EFFECTIVENESS OF Imperata cylindrica, Sida acuta, Chromolaena odorata AND Gmelina arborea AGAINST Sitophilus zeamais

The effectiveness of powdered leaves of Imperata cylindrica (Spear grass), Sida acuta (Wire weed), Chromolaena odorata (Siam weed) and Gmelina arborea (Gmelina) at different dosages (0, 2.5, 5.0 and 7.5 g) against Sitophilus zeamais infesting stored maize grains was assessed. Treatments were mixed with 100 g of maize grains (landrace, Esa’ mayewangha), infested with 30 adults S. zeamais and stored in 200 ml glass jars with perforated lids. The setup was maintained under ambient conditions (25 300C and 70 90% RH) between April and June, 2017. Mortality assessment was at 2, 4 and 6 days after treatment (DAT). The trial was laid out in a completely randomized design (CRD) and replicated four times. Analysis of variance showed that Cypermethrin caused significantly higher mortality than the tested plant powders. Cumulative mortality of adult S. zeamais significantly (P ≤ 0.05) increased with increased treatment dosages and durations of storage. There were significantly (P ≤ 0.05) higher mortality in maize grains treated with 7.5 g/100 g of S. acuta (55.00 and 64.17%) and I. cylindrica (53.33 and 60.00%) compared with C. odorata (44.17 and 50.83%) and G. arborea (35.83 and 40.00 %), respectively at 4 and 6 DAT.


Introduction
According to WASDE (2017), the world is projected to produce 1.04 billion metric tons of maize (Zea mays L.) in 2017 with United States leading with 384.7 million tons followed by China, 219.5 million tons.In Africa, South Africa has the highest with 13 million tons and Nigeria accounts for 7.2 million tons (WASDE, 2017).
In Nigeria, maize is the third most important crop after wheat and rice.It has the largest area devoted for cultivation (Adedire & Lajide, 2003), which has continued to expand because of technological advancements (Adedire & Lajide, 2003).Maize occupies less land area than either wheat or rice but has a greater average yield per unit area of about 5.5 tons per hectare (Ofori et al., 2004).The crop is grown throughout the year in all states in Nigeria for various purposes; including for fodder, human consumption and as a basic raw material for many industrial products (IITA, 2009) including for the production of starch, textile, etc.Despite its importance, much of the harvest is lost to infestation by the maize weevil (Sitophilus zeamais) which attacks both field crops and stored grains (Haines, 1991).Sitophilus species populations grow well in food that contains more than 10 % moisture (Haines, 1991).S. zeamais has been recognized as an increasingly important constraint to maize production in Africa (Markham et al., 1994).Adults and larvae of S. zeamais feed on undamaged grains and reduce them to powdery forms (Adedire, 2001).Voracious feeding by S. zeamais on the whole grain causes weight loss, fungal growth, and quality loss through the increase in free fatty acids which can completely destroy stored grains in all types of storage systems/facilities (Trematerra et al., 2007).Under serious infestations, the maize weevil can cause grain losses of up to 90 % on smallholder farms (Coyne & Hoeschle-Zeledon, 2001).S. zeamais is also implicated in the reduction in aesthetic and market value, germinability and nutritive value of maize (Pingali & Pandey, 2001).
There is a dire need for the use of a natural and sustainable method that would not only control the pest but pose no hazards to man and the environment (Isman, 2006;Arabi, 2008;Abdelgaleil, 2009).
Readily available and affordable plant materials such as Sida acuta, Imperata cylindrica, Chromolaena odorata and Gmelina arborea were screened against S. zeamais in stored maize grains to provide benign substitutes to synthetic chemicals.This study will therefore determine the efficacy and appropriate concentration of selected botanicals for the management S. zeamais in store maize grains.Information from this study will promote research aiming at the development of new biopesticides against this important pest.

Materials and Methods
The trial was conducted in the Postgraduate Laboratory, Department of Zoology and Environmental Biology, Michael Okpara University of Agriculture (MOUA), Umudike to determine the toxicity of powdered leaves of Imperata cylindrica, Sida acuta, Chromolaena odorata and Gmelina arborea at different dosages (2.5, 5.0 and 7.5 g) against Sitophilus zeamais infesting stored maize grains..

Leaves of Imperata cylindrica, Sida acuta, Chromolaena odorata
and Gmelina arborea (Table 1) were selected on the basis of their ethnomedical properties and endemicity (Ogban et al., 2015).They were collected from fields at MOUA, Umudike.Each was washed separately and air-dried in a well-ventilated area for two weeks; thereafter milled and sieved to obtain their respective powders.Plant powders were kept in clean air-tight opaque containers to maintain their potency.

Synthetic insecticide
Cypermethrin powder (Trade Name: Pestox, Ingredients: Cypermethrin 2.3%, Talc 97.5% and Fragrance 0.2% (Manufacturing date, 04-2016 and Expiry date, 12-2018) was bought from Arinzechi Agro Industrial Enterprises No. 17 Ohafia Street in Umuahia, Abia State, Nigeria, and stored in a cool dry place in the laboratory as directed by the manufacturer to effectively maintain its shelf life.

Test insects and maize
The initial stock of adult S. zeamais were obtained from infested maize grains and reared for six weeks; only adults were used for this experiment.The maize cultivar used for the trial was a local land race (Esa' mayewangha) obtained from cobs harvested at Ugep, Cross River State, Nigeria.To ensure that there was no postharvest treatment of the grains, they were de -threshed from the cobs and sun-dried for two weeks before storage in an airtight container.Maize grains were then placed in the oven (GNP-9082 model) at 60 ºC for 6 hours to disinfest prior to the experiment.S. zeamais adults were subsequently maintained on the sterilized maize grains in a 10 L plastic jar and kept in a laboratory under prevailing (as previously mentioned) conditions.On the seventh day, the adults were sieved out and eggs laid were allowed to develop to F1 progeny in order to obtain adult S. zeamais of uniform age (modified after Zakka et al., 2010).

Sexing of adult Sitophilus zeamais
Adults of S. zeamais were sexed using their morphological characteristics; the males have a rougher, distinctly shorter and wider rostrum when compared to the females (Ojo & Omoloye, 2012).

Infestation procedure
Treatments consisting of 2.5, 5.0 and 7.5 g of the four types of powders from I. cylindrical, S. acuta, G. arborea and C. odorata, and Cypermethrin, along with controls with no insecticide or plant powders were maintained in sixty-four glass jars (200 ml) containing 100 g of the maize cultivar.Thirty newly emerged (1-3 days) adult S. zeamais were introduced into each jar and was left undisturbed on a work bench.
The experiment was carried out in a completely randomized design (CRD) in which treatments and controls were replicated four times.

Tested end points Mortality
At 2, 4 and 6 days after treatment (DAT), the content of each jar was poured onto a transparent plastic tray and the numbers of adults were counted taking note of living and dead insects.

Statistical analysis
At 2, 4 and 6 DAT, the numbers of dead adult S. zeamais were counted after which it was subjected to a one-way ANOVA.Significant means were tested for using the Studentized Newman Keul's (SNK) test (p=0.05)(SAS, 2001).

Results
Table 2 presents variations in mortality levels in S. zeamais in maize grains treated with four selected plant powders and an insecticide over a six day trial.Cypermethrin treated jars recorded significantly (p < 0.05) higher mortality compared with those treated with the plant powders irrespective of the treatment dosage and storage duration.Mean mortality of maize grains treated with 2.5 g/100 g of S. acuta (25.83 %) and I. cylindrica (20.80 %) gave significantly (p< 0.05) higher mean mortality compared with those treated with C. odorata (8.33%) and G. arborea (2.50%) at 2 DAT.A similar trend was observed at 4 and 6 DAT in grains treated with 7.5 g / 100 g of plant powders.Sida acuta and I. cylindrica killed (55.00 and 64.17 %) and (53.33 and 60.00 %) of S. zeamais

Discussion
This study showed that ground leaves of S. acuta, I. cylindrica, C. odorata, and G. arborea bear insecticidal properties comparable to that of the synthetic commercial Cypermethrin against S. zeamais.
The However, the present study showed that plant species and their applied dosages influenced the degree of toxicity of the plant powders.Mulungu et al. (2007) work concluded that leaf powders have the tendency of blocking the spiracles of the insect thereby impairing respiration, leading to the death of the parent and F1 progeny weevils, which may have been the case in the present study.
The effectiveness of these botanical powders might be also attributed to feeding on whole grains by S. zeamais picking up lethal doses of the plant leaf powders thereby leading to stomach poisoning (Muzemu et al., 2013).An earlier report by Obeng-Ofori & Amiteye

Conclusions
The results from this study revealed that the tested botanicals significantly decreased the population of S zeamais on stored maize grains.Maize grains treated with S. acuta and I. cylindrica were significantly more toxic than those treated with C. odorata and G. arborea.Irrespective of the plant powder used, toxicity increased with increasing dosage and duration of storage with significantly more mortality recorded in grains treated with 7.5 g / 100 g of maize at 4 and 6 DAT. ( Youmsi, R.D.F., Fokou, P.V.T., Menkem, E.Z., Bakamga-Via, I., Keumoe, R., Nana, V., Boyam, F.F. ( 2017 efficacies of the powders of the different plants tested in this study were in the order; S. acuta>I.cylindrica>C.odorata>G.arborea.The utilization of different plant powders as stored grain protectants has been previously reported by Ogban et al., (2015) and Bhubaneshwari et al. (2014).A report by Akhtar & Isman (2004) stated that the effects of different plant materials on maize weevils may depend on several factors such as their chemical composition and the susceptibility of the species of maize weevils.

Table 1 .
Test botanicals and their phyto-chemical constituents

Table 2 .
Variation in percentage cumulative mortality levels (mean ± standard error) in Sitophilus zeamais treated with four selected plant powders and an insecticide over a six day trial.Mortality in controls is also shown for comparison management of Sitophilus zeamais in stored maize grains.