Management of Sitophilus zeamais Motshulsky ( Coleoptera : Ciurculionidae ) and Sitotroga cerealella ( Olivier ) ( Lepidoptera : Gelechidae ) using locally available inert materials in Southern Ethiopia

Abstract: Locally available inert materials including sawdust, coffee husk and wood ash were evaluated at different proportions against Sitophilus zeamais and Sitotrog cerealella in 2002 in Awassa National Maize Project entomology loboratory. The experiment was laid out incompletely Randomized design (CRD) in three replications. The insect pests were reared at laboratory condition before introducing into each treatment to obtain the same age group. Maize grain was disinfected to eliminate undiserable field infestation in refrigerator at –2 0 C before using for experimental purpose. The Treatments were 10% , 15%, 20% and 30% of coffee husk, 10%, 15%, 20% and 30% of saw dust, 10%, 15%, 20% and 30% of wood ash and 2% of Pirimiphos-methyl as standard check and untreated control. The efficacy of each treatment was evaluated with respect F1 progeny emergence of the pests, mean number of damaged kernels and germination percentage of maize kernels. Coffee husk and wood ash at all dosages were found to be effective in controlling S. zeamais and S. cerealella. Wood ash at all proportions gave the best control of the pests during the study period. Wood ash and coffee husk at higher rates were more effective in controlling the pests. Sawdust at all dosages was not different from the untreated control in controlling S. zeamais. However, sawdust at some dosages showed superior performance against S. cerealella.


INTRODUCTION
Maize (Zea mays L.) is the most important food crop grown in Africa and is capable of giving high yield (Assefa, 1981).It is grown on over a million hectares of land, which is 16 % of the total cultivated land in Ethiopia.Currently, it ranks first in total production and productivity among all cereals grown in southern Ethiopia.It covers 55.27 % of the total area covered by the crops and 74.29 % of the crop production of the region (CSA, 2002).
In the store, maize insect pests cause losses ranging from 20 to 30 % in Ethiopia (Abraham, 1991;Emana, 1993).In Bako area, farmers reported 25 -33% maize grain losses within six months of storage period.In Sidama administrative region, 30 -90 % losses could occur to maize grain stored for five to seven months (Emana, 1993).A number of experiments have been done on the management of storage pests at the farm storage level (Emana, 1999).Chemical control of insect pests has been the most efficient and effective means of protection of stored product (Emana, 1999).However, with the increasing cost of organic chemicals and their hazards to the environment, alternative control strategies are being exploited.One of the alternative control strategies is the use of locally available inert materials.Inert materials such as wood ash and similar fine substances are used in the control of storage pests by filling the space between maize kernels (Emana 1993;Gwinner et al., 1996).This means that newly hatched insect pests are deinied of their activities.They experience more difficulty in finding partners and as result are forced to deposit their entire stock of eggs on relatively few maize kernels.In general, identifying useful locally available inert materials against S. zeamais and S. cerealella may provide important component of storage pest management in maize grain in Southern Ethiopia.Therefore, the objective of this study was to evaluate the efficacy of locally available inert materials including coffee husk for the control of S. zeamais and S. cerealella in Southern Ethiopia.

S. zeamais
Adult S. zeamais of known age were produced in a sufficient number for the experiment following the rearing procedures of Strong and Subur (1968).About 25 kg of maize variety BH540 was cleaned to remove kernels with visible damage symptom and stored in a freezer at 0 to -2 0 C for one month to further clean the kernels from possible internal infestation (Strong et al., 1967).Grain moisture content was measured by moisture tester.Low moisture level was adjusted to 12.5 % by adding water, while high moisture level was adjusted to 12.5 % by allowing it to dry slowly (Wright et al., 1989).
Unsexed S. zeamais adults were collected from grain store of Awassa Agricultural Research Center and Debub University, the then Awassa College of Agriculture, and cultured on cleaned and disinfested maize in four replications.In each replication, 800 S. zeamais adults per 400 grams of grain were put in glass jar of three-liter capacity and covered with muslin cloth and fixed by rubber band.After seven days of oviposition period, all parent S. zeamais adults were removed from each replication and placed on another set of grain in the same condition.Such removal of parent S. zeamais adults and placement on a fresh grain medium was made three times, so that sufficient number of laboratory reared S. zeamais adults of known age were made available.
After the third transfer, parent S. zeamais adults were discarded.Then each grain lot where S. zeamais adults oviposited for seven days was kept for progeny emergence.Starting from 34 days after infestation of the maize grain in the different batches, counts of emerged adults were recorded daily until the 45 th day and those emerged on the same day were transferred to a glass jar of one liter capacity, so that each jar will contain S. zeamais adults of the same age.For the experiments, S. zeamais adults of known age were used.

S. cerealella
A new culture of S. cerealella was established by using maize kernels with 300 S. cerealella pupae as moths, which were collected from Debub University, the then called Awassa College of Agriculture, and put in three liters capacity jar containing 1.5 kilograms disinfected maize kernels (Emana, 1993 and1999).A total of four jars were used for culture establishment.After disinfesting maize kernels at 0 to -2 0 C, it was stored in the laboratory under room temperature in a clean three-liter capacity jar.Then maize with 300 S. cerealella pupae were introduced to lay eggs on the disinfected kernels.After nineteen days of introduction, all live and dead moths were removed from the jar.The jars were inspected on daily bases for recording emergence of F1 moths.Then maize kernels with S. cerealella pupae, which emerged as F1 moth, were used for experimental purpose.

S. zeamais
The local materials tested against S. zeamais include coffee husk, wood ash and sawdust.For each treatment, five hundred disinfested sound kernels were used in three liters capacity plastic bag and admixed at different proportions with different materials.Primiphos-methyl 2% dust at the rate of 10 ppm, as a standard check and the untreated control were included in the experiment for comparison.Fourteen sexed and ten-to-fourteen-day-old S. zeamais adults were introduced into each treatment.Then plastic bags were pin-holed to ensure adequate aeration and folded and stapled from top to prevent escape of S. zeamais adults.The experiment was done under ambient laboratory conditions.Parent S. zeamais adults' mortality was assessed after one, two, three and four weeks after treatment application and dead adult insects were counted and removed during each assessment.At 28 th day after the infestation, the remaining S. zeamais adults (dead and alive) were counted and removed together.The assessment periods were selected based on the earlier report by Dobie (1974).
After removing dead and live S. zeamais adults, the treatment remained under the same conditions to assess F1 progenies emergence.The F1 progeny of S. zeamais adults were removed and counted as soon as they emerged.This was continued up to 76 days according to Dobie (1974), Evans (1985) and Hodges and Meik (1986).At the end, weight loss of grain and number of damaged kernels were recorded by separating the admixture by winnowing in each treatment.Germination percentage of the grain was assessed by randomly picking one hundred kernels from each treatment and placing it on moist filter paper and kept for seven days.The experiment was laid out in Completely Randomized Design (CRD) in three replications.

S. cerealella
The local materials tested against S. cerealella include different proportions of coffee husk, wood ash and sawdust.For each treatment, five hundred disinfested sound kernels were used in three liters capacity plastic bag and admixed at different proportions with different materials.Primiphos-methyl 2% dust at the rate of 10 ppm as a standard check and the untreated control were included in the experiment for comparison.Twenty maize kernels with unsexed 20 pupae of S. cerealella were introduced into each treatment.Then plastic bags were pin-holed to ensure adequate aeration and folded and stapled from top to prevent escape of moths.The experiment was done under ambient condition.Parent adult moths' mortality was assessed after one, two and three weeks after treatment application and the remaining dead and live moths were discarded together from the treatment at 21 st day.Then, the treatment was kept under similar conditions to F1 progenies assessment.The F1 progeny of moths were counted and removed as soon as they were emerged.This continued up to 3 months.At the end, weight loss of grain and number of damaged kernels were recorded by separating the admixture by winnowing.Germination percentage of the kerenels was assessed by randomly picking one hundred kernels from each treatment and placing it on moist filter paper and kept for seven days.The experiment was laid out in Completely Randomized Design (CRD) in three replications.Percentage grain weight loss for all of the above experiments was calculated using Anon (1969) method.At the end of each experiment maize kernels were separated into two categories (undamaged and damaged) from each treatment.Grains in each category were counted and weighed separately and subjected to the following equation: Where

DATA ANALYSIS
Data on number of F1 emerged S. zeamais and S. cerealella adults, number of damaged maize kernels and weight loss of grain were transformed before being subjected to statistical analysis.The data obtained were subjected to analysis of variance using MSTATC computer program and means were separated using Duncan's Multiple Range Test (DMRT).

S. zeamais
The effects of inert materials in the control of S. zeamais are presented in (Table 1).Among inert materials tested All means followed by the same letter (s) within a column are not significantly different from each other at 5% (DMRT).Statistical tests were made with transformed values Key: SD=saw dust, WA=wood ash, CH=Coffee husk the pest, wood ash at all dosages showed superior performance in all parameters compared to the untreated check.Sawdust at four dosages was not better than the untreated control in all parameters.Very few F1 progeny emerged from kernels treated with all dosages of wood ash.However, higher dosages of wood ash were found to be more effective in suppressing development of F1 progeny.Lowest number of F1 progeny emerged from maize kernels treated with 15 % w/w wood ash, while highest F1 progeny emerged from kernels treated with sawdust at 20 % w/w.Coffee husk relatively at higher dosages, 20 % and 30 % w/w was found to be more effective in impending the development of F1 progeny compared to the untreated control.
There were significant differences in germination capacity of maize kernels treated with different inert materials and the untreated control.The highest germination percentage was recorded from kernels treated with wood ash 30 % w/w, while the lowest percentage was obtained from kernels treated with sawdust 30 % w/w (Figure 1).
The results of the present study agree with reports of previous workers.Achiano et al. (1999) indicated that mixing wood ash with maize kernels before it is stored resulted in 100 % S. zeamais adult mortality after 20 days of treatment.Moreover, a progressive increase in mortality with wood ash concentration was observed after 20 days.If added in sufficient quantity, wood ash can effectively protect grain stored in small lots by traditional Africa farmers (Golob et al., 1982).They indicated that the quantity must be as much as 20 % or more, in order to submerge the grain almost completely.Moreover, the abrasive properties of the materials may play some part in preventing the development of pests; it is more likely that the dust inhibit insect behavior, affecting movement and reproduction by blocking air and space between grains.
Locally available dusts will continue to play an important role as grain protectants in farm stores in African and other developing countries because they are readily available (Golob and Hanks, 1999;Emana, 1993).However, such practice will remain viable for small-scale use only, particularly for the preservation of small quantities of seed grains, because of excessive quantities of dust required and the implication of some quality problems.

S. cerealella
The effects of inert materials in the control of S. cerealella are presented in (Table 2).Among inert materials used, coffee husk at the rate of 20 % w/w followed by wood ash 15 % and 30 % highly restricted the development of F1   progeny of S. cerealella compared to the untreated control.Saw dust was not better than the untreated control in all parameters except germination capacity.However, relatively lower number of F1 progeny and mean number of damaged kernels were recorded from higher rates of sawdust compared to the untreated control.All inert materials tested against the pest had a significant effect with regards to germination capacity of the maize kernels compared to the untreated control (Figure 2).The highest germination percenage was recorded from kernels treated with wood ash 10 % w/w, while lowest germination percentage was recorded from untreated control.There was significant difference among inert materials and pirimiphos-methyl treatments in all parameters.Sawdust in four dosages showed significantly inferior performance with regards to mean number of damaged kernels, germination capacity of the kernels and F1 progeny emergence.However, the highest dosage, 30 per cent w/w of wood ash was not different from pirimiphos-methy treatment.In suppressing the development of F1 progeny emergence of the pest, coffee husk at 20 % w/w and wood ash at 15 and 30 % w/w showed similar performance with that of pirimiphos-methyl.These rates of indicated inert materials also showed similar performance with regards to mean number of damaged kernels.Except sawdust at the rate of 10 % w/w, coffee husk at 10 % w/w and wood ash at the rate of 20 % w/w, all dosages of inert materials were not significantly different from pirimiphos-methyl treatment with regard to germination.In general, lowest F1 progeny and mean numbers of damaged kernels were recorded from kernels treated with Pirimiphos-methyl.The best performance of pirimiphos-methyl in restricting development of F1 progeny as compared to almost all inert materials evaluated in this study agrees with reports of previous researchers.Emana (1993) reported that the highest dose of the local materials such as wood ash and tobacco dust was better than the lowest dose in controlling S. cerealella except sawdust.

CONCLUSION
Locally available inert materials including sawdust, coffee husk and wood ash were evaluated at different proportions against S. zeamais and S. cerealella.The efficacy of each treatment was evaluated with respect to F1 progeny emergence of the pests, mean number of damaged and germination percentage of maize seed.Coffee husk and wood ash at all dosages were found to be effective in controlling S. zeamais and S. cerealella.Wood ash at all proportions gave the best control of the pests during the study period.Wood ash and coffee husk at higher rates were more effective in controlling the pests.Sawdust at all dosages was not different from the untreated control in controlling S. zeamais.However, sawdust at some dosages showed superior performance against S. cerealella.Newly evaluated inert material like coffee husk should be re-tested to confirm the current result and sawdust, which showed inferior , Wu = Weight of undamaged grains N u = Number of undamaged grains W d = Weight of damaged grains N d = Number of damaged grains

Figure 1 .
Figure 1.Effect of different rates of agricultural waste on maize seed germination due to sitophilus zeamais after six months of storage.Bar on the graph are standard errors of the mean

Figure 2 .
Figure 2. Effect Effect of different rates of agricultural waste on maize seed germination due to Sitotroga cereallla after six months of storage.Bar on the graph are standard errors of the mean

Table 1 .
F1 progeny of S. zeamais, number of damaged maize kernels and weight loss as influenced by coffee husk inert materials, 2002.

Table 2 .
Effect coffee husk and inert materials on F1 progeny of S. cerealella, number of damaged maize kernels and weight loss, 2002.

Number of F1 Progeny emerged Number of damaged kernels/500 seeds %Weight loss
All means followed by the same letter (s) within a column are not significantly different from each other at 5% (DMRT).Statistical tests were made with transformed values