bean weevil infestations of stored cowpea.

2. Literature Review

2.1. Origin and Distribution of Cowpea

Cowpea (Vigna unguiculata L. Walp) is an annual grain legume within the pea family Fabaceae, genus Vigna, and species unguiculata. It originated in Africa and is widely spread across the tropics [16]. As Singh et al. [17] corroborate, in West Africa, cowpea production accounts for about 9 out of 14 million hectares of the world’s total area planted with cowpea.

Cowpea is a very important grain (legume) that is chiefly grown and widely consumed in the tropics and subtropical regions of the world [18]. Singh et al. [17] and Gomez [19] emphasize that cowpea’s economic importance is numerous; it is cheap and a major source of protein, vitamins, and minerals that farmers can harvest as nutritious fodder for their livestock. They further add that farmers can harvest it as seeds for consumption based on climatic and economic constraints.

2.2. The Cowpea Weevil: Callosobruchus maculatus

West Africa is known to be the place of origin of the cowpea weevil, and it is believed to have spread across the globe via the trading of legumes alongside other crops. Also, apart from its global spread through trading, this weevil has prevailed as an agricultural pest due to its tolerance for a high degree of inbreeding [20]. The cowpea weevil is sexually dimorphic; the females are easily distinguished from males. The sexes of the weevils can be visually determined by examining the anatomical (elytra, shape of the abdomen) pattern. The female of this species is dark-coloured with four elytral spots, while the male is pale brown and less distinctly spotted. Also, the plate that covers the end of the abdomen in females is large and dark-coloured along the sides but smaller without the dark areas in males [21].

2.3. Botany and Economic Importance

Taxonomically, the bean beetle is placed in the family Chrysomelidae: Bruchinae, genus Callosobruchus, and species C. maculatus. The bean weevil is a major and common field-to-storage agricultural pest of economically essential legumes, especially cowpea, in Tropical Africa [22, 23], and it is widely known as an essential pest of pulse crops in Africa and Asia under storage conditions [24, 25].

2.4. Control of Cowpea Weevil Using Plant Materials

Plant extracts and plant-dried powders that have insecticidal potentials and pose little or no threat to the ecosystem and the health of humans have been locally employed with varying levels of effectiveness in the management of crop pests such as neem oil, wood ash, lemon grass, ginger, and garlic [11]. Their insecticidal activities have been variously studied by different scholars, but over the years, the bean weevil has been chemically controlled by using synthetic insecticides [1]. Pirimiphos methyl and permethrin are effective synthetic insecticides when used against C. maculatus, but the hazards associated with their usage reduce their desirability [4]. Also, Ilesanmi and Gungula [26] aver that Phostoxin tablet, a fumigant, effectively protects cowpea seeds in storage against insect pests. Still, it is not readily sourced and is harmful to man and livestock.

More so, the use of various synthetic insecticides in the protection of cowpea seeds against insect attacks has not been successful because it has caused a lot of environmental setbacks, including pest resurgences, development of resistance to pesticides, lethal effects to nontarget organisms in the ecosystem, and toxic residues in food and water bodies. It may also cause direct toxicity to users [27]. All these shortfalls can be prevented by using plant-based insecticides, which are ecologically safe, cost-effective, and user-friendly [28].

There are numerous hazards associated with the use of synthetic chemicals, and these hazards are expressed based on toxicity. These hazards that are associated with the use of synthetic chemicals are a result of exposure via inhalation of droplets of chemicals and dermal contact with contaminated hands or food [29], which could have hazardous effects on users such as neurotoxic effects [30], mutagenic effects (changes in the gene or the chromosome), endocrine defects, cataract formation, oncogenic effects (production of tumours), and carcinogenic effects (production of cancer) [31].

In light of the above, it is imperative to adopt a safer insect control method as an alternative replacement for synthetic insecticides. As such, the adoption of an integrated pest management system based on the use of botanicals (insecticides derived from plants) has been employed in this study. Botanicals have advantages over synthetic chemicals in many ways. Weinzierl [32] and Scott et al. [33] posit that botanicals are of relatively lower risk to nontarget organisms; they are nontoxic to mammals; and environmentally, they do not persist because they rapidly break down and are metabolized easily by animals receiving sublethal doses [34]. Scholars [35] posit that they are more economical and more effective. The study of Dunkel et al. shows that neem oil and palm kernel oil in combination are effective as storage protectants against the cowpea weevil, beetles, and grain borers.

2.5. Analysis of the Chemical Composition of Neem Oil

Using neem oil as an insect protectant has proven effective due to neem’s primary active insecticidal ingredient, azadirachtin. It is a chemical compound that belongs to the limonoid group and is a secondary metabolite found in neem seeds. It has a chemical formula of C₃₅H₄₄O₁₆ and a molar mass of 720.721 g·mol⁻¹. It has a broad spectrum of activity and works as a repellant by disrupting the hormones involved with insect moulting, thereby preventing insect larvae from developing properly into adults. It also prevents oviposition and is a feeding inhibitor [36]. It does this by disrupting the bruchids’ sense of smell so that they can avoid ingesting azadirachtin-coated cowpea seeds that can inhibit the functions of their digestive enzymes [37].

The neem oil is obtained by cold-pressing the seed kernels of the neem. The oil extracted from the seed of the tree can be used directly as an insect and mite repellant, an insecticide, a fungicide, and an antifertility agent [38] and is the source of many commercial pesticide products such as dusts, granules, and concentrates because it contains azadirachtin which has a broad spectrum of activity [36]. Neem oil also contains disulphide, which contributes to its bioactivity. Interestingly, azadirachtin has been proven to have a low acute mammalian toxicity [39, 40]. Environmentally, Boursier et al. [41] assert that it does not persist due to its fast biodegradation in sunlight.

Palm kernel oil is the edible plant oil that is derived from the kernel of the oil palm tree (Elaeis guineensis Jacq.), and it has a wide amplitude of usage; it is used in industries (cosmetics) and in pharmaceuticals, as a biofuel and, more recently, as a biopesticide against storage pests as evidenced in the previous studies [42, 43]. Oils such as soybean, groundnut, olive, and palm have also been recently exploited for their protectant ability against storage pests [44, 45]. All these findings align with other research works conducted to test the insecticidal potential of plant extracts of different plants against storage insect pests. Based on the literature above, the researchers tested the following hypotheses:

H1. Phostoxin causes high mortality of adult C. maculatus in storage

H2. Neem and palm kernel oils admixed have ovicidal properties

H3. P_t and N₀P₀ encourage the emergence of adult C. maculatus

3. Materials and Methods

This study was conducted at the Department of Crop Science Teaching Laboratory, Faculty of Agriculture, University of Nigeria, Nsukka. This experiment was laid on a laboratory bench in a completely randomized design (CRD) with three replications. This study was conducted at an average temperature of 27.9°C (82.2°F) and a relative humidity of 77%.

The bean weevil used for this experiment was naturally sourced from an already infested stored cowpea which was kept in a transparent white container with a white lid for an efficient light interception to breed sufficient bruchid that was needed to carry out this experiment. The breeding container had twenty (20) perforations around it, and a circular cut was made in the middle of the lid (using a red-hot knife). It was covered with muslin cloth to facilitate aeration, mating, and reproduction.

The cowpea (California black-eye cowpea—subspecies of cowpea) used to carry out this research work was locally sourced from Ogige, Nsukka main market, Enugu State, Nigeria. After purchase, the seeds were thoroughly handpicked to eliminate contaminants, dry pods, and damaged seeds.

To disinfect, the clean seeds that have been selected were sun-dried for 72 hours (3 days) at 75°F and stirred several times a day to ensure even drying and eliminate all forms of incipient infestation that may be inherent in the cowpea seeds as well as to ensure zero infestation of the cowpea seeds before experimenting.

After disinfestation, 20 g of wholesome, uninfested cowpea seeds were accurately weighed out using a professional miniscale (digital pocket scale) into each of the uniform, blue-coloured cylindrical plastic experimental containers with a white lid that were used to carry out this experiment. Each plastic container had nine (9) uniform perforations that were made with a red-hot 1-inch nail and were covered with a well-fitted muslin cloth to provide adequate aeration and prevent the escape of adult bruchid upon introduction. The experimental containers were well labelled using masking tape and coloured markers (blue and red). The introduced adult bruchid and uninfested cowpea seeds were then allowed to stay until the emergence of the first filial generation (F₁) that was used to carry out this experiment. The sexes of the emerged bean weevils were determined visually by examining the anatomical (elytra and shape of the abdomen) pattern.

Cold-pressed neem oil that was used to carry out this experiment was sourced from Royal Neem Company, Gudu District, Abuja, Nigeria while the hot-pressed palm kernel oil (PKO) that was used to carry out this experiment was sourced from Ugo Tech. Industries Limited, Emene, Enugu, Nigeria.

Using a 5 ml calibrated syringe, neem oil (N) was measured at 0 ml, 1 ml, and 2 ml. Palm kernel oil (PKO) was also measured out using a 5 ml calibrated syringe at 0 ml, 1 ml, and 2 ml, while neem oil (N) and PKO were admixed in different ratios (in three different plastic mixing containers) as follows, 1N : 1P, 1N : 2P, and 1N : 3P (using 10 ml and 20 ml syringes), and measured out at different rates of 0 ml, 1 ml, and 2 ml. Phostoxin tablet was applied at 0.2 g/kg cowpea seed.

With the aid of the digital pocket scale, 20 g each of the cowpea seeds that had been disinfested was weighed out into the experimental plastic containers that had nine (9) perforations and were covered with the well-fitted muslin cloth. The different rates of neem oil and palm kernel oil treatments were carefully measured using clean and appropriately calibrated syringes of 5 ml, 10 ml, and 20 ml. Mixing containers were employed to properly mix the oils before applying them to the different rates of treatments using clean syringes of 1 ml and 2 ml, while a Phostoxin tablet was applied at the rate of 0.2 g/kg cowpea seeds to the breeding containers labelled Phostoxin, and nothing was applied to the containers labelled N₀P₀.

After adding the oil treatments, the containers were thoroughly shaken and randomly placed on a laboratory bench for observations in a completely randomized manner. Five adult male and five adult female bruchids were anatomically selected from the transparent insect culture container, where the bruchid was bred and introduced into the perforated experimental containers.

The treatment combinations were represented as follows: N₀P₀ = no neem, no PKO; N₁ = neem at 1.0 ml; N₂ = neem at 2.0 ml; 1N₁ : 1P₁ = 10 ml neem+10 ml PKO at 1.0 ml; 1N₂ : 1P₂ = 10 ml neem+10 ml PKO at 2.0 ml; 1N₁ : 2P₁ = 10 ml neem+20 ml PKO at 1.0 ml; 1N₂ : 2P₂ = 10 ml neem+20 ml PKO at 2.0 ml; 1N₁ : 3P₁ = 10 ml neem+30 ml PKO at 1.0 ml; 1N₂ : 3P₂ = 10 ml neem+30 ml PKO at 2.0 ml; P₁ = PKO at 1.0 ml; P₂ = PKO at 2.0 ml; and P_t = Phostoxin tablet at 0.2 g/kg cowpea grain.

3.1. Data Collection

Data on the effect of bean weevil on the cowpea were collected as follows: (1)Effect of treatments on the mortality of adult bruchids

This was done by counting, recording, and discarding the dead bruchids in each container at 1, 2, and 7 days after the commencement of the experiment. The insects were probed to confirm that they were dead using an office pin. The percent mortality was calculated using the following formula: . (2)Effect of treatments on the oviposition of adult C. maculatus

This was obtained by counting the number of eggs laid on ten (10) randomly selected seeds per container at 7, 14, 21, 28, 35, 42, and 49 days after infestation (DAI). (3)Effect of treatments on the emergence of adult C. maculatus

This was obtained by carefully observing and counting the number of emerged adults (dead and living) on the 1st, 2nd, 3rd, and seventh days after infestation (DAI). (4)Effect of treatments on emergence hole count, % damaged seeds, and weevil perforation index at 10 weeks after infestation (i)The total number of emergence hole count: the total number of emergence holes per seed from ten (10) randomly selected seeds at 10 weeks after infestation (WAI) was counted.(ii)(iii)Weevil perforation index (WPI): the weevil perforation index was calculated as

From the formula above, a weevil perforation index that is greater than 50% indicates the enhancement of infestation by the weevil or a negative ability of the plant material or insecticide(s) tested while a weevil perforation index that is less than 50% implies a positive protection of the seeds by the protectant (plant material). All the data collected were subjected to analysis of variance (ANOVA) according to the procedure outlined for completely randomized design (CRD). The detection of differences among treatment means for significance was done with Fisher’s least significant difference (F-LSD) at a 5% probability level.

4. Results

Table 1 shows the effect of the different treatments at different dosage rates on the mortality rate of adult C. maculatus at 1, 2, and 7 days after infestation. The treatments had a significant effect () on the mortality assessed for the study. From the result obtained, the botanical treatments have mortality potentials. However, Phostoxin (P_t) had a significantly high mortality effect, while the treatment N₀P₀ had the least significant effect on mortality, and this increased with time. This result supports this study’s first hypothesis, which states that Phostoxin causes high mortality of adult bruchids.

Table 2 shows the effect of the different treatments at different dosage rates on the oviposition of adult C. maculatus at 7, 14, 21, 28, 35, 42, and 47 days after infestation. The treatment N₀P₀ successively recorded the highest oviposition (egg laying) of adult bruchid, while the botanical treatments reduced the oviposition of adult C. maculatus. This result agrees with this study’s second hypothesis that neem and palm kernel oils admixed have ovicidal properties.

Table 3 shows the effect of the different treatments at different dosage rates on the emergence of adult C. maculatus at 1, 2, 3, 4, 7, 70, 77, and 84 days. All the treatments tested had no significant effect on the emergence of adult C. maculatus at 1, 2, 3, 4, and 7 DAI except for the treatment N₀P₀, which recorded an increasingly high adult emergence at 70, 77, and 84 DAI, and the treatment P_t also recorded a high adult emergence at 70, 77, and 84 DAI. This implies that both P_t and N₀P₀ encouraged the emergence of adult C. maculatus in stored cowpea seeds which can bring about qualitative and quantitative losses of stored seeds with time. This result aligns with the third hypothesis, which says that P_t and N₀P₀ encourage the emergence of adult C. maculatus.

Table 4 shows the effect of the different treatments on emergence hole count (EHC), percentage damaged seeds (% DG), and weevil perforation index (WPI). From Table 4, at 10 WAI, the control group (N₀P₀) statistically recorded the highest EHC followed by P_t, and the treatment means are different from each other (). All the treatments tested had a significant effect on the EHC of adult C. maculatus. The % DG was higher in the control group with a value of 59.5%, and all the treatments tested had a significant effect on the %DG. With regard to WPI, the highest statistical value was recorded in N₀P₀ (90.0) which shows a negative ability of the protectant tested. The treatments N₁ and P₁ recorded the least statistical value of 28.6%, implying that the treatments were able to protect the cowpea seeds against C. maculatus infestation in storage at 10 weeks after infestation.

Table 5 shows the sulfurous odour/bitterness level of the seeds treated with different dosage rates of the oils tested in this study. From Table 5, the seeds treated with 1N₂ : 3P₂ and 1N₁ : 3P₁ (10 ml neem+30 ml PKO at 2.0 ml and 10 ml neem+30 ml PKO at 1.0 ml) recorded low bitterness and reduced sulfurous odour. This reduced sulfurous odour/low bitterness level can be attributed to the increased quantity of palm kernel oil that was admixed with neem oil. The seeds treated with 1N₂ : 2P₂ and 1N₁ : 2P₁ (10 ml neem+20 ml PKO at 2.0 ml and 10 ml neem+20 ml PKO at 1.0 ml) were moderately bitter as the quantity of palm kernel oil admixed with neem oil was reduced by 10 ml. With an equal quantity of palm kernel oil admixed with neem oil, the seeds treated with 1N₂ : 1P₂ and 1N₁ : 1P₁ (10 ml neem+10 ml PKO at 2.0 ml and 10 ml neem+10 ml PKO at 1.0 ml) had a high sulfurous odour/bitterness level while the seeds that were treated with N₂ and N₁ (neem at 2.0 ml and neem at 1.0 ml) had a very high level of sulfurous odour/bitterness level. This is because the oil was not admixed with another oil that has the tendency to neutralize its bitterness like palm kernel oil.

5. Discussion

Although certain plant powders and plant extracts have been found to have insecticidal potentials over the years, Pavela [46] believes that their level of effectiveness has not been well assessed. From the results obtained in this study, Phostoxin caused the highest mortality of adult bruchids. However, it is not a readily available cowpea protectant against the cowpea weevil, and it is toxic to man and eco-unfriendly. Also, the different rates of the botanical oils tested were able to cause the death (mortality) of adult bruchids. It was observed that the mortality of adult bruchids increased with time (7 DAI>2 DAI>1 DAI) following the application of the treatments, and this corresponds with the mortality result obtained by Boulahbel et al. [36], whereas the control group N₀P₀ did not cause significant death of adult bruchids at the various intervals tested. It gave the least insecticidal protection of the cowpea seeds stored. Overall, the mortality rate of adult C. maculatus was significantly higher in treated cowpea seeds than in untreated cowpea seeds.

As shown in the result obtained for the effect of the treatments on the oviposition of adult bruchids, both neem oil and palm kernel oils at 1 ml (N₁ and P₁) significantly inhibited oviposition of adult bruchids while the control group (N₀P₀) encouraged oviposition at all the intervals tested. This implies that the botanical oils effectively prevent adult bruchids from laying eggs even at low concentrations (1 ml). This is in concordance with the result obtained by Akami et al. [47] when they tested the synergistic effects of wood ash and essential oils on the fecundity, pupal occlusion, and adult mortality of the cowpea seed weevil. The result they obtained revealed that wood ashes from the French digbe plant (Hymenocardia acida) and the dwarf red ironwood plant (Lophira lanceolata) and the essential oils of the lippia plant (Lippia adoensis) could be used to reduce C. maculatus infestation of stored cowpea. They equally assert that the essential oil had the inherent potential of preventing oviposition and progeny production of C. maculatus even at low concentrations.

Based on adult emergence, the botanical oils tested had adulticidal potential, and the different ratios of the oils tested considerably inhibited the emergence of adult bruchids unlike the treatments N₀P₀ and P_t that encouraged adult emergence of adult bruchids. This corresponds with the result obtained by Oni and Ogungbite [48] and Uddin II and Sanusi [49]. Uddin II and Sanusi tested the efficacy of three plant origin oils and palm kernel oil in the control of Callosobruchus maculatus (F.) in stored cowpea (Vigna unguiculata L. Walp) and found out that all the oils tested, especially palm kernel oil, were more effective against the F₁ progeny emergence. This is because the oils tend to flood the spiracles of the bruchids, thereby causing asphyxiation, which prevents adults from emerging. This is consistent with the result obtained by Durojaye et al. [50]. Based on the results of this study, it has been shown that both neem and palm kernel oils have insecticidal potentials to be used as biopesticides of stored insect pests of cowpea seeds. Even though the fumigant, Phostoxin tablet, was effective in protecting cowpea seeds in storage against insect pests, it is not recommended for storing cowpea seeds owing to its negative residual impacts and unavailability and the difficulty in sourcing it, as well as the harm it causes to man and livestock.

Concerning the percentage of seed damage of stored cowpea seeds, grain damage was higher in untreated seeds (59.5%) than in treated seeds (<12.4%) at 10 weeks after infestation. On the evaluation of the weevil perforation index (WPI), the control group (N₀P₀) recorded the highest perforation (least protection) of the stored cowpea seeds (90%) while the botanical oils, especially N₁ and P₁, caused the least seed perforation (28.6%) at 10 weeks after infestation. This portends a positive protectant ability of the botanical oils tested against the stored insect pest.

Moreso, the seeds treated with the oils tested at different dosage rates recorded varying levels of bitterness/sulfurous odour deposit. From Table 5, it can be seen that the higher the quantity of palm kernel oil admixed with neem oil, the lesser the bitterness level/sulfurous odour that is deposited on the seeds and vice versa. Researchers [15] emphasize that the major reason why neem oil is not widely accepted as a storage pest bioinsecticide is due to its bitter taste and sulfurous odour. This then implies that even though neem oil has been confirmed to have insecticidal properties, it is still recommended that higher quantities of plant origin oil should be admixed with it to overcome the sulfurous odour that neem oil deposits on the seeds that make it bitter and impact the acceptability and marketability of the treated seeds.

Although this study has revealed the synergistic interactions between the different proportions of the tested oils resulting in toxicity and a reduction in the number of eggs deposited, it has limitations, and one of such limitation is that other experiments like sublethal experiments, repellence, antifeedant, and fertility tests need to be added. In the second place, the GC-Ms of the oils used were not shown. It is recommended that future studies in this direction should include the GC-Ms of the oils used or the company’s chemical composition of the oils where it is procured. In the third place, a Phostoxin tablet was used in this study for disinfecting the cowpea seeds and also served as one of the treatments in this study. It is recommended that other disinfecting methods such as using sodium hypochlorite (NaOCl) or calcium hypochlorite solution can be employed.

Abbreviations

PKO:	Palm kernel oil
N:	Neem oil
DAI:	Days after infestation
AE:	Adult emergence
EHC:	Emergence hole count
%DG:	Percentage damaged grains/seeds
WPI:	Weevil perforation index.

Data Availability

The data used to support the findings of this study are included in the article.

Conflicts of Interest

The authors declare that they have no known financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Authors’ Contributions

Prof. B. C. Echezona of the Department of Crop Science, University of Nigeria, Nsukka, contributed to the design and acquisition of materials for this study. He also worked on the analysis and data interpretation while Mrs. Gever Esther Rita of the Department of Crop Science, University of Nigeria, Nsukka, drafted and revised this work critically for important intellectual content.

References

R. O. Akinkurolere, C. O. Adedire, and O. O. Odeyemi, “Laboratory evaluation of the toxic properties of forest anchomanes, Anchomanes difformis against pulse beetle Callosobruchus maculatus (Coleoptera: Bruchidae),” Insect Science, vol. 13, no. 1, pp. 25–29, 2006.
View at: Publisher Site | Google Scholar
H. A. Ajeigbe, A. K. Saidou, B. B. Singh, O. Hide, and T. SatohiC. A. Coulibaly, “Potentials for cowpea (Vigna unguiculata) for dry season grain and fodder production in the Sudan and Sahel zones of West Africa,” in Innovative Research along the Cowpea Value Chain, O. Boukar, Ed., pp. 189–202, International Institute of Tropical Agriculture (IITA), 2012.
View at: Google Scholar
E. Dube and M. Fanadzo, “Maximising yield benefits from dual-purpose cowpea,” Food Security, vol. 5, no. 6, pp. 769–779, 2013.
View at: Publisher Site | Google Scholar
G. B. Swella and D. M. K. Mushobozy, “Evaluation of the efficacy of protectants against cowpea bruchids (Callosobruchus maculatus (F.)) on cowpea seeds (Vigna unguiculata (L.) Walp.),” Plant Protection Science, vol. 43, no. 2, pp. 68–72, 2007.
View at: Publisher Site | Google Scholar
N. K. Dubey, B. Srivastava, and A. Kumar, “Current status of plant products as botanical insecticides in storage pest management,” Journal of Biopesticides, vol. 1, no. 2, pp. 182–186, 2008.
View at: Google Scholar
J. K. Kang, B. R. Pittendrigh, and D. W. Onstad, “Insect resistance management for stored product pests: a case study of cowpea weevil (Coleoptera: Bruchidae),” Journal of Economic Entomology, vol. 106, no. 6, pp. 2473–2490, 2013.
View at: Publisher Site | Google Scholar
K. D. Ileke, D. S. Bulus, and A. Y. Aladegoroye, “Effects of three medicinal plant products on survival, oviposition, and progeny development of cowpea bruchid, Callosobruchus maculatus (Fab.) [Coleoptera: Chrysomelidae] infesting cowpea seeds in storage,” Jordan Journal of Biological Science, vol. 6, no. 1, pp. 61–66, 2013.
View at: Publisher Site | Google Scholar
M. P. Lima, J. V. Oliveira, R. Barros, and J. B. Torres, “Identification of cowpea (Vigna unguiculata (L.) Walp.) genotypes resistant to Callosobruchus maculatus (Fabr.) (Coleoptera: Bruchidae),” Neotropical Entomology, vol. 30, no. 2, pp. 289–295, 2001.
View at: Publisher Site | Google Scholar
A. R. Oluwafemi, “Comparative effects of three plant powders and pirimiphos-methyl against the infestation of Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) in cowpea seeds,” SOAJ Entomol, vol. 1, pp. 87–99, 2012.
View at: Google Scholar
O. Koul, S. Walia, and G. Dhaliwal, “Essential oils as green pesticides: Potentials and constraints,” Biopesticides International, vol. 4, pp. 63–84, 2008.
View at: Google Scholar
G. M. Prowse, T. S. Galloway, and A. Foggo, “Insecticidal activity of garlic juice in two dipteran pests,” Agricultural and Forest Entomology, vol. 8, no. 1, pp. 1–6, 2006.
View at: Publisher Site | Google Scholar
M. B. Isman and M. L. Grieneisen, “Botanical insecticide research: many publications, limited useful data,” Trends in Plant Science, vol. 19, no. 3, pp. 140–145, 2014.
View at: Publisher Site | Google Scholar
S. A. M. Abdelgaleil, H. A. Gad, G. R. Ramadan, A. M. El-Bakry, and A. M. El-Sabrout, “Monoterpenes: chemistry, insecticidal activity against stored product insects and modes of action—a review,” International Journal of Pest Management, vol. 67, pp. 1–23, 2021.
View at: Publisher Site | Google Scholar
S. A. M. Abdelgaleil, H. A. Gad, M. S. Al-Anany, and A. A. Atta, “Monoterpenes improve the insecticidal efficacy of spinosad against Sitophilus oryzae (L.) on stored wheat,” International Journal of Pest Management, vol. 67, pp. 1–11, 2021.
View at: Publisher Site | Google Scholar
F. O. Ojiako, U. Zakka, S. A. Dialoke, C. E. Ahuchaogu, O. M. Nnebue, and C. P. Izuogu, “Impregnating storage materials with neem seed oil against Callosobruchus maculatus Fabricus (Coleoptera: Chrysomelidae: Bruchinae) in stored bambara seeds (Vigna subterranean L.) Verdcourt,” International Letters of Natural Sciences, vol. 52, pp. 28–42, 2016.
View at: Publisher Site | Google Scholar
Ecocrop, “Ecocrop database,” FAO, 2009, http://ecocrop.fao.org/ecocrop/srv/en/home.
View at: Google Scholar
B. B. Singh, P. Hartmann, C. Fatokun, M. Tamo, S. A. Tarawali, and R. Ortiz, “Recent progress in cowpea improvement,” Chronica Horticulturae, vol. 43, pp. 8–12, 2003.
View at: Google Scholar
R. O. Akinkurolere, “Comparative effects of three plant powders and primiphos-methyl against the infestation of Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) in cowpea seeds,” SOAJ of Entomological Studies, vol. 1, no. 2, pp. 108–117, 2012.
View at: Google Scholar
C. Gomez, “Cowpea: post-harvest operations,” in Post-Harvest Compendium, Mejia, Ed., pp. 1–71, AGST, FAO, 2004.
View at: Google Scholar
B. M. D. Tran and P. F. Credland, “Consequences of inbreeding for the cowpea seed beetle, Callosobruchus maculatus (F.) (Coleoptera: Bruchidae),” Biological Journal of the Linnean Society, vol. 56, no. 3, pp. 483–503, 1995.
View at: Publisher Site | Google Scholar
W. B. Christopher and S. B. Lawrence, “A Handbook on Bean Beetles” Callosobruchus maculatus, National Science Foundation, Emory University, or Morehouse College, 2014, http://beanbeetles.org.
H. Massango, L. Faroni, K. Haddi, F. Heleno, L. V. Jumbo, and E. Oliveira, “Toxicity and metabolic mechanisms underlying the insecticidal activity of parsley essential oil on bean weevil, Callosobruchus maculatus,” Journal of Pest Science, vol. 90, no. 2, pp. 723–733, 2017.
View at: Publisher Site | Google Scholar
N. Raja, S. Albert, A. Babu, S. Ignacimuthu, and S. Dorn, “Role of botanical protectants and larval parasitoid Dinarmus vagabundus (Timberlake) (Hymenoptera: Pteromalidae) against Callosobruchus maculates (F.) (Coleoptera: Bruchidae) infesting cowpea seeds,” Malaysian Applied Biology, vol. 29, no. 1-2, pp. 55–60, 2000.
View at: Google Scholar
F. A. Ajayi and N. E. Lale, “Seed coat textures, host species and how the time of application affects the efficacy of essential oils applied for the control of Callosobruchus maculates (F.) (Coleoptera: Bruchidae) in stored pulses,” International Journal of Pest Management, vol. 47, no. 3, pp. 161–166, 2001.
View at: Publisher Site | Google Scholar
L. A. Tapondjou, C. Adler, H. Bouda, and D. A. Fontem, “Efficacy of powder and essential oil from Chenopodium ambrosioides leaves as post-harvest grain protectants against six stored product beetles,” Journal of Stored Products Research, vol. 38, no. 4, pp. 395–402, 2002.
View at: Publisher Site | Google Scholar
J. Ilesanmi and D. Gungula, “Amino acid composition of cowpea seeds preserved with mixtures of neem (Azadirachta indica) and moringa (Moringa oleifera) seed oils,” American Journal of Food and Nutrition, vol. 4, pp. 150–156, 2016.
View at: Google Scholar
M. Suleiman and M. A. Yusuf, “The potential of some plant powders as biopesticides against Sitophilus zeamais (Motsch.) (Coleoptera: Curculionidae) and Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) on stored grains: a review,” Bayero Journal of Pure and Applied Sciences, vol. 4, no. 2, pp. 204–207, 2011.
View at: Google Scholar
C. O. Adedire, O. M. Obembe, R. O. Akinkurolere, and S. O. Oduleye, “Response of Callosobruchus maculatus (Coleoptera: Chrysomelidae: Bruchinae) to extracts of cashew kernels,” Journal of Plant Diseases and Protection, vol. 118, no. 2, pp. 75–79, 2011.
View at: Publisher Site | Google Scholar
I. C. Yadav, N. L. Devi, J. H. Syed et al., “Current status of persistent organic pesticides residues in air, water, and soil, and their possible effect on neighboring countries: a comprehensive review of India,” Science of The Total Environment, vol. 511, pp. 123–137, 2015.
View at: Publisher Site | Google Scholar
M. Jankowska, J. Rogalska, J. Wyszkowska, and M. Stankiewicz, “Molecular targets for components of essential oils in the insect nervous system—a review,” Molecules, vol. 23, no. 1, p. 34, 2018.
View at: Google Scholar
K. Owens, J. Feldman, and J. Kepner, “Wide range of diseases linked to pesticides,” Pesticides, vol. 30, pp. 13–21, 2010.
View at: Google Scholar
R. A. Weinzierl, “Botanical insecticides,” in Soaps and Oils: Biological and Biotechnological Control of Insect Pests, J. E. Rechcigl and N. A. Rechcigl, Eds., pp. 110–130, Lewis Publishers, Boca Raton, NY, USA, 2000.
View at: Google Scholar
I. M. Scott, H. Jensen, J. G. Scott, M. B. Isman, J. T. Arnason, and B. J. R. Philogene, “Botanical insecticides for controlling agricultural pests: Piperamides and the Colorado potato beetle Leptinotarsa decemlineata (Coleoptera: Chrysomelidae),” Archives of Insect Biochemistry and Physiology, vol. 54, no. 4, pp. 212–225, 2003.
View at: Publisher Site | Google Scholar
N. Ling, Rotenone: a Review of its Toxicity and Use for Fisheries Management, Science for Conservation 211. Department of Conservation, Wellington, New Zealand, 2003.
S. B. Padin, C. B. Fuse, M. I. Urrutia, and B. G. Dal, “Toxicity and repellency of nine medicinal plants against Triboliu castaneum in stored wheat,” Bulletin of Insectology, vol. 66, no. 1, pp. 45–49, 2013.
View at: Google Scholar
B. Boulahbel, N. Aribi, S. Kilani-Morakchi, and N. Soltani, “The activity of neem oil in Drosophila melanogaster: toxicity and delayed effect on the progeny,” Journal of Entomology and Zoology Studies, vol. 3, pp. 306–310, 2015.
View at: Google Scholar
S. Kilani-Morakchi, H. Morakchi-Goudjil, and K. Sifi, “Azadirachtin-based insecticide: overview, risk assessments, and future directions,” Frontiers in Agronomy, vol. 3, article 676208, 2021.
View at: Publisher Site | Google Scholar
C. Kaushic, The Antifertility Effect of Neem Oil and Its Mechanism of Action following Intrauterine Application, [Ph.D. thesis], National Institute of Immunology, 2004.
E. D. Morgan, “Azadirachtin, a scientific gold mine,” Bioorganic and Medicinal Chemistry, vol. 17, no. 12, pp. 4096–4105, 2009.
View at: Publisher Site | Google Scholar
A. Salehzadeh, A. Jabbar, L. Jennens et al., “The effects of phytochemical pesticides on the growth of cultured invertebrate and vertebrate cells,” Pest Management Science, vol. 58, no. 3, pp. 268–276, 2002.
View at: Publisher Site | Google Scholar
C. M. Boursier, D. Bosco, A. Coulibaly, and M. Negre, “Are traditional neem extract preparations as efficient as a commercial formulation of azadirachtin A?” Crop Protection, vol. 30, no. 3, pp. 318–322, 2011.
View at: Publisher Site | Google Scholar
S. A. Babarinde, M. A. Adebayo, and K. Oduyemi, “Integrating varietal resistance with Xylopia aethiopica (Dunal) A. Richard seed extract for the management of Sitophilus zeamais Motschulsky in stored maize,” African Journal of Biotechnology, vol. 7, no. 8, 2008.
View at: Google Scholar
D. Obeng-Ofori and S. Amiteye, “Efficacy of mixing vegetable oils with primiphos-methyl against the maize weevil, Sitophilus zeamais Motschulsky in stored maize,” Journal of Stored Products Research, vol. 41, no. 1, pp. 57–66, 2005.
View at: Publisher Site | Google Scholar
K. E. Law-Ogbomo and R. K. A. Egharevba, “The use of vegetable oils in the control of Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) in three cowpea varieties,” Asian Journal of Plant Sciences, vol. 5, no. 3, pp. 547–552, 2006.
View at: Publisher Site | Google Scholar
I. O. Udo and G. I. Harry, “Effect of groundnut oil in protecting stored cowpea (Callosobruchus maculatus),” Journal of Biology, Agriculture and Healthcare, vol. 3, no. 1, pp. 89–92, 2013.
View at: Google Scholar
R. Pavela, “Effectiveness of some botanical insecticides against Spodoptera littoralis Boisduvala (Lepidoptera: Noctudiae), Myzus persicae Sulzer (Hemiptera: Aphididae), and Tetranychus urticae Koch (Acari: Tetranychidae),” Plant Protection Science, vol. 45, no. 4, pp. 161–167, 2009.
View at: Publisher Site | Google Scholar
M. Akami, N. N. Elias, N. Changying, and V. V. Frederic, “Synergistic effects of wood ash and essential oil on fecundity, pupal eclosion and adult mortality of Callosobruchus maculatus (Coleoptera: Bruchidae) cowpea seed weevil,” American Journal of Experimental Agriculture, vol. 11, no. 6, pp. 1–12, 2016.
View at: Google Scholar
M. O. Oni and O. C. Ogungbite, “Entomotoxicant potential of powders and oil extracts of three medicinal plants in the control of Sitophilus zeamais infesting stored maize,” Journal of Plant and Pest Science, vol. 2, no. 1, pp. 8–17, 2015.
View at: Google Scholar
R. O. Uddin II and S. A. Sanusi, “Efficacy of olive oil, groundnut oil, soybean oil and palm kernel oil in the control of Callosobruchus maculatus (F.) in stored cowpea (Vigna unguiculata L. Walp),” Agrosearch, vol. 13, no. 2, pp. 67–72, 2013.
View at: Publisher Site | Google Scholar
O. O. Durojaye, T. O. Olumuyiwa, and A. O. Adefunke, “Effects of Cleistopholis patens (Benth) extracts of cowpea seed beetle, Callosobruchus maculatus (Fab.) (Coleoptera: Chrysomelidae) infesting cowpea seeds in storage,” International Journal of Tropical Insect Sciences, vol. 41, pp. 209–216, 2021.
View at: Google Scholar

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Copyright © 2023 Esther Rita Gever and Bonaventure C. Echezona. This is an open access article distributed under 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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