Pesticide Potential of Gmelina arborea Stem Bark and Leaf Powder against Dinoderus porcellus Infesting Yam Chips

Insect pest are a major problem to food security, most especially in developing countries like Nigeria. There is an urgent need towards mitigating the effects of these group of insects, and botanical extracts had played an increasing role as an alternative insecticide. The aim of the present study is to investigate the anti-feeding effect of different dosage of Gmelina arborea stem bark and leaf powder against Dinoderus porcellus infesting yam chips. The study was conducted at the Entomology Laboratory of Federal College of Forestry, Jos. Soxhlet extraction using methanol was used to extract plant part samples. Presence of phytochemicals contained in the plant were examined following standard protocols. The antifeedant effects of different dosage of Gmelina arborea leaf and stem bark powder on Dinoderus porcellus was determined by monitoring yam chips weight loss. Data collected was subjected to analysis of variance (ANOVA) at 1 % level of significance and the means separated using Duncan test. The results revealed presence of tannin, flavoid, saponins, alkaloids, reducing sugar and phenol with absence of steroid. The results also revealed that the various dosages have remarkable antifeedant effect on the development of D. porcellus. The weight loss of treated yam chips was significantly different from those of untreated yam chips. Therefore, the results obtained in this work accounts for the use of G. arborea plant parts powders as bio-preservative for yam chips against D. porcellus.


Introduction
Yams (Dioscorea spp) is considered a major staple food crop in the tropics. Asia, South America, and West Africa account for most of the yam grown in the world (Kambasaka et al., 2009). In 2017, the global production of yam was evaluated to be at 67.3 million tons (FAO, 2019). Yam alone account for 32% gross income obtained from crops by farmers in Nigeria (Bolarinwa and Oladeji, 2009). Yam tuber is essentially a starchy food which supply calories to the body. Yam is usually prepared in various forms for consumption, these include boiling, frying, baking, and processing into flour (Oguntade et al., 2010).
Despite the economic importance of yam, yam production is faced by many biotic (viruses, fungi, nematodes, and insects) and a biotic (infertile soil, climate changes) challenges in Africa (Oguntade et al., 2010). The challenge of fresh yam preservation leads to huge post-harvest losses. To overcome the challenge, most farmers and consumers transforms yams into chips which are sun dried traditionally (Hounhouigan et al., 2003). Yam chips preserved using traditional storage system have been found to be heavily attacked by Dinoderus porcellus (Vernier et al, 2005).
Dinoderus porcellus causes physical damage by penetrating the chips, leading to economic loss (Babarinde et al, 2013). The negative effect of insects on yam chips has led to the use of synthetic chemicals continuously (Loko et al, 2013). Synthetic pesticides over time endangers health of farmers, animals, and food consumers. This has led to a resurgence of interest in biological pesticide which are environmentally friendly and with no side effect on consumers.
Gmelina arborea a deciduous tree belonging to the family Verbenaceae possesses high medicinal properties (Banu et al., 2013). Several studies have revealed Gmelina arborea is an important source of insecticidal botanical. Study by Estelle et al. (2018) showed that extracts of three botanicals exhibited insecticidal properties against Dinoderus porcellus destroying yam chips and this, necessitated the present study. Hence, the present study was conducted to investigate the anti-feeding effect of different dosage of Gmelina arborea stem bark and leaf powder against Dinoderus porcellus infesting yam chips.

Samples Collection
Twenty (20)  Gmelina arborea, both the stem bark and leaf were collected with clean polythene bag from Federal College of Forestry, Jos and submitted to the herbarium for identification.

Plant Powder
The collected stem bark and leaf were washed under running water and dried under room temperature (37ºC) for 30days. The stem bark and leaf were pulverized into powder using mortar and pestle after drying. The powders were sieved to obtain fine particles (Loko et al., 2017). The fine powder obtained from both stem bark and leaf of Gmelina arborea were package in polyethylene bags and kept in dry place.

Extracts Preparation
Soxhlet extraction with methanol was done using 50 g of the dried and pulverized Gmelina arborea leaf and stem bark samples. Distillation was carried out and plant extracts collected through rotary evaporation and kept at 4°C in a refrigerator.

Phytochemical Screening of Gmelina arborea Leaf and Stem Bark Extract
The Gmelina arborea leaf and stem Bark extracts were examined for the presence of phytochemicals using standardized procedures described by Harborne (1984).

Processing of Yam Chips
The collected yam tubers were made clean by washing with water and peeled using sterile knife. The tubers were cut into slices of 2cm X 4cm. Precooking of the sliced yam obtained was done by heating in water at 50 o C for 2hours. Strained and dried slices were exposed to hot air oven at 60 o C for 3days. The chips were exposed to room temperature for 1h after being sterilized at 105 o C for 2h. The dried chips were stored in the laboratory at room temperature using polythene bags.

Rearing and Identification of Dinoderus porcellus
To obtain D. porcellus, infested yam chips were purchased from Filin Ball market and fed on fresh yam chips following procedure by Onzo et al. (2015). This was carried out in plastic containers opened at one end. For aeration, hole was made at the end of the box and covered with Muslim cloth to prevent insects from escaping. Dry yam chips (500g) were infested in the plastic boxes with four hundred and fifty (450) adults of D. porcellus. The plastic containers were kept on a stable surface at room temperature according to Oni and Omoniyi (2012). Following two weeks of exposure, emerging adult beetles were collected, and the insect was identified using

Feeding Deterrence Test
Antifeedant effect test was done using the method described by Isah et al. (2012). Here, fifty grams(50g) of uninfected yam chips were mixed with different dosages (5, 10, 15 and 20 g) of stem bark, leaf, and stem bark + leaf powder in an experimental box measuring 10cm in height and 12cm diameter. Untreated yam chips were used as negative control.
In each box, 20 adults of D. porcellus were introduced and covered with muslin cloths and each treatment replicated three (3)

Data analysis
Data collected was subjected to analysis of variance (ANOVA) at 1 % level of significance and the means separated using Duncan test. Results were presented in tables.

Results and Discussion
The results on Table 1   The lowest percentage weight loss of treated yam chips exposed to D. porcellus for 30 days was observed when 20 g of G. arborea Leaf +Bark powder was used (Table 2). Similar trends were also observed after exposure for 60 and 90 days, however, increase in time of the exposure of the treated yam chips to D. porcellus led to increased weight loss of yam chips.
The results on Table 4 showed 5.83 ± 0.90 % weight loss using 20 g Leaf +Bark powder yam chips after 90 days exposure to D. porcellus but this is lower compared to 33.27 ± 3.5 % weight loss of untreated yam chips indicating the preservative potential of G. arborea powder.    Table 5 showed the comparative percent antifeedant effect of various dosages of the different parts of G. arborea powders after 30 days exposure to D. porcellus. The results revealed there was no significant difference on the Percent Weight Loss of Yam at 5 g and 20 g powder using the 3 different plant parts. The plant parts provided protection against D. porcellus with 20 g dosage giving the lowest weight loss of treated yam chips, but no significant difference was observed among the different plant parts used after 30 days exposure to D. porcellus (Table 5). Similar trend continued after 60-and 90-days exposure (Table 6, 7). All the various dosages of the different plant parts used showed no significant difference on the weight loss of treated yam chips when compared except 15 g dosage ( Table  6).
The results on Table 7 indicated the lowest weight loss of treated yam chips was achieved when 20 g of Stem Bark and Leaf +Stem Bark G. arborea powders was used compared with 20 g leaf G. arborea powder. The result showed significant difference between 20 g leaf of G. arborea powder and 20 g stem Bark and Leaf+ Stem bark of G. arborea powders at 0.05 p value (Table 7). In general, the results from the comparatives studied revealed that all the plant parts at different dosages were effective against D. porcellus leading to reduction in weight loss of treated yam chips.   The findings of this present work showed that the combination of yam chips with leaf, stem bark and leaf + stem bark powder of G. arborea at 15g has antifeeding effect on D. porcellus. The weight losses induced by D. porcellus on treated yam chips at different dosage of Leaf, Stem bark and Leaf + Stem bark powder of G. arborea were low compared to the control (untreated). The low weight loss observed in this could be attributed to the insecticidal activities of the phytochemical constituents of the Leaf, Stem bark and Leaf + Stem Bark powder of G. arborea used (Chothani and Patel, 2018 The bioactive activities of G. arborea has been documented in many literatures. The different parts of G.arborea power showed the presence of tannins, saponins phenols, alkaloids, flavonoids and steroids. The antimicrobial activities of saponins provide safety for plants against insect attack. They are also known as plant defense systems (Lacaille-Dubois and Wagner, 2000). Alkaloids is also involved protecting and survival of plant species because they provide feeding deterrents against insects and herbivores (Attanayake et al., 2015).
The presence of pungent volatile substances like phenol in the plant parts could play a major role in deterring D. porcellus from feeding (Onzo et al., 2015). Furthermore, tannins contained in the plant parts powder as repulsive agents and act on insects' olfactory receptors (Moore and Lenglet, 2004). The synergistic effect of tannins and, saponin led to decreased weight losses caused by D. porcellus. These factors played a role in retarding D. porcellus feeding habit and hence lowered D. porcellus yam chips consumption rate.
Though the weight losses of the treated yam chip were attributed to the introduced D porcellus, previous studies by other researchers implicated other factors that cause yam chips weight loss. According to Chukwulobe and Echezona (2014), environmental conditions such as temperature and humidity could lead to weight losses. The texture of yam used for yam chips and pre-cooking which causes curing of the yam chips could also lead to weight loss (Estelle et al., 2018). However, the low weight loss of yam chips treated with Gmelina arborea powder compared to the untreated yam chips which have high weight loss, prove the effectiveness of the plant powders.

Conclusion
The results obtained from the present study revealed that Gmelina arborea parts powders contains significant amounts of phytochemicals. Our findings also showed that use of leaf, stem bark and leaf and stem bark powder of Gmelina arborea at different dosages studied have a strong bioactivity in control and prevention of D. porcellus infestation of yam chips. The highest activities were observed when 15 and 20 g powder of the botanical was used. However, further studies are required to identify the active constituent in the plant's materials responsible for bio-insecticidal activities.