Persistence Evaluation of Some Insecticidal Plants and Application Rate to Maize Weevil Damage in Stored Maize Grain

A study was conducted to evaluate the persistence of insecticidal effects of some of botanicals and application on adult parent mortality of maize weevil in infested maize grain. Seven botanicals ( Azadirachta indica (neem), Melia azedarach (melia), Parthenium hysterophorus (parthenium), Calpurnia aurea (calpurnia), Vernonia amygdalina (bitter leaf), Carica papaya (papaya) and Dichrocephala integrifolia ) were tested each at three different rates viz, 2.5, 5 and 10% w/w. Malathion 5% dust at 0.05% as standard check and untreated check were included for comparison. Twenty unsexed adult weevils were re introduced to treated maize grains at 90 DAT and parent mortality was recorded at 93, 100, 107, 114, and 121 DAT. The experiment was laid out in a completely randomized design (CRD) in factorial arrangement and replicated four times. The result showed that A. indica , M. azedarach and D. integrifolia at all rates caused equal cumulative mortality (100%) with the synthetic insecticide, but the time required to totally kill the insects varied. All treatments caused significantly higher mortality than the untreated check after four months of storage.

farmers, some studies made in the last decade have proved that there are certain botanicals which are reported to be effective at certain rates against the maize weevil on stored maize such as neem, melia, Mexican tea powder, datura, triplex and etc.
Presently, we can confidently say that farmers and responsible bodies are not using these botanicals as the first option due to different reasons, like absence of firm recommendation, low confidence, lack of knowledge of botanical preparation, and unavailability of recommended plants in the area. Therefore, studies on alternative botanicals which can be conveniently utilized by farmers, need to be given due consideration for stored grain pest management. Current study, therefore, undertaken with the objective of evaluating persistence efficacy of some of the locally available plants and their effective doses in reducing the adult parent mortality after 3months of application.

MATERIALS AND METHODS 2.1. Description of the Laboratory
The experiment was conducted in the laboratory of National Maize Research Program at Bako, West Shoa Zone of the Oromia Regional State from September 2012 to April 2013. Laboratory conditions during the experimental season indicated that the mean daily minimum, maximum and average air temperatures of the laboratory was 21.7, 27.8 and 24.7 o C, respectively. The minimum, maximum and average relative humidity was 52.99, 68.25 and 59.05%, respectively.

Preparation of Experimental Materials
Whole grain of maize hybrid BH-541 at 12-13% moisture content was used to rear the maize weevils. The seeds were sieved to remove any dirt, dust or broken seeds and stored at -20 ± 2 o C for two weeks to disinfest them from any infestations. The disinfested grains were placed in plastic bags and kept for two more weeks at the experimental conditions for acclimatization as used by Girma (2006).
Adults with known age were obtained by culturing 500 unsexed adult maize weevils in two liter plastic jars containing 500g of disinfested maize grains and maintained under laboratory conditions. The jars were covered with muslin cloth and fixed with rubber band to allow aeration and prevent possible escape of weevils. The insects were allowed for one week to oviposit before they were sifted and placed on another set of grain kept for the same purpose. Starting from the commencement of progeny development in each jar, new emerged weevils were removed daily until the progeny emergence ceased. Those emerged on the same day were transferred to fresh grain in other containers reserved with whole grain and kept at the experimental conditions (Abraham, 1991).
Seven botanicals were evaluated for their efficacy to maize weevil ( Table 1). Fruits of A. indica and M. azedarach were collected from Dire Dawa and Jigjiga, respectively. The leaves of V. amygdalina and D. integrifolia were collected from the road side in Nekemte town; P. hysterophorus and C. papaya from Sasiga around Nekemte and C. aurea from Hareto near Shambu town. The plant parts were allowed to dry under shade at room temperature. The dried samples were ground separately to fine powder using mortar and pestle and the powder passed through a 0.25 mm mesh sieve to obtain a fine dust. Prepared powders then separately maintained in a plastic bag and stored in the refrigerator at 13 o C for future use.

Treatment Application
Two hundred grams of disinfested and conditioned maize grain was added into glass jars of 250 ml capacity. Three different rates of each botanical viz, 2.5%, 5% and 10% (w/w) were weighed and added onto the grain in each of the jars with lids allowing ventilation. Malathion 5% dust at 0.05% w/w and untreated controls were included for comparison. The jars were well shaken to ensure proper mixture of grains with botanical and insecticide dust. Adult weevils of 1 to 3 days old were thoroughly mixed and randomly picked for use. Thirty unsexed adult maize weevils were introduced into each glass jar and the jars were covered with muslin cloth and fixed by rubber band to allow sufficient ventilation and to prevent escape of the weevils. The experiment was laid out in completely randomized design (CRD) in four replications arranged factorially. The glass jars were maintained in the laboratory at room temperature. Temperature and relative humidity of the room were recorded daily until the end of the experiment

Data Collection and Analysis
Treated jars were previously used for data collection for other studies and grains remaining in each jar, 20 unsexed adult weevils from the laboratory stock were re introduced at 90 DAT. Adult mortality was recorded at 3, 10, 17, 24 and 31 days after introduction (i.e. 93, 100, 107, 114, and 121 DAT). On the 31 st day all of the insects were removed and counted as the same procedure employed in the preceded experiment. Count data for adult mortality were converted to percentage, corrected mortality was computed and angular transformed. The transformed data were then subjected to analysis of variance by using GeneStat version 15 computer software program. Mean separation was done by using Tukey test at 0.05.

RESULT AND DISCUSSION
The botanicals and their rates of application had significantly different persistence and affected the mortality of adult weevils when introduced at 90 DAT.
Following 93 DAT, the highest adult mortality (92.37%) was on grains treated with malathion and the lowest mortality (8.82%) on the C. aurea 2.5% (Table 2). No mortality was observed on untreated grains. Meliaazedarach and A. indica, both at 10% w/w, caused relatively higher mortalities than the other botanical treatments. C. aurea, V. amygdalina and P. hysterophorus at 2.5% and 5% rates caused less mortality, but significantly more effective than the untreated check.
A. indicaat 10% w/w was as effective as the synthetic insecticide (malathion) at 100 DAT and both of them caused 100% adult mortality ( Table 3). Some of the treatments did not show significant differences when applied at 2.5% and 5% w/w. Dichrocephala integrifolia and M. azedarach at 10% w/w caused relatively higher mortality than the rest treatments.

Table 2. Effects of botanicals and rates on percent of adult weevil mortality at 93 DAT
Values in parentheses are untransformed means; mean separation was done with angular transformed values; means followed by the same letter(s) are not significantly different from each other at 5% level of significance by Tukey.
At 107 DAT, A. indica at 2.5 and 5%, D. integrifolia at 10% and M. azedarach at 10% resulted in 100% mortality while the mortality caused in the untreated check was 0% ( Table 4). All of the treatments caused significantly higher mortality than the untreated check and D. integrifolia at 5% w/w caused relatively higher mortality than the rest botanical treatments.
Following 114 DAT the highest (100%) mortality was observed in D. integrifolia at 2.5% and 5% w/w while the mortality recorded in the untreated check was 0% ( Table 5). All of the other treatments also caused significantly higher mortality than the untreated check. The increase in efficacy of D. integrifolia as the rate increase in the present study is similar with the result of Pone et al. (2013) who reported that the ethanolic leaf extract of D. integrifolia inhibited embryonation, egg hatch and larval survival of gastro-intestinal nematode parasite of mice (Heligmosomoides bakeri) at various concentrations when compared with the control and the extract with higher concentrations showed more activity than the extract with lower concentration. At 121 DAT, significantly the highest adult mortality was observed in M. azedarach at 2.5% and 5% w/w, while there were no dead weevils recorded in the untreated check ( Table 6). The efficacy of each treatment was increased in increase with rate of application and duration. This might be due to the fact that botanicals have long persistence effect. Tigist (2004) also suggested that natural pesticides could have direct or delayed insecticidal effects. The delayed effect is inhibition of reproduction and development by hampering oviposition, larval penetration into the seed and adult emergence. Generally, the present result suggests that all of the tested botanicals remained effective against the maize weevil at least for four months. 4.51 CV (%) 5.7 Values in parentheses are untransformed means; mean separation was done with angular transformed values; means followed by the same letter(s) are not significantly different from each other at 5%level of significance (Tukey). nd:-indicates no data was recorded since all the weevils dead previously. Values in parentheses are untransformed means; mean separation was done with angular transformed values; means followed by the same letter(s) are not significantly different from each other at 5% level of significance (Tukey). nd:-indicates that no data was recorded since all the weevils dead previously. 4.3 Values in parentheses are untransformed means; mean separation was done with angular transformed values; means followed by the same letter(s) are not significantly different from each other at 5% level of significance (Tukey). nd:-indicates that no data was recorded since all the weevils dead previously.

SUMMARY AND CONCLUSIONS
Plants with insecticidal properties are locally available; however, farmers lack adequate know-how about their benefits. Unlike synthetic chemicals, botanicals do not affect the environment, have no residual effects and are inexpensive. In this study, all the tested botanicals showed insecticidal properties with varying degrees and were significantly different from the untreated check.
Significant differences in the percentage of damaged grains and grain weight losses were noted among the botanicals. Among the botanical treatments the highest level of seed damage was recorded in C. aurea at 2.5% and the highest level of grain weight loss was recorded in grains treated with C. aurea and V. amygdalina both at 2.5, 5 and 10% w/w, while there was no seed damage and weight loss recorded in grains treated with A. indica at all rates. Generally, percentage of damaged grains and grain weight losses were lower in all botanical treatments than in the untreated check. On the other hand, the botanicals did not negatively affect the seed germination.
Although this study showed existence of the potentials of some botanicals in controlling the maize weevil on maize grain, further research is needed to determine the active ingredients and mode of action of the botanicals, and it is essential that trials be also carried out to investigate the responses which would be observed under real farm conditions, such as fluctuating ambient climatic conditions, continuous disturbance of grain by the family itself and a complex of insect pest species and also the effects of store design and structure since this laboratory based and short duration study may not be enough for the final recommendation. It is also important to investigate how long these botanicals can further remain active in reducing F 1 progeny development, seed damage, weight loss and retaining viability.