Physical Disturbance As a Non-Chemical Approach to Control Weevils in Stored Maize

Iowa State University Capstones, Theses and Graduate Theses and Dissertations Dissertations

2020

Physical disturbance as a non-chemical approach to control weevils in stored maize

Mike Sserunjogi Iowa State University

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This Thesis is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Graduate Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Physical disturbance as a non-chemical approach to control weevils in stored maize

Mike Sserunjogi

A thesis submitted to the graduate faculty

In partial fulfillment of the requirements for the degree of

MASTER OF SCIENCE

Major: Agricultural and Bio-systems Engineering

Program of Study Committee: Carl J. Bern, Co-major Professor Thomas J. Brumm, Co-major Professor Dirk E. Maier

The student author, whose presentation of the scholarship herein was approved by the program of study committee, is solely responsible for the content of this thesis. The Graduate College will ensure this thesis is globally accessible and will not permit alterations after a degree is conferred.

Iowa State University

Ames, Iowa

2020

DEDICATION

Working in the rural communities of Kamuli – Uganda, paved the way for my passion in global food security.

I dedicate this thesis to the Iowa State University Uganda Program (ISU-UP) under the

Center for Sustainable Rural Livelihoods (CSRL) at Iowa State University.

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TABLE OF CONTENTS

Page

LIST OF FIGURES ...... vi

LIST OF TABLES ...... viii

NOMENCLATURE ...... xi

ACKNOWLEDGMENTS ...... xii

ABSTRACT ...... xiv

CHAPTER 1. GENERAL INTRODUCTION ...... 1 General Objectives ...... 2 Literature Review ...... 2 What is Maize? ...... 2 Maize Production ...... 4 Maize Consumption ...... 6 Storage of Harvested Maize ...... 8 Post-Harvest Losses of Stored Maize ...... 9 Maize Weevils ...... 10 Physical Disturbance of Grains ...... 12 Steel Grain Bins...... 15 Stirring Machines ...... 16 References ...... 17

CHAPTER 2. DESIGN AND CONSTRUCTION OF AN AUTOMATED PHYSICAL DISTURBANCE MACHINE TO CONTROL GRAIN STORAGE INSECT PESTS ...... 22 Abstract ...... 22 Introduction ...... 23 Materials and Methods ...... 24 Machine Design and Construction ...... 24 Jars and Screens...... 25 Motor ...... 27 Control System ...... 27 Circuit Layout...... 29 Maize and Maize Weevils ...... 30 Results and Discussion ...... 30 Testing the Disturbance Machine ...... 30 Conclusion ...... 32 References ...... 32 Appendix: Drawings of the physical disturbance machine ...... 33

CHAPTER 3. PHYSICAL DISTURBANCE TIME INTERVAL FOR CONTROL OF MAIZE WEEVILS IN STORED MAIZE ...... 34 Abstract ...... 34 Introduction ...... 35 Methods and Materials ...... 37 Maize and Weevils ...... 37 Experimental Design and Set Up ...... 37 Response Measurements ...... 39 Data Analysis ...... 40 Results and Discussion ...... 40 Live Maize Weevils...... 40 Moisture Content ...... 43 Test Weight ...... 44 Broken Corn and Foreign Materials ...... 45 Insect Damage ...... 47 Mold Damage ...... 48 Conclusion ...... 51 References ...... 51 Appendix: Raw data of the experiment determining the physical disturbance time interval that best controls maize weevils while maintaining the quality of stored maize...... 53

CHAPTER 4. MECHANICAL STIRRING OF MAIZE STORED IN ON-FARM STEEL BINS TO CONTROL MAIZE WEEVILS ...... 58 Abstract ...... 58 Introduction ...... 59 Materials and Methods ...... 61 Steel Grain Bins...... 61 Maize and Maize Weevils ...... 62 Insect Probe Traps ...... 63 Experimental Design ...... 64 Response Measurement ...... 64 Statistical Analysis ...... 65 Results and Discussion ...... 65 Live Maize Weevils...... 65 Other Insect Species ...... 68 Moisture Content ...... 69 Test Weight ...... 71 Broken Corn and Foreign Material ...... 73 Insect Damage ...... 76 Mold Damage ...... 77 Conclusion ...... 79 References ...... 79 Appendix A: Raw data of the experiment with mechanical stirring to control maize weevils in an on-farm steel bin...... 82 Appendix B: Unites States Department of Agriculture permit to move live maize weevils ...... 91 v

CHAPTER 5. GENERAL CONCLUSIONS ...... 95 Future Research Recommendations ...... 96 vi

LIST OF FIGURES

Page

Figure 1.1. Schematic of the parts of a maize plant (Encyclopedia Britannica, Inc.) ...... 3 Figure 1.2. Cross sectional view through a single Maize kernel (Center for Crops Utilization Research, Iowa State University, Ames, 2013) ...... 4 Figure 1.3. USA maize production and consumption in 2010; (source: Corn Corps Blog. corncorps.ilcorn.org) ...... 7 Figure 1.4. Adult maize weevil (Georg Goergen/IITA Insect Museum, Cotonou, Benin) ...... 11 Figure 1.5. Schematic of a farm size steel bin (edited from Bern (2013)) ...... 15 Figure 1.6. Sukup Manufacturing Company has commercialized five auger Fastir plus stirring system installed in a 13 to 15 m (42 to 48 ft) diameter grain bin ...... 16 Figure 2.1. Automated disturbance machine with jars loaded with 1 kg of maize and 25 adult maize weevils rotated through about 1.25 revolutions for 3 seconds...... 25 Figure 2.2. 3.8 L plastic jar with wooden baffles...... 26 Figure 2.3. Screens between the lids and holes on the wooden disk...... 26 Figure 2.4. Graphical User Interface (GUI) from MS-VB software, 2008 for three machines at set intervals of 8, 12 and 24 h...... 28 Figure 2.5. Logic Flow Chart for the control system of the disturbance machine running at a set time interval for 3 seconds...... 29 Figure 2.6. Schematic of the circuit diagram for the wiring of the disturbance machine...... 30 Figure A.1. Assembly drawing of the disturbance machine in Autodesk Inventor...... 33 Figure A.2. Isometric and Orthographic views of the disturbance machine in Autodesk Inventor...... 33 Figure 3.1. Disturbance machine placed on metallic racks in the growth chamber maintained at 270C and 70% relative humidity and 12 h light and dark phases...... 39 Figure 3.2. Live maize weevils in stored maize at different sampling times (days) for three different disturbances intervals (8, 12 and 24 h) versus control except for missing data from 12 h disturbance at 120 days and one replicate at 160 days. Vertical bars indicate standard errors...... 41 Figure 3.3. Broken corn and foreign material (BCFM) in stored maize at different sampling times (days) for three different disturbances intervals (8, 12 and 24 h) versus control except for missing data from 12 h disturbance at 120 days and one replicate at 160 days. Vertical bars indicate standard errors...... 46 vii

Figure 3.4. Mold damage in stored maize at different sampling times (days) for three different disturbance intervals (8, 12 and 24 h) versus control except for missing data from 12 h disturbance at 120 days and one replicate at 160 days. Vertical bars indicate standard errors...... 49 Figure 4.1. Schematic of the location of probe traps and maize sampling in the stirred (T1 to T5) and unstirred bins (C1 to C5)...... 64 Figure 4.2. Live maize weevils per kg maize in samples collected at four grain depths (0 m = surface layer; 2.7 m = bottom layer) in the stirred and unstirred bins at four time intervals during the 40-day storage period. Vertical bars indicate standard errors...... 66 Figure 4.3. Broken corn and foreign material (BCFM) in samples collected at four grain depths (0 m = surface layer; 2.7 m = bottom layer) in the stirred and unstirred bins at four time intervals during the 40-day storage period. Vertical bars indicate standard errors...... 74 Figure 4.4. Insect Damage (%) in samples collected at four grain depths (0 m = surface layer; 2.7 m = bottom layer) in the stirred and unstirred bins at four time intervals during the 40-day storage period. Vertical bars indicate standard errors...... 76

viii

LIST OF TABLES

Page

Table 1.1. Maize production and yield in 2017 from the top ten countries worldwide (FAOSTAT, 2017)...... 5 Table 1.2. Maize production and yield in 2017 from the top ten African Countries (FAOSTAT, 2017)...... 5 Table 1.3. Top 10 countries with the highest maize consumption (g/person/year) in SSA (Ranum et al., 2014)...... 7 Table 2.1. Screw and Fastener sizes to fasten parts of the disturbance machine...... 27 Table 2.2. The effect of rotating the motor at 25 rev/min on the suppression rate of maize weevils as a function of rotation time in 3.8 L plastic jars with 25 adult maize weevils...... 31 Table 3.1. Average live maize weevils for stationary jars and 8, 12 and 24 h disturbance intervals from 0 to 160 days of storage...... 42 Table 3.2. Average moisture content for stationary jars and 8, 12 and 24 h disturbance intervals from 0 to 160 days of storage...... 44 Table 3.3. Average test weight for stationary jars and 8, 12 and 24 h disturbance intervals from 0 to 160 days of storage...... 45 Table 3.4. Average broken corn and foreign material for stationary jars and 8, 12 and 24 h disturbance intervals from 0 to 160 days of storage...... 47 Table 3.5. Average insect damage for stationary jars and 8, 12 and 24 h disturbance intervals from 0 to 160 days of storage...... 48 Table 3.6. Average mold damage for stationary jars and 8, 12 and 24 h disturbance intervals from 0 to 160 days of storage...... 49 Table 3.7. Correlation between live maize weevils and moisture content, test weight, broken corn and foreign material, mold damage and insect damage of maize in stationary jars and jars disturbed every 8, 12 and 24 h from 0 to 160 days of storage...... 50 Table A.1. Raw data of the experiment determining the physical disturbance time interval that best controls maize weevils while maintaining the quality of stored maize...... 53 Table A.2. ANOVA table for depend variable live maize weevils...... 55 Table A.3. Type III SS table for depend variable live maize weevils...... 55 Table A.4. ANOVA table for depend variable moisture content...... 55 Table A.5. Type III SS table for depend variable moisture content...... 55 ix

Table A.6. ANOVA table for depend variable test weight...... 56 Table A.7. Type III SS table for depend variable test weight...... 56 Table A.8. ANOVA table for depend variable broken corn and foreign material...... 56 Table A.9. Type III SS table for depend variable broken corn and foreign material...... 56 Table A.10. ANOVA table for depend variable insect damage...... 56 Table A.11. Type III SS table for depend variable insect damage...... 57 Table A.12. ANOVA table for depend variable mold damage...... 57 Table A.13. Type III SS table for depend variable mold damage...... 57 Table 4.1. Average count of live maize weevils per kg maize in the stirred and unstirred bins at 0 to 40 days of storage...... 67 Table 4.2. Counts of other insect species apart from maize weevils in the probe traps after 8 weeks of bin infestation and vacuum probed samples after 40 days of storage both in the stirred and unstirred bins...... 68 Table 4.3. Average moisture content of maize in the stirred and unstirred bins at 0 to 40 days of storage...... 70 Table 4.4. Average temperature and moisture content, allowable storage time, and change in points of moisture between the stirred and unstirred bins during 40 days of maize storage...... 71 Table 4.5. Average test weight of maize in the stirred and unstirred bins at 0 to 40 days of storage...... 72 Table 4.6. Average test weight, insect damage and mold damage, and percent differences for maize samples taken from the stirred versus unstirred bins during storage...... 73 Table 4.7. Average broken corn and foreign material of maize in the stirred and unstirred bins at 0 to 40 days of storage...... 74 Table 4.8. Average BCFM from samples taken during unloading of the unstirred bin and samples collected from the sweepings at four locations in both bins...... 75 Table 4.9. Average insect damage of maize in the stirred and unstirred bins at 0 to 40 days of storage...... 77 Table 4.10. Average mold damage of maize in the stirred and unstirred bins at 0 to 40 days of storage...... 78 Table 4.11. Correlation between live maize weevils/kg and moisture content, test weight, broken corn and foreign material, mold damage and insect damage...... 79 Table A.1. Raw data of the experiment using mechanical stirring to control maize weevils in an-on farm steel bin...... 82 Table A.2. ANOVA table for depend variable live maize weevils/kg maize...... 87 x

Table A.3. Type III SS table for depend variable live maize weevils/kg maize...... 87 Table A.4. ANOVA table for depend variable moisture content...... 88 Table A.5. Type III SS table for depend variable moisture content...... 88 Table A.6. ANOVA table for depend variable test weight...... 88 Table A.7. Type III SS table for depend variable test weight...... 88 Table A.8. ANOVA table for depend variable broken corn and foreign material...... 89 Table A.9. Type III SS table for depend variable broken corn and foreign material...... 89 Table A.10. ANOVA table for depend variable insect damage...... 89 Table A.11. Type III SS table for depend variable insect damage...... 89 Table A.12. ANOVA table for depend variable mold damage...... 90 Table A.13. Type III SS table for depend variable mold damage...... 90

NOMENCLATURE

BCFM Broken corn and foreign material FAOSTAT Food and Agriculture Organization Statistical Database GUI Graphical User Interface ID Insect Damage MC Moisture content MD Mold Damage Mg Mega gram SSA Sub Saharan Africa TW Test weight xii

ACKNOWLEDGMENTS

I am grateful to Sukup manufacturing company, Sheffield, Iowa for their gift to support my research assistantship at Iowa State University. My major professors Dr. Carl Bern and Dr.

Thomas Brumm have been fundamental in my research and life in graduate school. Thank you for the encouragement and trusting me to undertake this research, which I count on as an incredible opportunity influencing the world with breakthrough solutions on food security. I echo the same words to Dr. Dirk Maier who accepted to be part of my POS committee and for being resourceful towards my professional development.

Dr. Thomas Phillips from the entomology department at Kansas State University (KSU) supplied additional maize weevils for the stirring experiment. Together with Michael Aikins, thank you for teaching me how to identify insect species. I extend my appreciation to Dr. Steven

Hoff who worked with me on automating disturbance machines and he reviewed part of my work. I would like to thank Mr. Bbosa Denis for the necessary guidelines and directions in my graduate school.

The list is long but I want to thank these students for helping me out in my research;

Kalyango Moses, Hui-Yee Tan, Guy Aby Roger, Hory Chikez, Jack Schwickerath, Michelle

Friedmann, Akitwine Francis, Fernando Vinicius da, Schuyler Smith and Mayanja Ismael. I am indebted to thank all members of our post-harvest engineering and feed technology research group. Your feedback in our weekly discussions on issues pertinent to food security was treasured.

Thumbs up to the following ISU staff who provided necessary assistance towards my research: Patrick Murphy, Robert Hartmann, Jake Behrens and Peter Lelonek. I want to express my appreciation to the staff at the Agricultural Engineering and Agronomy research farm where xiii the stirring experiment was conducted; Michael Fiscus, Nathan Meyers and Nick Upah. We express our gratitude to Curtis Lilleodden, Regional Manager with Fumigation Service and

Supply and his team for fumigating the two storage bins upon completion of the experiments free of charge.

I cherish Garett, Brenda, Donald and Ryan Onstot together with Kerri and the Carleton crew for taking me around the mid-west and welcoming me into their families. The international friendship connection and weekly family group meetings played a vital role in my spiritual life at

Iowa State University. On the same note, the Ugandan community in Iowa has also been more than another family away from home.

Above all, I thank my parents and siblings for supporting and believing in me until now.

You have seen me through all the steps of my life and never stopped encouraging me. I would not be motivated if it were not for your kind words and jokes. I cannot wait to see you again.

In capital letters, without God’s grace and mercy, I would toil in vain. xiv

ABSTRACT

Maize is among the top three cereals grown in the world, and a daily source of food calories for over 50% of the populace in Sub Saharan Africa (SSA). Since the population of SSA will double by the year 2050, the demand for maize will triple following this trend. Maize weevils (Sitophilus zeamais) cause significant post-harvest losses of untreated stored maize. To meet the future demand of maize in SSA, post-harvest interventions are necessary to reduce tonnages of maize lost from stored grain insect pests.

Research in using physical disturbance has been effective in reducing populations of weevils in stored maize. Unlike chemical treatment, disturbance is cost effective and does not leave residues in the food supply chain. In this context, this study investigated physical disturbance as a non-chemical approach to suppress maize weevils in stored maize. The study included: i) design and construction of automated physical disturbance machines, ii) determining the best physical disturbance time interval that suppresses weevils in stored maize, and iii) stirring of maize stored in an on-farm bin to suppress maize weevils.

The first experiment tested the disturbance machines on infested maize rotated through about 1.25 revolutions in 3 seconds. The initial population of 25 live maize weevils reduced in a range of 1 to 4 weevils at all machine run times. The absence of physical damage on the appendages of adult maize weevils indicated that the selected disturbance rate of 1.3 m/s did not injure adult maize weevils.

The second experiment determined the effective disturbance over time to reduce populations of maize weevils. The results showed that disturbance intervals of 8, 12 and 24 h reduced the populations of maize weevils by 75%, 95% and 94%, respectively, compared to the undisturbed jars after 160 days of maize storage. In addition, the results indicated that xv disturbance once per day was the best interval in controlling weevil populations after 160 days of maize storage. The quality of maize in the disturbed jars was better than that in the undisturbed jars.

The third experiment evaluated the effect of mechanical stirring infested maize on the population of weevils in a corrugated steel bin filled with 127 Mg of maize. While the population of live maize weevils in the unstirred bin was increasing, stirring achieved 100% control of S. zeamaiz after 40 days. Additionally, maize in the stirred bin was of a better quality compared to maize in the unstirred bin.

Overall, disturbance once per day (24 h) was effective in suppressing maize weevil populations during grain storage. This non-chemical approach is simple and affordable, and holds great potential for the smallholder farmers to protect their stored maize. This study also documented that physical disturbance can be scaled-up using commercially available stirring machines to suppress stored grain insects in grain bins with a storage capacity up to 1651 Mg. 1

CHAPTER 1. GENERAL INTRODUCTION

Maize (Zea mays) is a cereal plant believed to have originated from the Mexican highlands and later spread to the rest of the world through trade. At maturity, the ears of the maize plant, yield grains or seeds between 500 and 1000 kernels. The embryo of the kernel contains high levels of proteins and oils, surrounded by the endosperm of high starch concentration but less protein. Additionally, maize is a source of minerals and some important vitamin B categories. However, maize grown throughout the world differs by color, which ranges from white to yellow to red to black.

Maize production and consumption varies across the globe driven by the demand of maize and maize products. The United States of America (USA), the largest global producer processes most of the maize into fuel ethanol and animal feed. Exports and processed food products are the smallest percentage of the US maize. Yet, maize is a major staple on the African continent with 95% of maize consumed as food. In Sub Saharan Africa (SSA), both maize flour and meal are the dominant food products.

Despite maize being the main source of income and food in SSA, 20% of the maize is imported to meet the regional demand. The bottleneck is that maize production in SSA is 3.5

Mg/hectare/year less than the average global maize production at 5.5 Mg/hectare/year. The projected increase in the population of SSA within the next 30 years will raise the current demand for maize.

While post-harvest losses of maize occur almost at every stage in handling harvested maize, maize weevils reportedly contribute up to 40% losses of stored maize in low-income countries. Losses of maize from maize weevils significantly affect the food security of the rural poor in SSA. Temperatures, 250C to 300C and humidity, 70% to 80% in SSA favor the survival 2 of maize weevils. Post-harvest interventions to reduce losses of maize are vital to promote food security in low-income countries. However, with the majority of farmers in SSA being smallholders who are below the global poverty line, the proposed post-harvest methodologies should be affordable, reliable and yet effective in the protection of stored maize.

Chemical approaches to control maize weevils have gained social, economic and environmental concerns limiting their wide application in maize storage. In the context of the global awareness against the use of pesticides in stored food and food products, non-chemical methods will gain preference in the future.

Physical disturbance is such a non-chemical approach of controlling maize weevils in stored maize. The approach is simple and affordable, with energy and knowledge being the main inputs required from smallholder farmers.

General Objectives

The research objectives were to:

1. Design, construct and test automated physical disturbance machines.

2. Determine the time interval that best controls maize weevils and maintains quality

of stored maize subjected to physical disturbance.

3. Determine the effects of stirring weevil-infested maize in a farm sized bin on the

population of maize weevils and the quality of maize.

Literature Review

What is Maize?

The dictionary defines maize as a cereal plant, which yields large grains set in rows on a cob. Scientifically, maize is classified in the grass family Poaceae, Genus Zea and species maiz

(The Biology of Zea mays, 2008). Researchers attach the origin of maize to native people that habited the Mexican highlands 10,000 years ago and later spread to Europe, America, Asia and 3

Africa through trade (Matsuoka et al., 2002; Vigouroux, Matsuoka and Doebley, 2003). The word corn is widely used instead of maize in the USA and Canada.

The tassel at the top of the plant has anthers that disperse mature pollen grains to fertilize carpels on the silks that emerge from the husks at the end of the ear (Figure 1.1). The ears yield grains or seeds, which are the fruits or kernels (Aylor, Schultes and Shields, 2003) and can approximate between 500 and 1000 kernels per ear (FAO, 1992; Nuss and Tanumihardjo, 2010).

The embryo of the kernel contains high levels of proteins and oils, surrounded by the endosperm of high starch concentration but fewer proteins (Figure 1.2).

Figure 1.1. Schematic of the parts of a maize plant (Encyclopedia Britannica, Inc.)

Figure 1.2. Cross sectional view through a single Maize kernel (Center for Crops Utilization Research, Iowa State University, Ames, 2013)

Maize Production

FAOSTAT (2017) estimates global production of maize at 1,135 million Mg per year with more than 60% production only in USA (33%), China (23%) and Brazil (9%) (Ranum et al.,

2014). Table 1.1 ranks the top ten countries in maize production worldwide. Within the USA,

Iowa State in the Midwestern region, is the largest producer of maize with annual production three times that of Mexico. Maize production in Iowa from 2017 totaled to 66.3 million Mg at a yield of 13 Mg/hectare (USDA, 2018; USDA-NASS, 2019). On the African continent, South

Africa leads annual maize production with 16.8 million Mg as shown in Table 1.1 and Table 1.2.

Maize production from all African countries in 2017 totaled to 84 million Mg on 40.6 million hectares. This approximated to 7.4% of the total maize globally produced and 20.6% of the total area harvested worldwide. 5

Table 1.1. Maize production and yield in 2017 from the top ten countries worldwide (FAOSTAT, 2017).

Country Production Quantity (million Mg) Yield (Mg/hectare/year) USA 371.0 11.1 China 259.2 6.1 Brazil 97.7 5.6 Argentina 49.5 7.6 India 28.7 3.1 Indonesia 28.0 5.2 Mexico 27.8 3.8 Ukraine 24.7 5.5 South Africa 16.8 6.4 France 14.1 8.7 Canada 14.1 10.5

Table 1.2. Maize production and yield in 2017 from the top ten African Countries (FAOSTAT, 2017).

Country Production Quantity (million Mg) Yield (Mg/hectare/year) South Africa 16.8 6.4 Nigeria 10.4 1.6 Ethiopia 8.1 3.7 Ghana 8.1 2.0 Egypt 7.1 7.7 Tanzania 5.9 1.5 Zambia 3.6 2.5 Malawi 3.5 2.0 Kenya 3.2 1.5 Uganda 3.0 2.5

Maize production in most of the African countries is about 2 Mg/hectare/year which is

3.5 Mg/hectare/year less than the average global maize production (Cairns, Hellin and Sonder,

2013; Outreach I.P.B, 2017). Therefore, African countries meet their demands by importing more than 20% of maize from non-African countries (IITA, 2011; Shiferaw et al., 2011; Cairns et al., 2013).

Maize Consumption

Maize grown throughout the world differs by color, which ranges from white to yellow to red to black. While yellow maize is prevalent in USA, white maize is common in Africa, Central

America and Southern United States (Ranum et al., 2014). Maize is a source of minerals and some important vitamin B categories (Prasanna et al., 1988; Nuss et al., 2010) with an energy density of 365 kcal/100g (USDA Natl. Nutrient Database). Maize supplies daily calories all over the world and is a major staple on the African continent with 95% of maize consumed as food

(Shiferaw et al., 2011).

In Sub Saharan Africa (SSA), maize remains an important cereal crop with almost all parts of the plant used for food and non-food purposes. Maize consumption is highest in Lesotho estimated at 328 g/person/day as well as 293 g/person/day in Malawi and more than 200 g/person/day for Zambia, Zimbabwe and South Africa. While Mexico has a consumption of 267 g/person/day, consumption of maize is not more than 200 g/person/day in the rest of the world.

Table 1.3 shows the top ten countries in SSA with the highest maize consumption in g/person/year.

Table 1.3. Top 10 countries with the highest maize consumption (g/person/year) in SSA (Ranum et al., 2014).

Country Maize Consumption (1000 g/person/year) Lesotho 120 Malawi 107 Zambia 89 Zimbabwe 88 South Africa 81 Kenya 62 Togo 58 Swaziland 56 Tanzania 47 Namibia 46

Whilst maize consumption and usage varies across regions in SSA, both maize flour and meal are the dominant products (Lindsay et al., 2010). The United States uses maize mostly for biofuels and animal feeding as compared to human food (Figure 1. 3).

Figure 1.3. USA maize production and consumption in 2010; (source: Corn Corps Blog. corncorps.ilcorn.org)

Ethanol production from maize starch grew up to 20% per year in less than 10 years of the fuel industry (Wallington et al., 2012). Maize is also a major ingredient and source of calories in 8 animal feed formulations. Distillers’ dried grains (DDS), a byproduct of ethanol production has become a valued livestock feed (Arora et al., 2010; Mueller et al., 2011).

Maize is consumed directly off the cob, steamed, fried or roasted. The flour after milling is cooked into dishes, porridge, fermented for use in cakes, breads, tortillas and alcohol.

Additionally, processing maize yields thickeners, oils and sweeteners (Gardner and Inglett, 1971;

Nuss et al., 2010). While the demand of maize for human food, livestock feed, biofuel and other industrial purposes is increasing, global maize production will rise over 60% within the next 30 years. Therefore, there is a need to meet maize demands propelled by the skyrocketing human population, mostly in low income countries (Godfray et al., 2010; Ray et al., 2013). Sustainable approaches to maize storage are key in promoting global food security for the rural poor populace in SSA where maize is a major source of income and food (FAO/WFP/IFAD, 2012).

Storage of Harvested Maize

Maize is a seasonal crop but its demand continues throughout the year. Storage is a unit operation of keeping grains for an intended use in the food supply chain. Storage, therefore, is substantial in supplying maize for year-round demand (Nukenine, 2010). Grain storage should be efficient in maintaining the quality and quantity of the stored maize until the next harvest (FAO,

2011; Oyekale et al., 2012). In addition, storage balances the supply and demand of maize by claiming the surplus from the market and release it on demand which controls fluctuations in market prices (FAO, 1994). Smallholder farmers in low-income countries primarily store grains for food security, economic value and seed for the next season.

The type of storage structure depends on the quantity of maize harvested, storage requirements, unit cost of storage and maize on the cob versus shelled maize. According to

Nukenine (2010) and FAO (2011), storage can be broadly categorized into three practices; 9

1. Traditional storage mainly for smallholders, which includes; gourds, clay pots,

local cribs, fireplaces, roofs, open fields, raised mud-plastered baskets and mud-

walled silos. These hold a maximum of 3 Mg of maize. The main limitation for

the traditional storage facilities is durability and protection against insects, rodents

and direct moisture loss.

2. Improved storage structures, which include improved traditional pits, ventilated

cribs, underground pits, and brick, walled silos, reinforced concrete silos, steel

bins, bag storage, storage warehouses and open bulkheads.

3. Bulk storages, which include solid-wall bins and concrete silos holding more than

25.4 Mg of maize.

Post-Harvest Losses of Stored Maize

Losses of maize occur at every stage in the unit operations including; harvesting, threshing, cleaning, storage, transport, milling, wholesale and retail distribution. Maize is susceptible to attack from weevils, rodents, mites, microorganisms and birds (Barney et al.,

1995; Weinberg et al., 2008; FAO, 2011), both in the field and during storage. High-income countries mainly store maize in commercial silos while fumigating and controlling storage conditions to eliminate insect pests. Low-income countries have limited control measures for storage conditions with low protection from insect pest infestation. Despite the type of storage, global post-harvest losses of maize can reach 37% (FAO, 1993). The USA alone loses between

33 and 123 million Mg equivalent to $18.8 billion annually (Chuck-Hernández et al., 2012).

In tropical climates, maize weevils are the major storage pests of maize (Kanyamasoro et al., 2012) contributing up to 80% losses of untreated maize (Agoda et al., 2011). Bern, Hurburgh and Brumm (2013), discussed respiration and deterioration of stored maize. Increase in temperatures from the respiring maize favors weevil multiplication during storage. Additionally, 10 maize weevils thrive at temperatures between 250C and 300C and relative humidity between 70% and 80% (Throne, 1994). Maize, like other grains is hygroscopic; absorbs and releases water leading to rotting (Devereau et al., 2002). In hot and humid weather of the tropical and subtropical countries, maize stored in warm and moist conditions is subject to fast deterioration

(Weinberg et al., 2008).

Qualitative losses of maize are grouped into germination rate, infestation rate, mold growth, nutritional value and color changes (Boxall, 1991; Chuck-Hernández et al., 2012).

Quantitative losses of maize include weight and germination losses (Boxall, 1991). Insect infestation is also associated with maize dry matter loss from primary and secondary insect feeders (Tuite and Foster, 1979; Maier et al., 1996; Bern et al., 2002). A combination of temperature, moisture, oxygen and insect activity influence bio deterioration of maize (Alborch et al., 2011; FAO, 2011; Yakubu et al., 2011). Boxall (1991) estimates losses of stored grain by insects and mold growth of up to 35% in low-income countries.

Fungi of economic importance in maize include Aspergillus flavus and Fusarium sp.

Fungi produces mycotoxins especially aflatoxin in maize. Contamination of maize with mycotoxin has safety and health concerns to humans and animals (Bankole and Adebanjo, 2003;

Williams et al., 2004; Lukwago et al., 2019). Deterioration may not be stopped but can be slowed by preservation approaches (Bern et al., 2013). Therefore, properly designed, constructed and managed stores lower the rate of maize deterioration and infestation from maize weevils.

Maize Weevils

Maize weevils, Sitophulus zeamais Motschulsky, belong to order Coleoptera, family

Curculionadae and have a maximum body length of 4 mm (Rees, 2004; Bell, 2014). S. zeamais have a snout and a pair of mandibles attached to the head (Figure 1.4). The color varies from dull red-brown to nearly black with four light reddish spots on the back (USDA, 2019). Temperature 11 and relative humidity at 300C and 70% especially in the tropical environments favor survival of maize weevils (Birch, 1948; Throne, 1994).

Figure 1.4. Adult maize weevil (Georg Goergen/IITA Insect Museum, Cotonou, Benin)

Insect development and complete metamorphosis takes up to 40 days and 110 days in favorable and unfavorable conditions respectively (Howe, 1952; McFarlane, 1989). The female weevil uses its mandibles to chew a hole in the kernel and seals it with a waxy secretion after depositing an egg. Under favorable conditions, a female weevil lays between 300 and 400 eggs with a single egg laid per kernel. It takes approximately 6 days for the egg to hatch at 25 0C (Rita

Devi et al., 2017). The rate of oviposition tends to slow down at temperatures below 20 0C or above 320C and moisture content below 12% (Howe, 1952). According to Giles (1969), maize weevils internally feed on the endosperm of the kernels with the egg, larvae and pupae development stages found entirely inside the kernel. Feeding on the endosperm of the grain starts from pupae that bores a tunnel as it develops to the emergence of the new adult that makes its way out of the kernel.

Irregular edges identify holes showing emergence of adults from the kernels. The boring and chewing of kernels from maize weevils gives way to infestation from secondary feeders.

Adult maize weevils have well-developed wings and can fly for short distances. The ability of 12 the weevils to fly results into infestation which starts from the field with adult weevils invading mature crops and hence distributed largely over 100 countries globally (Champ and Dyte, 1977).

Effects of weevil infestation on maize include grain heating, insect damaged kernels (IDK), reduced grain quality, mold spread and economic loss.

Maize weevils account for up to 40% losses of stored grain which significantly impact the food security of the rural poor in low income countries (Gitonga et al., 2013; García-Lara and

Bergvinson, 2014; Tefera et al., 2016). Though common in maize, weevils can thrive well on a range of other cereals including rice, sorghum, wheat, rye and barley as well as a few grain products like pasta and pet food.

Physical Disturbance of Grains

Physical control processes during grain handling include but not limited to cooling, heating, ionizing radiation, inert dust, hermeticity, hand picking and physical disturbance.

Among these practices, physical disturbance applies a force, which interferes with the steady state of the grain mass. Moving grains and storage equipment changes the location of the kernels, insects and fluss, creating unsuitable conditions for insect pests (Banks, 1986; White et al., 1997;

Paliwal et al., 1999).

Physical control techniques for grain preservation date back before wide application of insecticides and pesticides (Banks, 1986). Such non-chemical approaches will gain preference in the future to control insect pests in stored grains and grain products. While most chemical preservation approaches on grains leave residues in the food supply chain and can cause insect pest resistance, physical disturbance does not (Banks, 1986). In addition, environmental and health concerns associated with synthetic insecticides sometimes limit their application in grain handling and storage. There is a need for effective and affordable post-harvest approaches which can reduce losses of maize from insect pests (Boxall, 2001). 13

Physical disturbance means moving all corn kernels in a storage container with respect to each other. Physical disturbance of infested maize is simple and affordable (Banks, 1986; White et al., 1997) with energy and knowledge being the main inputs from farmers. Increase in demand and prices of insecticide free-products together with policies restricting use of certain pesticides is an opportunity for wide adoption of physical disturbance (Banks, 1986).

Bailey (1962), demonstrated that disturbances of small magnitude were sufficient enough to account for the high suppression rate of the adult granary weevil (Sitophilus granaries (L.)) and its immature stages living outside the kernels. However, velocities of grains beyond 45.7 m/s targeting immature stages inside the kernels damaged wheat granules. In another laboratory study, Joffe and Clarke (1963), investigated the effect of physical disturbance on the development stages of rice weevils (Sitophilus oryzae L.). The suppression rate and oviposition of rice weevils depended on manual rotations (1.5 seconds per rotation), pouring (1.7 m), dropping (up to 1 m) and/or a combination of these treatments. Periodic disturbance had a significant and severe effect on the emergence of the insect progeny.

In an earlier study, Joffe (1963) occasionally moved infested maize from one bin to another at the commercial grain elevators in South Africa. The process involved unloading maize into a railway truck, then mechanically conveyed to the same bin through belts and bucket elevators. Results showed that periodic disturbance significantly reduced the population of adult

Sitophilus oryzae L. and the flour beetle (Tribolium spp.). Bailey (1969), modified the experimental design by Joffe and Clarke (1963), with different disturbance velocities. He noticed that the suppression rate of immature stages of the grain weevil (Sitophilus granaries (L.)) increased with flow rates of infested wheat. 14

Muir et al. (1977), reduced the populations of the rusty grain beetle; Cryptolestes ferrugineus (Stephens), in infested wheat by transferring wheat between grain bins kept at low winter temperatures. Grain movement effectively inhibited population recovery of the rusty grain beetles after temperature rise of 300C in the grain bin. Additionally, Loschiav (1978), disturbed wheat infested with four insect species, vis. rusty grain beetle, red flour beetle, granary weevil and rice weevil. Infested wheat was dropped in sacks or a tubular height of 14.1 m then rotated.

Suppression rate of rusty grain beetle and red flour beetle increased with the magnitude of disturbance.

In the same study, the suppression rate of adult granary and rice weevils dropped in sacks reached 96%. Rusty grain beetles had the highest suppression rate in free falling wheat along with tumbled and rotated sacks. Ungsunantwiwat and Mills (1979), observed fewer progeny of S. zeamais and S. granaries compared to S. oryzae L., emerging into adults after mechanical disturbance of infested grains. Quentin et al., (1991) manually rolled 0.8 L glass jars and 16 L cylindrical containers half-filled with red kidney beans (Phaseolus vulgaris L.) through 1 circumference, and periodically turned 45 kg gunnysacks half-filled with red kidney beans. The beans had been infested with bean weevils (Acanthoscelides obtectus (Say)). The study achieved

97% suppression rate of the bean weevils relative to the undisturbed treatments.

Bbosa, (2014) manually rolled 2.6 L reusable coffee plastic containers through one circumference per day. Disturbing maize infested with S. zeamais achieved 93% control of the maize weevils compared to the stationary containers. In rural Tanzania, periodic shaking of 20 L jerry cans with 10 kg of white dent maize infested with 0.5 kg of maize weevils achieved 98% suppression rate of maize weevils (Suleiman et al., 2016). 15

Disturbance has proven effective in reducing insect pest populations during grain storage.

However, disturbance experiments in the literature do not propose a standard disturbance time interval to control insect pests of stored grains.

Steel Grain Bins

Maize can be stored in farm sized steel bins right after harvesting and or drying. The steel bins are cylindrical with vents in the conical roof. Maize is conveyed by screw augers, bucket elevators or pneumatic conveyors then distributed by spreaders across the bin diameter as it falls into the bin (Figure 1. 5). Spreaders eliminate the concentration of BCFM in the center of the bin. Temperature and relative humidity cables hung from the bin roof extend into the grain mass to monitor the conditions of the stored maize. Modern cables respond wirelessly by sending information about the status of the maize to the computer or phone of the farmer.

Figure 1.5. Schematic of a farm size steel bin (edited from Bern (2013))

During unloading, a sweep auger on the floor of the bin consolidate maize to the discharge outlet for loading in the trucks or wagons. The perforated steel floor (Figure 1. 5) 16 allows contact of the grain mass with air. Fans blow ambient or heated air into the grain mass from the bottom of the bin. Vents exit drying air allowing air exchange between the bin and the outside environment.

Stirring Machines

Stirring machines are open screw augers vertically suspended in the grain mass to turn and mix stored grain for uniform drying (Figure 1.5 and Figure 1.6). Stirring mixes drier maize at the bin bottom with wetter maize at the top resulting in a uniform moisture content in the bin.

Bern et al. (1982), reported that stirring decreases airflow resistance and static pressure by loosening caked maize. Bern et al. (2013), stated that stirring together with drying high moisture shelled maize increases its allowable storage time. The economic importance of stirring machines may include cutting of drying costs.

Figure 1.6. Sukup Manufacturing Company has commercialized five auger Fastir plus stirring system installed in a 13 to 15 m (42 to 48 ft) diameter grain bin

For decades, stirring machines run in the grain mass to achieve efficient grain drying and higher airflows. Up until now, no research has investigated the effect of stirring stored grains to control stored grain insect pests. 17

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CHAPTER 2. DESIGN AND CONSTRUCTION OF AN AUTOMATED PHYSICAL DISTURBANCE MACHINE TO CONTROL GRAIN STORAGE INSECT PESTS

M. Sserunjogi; C. J. Bern; T. J. Brumm Department of Agricultural and Biosystems Engineering Iowa State University

Modified from a manuscript to be submitted to Journal of Stored Product Research

Abstract

Physical disturbance moves stored grains with respect to each other causing unfavorable conditions for the survival of stored product insect pests. Manual disturbance has proven effective in suppressing maize weevils in maize stored by smallholder farmers. One study involved periodic shaking of non–hermetic 20 L jerry cans with 10 kg of clean white dent maize mixed with 0.5 kg of infested maize. Another study manually rolled non-hermetic 2.6 L recycled ground coffee plastic containers through one circumference twice a day. Containers were loaded with 1 kg of maize and 25 adult maize weevils. We have not found any literature discussing automation of physical disturbance to control stored grain insect pests.

The goal this study was to design, construct and test automated physical disturbance machines for the subsequent disturbance experiments. The machines supported and rotated 12 -

3.8 L jars loaded with one kg of maize and 25 adult maize weevils. Baffles in the jars mixed maize and maize weevils when the jars rotated through about 1.25 revolutions for 3 seconds.

Two jars were randomly selected from the test machine and analyzed at specified run time up to

100 minutes. Live maize weevils reduced from the initial population in a range of 1 to 4 weevils.

Suppression rate up to 8% indicated that disturbances generated by the machine could not crush adult maize weevils. 23

There was no physical damage on the appendages of adult maize weevils. Therefore, control of maize weevils would be caused by other factors rather than such disturbances of low magnitude. The machines were prepared for experiments comparing the effect of different disturbance time intervals on the population of maize weevils and change in the quality of stored maize.

Key words: non-hermetic, smallholder

Introduction

Physical disturbance stresses life cycle stages of insect pests in stored grain by mixing up the insect pests, the kernels, and fluss derived from insects’ activity on the grains. The effects of disturbance depend on the magnitude of the force applied to the grains. Ultimately, this creates conditions that are stressful and unfavorable for the survival of the insect pests. Physical control approaches of stored grain insect pests are preferred relative to chemical treatments because they leave no residues in the food, have low chances of developing insect resistance, and can be built from locally available materials with less energy input (Banks, 1986).

Quentin et al. (1991), manually rolled non hermetic 0.8 L glass jars and 16

L polyethylene food buckets through one circumference, half filled with infested dry red kidney beans (Phaseolus vulgaris L.). The same study used mouth tied gunny sacks half filled with 22.7 kg of insect infested dry red kidney beans turned through 1800. Results showed that daily periodic tumbling was 96% efficient in controlling populations of bean weevils (Acanthoscelides objectus) relative to the undisturbed containers.

Bbosa (2014), manually rolled non-hermetic 2.6 L recycled ground coffee plastic containers through one circumference twice a day. Each container was loaded with 1 kg of maize

(Zea mays) and 25 adult unsexed weevils (Sitophilus zeamais Motschulsky). Populations of live 24 maize weevils in the disturbed containers reduced by 81% relative to the stationary containers after 160 days. In rural Tanzania, daily periodic shaking of non–hermetic 20 L jerry cans with 10 kg of clean white dent maize mixed with 0.5 kg of infested maize achieved 98% suppression rate of the maize weevils compared to the undisturbed jerry cans after 90 days (Suleiman et al.,

2016).

The effect of frequency, timing and type of physical disturbance with rotation, pouring and dropping was effective on the suppression rate and emergence of adult rice weevils

(Sitophilus oryzae) (Joffe and Clarke, 1963). Bailey (1969), performed similar disturbance experiments on wheat infested with granary weevil (Sitophilus granarius). Results showed that several disturbances and combinations of rotation, pouring and dropping affected different lifecycle stages of S. oryzae and S. granarius.

To date, there is no literature on the automation of physical disturbance of stored grains to control maize weevils during laboratory studies. The objective of this study was to design, construct and test automated physical disturbance machines for subsequent disturbance experiments.

Materials and Methods

Machine Design and Construction

The goal of this study was to design and build machines, which support and rotate twelve

3.8 L jars loaded with one kg of maize. In Figure 2.1, there are two wooden disks (BC Plywood, diameter 508 mm and thickness 19 mm) with six holes (diameter 102 mm) at 254 mm from the centerline of the wooden disk. Aluminum disks (diameter 279 mm and thickness 5 mm) were concentrically stacked and joined to the wooden disks with five equally spaced stainless steel screws (Table 2.1) at a radial distance of 76.2 mm. 25

Disks and holes were cut with a water jet (FlowMACH2B) operated at 3447.4 N/mm2.

The aluminum disks prevented failure of the wooden disks and supported the aluminum shaft through the 51 mm centric holes in the wooden disks. Wood bearings supported the shaft and connected it to the motor shaft with couplers (Table 2.1). Bearings and couplers limited slack in the moving parts of the machine during rotations.

A pivotal wooden piece 51 mm x 51 mm x 102 mm between the disks supported the shaft. A wooden piece (76 mm x 76 mm x 127 mm) with a cut out hole of diameter 76 mm for the motor shaft supported the motor at the proximity end of the machine. The base of the disturbance machine had two sets of wooden pieces of rectangular cross section resting on a flat surface and supporting the weight of the disks with loaded jars. Exterior screws (Table 2.1) joined the base wooden pieces both of dimensions 76 mm x 102 mm x 76 mm and 102 mm x 127 mm x 76 mm. Lubrication with silicone spray limited friction between the shaft of the disturbance machines and the wood bearings.

Figure 2.1. Automated disturbance machine with jars loaded with 1 kg of maize and 25 adult maize weevils rotated through about 1.25 revolutions for 3 seconds.

Jars and Screens

Clean and clear-wide mouthed polyethylene terephthalate (PET) plastic jars (The Cary

Company, 1195 W Fullerton Ave, Addison, IL) of 3.8 L, neck size 110 mm, straight-line profile 26 with a slightly rounded shoulder and base were used (Figure 2.2). Jar selection was based on convenience for modification and observation of the maize weevil activity during the physical disturbance experiments. Two wooden baffles (38 mm x 38 mm x 152 mm) (Figure 2.2) were fixed along the inner walls of each jar at 1800 apart with pan head stainless steel screws (Table

2.1). While motors rotated the jars, baffles mixed maize and maize weevils in the jars generating a physical disturbance of maize.

Figure 2.2. 3.8 L plastic jar with Figure 2.3. Screens between the wooden baffles. lids and holes on the wooden disk.

The lids on the jars were black ribbed – sided plastic polypropylene with internal diameter 110 mm (Figure 2.3). Holes of diameter 70 mm were made through the lids with a hole cutter. Ultra sun block solar screens (New York Wire, P.O Box 866, Mt. Wolf, PA 17347, USA) with diameter 108 mm placed between the top face of the lids and the holes of the wooden disks were concentrically joined by pan head stainless steel screws (Table 2.1). The underside of the lids with rings attached loaded jars to the wooden disks. Physical disturbance of maize and weevils in this experiment was non hermetic. Screens allowed air exchange between the jars and the ambient. 27

Table 2.1. Screw and Fastener sizes to fasten parts of the disturbance machine.

Screw and Screw and Fastener type Parts of the machine fastened Fastener sizes No. 8 x ¾” Pan head stainless steel Aluminum and Wooden disk No. 2-1/2” x 9 Exterior screws All rectangular wooden pieces No. 8 x ½” Pan head stainless steel Wooden baffles and the walls of the jar Jar lids and screens to the wooden disks No. 10 – 32 x 3” Round Combo with nuts Bolting geared motor to the 76 mm x 76 mm x 76 mm vertical wooden piece Bearing Metallic shaft and wooden disk Couplers and pins Motor shaft and the shaft

Motor

Single phase shaded pole AC geared motor; 115 VAC, 1.3 A, 40.7 Nm, 60 Hz and 25

RPM (Grainger Inc., Minooka, IL) was chosen to achieve about 1.25 revolutions in 3 seconds.

Rotation time simulated the physical disturbance experiment by Bbosa (2014) who manually rolled plastic coffee containers with maize and adult weevils through one circumference. The motor maximum torque of 40.7 Nm was able to rotate the load of maize and the disks.

Control System

The code automating the disturbance machines was written in the programming environment of Microsoft Visual Basic (MS-VB) 2008, a free offline software package. MS-VB programming environment allows the user to interact with its graphical user interface (GUI)

(Figure 2.4) with several control tools. The experiment used USB-1208FS –Plus (Measurement

Computing Corporation, 10 Commerce Way Norton, MA) an analog and digital I/O data acquisition device. USB-1208FS-Plus had 8 analog input channels which were software 28 configurable for either eight 13-bit single-ended inputs or four 14-bit differential inputs. Five volts direct current (+5 V DC) USB supply from the computer powered the USB-1208FS.

This study used a normally open (NO) single pole single throw (SPST) solid state relay

(SSR) to switch the motor. With a start button on the GUI, timers in the MS-VB triggered the data acquisition system (DAQS) to send logic high signals to the solid state relay to run the motor for three seconds before sending a logic low (Figure 2.5). Logic 1 (high) and 0 (low) raised and lowered the input voltages respectively at the SSR terminals. The relay disconnected power from the load (motor) in the inactive state (logic low). Logic high applied current to the coil generating magnetic field which pulled the armature to close the contact powering the motor. Logic high was a voltage between 2 V DC and 5 V DC at the input terminal of the SSR which generated 120 V DC at the output terminal. High voltage turned on the geared motor which rotated the aluminum pipe, wooden disks and jars.

Figure 2.4. Graphical User Interface (GUI) from MS-VB software, 2008 for three machines at set intervals of 8, 12 and 24 h.

Figure 2.5. Logic Flow Chart for the control system of the disturbance machine running at a set time interval for 3 seconds.

Circuit Layout

The machine was powered by an uninterruptable power supply (UPS) with an output of

120 Volts (Source). The UPS powered the machine up to 15 minutes in case of power shutdown so that disturbance intervals could not be interrupted during abrupt load sheds.

The wire cord (3 × 1.31푚푚2(16퐴푊퐺) 600퐶 300푉) powered the AC geared motor and solid state relay from the UPS (Figure 2.6). The signal wire (퐴푊푀 퐼 퐴⁄퐵 퐹푇1 800퐶 300푉) connected the solid state relay to USB1208FS-Plus which was powered by a USB 2.0

(퐴푊푀 퐼⁄퐼퐼 퐴⁄퐵 800퐶 30푉 퐹푇1 ) hooked up to the USB port of the computer to generate 5 volts. 30

Figure 2.6. Schematic of the circuit diagram for the wiring of the disturbance machine.

Maize and Maize Weevils

Maize used was commercial hybrid Pioneer P0339AMXT, combine harvested on

November 1, 2018 at 15.6% moisture content from the Agricultural Engineering and Agronomy

Research Farm at Iowa State University. Maize weevils came from colonies raised at the

Department of Agricultural and Biosystems Engineering, Iowa State University, Ames, Iowa in a chamber maintained at 60% RH and 270C.

Results and Discussion

Testing the Disturbance Machine

The machines rotated jars loaded with 1 kg of maize and 25 adult weevils through about

1.25 revolutions over a period of 100-minute (Table 2.2). Two jars were randomly selected off the machine at specific intervals of machine run time for data analysis. The samples were screened through 12/64-inch (4.8 mm) round hole sieves to separate maize weevils from the maize. Some maize weevils were lodged in the spaces between the lids and the screens which resulted in the total of live and dead weevils lower than the initial population. A layer of silicone sealant (Momentive Performance Materials Inc., Huntersville, NC 29078) closed the lodging areas of maize weevils between the screen and the lining of the cutout holes from the lids. 31

This study rotated jars with infested maize at a mechanical rate below that reported by

Bailey (1969) who subjected wheat infested with Sitophilus granarius to a minimum impact velocity of 1.49 m/s at frequencies of 2 and 200 drop times. Only at higher disturbance frequencies was 7% and 10% suppression detected for disturbances daily and twice weekly respectively.

Table 2.2. The effect of rotating the motor at 25 rev/min on the suppression rate of maize weevils as a function of rotation time in 3.8 L plastic jars with 25 adult maize weevils.

Time (min) Live maize weevils Dead maize weevils Suppression rate (%) 5 25 0 0 5 23 0 0 10 23 0 0 10 25 0 0 20 24 1 4 20 24 1 4 30 23 0 0 30 24 0 0 50 23 2 8 50 21 1 4 100 24 0 0 100 23 1 4

Disturbance machines rotated jars of infested maize at about 1.3 m/s causing maximum suppression rate of 8% at 50 minutes. Direct physical damage on the appendages of adult maize weevils was not observed. Adult maize weevils could not be crushed by the disturbance of maize mixed by the baffles in the jars. Control of maize weevils from the disturbance machine could be a result of other factors rather than such disturbances of low magnitude. 32

Conclusion

1. Disturbance machines were designed, constructed and tested rotating jars loaded

with 1 kg of maize and 25 adult maize weevils through about 1.25 revolutions in 3

seconds.

2. Live maize weevils reduced from the initial population (25 weevils per jar) in a

range of 1 to 4 weevils at all motor run time.

3. Disturbance machines disturbed maize at a rate of 1.3 m/s causing suppression

rates of 4 and 8% at different motor run times.

4. Direct physical damage on the appendages of adult maize weevils was not

noticed. It was concluded that control of maize weevils in the subsequent

disturbance experiments would be a result of other factors rather than such

disturbances of low magnitude.

References

Bailey, S. W. (1969). The effects of physical stress in the grain weevil Sitophilus granarius. Journal of Stored Products Research, 5(4), 311–324.

Banks, H. J. (1986). Impact, physical removal and exclusion for insect control in stored products. In E Donahaye and S Navarro (Ed.), Proc. 4th Int. Conf. Store Products Protection,21– 26 (pp. 165–184). Tel Aviv, Israel.

Joffe, A., Clarke, B. (1963). The effect of physical disturbance or ‘turning’of stored maize on the development of insect infestations—II. Laboratory studies. S. Afr. J. Agric. Sci, 6, 65–84.

Muir, W. E., Yaciuk, G., Sinha, R. (1977). Effects of temperature and insect amd mite populations of turning and transferring farm-stored wheat. Canadian Agricultural Engineering, 19(1), 25–28.

Paliwal, J., Jayas, D. S., White, N. D. G., Muir, W. E. (1999). Effect of pneumatic conveying of wheat on mortality of insects. Applied Engineering in Agriculture, 15(1), 65–68.

Quentin, M. E., Spencer, J. L., Miller, J. R. (1991). Bean tumbling as a control measure for the common bean weevil, Acanthoscelides obtectus. Entomologia Experimentalis et Applicata, 60(2), 105–109.

Suleiman, R., Rosentrater, K., Chove, B. (2016). Periodic Physical Disturbance: An Alternative Method for Controlling Sitophilus zeamais (Maize Weevil) Infestation. Insects, 7(4), 51.

Appendix: Drawings of the physical disturbance machine

Figure A.1. Assembly drawing of the disturbance machine in Autodesk Inventor.

Figure A.2. Isometric and Orthographic views of the disturbance machine in Autodesk Inventor. 34

CHAPTER 3. PHYSICAL DISTURBANCE TIME INTERVAL FOR CONTROL OF MAIZE WEEVILS IN STORED MAIZE

M. Sserunjogi; C.J Bern; T.J Brumm; D.E Maier Department of Agriculture and Biosystems Engineering Iowa State University

Modified from a manuscript to be submitted to Journal of Stored Product Research

Abstract

Maize is an important cereal providing daily calories to over 50% of the population in

Sub Saharan Africa (SSA). Despite the importance of maize, insect pests threaten maize storage especially in the tropics. Physical disturbance of maize in storage containers is a non-chemical approach that can suppress populations of insect pests in stored grains. Disturbance has proved successful with bean weevils, lesser grain borers, and maize weevils. Prior research on disturbance has not established a standard disturbance interval to suppress stored product insect pests. This research identifies a disturbance frequency that best suppresses maize weevils in infested maize.

A storage experiment of maize infested with weevils was conducted with four treatments: undisturbed containers (control) and containers disturbed at intervals of 8, 12 and 24 hours.

Jars containing one kg of 16% moisture maize and 234 adult maize weevils were stored at 270C and 65% RH and were rotated by electric motors through about 1.25 revolutions in 3 seconds.

After 40, 80, 120 and 160 days, three jars were selected randomly from each treatment and then analyzed.

Reduction in maize weevil populations was 75%, 95% and 94% for 8, 12 and 24 h intervals, respectively, compared to the undisturbed jars after 160 days. The quality of maize in 35 the disturbed jars was better than that in the undisturbed jars which had a higher moisture content, higher broken corn and foreign material, higher insect damage, higher mold damage and lower test weight.

Disturbance once per day (24 h) proved the best interval in suppressing weevil populations and maintaining the quality of maize for a 160-day period of maize storage.

Disturbance once per day may be an effective non-chemical approach to suppress maize weevils in maize stored by smallholder farmers.

Keywords: smallholder farmers, test weight, broken corn and foreign material, moisture content, insect damage, mold damage

Introduction

Maize is among the most widely grown cereals on the African continent (IITA, 2011a;

FAO, 2018). Maize is a daily source of food calories for over 50% of the populace in Sub

Saharan Africa (SSA) (Ekpa et al., 2018). With the population of SSA expected to double by the year 2050, the demand for maize is expected to triple following this trend (Rajaram, 2016; M.

Van Ittersum et al., 2017). The future demand for maize in SSA can be satisfied by integrating current maize production with appropriate storage practices.

Post-harvest interventions are necessary to reduce tonnages of maize lost during storage.

Losses of maize due to maize weevils (Sitophilus zeamais) can be severe and reportedly reach

36% in SSA (Abass et al., 2014; World Bank, 2011a). Losses from maize weevils can also reach

90% from untreated maize stored in the tropical and subtropical regions (Tefera et al., 2011a;

Zone et al., 2015). Many smallholder farmers in SSA cannot afford insecticides to preserves maize in storage. The lack of sufficient knowledge to propagate safe use of grain chemical preservatives has also created environmental and food safety concerns in grain storage (Bell,

2014). 36

Disturbance is such a nonchemical method of grain storage that moves maize kernels in storage with respect to each other. Bailey (1969) showed that forces of low magnitude under regular disturbances could cause significant control of insect pests. While high impact forces on infested maize kill the pre-emergent stages of maize weevils, they have found resistance from damaging the grains. For instance, in a study by Bailey (1962), percussive forces of 45.72 m/s effectively killed the pre-emergent stages of Sitophilus granaries in wheat but caused significant wheat damage up to 20%. This suggests the need for gentle and non-destructive forces to control weevils in stored maize.

Joffe et al. (1963) analyzed disturbance methods of rotation, pouring, dropping and their additive effects on oviposition of mature rice weevils (Sitophilus oryzae). The disturbance intervals were daily, weekly, twice weekly and once in two, three and four weeks. Overall, physical disturbance reduced the number of pre-adult progeny compared to the undisturbed containers. In similar disturbance experiments on common bean weevils, Acanthoscelides obtectus, Quentin et al. (1991) achieved up to 98% control of bean weevils from storage containers which were manually rolled through one circumference at a daily time interval of 8 h.

The same study achieved 98% and 97% control of bean weevils from disturbing plastic buckets and gunny sacks, respectively, two to three times every day.

Bbosa (2014b) stated that by manually turning storage containers with 1 kg of weevil- infested maize through one circumference every 12 h, the adult maize weevil population was reduced by 93% after four insect life cycles. In another study in SSA, Suleiman et al. (2016) disturbed 20-L storage containers with white dent corn and maize weevils twice a day. The suppression rate of maize weevils was over 96% after two weevil life cycles. 37

Physical disturbance of storage containers has proved effective in reducing weevil populations during maize storage. However, we have not found any studies on physical disturbance that proposes a standard disturbance frequency to suppress maize weevils in stored maize. The objective of this research was to determine the time interval that best controls maize weevils and maintain the quality of stored maize subjected to physical disturbance.

Methods and Materials

Maize and Weevils

Maize of commercial hybrid Pioneer 1197AMXT was combine harvested in November

2018 at 15.6% moisture content from the Agricultural Engineering and Agronomy research farm,

Iowa State University, Ames, Iowa. A Carter day dockage tester machine (Carter Day international Minneapolis, MN) with round hole screens of 12/64 in. (4.8 mm) separated broken corn and fine material (BCFM) from the maize used in the experiment. Since freezing below -

100C is fatal to all life cycle stages of the maize weevils (Bell, 2014), the cleaned maize was frozen for 72 hours in a room maintained at -200C. This practice eliminated possible stages of maize weevils carried along with maize from the field. Maize was then stored in a room maintained at 40C until it was used for the experiment.

Maize weevils (Sitophilus zeamais) for this experiment came from colonies raised in an environmental chamber (Thermo Scientific™ 3940, Fisher Scientific) maintained at 270C and

60% relative humidity. Adult S. zeamais were carefully screened out of the colony and collected on a pan with minimal disturbances. Active maize weevils that climbed up the ring of the pan were selected for the experiment.

Experimental Design and Set Up

Holes (75 mm diameter) were cut out through the 1.9 L jar lids (Farm & Fleet of

Janesville, Inc., WI) and covered with ultra-sun block solar screens (New York wire, Mt. Wolf, 38

PA). This prevented weevils from escaping during the experiment and allowed air circulation between jar contents and ambient air. Each jar was loaded with one kg maize and infested with

25 adult maize weevils. Maize weevils were allowed to reproduce undisturbed for one life cycle

(40 days) before the treatments were applied, in an environmental chamber maintained at 270C and 65% RH (Thermo Scientific™ 3940, Fisher Scientific). This process simulated the invasion of mature maize in the field by adult maize weevils and pre-emergent stages which get carried along with the maize kernels into storage structures.

After one life cycle (40 days), maize and weevils in each of the 1.9 L jars were transferred into 3.8 L plastic jars (The Cary Company, 1195 W Fullerton Ave, Addison, IL) with as little disturbance a possible filling the jars to approximately less than one half of capacity. 12 jars each were randomly assigned to either the control (undisturbed) or three disturbance machines (described in chapter two of this thesis). The machines were placed on metallic racks in the growth chamber (Percival Scientific Inc., Perry, Iowa) set at 270C, 70% RH and 12 h light and dark phases (Figure 3.1).

The undisturbed jars were laid longitudinally on a flat raised wooden platform resting on the floor under but not touching the racks. The position of the undisturbed jars allowed air circulation from the floor of the chamber yet eliminating vibrations from the disturbance machines to the stationary jars. The machines were disturbed at either 8, 12 or 24 h time intervals. Electric motors rotated the jars through about 1.25 revolutions in 3 seconds at the end of each disturbance interval. 39

Figure 3.1. Disturbance machine placed on metallic racks in the growth chamber maintained at 270C and 70% relative humidity and 12 h light and dark phases.

Response Measurements

Three jars were randomly selected from the 1.9 L jars to determine the initial number of live maize weevils and maize quality following the protocol in the grain inspection handbook

(USDA, 2013a). During the disturbance experiment, twelve 3.8 L plastic jars (three jars per treatment) were selected randomly at 40, 80, 120 and 160 days of storage. Live maize weevils were manually screened out of the infested maize through 12/64 in. (4.8 mm) sieves and collected on the steel pan. A hand held mechanical tally counter was used to count the total walking live maize weevils. The criteria for identifying inactive live maize weevils from dead weevils was based on the protocol described by Yakubu et al.(2011).

Determining Moisture content (MC), Test weight (TW), broken corn and foreign material

(BCFM), insect damage (ID) and mold damage (MD) of maize followed the counting of maize weevils. Live maize weevil counts from some jars with high populations of weevils were determined on the weight basis of 3.6 g per 1000 weevils (Bbosa et al., 2017). 40

Data Analysis

Two-way ANOVA was performed with Statistical Analysis System (SAS) software (SAS

9.4 for windows x64 Based Systems; Copyright @ 2002-2012, SAS Institute Inc., Cary, NC,

USA). A general linear model (PROC GLM) was used to determine the mean difference between the treatments and control at the 5% probability level. Least square means using Type III sum of square errors with Tukey’s adjustment for pair wise comparison generated the correct p-values.

Plots of the data were generated with R studio (Version 1.1.442 - @ 2009 – 2018 R studio, Inc.). Correlations between live maize weevils and moisture content, test weight, broken corn and foreign material, mold damage and insect damage were performed in R statistical package at P < 0.05 level.

Results and Discussion

Live Maize Weevils

Disturbance intervals (8, 12 and 24 h) reduced live maize weevils compared to the undisturbed jars (0 h) at every storage time (Figure 3.2 and Table 3.1). Live maize weevils in the undisturbed jars increased exponentially after 40 days up to a 34-fold increase at 120 days of maize storage. Bbosa et al. (2014) observed a similar exponential growth when raising maize weevils on yellow dent corn. The exponential trend of live weevils in stationary jars might have been from unaltered oviposition and access to food. Live maize weevils at 80, 120 and 160 days in the undisturbed jars were similar but statistically different from live maize weevils at 40 days of maize storage.

While disturbance three times a day (8 h) had fewer live maize weevils than disturbance twice a day (12 h) at 40 and 80 days, an 8 h disturbance interval had more live weevils at 160 days of storage. It is likely that frequent disturbance stimulated oviposition of maize weevils at

160 days. Live maize weevils from disturbance once a day (24 h) were not statistically 41 significant (p value = 0.058) with disturbance twice a day (12 h) at 160 days. Disturbance once a day (24 h) maintained the lowest number of live maize weevils.

Figure 3.2. Live maize weevils in stored maize at different sampling times (days) for three different disturbances intervals (8, 12 and 24 h) versus control except for missing data from 12 h disturbance at 120 days and one replicate at 160 days. Vertical bars indicate standard errors.

Samples from the 12 h disturbance interval at 120 days and one replicate at 160 days were excluded from the general data analysis due to anomalies in the live maize weevils counts.

Joffe and Clarke (1963) stated that the sensitivity to disturbance of the pre-emergent stages of weevils tend to vary. This may account for the anomalies in the live maize weevil counts from the 12 h disturbance interval.

Live maize weevils in disturbed jars were not significantly different at all days of storage except when disturbed three times (8 h) and once per day (24 h) at 160 days (p value = 0.040).

Moreover, live maize weevils from disturbed jars remained similar to the initial populations of maize weevils except when disturbed three times a day (8 h) at 160 days. Disturbing twice a day

(12 h) was not significantly different with undisturbed jars (0 h) at 40 days (p value = 0.203). 42

Though this study did not achieve 100% maize weevil suppression, live maize weevils were reduced by 75%, 95% and 94% with disturbance intervals of 8, 12 and 24 h intervals respectively as compared to the undisturbed jars at 160 days of maize storage. These results showed the potential of disturbance to suppress the multiplication of weevils in stored maize by smallholder farmers.

Table 3.1. Average live maize weevils for stationary jars and 8, 12 and 24 h disturbance intervals from 0 to 160 days of storage.

Disturbance Sampling Time (days) interval (hours) 0 40 80 120 160

Stationary 234±51Aa 2664±1245Ab 7852±158Ac 8361±223Ac 7898±876Ac

8 234±51Aa 822±295Bac 921±44Bac 1090±546Bac 1979±403Bc

12 234±51Ab 1442±443ABb 1268±798Bb N.D 428±288BCb

24 234±51Ab 533±127Bb 712±106Bb 418±293Bb 467±146Cb

Means ± standard deviation not followed by same upper-case letter within columns and means ± standard deviation not followed by same lower case letter within rows are significantly different at the 5% significant level. N.D = not defined of samples from 12 h disturbance interval at 120 days excluded from the general data analysis.

This study did not dissect the kernels to examine the pre-emergent stages or analyze the cuticle of the dead weevils for the effect of disturbance as did Bailey (1969). No physiological damage of weevil appendages was observed with unaided eyes. Almost all the dead weevils had their legs and main body parts intact. In the light of this, may be stressing weevils had a harmful effect on their reproduction cycle. Maize weevils from undisturbed jars were more aggressive with a higher ability to crawl to the top of the jars compared to weevils from disturbed jars.

Bailey (1969) noticed significant suppression of maize weevils from regular disturbance with speeds of very low magnitude. Our results also agree with Joffe (1963), Joffe and Clarke 43

(1963) and Loschiav (1978) that disturbance lowered the oviposition rate of weevils and had a lethal effect on the pre-emergent stages of maize weevils. Quentin et al (1991) also suggested that tumbling may have reduced fecundity of the weevils and that larvae would die from exhaustion of energy trying to bore holes in disturbed seeds.

Moisture Content

Moisture content (MC) increased at all days of storage in the undisturbed jars, gaining 5 percentage points of moisture at 160 days (Table 3.2). MC was not significantly different after

80 days in the undisturbed jars. Moisture is a product of respiration which directly changes by the number of live maize weevils present in stored maize (FAO, 1994). This accounted for the high initial MC (16%) after the infested maize was allowed to go through a complete life cycle.

The MC from disturbed jars was similar at 80, 120 and 160 days of maize storage but significantly different from the undisturbed jars. Among the disturbed jars, 24 h disturbance interval had the lowest MC at around 12% wet basis, below the equilibrium MC of 13.5% wet basis in the growth chamber. This loss in MC was anticipated from the location of the jars disturbed once per day (24 h) in the growth chamber.

The MC of maize disturbed twice a day (12 h) was similar to MC of maize from undisturbed jars at 40 days of maize storage (p value = 0.329). This trend was a result of maize weevils at 12 h disturbance interval which were higher than at other disturbance intervals. The

MC from jars disturbed at 8 and 12 h intervals at 160 days was not significantly different. Unlike disturbing three times a day, live maize weevils in jars disturbed twice a day reduced significantly at 160 days of storage. Therefore, the increase in MC in the jars disturbed twice a day (12 h) at 160 days of storage may not be explained by the scope of this study.

Table 3.2. Average moisture content for stationary jars and 8, 12 and 24 h disturbance intervals from 0 to 160 days of storage.

Disturbance Sampling Time (days) interval 0 40 80 120 160 (hours)

Stationary 16.0±0.7Aa 17.1±1.5Aab 18.7±0.4Aabc 19.2±0.3Abc 21.0±1.0Ac

8 16.0±0.7Aa 13.0±0.8Bb 12.9±0.2Bb 13.5±1.1Bab 14.6±1.1Bab

12 16.0±0.7Aa 15.6±1.1ABCa 13.4±1.4Ba N.D 13.0±0.7Ba

24 16.0±0.7Aa 12.0±0.1BDb 12.0±0.3Bb 12.0±1.1Bb 12.2±1.3Bb

Test Weight

Test weight (TW) in the undisturbed jars decreased significantly by 32.7 lb/bu at 160 days, which was similar to TW at 80 and 120 days of maize storage (Table 3.3). TW at 40 d in the undisturbed jars was significantly different from all other days of maize storage. Increase of weevil infestation on the same quantity of maize increased insect activity feeding on the endosperm of the same kernel which lowered the density of maize. In addition, female adult maize weevils lay eggs in the holes bored into the kernels. The larvae emerge from the egg and feed on the endosperm of the kernel until it exits as an adult leaving the kernel empty with holes

(Ferreira-Castro et al., 2012). This accounted for the lower initial TW (50.2 lb/bu) when the infested maize was allowed to go through one complete weevil life cycle. 45

Table 3.3. Average test weight for stationary jars and 8, 12 and 24 h disturbance intervals from 0 to 160 days of storage.

Disturbance Sampling Time (days) interval 0 40 80 120 160 (hours)

Stationary 50.22±1.1Aa 38.73±4.9Ab 22.97±1.2Ac 22.36±2.0Ac 17.52±1.2Ac

8 50.22±1.1Aa 47.25±2.0Ba 45.9±0.7Ba 43.16±4.3Ba 35.61±0.4Bc

12 50.22±1.1Aa 43.48±3.0Aa 45±4.8Ba N.D 46.53±1.5Ca

24 50.22±1.1Aa 47.92±0.5Ba 47.43±0.8Ba 47.55±3.7Ba 45.8±1.1Ca

The TW in disturbed jars were significantly different from undisturbed jars except for disturbance twice a day at 40 days (p value = 0.295). Disturbing jars twice a day had more live maize weevils compared to other disturbance intervals at 40 d. Furthermore, TW from jars disturbed every 8 h at 160 days was statistically different from other storage days of maize.

Disturbance three times a day had the lowest test weight compared to 12 h and 24 h disturbance intervals after 120 days. This change in TW was caused by consistently higher populations of live maize weevils from jars disturbed three times a day. We noticed that at disturbances twice a day and once a day, TW did not differ significantly except at 40 days.

Broken Corn and Foreign Materials

Broken corn and foreign material (BCFM) increased from 0% to 68% in the undisturbed jars at 160 days (Figure 3.3 and Table 3.4). BCFM from stationary jars remained statistically similar after 80 days of maize storage. This is because live maize weevil populations in the undisturbed jars increased after 40 d and the exponential trend stabilized after 80 d. In this 46 context, maize weevil activity on the endosperm of maize generated BCFM from different life cycle stages of the maize weevils boring through the maize kernels.

Figure 3.3. Broken corn and foreign material (BCFM) in stored maize at different sampling times (days) for three different disturbances intervals (8, 12 and 24 h) versus control except for missing data from 12 h disturbance at 120 days and one replicate at 160 days. Vertical bars indicate standard errors.

Disturbed jars differed significantly with undisturbed jars at 80, 120 and 160 d. Among the disturbed jars, 8 h interval at 160 days was significantly different with other disturbance intervals, and with other days of maize storage except 120 d (p value = 0.658). The initial BCFM was statistically different from BCFM generated by disturbing jars every 8 h both at 120 d (p value = 0.011) and 160 d (p value = <0.001). While BCFM increased from all treatments, 12 h and 24 h disturbance intervals were not significantly different at all days of maize storage.

Table 3.4. Average broken corn and foreign material for stationary jars and 8, 12 and 24 h disturbance intervals from 0 to 160 days of storage.

Disturbance Sampling Time (days) interval 0 40 80 120 160 (hours)

Stationary 0.0±0.0Aa 6.8±4.3Aa 59.7±4.5Ab 69.1±3.0Ac 68.0±3.9Ac

8 0.0±0.0Aa 2.9±1.2Aab 3.3±0.6Bab 8.9±4.3Bbc 13.8±0.5Bc

12 0.0±0.0Aa 5.0±3.1Aa 6.0±2.7Ba N.D 6.1±1.3Ca

24 0.0±0.0Aa 2.3±1.0Aa 3.3±0.5Ba 4.8±3.4Ba 6.8±1.6Ca

Insect Damage

Insect damage (ID) in the undisturbed jars increased from 36.6% to 90.4% at 40 d, then to 100% at 80 d and remained constant (Table 3.5). High initial ID (36.6%) accounts for the infested maize which went through one complete life cycle. The increase in ID in the undisturbed jars followed the exponential growth of maize weevils. The initial ID was statistically different from jars disturbed three times a day (8 h) at 160 d (p value = 0.003) and twice a day at 40 d (p value = 0.001). Moreover, 12 h and 24 h disturbance intervals were significantly different from 8 h disturbance interval at 160 d of disturbance. Disturbing maize once a day had the lowest ID at all days of maize storage.

Table 3.5. Average insect damage for stationary jars and 8, 12 and 24 h disturbance intervals from 0 to 160 days of storage.

Disturbance Sampling Time (days) interval 0 40 80 120 160 (hours)

Stationary 36.6±14.5Aa 90.4±2.5Ab 100±0.0Ab 100±0.0Ab 100±0.0Ab

8 36.6±14.5Aa 67.6±9.9Bac 58.8±6.1Bac 61.9±23.4Aac 86.1±3.0Bc

12 36.6±14.5Aa 89.9±5.9Ab 67±21.3Bab N.D 56.5±0.5Cab

24 36.6±14.5Aa 65.8±3.7Ba 56.9±2.3Ba 52.2±27.5Aa 67.9±7.1Ca

Mold Damage

Initial mold damage (MD) increased from 0.9% to 26.7% at 160 d in the undisturbed jars

(Figure 3.4 and Table 3.6). Initial mold growth occurred from infested maize allowed to go through one complete weevil life cycle. Mold was a result of increased water activity due to respiration from high insect infestation which increased moisture content in the undisturbed jars.

The initial MD in the stationary jars was significantly different with MD both at 120 d (p value =

0.024) and 160 d (p value <0.001) of maize storage. The MD in the undisturbed jars at 160 d was significantly different from MD both at 40 d (p value < 0.001) and 80 d (p value = 0.007). The

MD in the undisturbed jars at 80 d and 120 d of maize storage was statistically similar to MD at

40 d.

Table 3.6. Average mold damage for stationary jars and 8, 12 and 24 h disturbance intervals from 0 to 160 days of storage.

Disturbance Sampling Time (days) interval 0 40 80 120 160 (hours)

Stationary 0.9±1.0Aa 2.9±3.5Aab 8.0±2.9Aab 17.9±12.6Abc 26.7±17.2Ac

8 0.9±1.0Aa 0.1±0.1Aa 0.4±0.4Ba 0.6±0.4Aa 0.1±0.2Ba

12 0.9±1.0Aa 0.0±0.0Aa 0.1±0.1Ba N.D 0.6±0.1ABa

24 0.9±1.0Aa 0.1±0.2Aa 0.3±0.2Ba 0.9±0.5Aa 0.4±0.3Ba

While undisturbed jars had black clumps of moldy maize, none was observed in any of the disturbed jars. The MD from 12 h disturbance interval was similar to undisturbed jars at 160 50 days (p value = 0.064). The MD in the disturbed jars was statistically similar to MD in the undisturbed jars at 40 d but not at 80 d. Disturbing jars maintained MD at or below 0.9% at all days of the experiment. Disturbance reduced the insect population, and therefore respiration and mold growth in stored maize.

Correlations between live maize weevils and moisture content, test weight, broken corn and foreign material, mold damage and insect damage are presented in Table 3.7.

Table 3.7. Correlation between live maize weevils and moisture content, test weight, broken corn and foreign material, mold damage and insect damage of maize in stationary jars and jars disturbed every 8, 12 and 24 h from 0 to 160 days of storage.

Disturbance Intervals Stationary 8 h 12 h 24 h Corr P-Value Corr P-Value Corr P-value Corr P-value MC 0.84 <0.001 0.02 0.93 0.22 0.506 -0.35 0.205 TW -0.97 <0.001 -0.96 <0.001 -0.94 <0.001 -0.64 0.011 BCFM 0.98 <0.001 0.93 <0.001 0.75 0.007 0.44 0.100 MD 0.56 0.030 -0.41 0.13 -0.53 0.093 -0.46 0.088 ID 0.83 <0.001 0.88 <0.001 0.85 <0.001 0.63 0.012 Corr = correlation coefficient, MC = Moisture Content, TW = Test weight, BCFM = broken corn and foreign material, MD = Mold Damage, and ID = Insect Damage. Samples from 12 h disturbance interval at 120 days and one replicate at 160 days were excluded from the data analysis. P-value was determined at the 5% significant level.

Strong correlation was detected with test weight, broken corn and foreign material and insect damage from all treatments. The weak correlation between live maize weevils and BCFM at 24 h disturbance interval was not significant. Increased infestation on the same quantity of maize generates more BCFM, increases insect damage and lowers the test weight of maize. The negative weak correlation of mold damage in the disturbed jars was not significant (P-value >

0.05). A weak correlation with moisture content in the disturbed jars was not significant. There 51 was not sufficient evidence to conclude that a linear relationship existed between live maize weevils and moisture content in the disturbed jars.

Conclusion

This study compared three disturbance time intervals to suppress maize weevils in maize held in plastic jars and disturbed intermittently by rotation. We found that;

1. Disturbing maize effectively reduced live maize weevil populations by 75%, 95%

and 94% for 8, 12 and 24 h intervals, respectively, compared to undisturbed jars

after 160 days.

2. Quality of maize in the disturbed jars was better than that in the undisturbed jars

including higher test weight, lower moisture content and lower broken corn and

foreign material (BCFM) at 160 days of maize storage.

3. Insect damage reached 100% at 80 days while mold damage increased up to

26.7% with black clumps of moldy maize in the undisturbed jars.

4. Disturbance once per day (24 h) was the most effective interval in controlling

weevil populations for a 160-day period of maize storage. 24 h disturbance

interval showed potential as a non-chemical approach to control maize weevil

infestation in maize stored by smallholder farmers.

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Appendix: Raw data of the experiment determining the physical disturbance time interval that best controls maize weevils while maintaining the quality of stored maize.

Table A.1. Raw data of the experiment determining the physical disturbance time interval that best controls maize weevils while maintaining the quality of stored maize.

Disturbance Sampling Interval (h) Time (days) LW MC (%) TW (Ib/bu) BCFM (%) ID (%) MD (%) 0 0 236 15.6 51.26 0 20.5 0.2 0 0 283 16.8 49.07 0 40.7 2.1 0 0 182 15.5 50.33 0 48.7 0.5 8 0 236 15.6 51.26 0 20.5 0.2 8 0 283 16.8 49.07 0 40.7 2.1 8 0 182 15.5 50.33 0 48.7 0.5 12 0 236 15.6 51.26 0 20.5 0.2 12 0 283 16.8 49.07 0 40.7 2.1 12 0 182 15.5 50.33 0 48.7 0.5 24 0 236 15.6 51.26 0 20.5 0.2 24 0 283 16.8 49.07 0 40.7 2.1 24 0 182 15.5 50.33 0 48.7 0.5 0 40 1306 15.7 43.56 2.8 89.9 0 0 40 3751 18.7 33.76 11.4 88.2 6.8 54

Table A.1. Continued.

Disturbance Sampling Interval (h) Time (days) LW MC (%) TW (Ib/bu) BCFM (%) ID (%) MD (%) 0 40 2934 16.9 38.86 6.2 93.1 1.8 8 40 505 12.2 49.47 1.7 56.2 0 8 40 875 12.9 46.7 4 72.7 0.2 8 40 1087 13.8 45.57 3.1 73.9 0 12 40 934 14.3 46.89 1.6 83.2 0 12 40 1743 15.9 41.91 7.6 92.3 0 12 40 1650 16.5 41.64 5.8 94.2 0 24 40 670 11.9 47.48 3.4 69.4 0 24 40 510 11.9 47.87 1.6 62.1 0.3 24 40 420 12.1 48.41 1.8 65.9 0 0 80 7761 18.4 21.7 61.4 100 9 0 80 7761 19.1 24 54.6 100 4.7 0 80 8034 18.6 23.2 63 100 10.2 8 80 933 12.7 45.6 4 59.9 0 8 80 873 12.8 45.4 3 52.2 0.4 8 80 958 13.1 46.7 2.8 64.2 0.7 12 80 2179 15 39.8 8.9 87.9 0 12 80 692 12.3 49.3 3.5 45.3 0.2 12 80 932 13 45.9 5.7 67.9 0.2 24 80 638 11.6 48.3 2.7 54.3 0.5 24 80 665 12.2 47.2 3.6 57.9 0.4 24 80 834 12.1 46.8 3.5 58.6 0.1 0 120 8306 18.9 24.61 68.6 100 6 0 120 8606 19.5 21.81 66.4 100 16.5 0 120 8170 19.3 20.67 72.3 100 31.1 8 120 482 12.4 48.01 4 36.2 1 8 120 1249 13.5 41.74 10.9 67.8 0.6 8 120 1539 14.5 39.73 11.9 81.8 0.3 24 120 437 12.5 47.58 4.9 58.7 0.4 24 120 701 12.8 43.81 8.2 75.9 0.8 24 120 117 10.8 51.27 1.4 22 1.4 0 160 8606 19.8 17.19 72.2 100 17.5 0 160 6919 21.3 16.56 64.6 100 46.6 0 160 8170 21.8 18.82 67.3 100 16.1 8 160 2244 14.7 35.13 14.2 86 0.3 8 160 1515 13.5 36.01 13.3 83.1 0 8 160 2179 15.6 35.68 13.8 89.1 0 12 160 225 12.5 47.61 5.2 56.8 0.5 12 160 632 13.5 45.46 7 56.1 0.6 55

Table A.1. Continued.

Disturbance Sampling Interval (h) Time (days) LW MC (%) TW (Ib/bu) BCFM (%) ID (%) MD (%) 24 160 410 11.5 45.52 8.2 75 0.8 24 160 633 13.7 46.97 5.1 60.8 0.2 24 160 358 11.4 44.92 7.2 67.8 0.3

Table A.2. ANOVA table for depend variable live maize weevils.

Source DF Sum of Squares Mean Square F Value Pr > F Model 18 410828354.1 22823797.4 106.64 <.0001 Error 37 7919096.5 214029.6 Corrected Total 55 418747450.6

Table A.3. Type III SS table for depend variable live maize weevils.

Source DF Type III SS Mean Square F Value Pr > F interval 3 231269084.8 77089694.9 360.18 <.0001 time 4 60513632.7 15128408.2 70.68 <.0001 interval*time 11 110060721.1 10005520.1 46.75 <.0001

Table A.4. ANOVA table for depend variable moisture content.

Source DF Sum of Squares Mean Square F Value Pr > F Model 18 381.1009524 21.1722751 26.01 <.0001 Error 37 30.1133333 0.8138739 Corrected Total 55 411.2142857

Table A.5. Type III SS table for depend variable moisture content.

Source DF Type III SS Mean Square F Value Pr > F interval 3 262.2681270 87.4227090 107.42 <.0001 time 4 22.9394048 5.7348512 7.05 0.0003 interval*time 11 96.1069350 8.7369941 10.74 <.0001

Table A.6. ANOVA table for depend variable test weight.

Source DF Sum of Squares Mean Square F Value Pr > F Model 18 5542.759121 307.931062 52.76 <.0001 Error 37 215.933250 5.836034 Corrected Total 55 5758.692371

Table A.7. Type III SS table for depend variable test weight.

Source DF Type III SS Mean Square F Value Pr > F interval 3 2742.786252 914.262084 156.66 <.0001 time 4 1315.066400 328.766600 56.33 <.0001 interval*time 11 1293.824953 117.620450 20.15 <.0001

Table A.8. ANOVA table for depend variable broken corn and foreign material.

Source DF Sum of Squares Mean Square F Value Pr > F Model 18 29141.97524 1618.99862 258.66 <.0001 Error 37 231.59333 6.25928 Corrected Total 55 29373.56857

Table A.9. Type III SS table for depend variable broken corn and foreign material.

Source DF Type III SS Mean Square F Value Pr > F interval 3 13841.80825 4613.93608 737.14 <.0001 time 4 5666.66496 1416.66624 226.33 <.0001 interval*time 11 8681.58014 789.23456 126.09 <.0001

Table A.10. ANOVA table for depend variable insect damage.

Source DF Sum of Squares Mean Square F Value Pr > F Model 18 26644.26548 1480.23697 9.59 <.0001 Error 37 5712.99167 154.40518 Corrected Total 55 32357.25714 57

Table A.11. Type III SS table for depend variable insect damage.

DF Type III SS Mean Square F Value Pr > F Source interval 3 7411.42484 2470.47495 16.00 <.0001 time 4 14028.62733 3507.15683 22.71 <.0001 interval*time 11 4643.46150 422.13286 2.73 0.0108

Table A.12. ANOVA table for depend variable mold damage.

Source DF Sum of Squares Mean Square F Value Pr > F Model 18 2703.534821 150.196379 5.78 <.0001 Error 37 962.185000 26.005000 Corrected Total 55 3665.719821

Table A.13. Type III SS table for depend variable mold damage.

Source DF Type III SS Mean Square F Value Pr > F interval 3 1243.653032 414.551011 15.94 <.0001 time 4 341.901071 85.475268 3.29 0.0211 interval*time 11 1031.536374 93.776034 3.61 0.0016

CHAPTER 4. MECHANICAL STIRRING OF MAIZE STORED IN ON-FARM STEEL BINS TO CONTROL MAIZE WEEVILS

M. Sserunjogi1; C.J. Bern1; T.J. Brumm1; D.E Maier1; T.W Phillips2 1Department of Agricultural and Biosystems Engineering, Iowa State University 2Department of Entomology, Kansas State University

Modified from a manuscript to be submitted to Journal of Stored Product Research

Abstract

Physical disturbance can be an effective non-chemical approach of suppressing insect pests of stored grain. Previous laboratory studies with mechanical stirring machines using a 12 h disturbance interval achieved 100% control both for the maize weevils in maize and lesser grain borer in wheat after a storage period of 40 days. This study investigated the effectiveness of mechanical stirring infested maize in a 9.8 m diameter farm steel bin holding 127 Mg of maize to suppress maize weevils. The control bin (unstirred) had a diameter of 7.3 m holding 102 Mg of maize. Both bins were loaded with maize at 13% moisture to a depth of 2.7 m.

The maize in both bins was infested with maize weevils at a commercial tolerance rate of

2 weevils/kg of maize. Probe traps placed at five locations in each bin monitored the presence and density of any insect species prior to stirring. Maize samples were collected at 0, 0.9, 1.8 and

2.7 m depth with a vacuum-probe sampler, before stirring and at 10, 20, 30 and 40 days of continuous stirring machine operation.

While stirring achieved 100% control of live maize weevils per kg maize, the population of live weevils in the unstirred bin was increasing after 40 days of storage. Although the quality of maize in both bins changed at different depths and storage times, the maize in the stirred bin had a higher test weight (57.0 lb./bu. to 59.7 lb./bu.), lower insect damage (0.1% to 0.9%), and 59 higher allowable storage time (AST) (124 days to > 249 days). Moisture content and mold damage of maize in the unstirred bin increased up to 26.4% points and 0.6% to 3.2% respectively after 40 days of maize storage.

Average BCFM on the floor of the emptied bin with stirring machines was 6.5 times more than in the emptied unstirred bin. The predicted packing factors were 1.2 and 1.4 in the sweepings from the stirred and unstirred bins, respectively, during the period of warming the maize with heated air.

Keywords: Physical disturbance, probe traps, moisture content, test weight, broken corn and foreign material, insect damage, mold damage.

Introduction

Maize is a cereal crop grown for human consumption and for other economic purposes.

In the global nutrition, maize supplies daily calories and proteins for more than 200 million people worldwide (Nuss and Tanumihardjo, 2010). Despite the significance of maize, losses of stored maize from insect pests can reach 30% mainly in the tropics (Boxall, 1991; Rembold et al., 2011; Tefera et al., 2016), which threatens the food security, safety and economic value of maize (Gitonga et al., 2013). Maize weevil (Sitophilus zeamais) a major pest of stored maize has been detected in 112 countries worldwide (López-Castillo et al., 2018).

Infestation starts from the field with flying adults of S. zeamais attacking standing crops

(Giles, 1969) and continues when life cycle stages are conveyed with harvested maize into storage bins. Grain residues and dust on the walls of the farm steel grain bin and ledges may favor S. zeamais survival and multiplication (Hagstrum et al., 1999). Given suitable environmental conditions, the increase in populations of S. zeamais is 10 to 15 fold within two months (Bbosa et al., 2014; Bell, 2014). Maize weevil activity in the grain bin generates spots of elevated temperature and moisture facilitating mold growth (Sone, 2000; Sone, 2001). 60

Global food and consumable product standards emphasize eliminating maize weevils from the food supply chain. For decades, however, chemical treatment of farm steel grain bins has been the global norm to control maize weevils. Insecticide application is recommended before loading bins with maize to kill any persisting life stages of maize weevils along the bin walls, eaves and perforated floor (Jones et al., 2012). Fumigation may be applicable during storage when insects are detected in the grain bin (Phillips et al., 2012). Insecticides and fumigants usage has raised concerns with the environment, consumer preference, workers’ safety and resistance of S. zeamais from the active ingredient in the chemicals (Tilley et al., 2007).

There is a need to explore other alternatives to chemical treatment of stored maize.

Physical disturbance has proven to be effective in the past and now gaining interest as a non-chemical approach to control maize weevils (Bbosa, 2014; Suleiman et al., 2016). Although previous research on manual disturbance experiments targeted small holder farmers, the need for similar approaches on a large scale or for advanced and automated storage systems is now present. In the grain elevator experiment by Joffe (1963), turning the same maize between grain storage bins biweekly for 8.5 months had a direct and deleterious effect on the adult and premature stages of the primary and secondary feeders.

Two other experiments tested the Sukup Stirway stirring machines on maize infested with maize weevils (Rau, in preparation for publication) and wheat infested with lesser grain borer

(Rhyzopertha dominica) (Friedmann, in preparation for publication). Stirring was done every 12 h by automated augers programmed to move through one length of the container, 76 cm in 20 min. After 40 d of storage, stirring achieved 100% control both for R.dominica and S. zeamais.

Farm steel grain bins can have stirring augers suspended from the bin roof and sidewall with one or more vertical augers extending through the grain mass nearly to the bin drying floor. 61

The augers rotate continuously through the grain mass lifting maize kernels from bottom to top of the bin. Mixing wet and dry maize reduces the moisture gradient at different layers of the grain mass (Jones et al., 2012). Stirring to mix maize with insects has not been explored beyond uniform in-bin drying. The objective of this research was to determine effects of stirring weevil infested maize in a farm sized bin on the population of maize weevils (S. zeamais) and quality of the maize.

Materials and Methods

Steel Grain Bins

This research was conducted between mid-summer and late-fall (July and November,

2019) at Agricultural Engineering and Agronomy Research Farm, Iowa State University, Ames,

Iowa. A steel grain bin with a diameter 9.8 m (254 Mg of maize at full capacity), height 4.9 m with a stirring machine was the stirred bin. A steel grain bin with a diameter 7.3 m (178 Mg of maize at full capacity), height 5 m with no stirring machine was the unstirred bin. The heights were measured from the drying concrete floor to the eave of the bin.

The stirring machine in the stirred bin was a Sukup fastir plus triple auger with a mechanical reversing drive (Sukup Manufacturing Company, Sheffield, Iowa). The stirring machine had a stationary carriage with the outside drive moving along the wall of the bin. Twin down augers fastened together with an arm bar moved forward and reversed along the stirring tube. The augers ran continuously and stopped momentarily during sample collection.

The fan on the stirred bin was Sukup axial fan (power: 5.2 kW, airflow of 0.0003 m3/s) with a burner using liquid petroleum gas (Sukup manufacturing company, Sheffield, Iowa). The unstirred bin had an axial fan (power: 5.2 kW, airflow: 0.0015 m3/s) with a heater (Brock Grain

Systems, Milford, IN) using liquid petroleum gas. Air in the bins was supplied through the perforated floor, 0.3 m above the concrete base. Static pressure in the plenum of the bins was 62 measured by 0.127 m of water manometer and airflows computed from online website of

University of Minnesota fan selection for grain bins (bbefans.cfans.umn.edu). The fan size and airflow were the basis for grain aeration with recommendations from the MidWest Plan Service

(MWPS) handbook.

Warming with ambient air between August and September achieved temperatures up to

300C suitable for weevil activity and multiplication in the grain bin. Warming in late October used burners but 300C was never achieved. Humidity and temperature meter (VAISALA HM70), and temperature and moisture cable (OPI Blue) probed in unstirred and stirred bins respectively monitored the changes in temperature and humidity for decisions on aeration. Carbon dioxide concentrations from insect activity were monitored by CO2 sensor (Telaire T7001). All measurement instruments were removed from the grain mass prior to stirring.

Maize and Maize Weevils

Maize was a mixture of several varieties combine harvested in October 2018 and stored in the bin having stirring augers. Initially, 101.6 Mg of maize was unloaded and conveyed to the bin without stirring augers up to a height of 2.7 m leaving 127 Mg of maize at a height of 2.8 m above the perforated floor of the stirred bin. The United States Department of Agriculture

(USDA) commercial infestation tolerance rate of 2 live weevils per kg (USDA, GIPSA and

FGIS, 2013) was the benchmark for calculating the targeted populations of maize weevils. The stirred and unstirred bins needed approximately 255,000 and 204,000 weevils respectively.

Weevils were raised in 1 L glass jars and 19 L buckets covered with 3.2 mm screens for aeration and maintained at 270C and 65% RH. Glass jars and buckets were assumed to hold 500 and 3000 live maize weevils after 60 days at an initial rate of 25 live weevils per kg maize

(Bbosa et al., 2014). Colonies of S. zeamais were raised both from the Department of 63

Agricultural and Biosystems Engineering, Iowa State University, Ames, Iowa and Department of

Entomology, Kansas State University, Manhattan, Kansas.

During early August to late September, colonies were gently released across the top of the grain mass and the locations flagged. Early infestation intended to achieve an exponential increase in population of weevils in the bins. A ratio of 5:4 jars or buckets was used to partition weevils in the stirred and unstirred bin to account for the difference in bin diameters and capacity.

Insect Probe Traps

Unbaited cylindrical plastic WB probe II traps (Trécé Inc. Adair, OK) 444.5 mm long, 38 mm internal diameter and 6.4 mm round holes were used to monitor the mobile adult stages of insects in the bins. The perforated region of the traps was inserted completely below the maize grain mass surface as described by Toews and Christian (2012) at the bin center and four cardinal directions 1 m away from the bin wall (Figure 4.1). T1 to T5 and C1 to C5 show locations of probe traps in the stirred and unstirred bins respectively.

Insect trapping simultaneously started with bin infestation with maize weevils. Traps were left in the grain mass and monitored weekly for changes in insect population before stirring.

After each 7-d period, the probes were removed from the grain mass and the contents (insects, debris and BCFM) in each trap emptied into labelled containers. Maize weevils found in the probe traps were returned to the same bin because the goal of setting traps was to detect other insect species infesting the bins. Trapped insects were frozen for 24 h in a chamber maintained at

-200C to kill adult insects which then were identified and counted to account for insect densities and species in each bin. Probe traps were removed from the bins prior to stirring. 64

Figure 4.1. Schematic of the location of probe traps and maize sampling in the stirred (T1 to T5) and unstirred bins (C1 to C5).

Experimental Design

The experiment followed a 3 factorial design with 2 bins (stirred and unstirred)

(Figure 4.1), 4 sampling depths (0, 0.9, 1.8 and 2.7 m) and 5 sampling days (0, 10, 20, 30 and

40). Samples were drawn from locations T1 to T5 in the stirred bin and C1 to C5 in the unstirred bin. A total of 20 samples were drawn from each bin on each sampling day. Representative samples of maize and weevils were vacuum probed with a Vac-A-Sample Pneumatic Sampler

(Seedburo Equipment Co.), emptied in labelled ziplock bags and carried to the lab for data collection.

Response Measurement

Samples were analyzed for live weevils/kg of maize, presence of other insect species and maize quality which included moisture content (MC), test weight (TW), broken corn and foreign material (BCFM), insect damage (ID) and mold damage (MD). Data collection from the samples followed the protocol in the grain inspection handbook (USDA, 2013a). Different insect species were manually sieved from the maize through 12/64 in (4.8 mm) sieves and collected on the steel pan then counted. The criteria of separating inactive insects from those that are completely dead followed the description by Yakubu et al., (2011). 65

During unloading of the unstirred bin, loads of maize were collected at different time intervals to quantify the BCFM in the grain layers. The stirred bin was assumed to concentrate

BCFM at the bin bottom. Samples were collected from the sweepings in both bins after the last load out in the unstirred bin and after the sweep auger ended in the stirred bin. Sampling was done from each quadrant in cardinal directions of North East (NE), North West (NW), South

East (SE) and South West (SW). BCFM was determined following the protocol in the grain inspection handbook (USDA, 2013a).

Statistical Analysis

Two-way ANOVA was performed with Statistical Analysis System (SAS) software (SAS

9.4 for windows x64 Based Systems; Copyright @ 2002-2012, SAS Institute Inc., Cary, NC,

USA). A general linear model (PROC GLM) was used to determine the mean difference between the stirred and unstirred bins at the 5% probability level. Least square means using Type III sum of square errors with Tukey’s adjustment for pair wise comparison generated the correct p- values.

Plots of the data were generated with R studio (Version 1.1.442 -@ 2009 –2018 R studio,

Inc.). Correlations between live maize weevils per kg and moisture content, test weight, broken corn and foreign material, mold damage and insect damage were performed in R statistical package at P < 0.05 level.

Results and Discussion

Live Maize Weevils

Initially, live maize weevils per kg in both bins were not significantly different at all depth of maize (Figure 4.2, Table 4.1). After 10 d, live weevils were found only at 0.9 m and 2.7 m in the stirred bin while the unstirred bin had live weevils at all depths of maize. The increase in live weevils at 2.7 m in the stirred bin can be explained by the augers turning maize and 66 relocating live weevils to the bottom of the grain mass. Rotation of the augers might also explain the absence of live weevils in the stirred bin at 1.8 m after 20 d.

No live weevils were found beyond 0.9 m of the grain depth in the stirred bin at 30 d.

There is a possibility that running augers might have injured and killed live maize weevils.

The oviposition rate of female maize weevils feeding on maize starts after 24 h (Throne, 1994;

Mathias et al., 2015). Disturbing maize might have disrupted the fecundity of female maize weevils with fewer eggs laid in the kernels. The difference in live maize weevils per kg between the stirred and unstirred bin was significantly different both at the grain surface, 10 d (p value =

0.024, estimate = -4.12) and at 1.8 m, 40 d (p value < 0.001, estimate = -6.74).

Figure 4.2. Live maize weevils per kg maize in samples collected at four grain depths (0 m = surface layer; 2.7 m = bottom layer) in the stirred and unstirred bins at four time intervals during the 40-day storage period. Vertical bars indicate standard errors.

The decrease in live maize weevils in the unstirred bin at the grain surface after 20 d and

40 d can be attributed to the cool environment around the surface of the grain mass with ambient air temperatures dropping below 170C in October (Table 4.4). FAO (1994) states that stored grain insect pests like maize weevils cannot infest maize at temperatures below 170C. Live maize 67 weevil population increased at the grain surface and at 1.8 m depth of maize after warming of maize with heated air between 20 d (170C) and 30 d (230C). The collapse of live weevil populations at 0.9 m might be a result of weevils that were missed from sampling at that depth.

Table 4.1. Average count of live maize weevils per kg maize in the stirred and unstirred bins at 0 to 40 days of storage.

Bin depth Sampling Time (d) (m) 0 10 20 30 40 stirred 0 0.49±0.5Aa 0.00±0.0A a 0.13±0.3Aa 0.10±0.2Aa 0.00±0.0Aa stirred 0.9 0.13±0.3Aa 0.21±0.5Aa 0.23±0.3Aa 0.18±0.4Aa 0.00±0.0Aa stirred 1.8 0.37±0.6Aa 0.00±0.0Aa 0.00±0.0Aa 0.00±0.0Aa 0.00±0.0Aa stirred 2.7 0.98±0.8Aa 3.29±2.0Aa 2.01±1.9ABa 0.00±0.0Aa 0.09±0.2Aa unstirred 0 2.29±2.2Aa 4.13±8.2Aa 1.33±1.4ABa 1.99±2.6Aa 0.81±0.7Aa unstirred 0.9 1.16±1.6Aa 0.83±0.7Aa 3.04±2.5Ba 1.15±1.2Aa 1.69±1.9Aa unstirred 1.8 0.35±0.5Aa 3.22±3.1Aa 0.74±0.3ABa 1.89±1.0Aa 6.75±14.5Aa unstirred 2.7 0.87±0.8Aa 1.76±1.4Aa 0.46±0.8Aa 0.00±0.0Aa 0.30±0.5Aa Means ± standard deviation not followed by same upper case letter within columns and means ± standard deviation not followed by same lower case letter within rows are significantly different at the 5% significant level.

Temperatures beyond 300C of the warm front supplied from the plenum dried maize at the bottom of the bins to moisture below 8% points. Weevils moved as a function of temperature away from dry maize to depths towards the surface of the grain mass. In the situation of no warming front at 40 d, temperatures around 210C in the unstirred bin (Table 4.4) favored flourishing of live weevils at all depths of maize. Large variability in the populations of live maize weevils in the unstirred bin suggests that samples collected might not have been representative of the entire bin.

However, the effect of stirring to suppress maize weevils was observed starting at 10 d of the experiment prior to warming of maize. Maize weevils in the stirred bin were found at specific 68 depths both at 10 d and 20 d suggesting the efficacy of stirring. Our results show that stirring achieved 100% control of live maize weevils by 40 d of maize storage.

Other Insect Species

Table 4.2 shows counts of insect species other than maize weevils found in the probe traps and vacuum probed samples. The majority of the insects were beetles trapped in the unstirred bin which included the hairy fungus (Typhaea stercorea) and foreign grain beetles

(Ahasuerus advena). It is likely that maize conveyed from the stirred bin to the unstirred bin carried the initial beetle populations. According to FAO (1994), drop in the ambient temperatures below 200C might have reduced the activity and reproduction of beetles in the unstirred bin.

Table 4.2. Counts of other insect species apart from maize weevils in the probe traps after 8 weeks of bin infestation and vacuum probed samples after 40 days of storage both in the stirred and unstirred bins.

Probe traps Vacuum probed samples

Insect Species Stirred bin Unstirred bin Stirred bin Unstirred bin hairy fungus beetle 7278 26525 3 95 foreign grain beetle 1154 3535 74 1343 larger black flour beetle 56 268 3 45 flat grain beetle 15 222 5 127 Stored grain fungus beetle 28 178 0 6 rove beetle 2 117 0 1 red flour beetle 22 97 0 15 minute mould beetle (Latridius spp.) 11 64 0 2 dried fruit beetle 11 47 0 1 parasitoid wasp 8 23 1 163 antlike flower beetle 9 16 0 0

Table 4.2. Continued.

Probe traps Vacuum probed samples

Insect Species Stirred bin Unstirred bin Stirred bin Unstirred bin cereal bug 3 11 0 0 mould/plaster beetle 1 11 0 0 clown beetles 0 2 0 0 black fungus beetle 1 2 0 0 minute mould beetle (Cartodere spp.) 0 1 0 2 lesser grain borer 1 1 0 0 spring tail 0 1 0 0 booklice 2 0 0 0

Higher populations of parasitoid wasps (Hymenoptera) in the unstirred bin might also account for the reduction in beetles. Wasp larvae develop on the host tissue which then kill their host during pupation or as they emerge as mature adult wasps. Parasitoid wasps have been identified as a potential biological method for suppressing beetles in stored grain (Rees, 2004).

Based on probe trap counts, mechanical stirring achieved a substantial 2426 times and 16 times reduction both for hairy fungus and foreign grain beetle populations respectively after 40 d.

Moisture Content

The variation in moisture content (MC) in the stirred bin was lower than in the unstirred bin. MC in the unstirred bin at the grain surface was highest (26.4% points) after 40 days and significantly different with other days of maize storage (Table 4.3). High MC at the grain surface in the unstirred bin can be explained by either a drop in ambient air temperatures below 170C with sweating of maize at the bin wall or moisture as a product of respiration from insect activity

(FAO, 1994, Sone, 2001). 70

Though MC in each bin remained similar between 0.9 and 1.8 m depth of maize, there was a negative change in points of moisture between the stirred and unstirred bins (Table 4.4).

Bern et al. (1982) stated that unlike unstirred maize, stirring loosens caked grain getting rid of moist spots and allows air flow in the grain mass to bring maize to a uniform MC.

Table 4.3. Average moisture content of maize in the stirred and unstirred bins at 0 to 40 days of storage.

Bin depth (ft) Sampling Time (d) 0 10 20 30 40 stirred 0 14.9±0.2Aa 13.3±0.2Aab 13.2±0.1Aab 13.0±0.5Ab 12.8±0.3Ab stirred 0.9 13.9±0.3Ba 13.2±0.1ABa 13.2±0.1Aa 12.8±0.4Aa 12.6±0.5Aa stirred 1.8 12.8±0.1Ca 13.3±0.1Aa 13.2±0.2Aa 12.9±0.4Aa 12.7±0.5Aa stirred 2.7 12.5±0.2Ca 12.5±0.2Da 12.4±0.2Ba 7.8±1.6Bb 6.9±0.4Bb unstirred 0 16.9±0.5Da 19.2±0.2Eb 17.9±0.7Cab 20.0±1.2Cb 26.4±2.9Cc unstirred 0.9 15.1±0.1Aa 15.0±0.1Fa 14.6±0.2Da 14.9±0.2Da 14.5±0.1Aa unstirred 1.8 15.0±0.3Aa 14.8±0.1Fa 14.3±0.1Da 14.4±0.2ADa 13.5±0.9Aa unstirred 2.7 13.8±0.4Ba 13.6±0.3ACa 13.1±0.4Aa 7.6±1.3Bb 6.7±0.9Bb Means ± standard deviation not followed by same upper case letter within columns and means ± standard deviation not followed by same lower case letter within rows are significantly different at the 5% significant level.

The MC at 2.7 m depth of maize at 30 and 40 days reduced significantly between 6.7% and 7.8% points after warming maize in both bins. Though average temperature of maize in both bins was around 230C after 30 d, maize at the bottom of the bin was not cooled to regain moisture (Table 4.3). The loss in MC at 2.7 m in the stirred bin is a result of the stirring augers being too short to reach and disturb the bottom layer of the grain mass. This created similar conditions in the both bins as a result of grain temperature and moisture content equilibrating with the prevailing air conditions in the plenum. Fans connected to each plenum remained unsealed allowing air exchange between the outside and insider of the bin as a function of ambient conditions and wind. 71

Table 4.4 shows that the allowable storage time (AST) without spoilage of maize was greater in the stirred bin (124 days to > 249 days) as compared to the unstirred bin (32 days to

249 days).

Table 4.4. Average temperature and moisture content, allowable storage time, and change in points of moisture between the stirred and unstirred bins during 40 days of maize storage.

Time Temperature (0C) MC (%) Allowable Storage Time Diff (%) (days) (days) stirred Unstirred stirred Unstirred stirred Unstirred bin bin bin bin bin bin 0 31 31 13.5 15.2 > 55 55 -1.7 10 22 25 13.1 15.7 > 139 <60 -2.6 20 17 17 13.0 15.0 > 249 249 -2.0 *30 23 22 12.9 16.4 > 124 75 -3.5 *40 21 21 12.7 18.1 > 157 32 -5.4 MC = moisture content, Diff. = change in percentage points of moisture between the stirred and unstirred bins. * Excluded MC at 2.7 m depth of maize in both bins because warming resulted in moisture loss of maize.

Test Weight

Test weight (TW) remained similar in each bin at each depth of maize and sampling time except in the unstirred bin at the top surface of the grain mass where TW was similar at 0 d with

20 d and at 10 d with 30 d (Table 4.5). While TW at the grain surface in the unstirred bin reduced by 13% at 40 d, it was significantly different from maize samples at other depths. This trend was likely a result of higher MC at the grain surface. As a rule of thumb, test weight of maize reduces when its moisture increases (FAO, 1994). 72

Table 4.5. Average test weight of maize in the stirred and unstirred bins at 0 to 40 days of storage.

Bin depth (ft) Sampling Time (d)

0 10 20 30 40 stirred 0 57.6±0.4Aa 57.7±0.5Aa 57.6±0.4Aa 57.3±0.5Aa 57.0±0.1Aa stirred 0.9 56.9±0.7ABa 58.3±0.4ABa 58.1±0.6ABa 57.8±0.4ABa 57.4±0.2ABa stirred 1.8 58.8±0.4Ca 58.0±0.4Aa 57.8±0.3ABCa 57.6±0.4Aa 57.4±0.3Aa stirred 2.7 59.3±0.6Ca 59.7±0.4Ca 59.2±0.5Da 59.4±0.4Ba 58.9±1.4Ba unstirred 0 55.0±0.7Da 51.8±0.6Db 54.3±0.8Ea 52.2±2.1Cb 47.9±1.4Cc unstirred 0.9 56.5±0.6Ba 56.8±1.2Aa 56.6±0.4Aa 56.5±0.4Aa 56.6±0.3Aa unstirred 1.8 56.5±0.2ABa 56.8±0.4Aa 57.0±0.7ACa 57.0±0.3Aa 57.0±0.6Aa unstirred 2.7 57.0±0.3ABa 57.2±0.4ABa 57.4±0.3ABCa 57.4±0.4Aa 57.7±0.6ABa Means ± standard deviation not followed by same upper case letter within columns and means ± standard deviation not followed by same lower case letter within rows are significantly different at the 5% significant level.

Infested maize added to the top layer of the grain mass at the time of infesting the bin might have contributed to the lower TW in the top layer of the unstirred bin. Conversely, reduction in TW was not observed at 0.9 and 1.8 m depths of maize in the unstirred bin which had the majority of live maize weevils. This suggests that perhaps maize weevils relocated to warmer depths below the grain surface after infesting maize from the top layer. Mixing of maize top to bottom by the mechanical augers resulted in larger differences in TW between the bins

(Table 4.6). Average TW was higher in maize sampled from the stirred versus unstirred bin at all sampling days.

Table 4.6. Average test weight, insect damage and mold damage, and percent differences for maize samples taken from the stirred versus unstirred bins during storage.

Time Test weight Insect Damage Mold Damage (days) Stirred Unstirred Diff Stirred Unstirred Diff Stirred Unstirred Diff bin bin (Ib/bu) bin bin (%) bin bin (%) 0 58.1 56.3 1.8 0.1 0.7 -0.6 0.7 1.2 -0.5 10 58.4 55.7 2.7 0.3 0.7 -0.4 1.0 1.4 -0.4 20 58.2 56.3 1.9 0.3 0.8 -0.5 1.0 1.0 0.0 30 58.1 55.8 2.3 0.2 0.8 -0.6 0.9 0.9 0.0 40 57.7 54.8 2.9 0.5 1.5 -1.0 1.2 1.6 -0.4 TW = test weight, ID = insect damage, MD = mold damage and Diff = difference between average values of the stirred and unstirred bins.

Broken Corn and Foreign Material

Broken corn and foreign material (BCFM) was not significantly different at any depth in either bin during maize storage (Figure 4.3). The highest BCFM (22.7%) was found in the stirred bin at 2.7 m after 10 d (Table 4.7). BCFM was significantly different at 2.7 m and 10 d (p value

= 0.015, estimate = 16%) between the two bins. Stirring augers concentrated BCFM at the bottom of the bin, a layer where mechanical stirrers could not disturb maize. BCFM was present in each layer sampled from the unstirred bin and initially which was representative of a portion of maize transferred from the stirred bin. The increase in live maize weevils in the unstirred bin at 0.9 and 1.8 m depth of maize likely caused the observed increases in BCFM.

The reduction in BCFM in the stirred bin at 40 d is perplexing and may be a result of sampling error perhaps due to repeated sampling from the same location. A decreasing trend of

BCFM was observed over time in the unstirred bin which too may be due to the same sampling error. 74

Figure 4.3. Broken corn and foreign material (BCFM) in samples collected at four grain depths (0 m = surface layer; 2.7 m = bottom layer) in the stirred and unstirred bins at four time intervals during the 40-day storage period. Vertical bars indicate standard errors.

Table 4.7. Average broken corn and foreign material of maize in the stirred and unstirred bins at 0 to 40 days of storage.

Bin depth Sampling Time (d) (ft) 0 10 20 30 40 stirred 0 0.0±0.0Aa 0.8±0.2Aa 0.5±0.5Aa 0.7±0.9Aa 0.1±0.2Aa stirred 0.9 0.2±0.1Aa 15.6±29.8Aa 1.7±1.9Aa 9.4±18.7Aa 0.1±0.0Aa stirred 1.8 0.3±0.3Aa 5.8±11.1Aa 1.2±0.5Aa 1.5±1.2Aa 0.1±0.1Aa stirred 2.7 0.3±0.2Aa 22.7±40.5Aa 11.2±7.9Aa 16.8±8.2Aa 0.5±0.2Aa unstirred 0 0.4±0.3Aa 5.0±2.4Aa 3.7±2.1Aa 3.2±2.2Aa 0.1±0.0Aa unstirred 0.9 0.6±0.5Aa 12.3±18.4Aa 8.6±9.9Aa 7.8±8.6Aa 0.6±0.9Aa unstirred 1.8 0.6±0.7Aa 11.8±16.4Aa 6.6±6.5Aa 5.9±4.7Aa 4.4±9.3Aa unstirred 2.7 0.5±0.6Aa 6.7±7.5Aa 7.2±6.9Aa 7.4±6.2Aa 0.4±0.3Aa Means ± standard deviation not followed by same upper case letter within columns and means ± standard deviation not followed by same lower case letter within rows are significantly different at the 5% significant level.

Some amount of BCFM was likely consumed by the insects but whether they consumed the difference in the measured amounts is speculative. However, the trend of BCFM in the unstirred 75 bin followed the change in populations of live maize weevil. Our experiment did not last long enough to allow for multiple life cycles to cause significant BCFM from weevil activity.

Table 4.8 shows average BCFM from samples (loads 1 to 6) taken during unloading of the unstirred bin, and from sampling the sweepings in both bins after unloading with the sweep augers ended. BCFM in the unstirred bin ranged from 0.6% to 3.0% compared to BCFM from

5.9% to 10.9% in the stirred bin. BCFM on the floor of the emptied stirring bin was 6.5 times more than on the floor of the emptied unstirred bin. Accumulation of BCFM in the bottom layer of the grain mass may increase resistance to airflow and thus decrease airflow rate (Grama et al.,

1984) which proportionally increases the time to move a cooling or warming front through the grain. However, stirring machines reduce the static pressure drop through the depth of a grain mass which greatly aids in drying and cooling of the grain mass (Bern et al., 1982).

Predicted packing factors of 1.2 and 1.4 for the sweepings in the stirred and unstirred bins, respectively, were calculated as described by Grama et al. (1984). The calculated packing factors were less than 1.5, the common value assumed by industries when grain conditions are unknown (Bern et al, 2013).

Table 4.8. Average BCFM from samples taken during unloading of the unstirred bin and samples collected from the sweepings at four locations in both bins.

BCFM (%) Quarter of the bin Stirred bin Unstirred bin North East (sweepings) 10.2 0.6 South East (sweepings) 8.6 1.0 North West (sweepings) 10.9 0.9 South West (sweepings) 5.9 3.0 Loads 1 to 6 (Bin unloading) 0.1 Average 8.9 1.1

Insect Damage

Initially, the stirred bin had insect damaged kernels at the grain surface and 0.9 m level of the grain mass which spread to other depths after 10 d (Figure 4.4, Table 4.9). Infested kernels were added to the top layer of the grain mass during bin infestation but stirring machines distributed maize weevils throughout the grain mass. The change in ID was greater in the unstirred bin compared to the stirred bin at all sampling days (Table 4.6). Only at 40 d of the experiment did the ID in the unstirred bin at 0.9 m and 1.8 m exceed that at top surface of maize.

Figure 4.4. Insect Damage (%) in samples collected at four grain depths (0 m = surface layer; 2.7 m = bottom layer) in the stirred and unstirred bins at four time intervals during the 40-day storage period. Vertical bars indicate standard errors.

Insect damage remained similar in each bin except at 1.8 m depth of maize, at 0 d and 40 d (p value = 0.032) in the unstirred bin. The change in ID was consistent with the trend of live maize weevils. The decrease in ID in the unstirred bin at 2.7 m where maize weevils and other insect populations had reduced could be from sampling error. The increase in ID at 2.7 m and 40 d in the stirred bin might reflect further accumulation of kernels damaged by weevils from the upper layers. 77

Table 4.9. Average insect damage of maize in the stirred and unstirred bins at 0 to 40 days of storage.

Bin depth (ft) Sampling Time (d) 0 10 20 30 40 stirred 0 0.4±0.5Aa 0.3±0.2Aa 0.3±0.1Aa 0.3±0.2Aa 0.4±0.2Aa stirred 0.9 0.1±0.2ABa 0.3±0.2Aa 0.3±0.1Aa 0.2±0.2ABa 0.4±0.3Aa stirred 1.8 0.0±0.1ABa 0.3±0.2Aa 0.2±0.1Aa 0.3±0.1Aa 0.3±0.1Aa stirred 2.7 0.0±0.1ABa 0.2±0.2ABa 0.3±0.4Aa 0.1±0.1ABa 0.9±1.6Aa unstirred 0 2.1±2.5ACa 1.4±1.4ACa 1.9±1.1Ba 1.7±2.0ACa 1.2±1.7Aa unstirred 0.9 0.2±0.1ABa 0.3±0.1Aa 0.3±0.2Aa 0.4±0.4Aa 1.7±1.0Aa unstirred 1.8 0.3±0.3Aa 0.5±0.4Aab 0.6±0.3Aab 0.6±0.3Aab 2.7±3.3Ab unstirred 2.7 0.3±0.3Aa 0.6±0.3Aa 0.2±0.2Aa 0.3±0.3Aa 0.2±0.2Aa Means ± standard deviation not followed by same upper case letter within columns and means ± standard deviation not followed by same lower case letter within rows are significantly different at the 5% significant level.

Mold Damage

The highest mold damage in the stirred bin was one half of the highest MD in the unstirred bin (3.2%) (Table 4.10). When maize kernels, fungi and weevils respire, they produce carbon dioxide, water, and heat which cause fungal spores to grow and grain to eventually spoil.

These biological activities result in self-heating and hot spots which favor further mold growth and insect multiplication (FAO, 1994). Both hairy fungus and foreign grain beetles are mold feeders and so their high initial populations indicated the presence of moldy maize in the bins.

There was no change in MD between the bins at 20 and 30 d (Table 4.6). The difference in MD between the stirred and unstirred bins was significantly different at 0 m and 0 d (p value =

0.015, estimate = -1.8%), at 0 m and 30 d (p value = 0.033, estimate = -0.7%), and at 2.7 m and

40 d (p value = 0.014, estimate = 0.9%). Moldy kernels were seen only in the top layer of maize around the inner wall of the unstirred bin. Joffe (1963) did not also observe grain spoilage from grain turned between elevators. 78

Table 4.10. Average mold damage of maize in the stirred and unstirred bins at 0 to 40 days of storage.

Bin depth Sampling Time (d) (ft) 0 10 20 30 40 stirred 0 0.3±0.1Aa 0.8±0.3Aa 1.0±0.5Aa 0.7±0.5Aa 1.0±0.3Aa stirred 0.9 1.2±0.9ABa 0.7±0.4Aa 1.1±0.2Aa 0.6±0.5Aa 1.1±0.4Aa stirred 1.8 0.7±0.4ABa 0.8±0.2Aa 0.9±0.3Aa 1.1±0.4Aa 1.1±0.3Aa stirred 2.7 0.6±0.9ABa 1.6±0.7Aa 1.0±0.3Aa 1.3±0.2Aa 1.7±0.7Aa unstirred 0 2.1±1.5Ba 3.0±0.9Bab 1.5±0.3ABac 1.4±0.7Aac 3.2±1.2Bab unstirred 0.9 1.1±0.4ABa 1.0±0.5Aa 0.8±0.2ACa 0.9±0.3Aa 1.1±0.6Aa unstirred 1.8 0.6±0.2ABa 0.6±0.4Aa 0.9±0.3Aa 0.7±0.4Aa 1.2±0.4Aa unstirred 2.7 0.8±0.7ABa 1.0±0.3Aa 0.7±0.4ADa 0.7±0.2Aa 0.9±0.12Aa Means ± standard deviation not followed by same upper case letter within columns and means ± standard deviation not followed by same lower case letter within rows are significantly different at the 5% significant level.

Correlations in each bin between live maize weevils per kg maize and moisture content, test weight, broken corn and foreign material, mold damage and insect damage are presented in

Table 4.11. Weak but significant positive correlation was detected with test weight in the stirred bin and BCFM in both bins. Samples collected might not have been representative of the entire bins resulting in weak correlations.

There was not sufficient evidence to conclude that live maize weevils had a linear relationship with moisture content and mold damage in both bins. Relatively high but significant positive correlation was detected with insect damage in the unstirred bin. This relationship could be from live maize weevils that thrived in the unstirred bin.

Table 4.11. Correlation between live maize weevils/kg and moisture content, test weight, broken corn and foreign material, mold damage and insect damage.

Stirred Bin Unstirred Bin Correlation P-Value Correlation P-Value Moisture Content 0.06 0.555 0.09 0.374 Test Weight 0.40 <0.001 0.02 0.867 Broken Corn and Foreign Material 0.27 0.007 0.27 0.006 Mold Damage 0.10 0.326 -0.08 0.448 Insect Damage 0.07 0.513 0.64 <0.001

Conclusion

1. Stirring achieved 100% control of S. zeamais after 40 days while the population

of live weevils in the unstirred bin was increasing.

2. The quality of maize in both bins changed at different depths and storage times.

The stirred bin had a higher test weight and lower insect damage of maize.

Molded kernels around the bin inner walls and higher moisture content reduced

the allowable storage time of maize in the unstirred bin. Longer storage time with

little or no changes in maize quality was achieved in the stirred bin.

3. Stirring machines concentrated broken corn and foreign material at the bin

bottom. The predicted packing factors for the sweepings in the stirred and

unstirred bins were 1.2 and 1.4 respectively.

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Sone, J., 2001. Mold Growth in Maize Storage as Affected by Compound Factors: Different Levels of Maize Weevils, Broken Corn and Foreign Materials, and Moisture Contents. J. Asia. Pac. Entomol. 4, 17–21. https://doi.org/10.1016/S1226-8615(08)60096-5

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Appendix A: Raw data of the experiment with mechanical stirring to control maize weevils in an on-farm steel bin.

Table A.1. Raw data of the experiment using mechanical stirring to control maize weevils in an- on farm steel bin.

Sampling Time Bin Depth (days) LW MC (%) TW (Ib/bu) BCFM (%) MD (%) ID (%) W (g) LW/kg stirred 0 foot 0 0 14.9 57.5 0.0 0.3 0.2 1722 0.00 stirred 3 feet 0 0 13.7 57.2 0.2 0.5 0.0 1495 0.00 stirred 6 feet 0 0 13.0 59.4 0.2 0.6 0.0 1313 0.00 stirred 9 feet 0 2 12.8 58.3 0.4 0.0 0.1 1436 1.39 stirred 0 foot 0 1 14.8 57.7 0.1 0.3 0.1 1562 0.64 stirred 3 feet 0 0 13.5 56.8 0.2 1.2 0.0 1789 0.00 stirred 6 feet 0 0 12.8 59.0 0.1 0.6 0.1 1855 0.00 stirred 9 feet 0 1 12.5 59.7 0.1 2.1 0.0 1380 0.72 stirred 0 foot 0 0 14.6 58.2 0.0 0.1 0.0 1504 0.00 stirred 3 feet 0 0 14.1 55.9 0.2 1.6 0.0 1578 0.00 stirred 6 feet 0 0 12.8 58.5 0.1 0.1 0.0 1478 0.00 stirred 9 feet 0 1 12.3 59.8 0.2 0.4 0.0 1629 0.61 stirred 0 foot 0 2 15.0 57.4 0.0 0.2 1.2 1626 1.23 stirred 3 feet 0 1 14.2 56.9 0.3 2.5 0.4 1527 0.65 stirred 6 feet 0 2 12.9 58.6 0.1 1.1 0.0 1523 1.31 stirred 9 feet 0 4 12.7 59.4 0.3 0.2 0.1 1862 2.15 stirred 0 foot 0 1 15.0 57.0 0.1 0.3 0.2 1797 0.56 stirred 3 feet 0 0 13.9 57.8 0.1 0.2 0.0 1705 0.00 stirred 6 feet 0 1 12.7 58.4 0.8 0.9 0.0 1938 0.52 stirred 9 feet 0 0 12.4 59.4 0.6 0.1 0.0 1706 0.00 unstirred 0 foot 0 0 17.2 55.0 0.2 3.5 0.4 1567 0.00 unstirred 3 feet 0 0 15.2 56.3 0.2 0.8 0.1 1561 0.00 unstirred 6 feet 0 1 14.6 56.7 0.3 0.8 0.7 1727 0.58 unstirred 9 feet 0 1 13.4 57.0 0.2 0.3 0.4 1477 0.68 unstirred 0 foot 0 11 16.1 56.0 0.9 0.5 4.0 1862 5.91 unstirred 3 feet 0 4 14.9 57.5 1.3 0.9 0.1 1484 2.70 unstirred 6 feet 0 0 15.3 56.6 1.8 0.8 0.1 1760 0.00 unstirred 9 feet 0 0 14.1 57.5 1.6 0.3 0.7 1527 0.00 unstirred 0 foot 0 3 17.4 54.5 0.2 0.4 0.2 1804 1.66 unstirred 3 feet 0 0 15.2 56.5 0.3 1.7 0.1 1465 0.00 unstirred 6 feet 0 2 15.2 56.7 0.2 0.4 0.7 1739 1.15 unstirred 9 feet 0 2 14.3 57.0 0.2 1.0 0.1 1611 1.24 unstirred 0 foot 0 4 17.0 55.1 0.5 3.0 0.4 1640 2.44 unstirred 3 feet 0 5 15.2 55.9 0.9 1.0 0.3 1608 3.11 83

Table A.1. Continued.

Sampling Time Bin Depth (days) LW MC (%) TW (Ib/bu) BCFM (%) MD (%) ID (%) W (g) LW/kg unstirred 6 feet 0 0 15.1 56.3 0.2 0.3 0.0 1740 0.00 unstirred 9 feet 0 3 13.8 57.0 0.2 0.4 0.1 1520 1.97 unstirred 0 foot 0 2 16.8 54.2 0.2 2.8 5.5 1376 1.45 unstirred 3 feet 0 0 15.2 56.2 0.2 1.3 0.1 1644 0.00 unstirred 6 feet 0 0 15.0 56.3 0.4 0.5 0.1 1452 0.00 unstirred 9 feet 0 1 13.6 56.7 0.3 2.0 0.0 2080 0.48 stirred 0 foot 10 0 13.2 57.5 0.8 0.6 0.4 1715 0.00 stirred 3 feet 10 0 13.2 58.3 5.8 0.3 0.2 1736 0.00 stirred 6 feet 10 0 13.4 57.7 1.0 0.8 0.2 1546 0.00 stirred 9 feet 10 11 12.8 59.6 5.0 1.6 0.1 1772 6.21 stirred 0 foot 10 0 13.3 58.3 0.8 0.6 0.0 1562 0.00 stirred 3 feet 10 0 13.2 58.5 1.4 1.2 0.7 1594 0.00 stirred 6 feet 10 0 13.3 57.8 1.2 0.8 0.3 1782 0.00 stirred 9 feet 10 3 12.4 59.6 5.2 2.2 0.1 1825 1.64 stirred 0 foot 10 0 13.2 58.0 0.6 1.2 0.4 1642 0.00 stirred 3 feet 10 0 13.2 58.5 0.8 0.3 0.4 1584 0.00 stirred 6 feet 10 0 13.2 58.7 0.4 0.5 0.4 1684 0.00 stirred 9 feet 10 3 12.3 60.1 5.2 2.2 0.0 1785 1.68 stirred 0 foot 10 0 13.6 57.9 1.0 1.1 0.4 1694 0.00 stirred 3 feet 10 0 13.3 57.7 1.0 0.4 0.3 1616 0.00 stirred 6 feet 10 0 13.4 58.0 0.8 0.8 0.0 1691 0.00 stirred 9 feet 10 8 12.6 60.3 3.2 1.1 0.2 1861 4.30 stirred 0 foot 10 0 13.3 57.1 1.0 0.6 0.6 1637 0.00 stirred 3 feet 10 2 13.3 58.7 68.8 1.0 0.1 1907 1.05 stirred 6 feet 10 0 13.4 57.6 25.6 1.0 0.5 1909 0.00 stirred 9 feet 10 5 12.4 59.2 95.1 0.6 0.6 1917 2.61 unstirred 0 foot 10 3 19.1 51.7 7.4 3.9 0.7 1625 1.85 unstirred 3 feet 10 1 15.1 56.1 4.2 1.1 0.3 1560 0.64 unstirred 6 feet 10 10 14.6 56.4 5.0 1.1 0.8 1701 5.88 unstirred 9 feet 10 5 13.4 57.3 3.4 0.6 0.8 1742 2.87 unstirred 0 foot 10 30 19.1 52.5 7.8 1.6 3.1 1596 18.80 unstirred 3 feet 10 1 14.8 58.9 45.1 0.6 0.1 1933 0.52 unstirred 6 feet 10 12 14.9 57.1 41.2 0.0 0.0 1693 7.09 unstirred 9 feet 10 5 13.7 57.8 20.0 0.8 1.0 1747 2.86 unstirred 0 foot 10 0 19.4 51.0 2.8 3.4 0.0 1445 0.00 unstirred 3 feet 10 0 15.0 56.3 4.8 1.7 0.4 1648 0.00 unstirred 6 feet 10 3 14.9 56.6 3.8 0.9 1.0 1557 1.93 84

Table A.1. Continued.

Sampling Time Bin Depth (days) LW MC (%) TW (Ib/bu) BCFM (%) MD (%) ID (%) W (g) LW/kg unstirred 9 feet 10 0 14.0 57.0 3.2 0.9 0.5 1727 0.00 unstirred 0 foot 10 0 18.9 51.9 3.2 2.4 2.8 1672 0.00 unstirred 3 feet 10 2 14.9 56.3 3.8 1.1 0.5 1677 1.19 unstirred 6 feet 10 1 14.8 57.3 4.8 0.9 0.5 1745 0.57 unstirred 9 feet 10 4 13.6 56.7 2.6 1.3 0.2 1611 2.48 unstirred 0 foot 10 0 19.4 52.1 3.8 3.5 0.4 1588 0.00 unstirred 3 feet 10 3 15.0 56.5 3.4 0.3 0.2 1673 1.79 unstirred 6 feet 10 1 14.8 56.5 4.2 0.3 0.2 1531 0.65 unstirred 9 feet 10 1 13.3 57.3 4.4 1.4 0.4 1675 0.60 stirred 0 foot 20 0 13.2 57.4 1.2 1.3 0.2 1633 0.00 stirred 3 feet 20 0 13.1 57.5 1.6 1.4 0.3 1486 0.00 stirred 6 feet 20 0 13.1 57.6 1.0 0.6 0.3 1449 0.00 stirred 9 feet 20 10 12.7 58.7 9.8 1.0 1.0 1900 5.26 stirred 0 foot 20 0 13.1 57.8 0.0 0.6 0.5 1671 0.00 stirred 3 feet 20 0 13.1 57.7 0.6 1.2 0.5 1575 0.00 stirred 6 feet 20 0 13.1 57.6 1.5 0.7 0.1 1611 0.00 stirred 9 feet 20 1 12.1 59.6 7.8 1.3 0.1 1666 0.60 stirred 0 foot 20 1 13.1 57.8 0.4 0.7 0.4 1583 0.63 stirred 3 feet 20 1 13.3 58.3 0.4 0.8 0.2 1666 0.60 stirred 6 feet 20 0 13.2 58.0 0.4 1.3 0.4 1688 0.00 stirred 9 feet 20 2 12.4 59.9 4.6 0.9 0.0 1593 1.26 stirred 0 foot 20 0 13.2 58.1 0.2 0.7 0.3 1699 0.00 stirred 3 feet 20 0 13.3 59.0 1.0 1.0 0.4 1936 0.00 stirred 6 feet 20 0 13.5 58.2 1.2 0.9 0.3 1820 0.00 stirred 9 feet 20 3 12.3 59.0 9.0 1.2 0.2 1739 1.73 stirred 0 foot 20 0 13.2 57.1 0.6 1.9 0.3 1522 0.00 stirred 3 feet 20 1 13.3 57.7 5.0 1.0 0.4 1743 0.57 stirred 6 feet 20 0 13.3 57.4 1.8 1.0 0.1 1655 0.00 stirred 9 feet 20 2 12.4 59.0 24.8 0.5 0.2 1627 1.23 unstirred 0 foot 20 0 17.2 55.3 5.4 1.4 1.6 1537 0.00 unstirred 3 feet 20 10 14.6 56.2 6.0 0.9 0.3 1667 6.00 unstirred 6 feet 20 1 14.2 56.7 5.8 0.7 0.4 1750 0.57 unstirred 9 feet 20 3 12.7 57.4 4.8 0.7 0.3 1685 1.78 unstirred 0 foot 20 5 19.0 54.1 6.4 1.5 3.5 1575 3.18 unstirred 3 feet 20 1 14.4 57.1 26.2 1.1 0.1 1743 0.57 unstirred 6 feet 20 2 14.4 58.1 18.0 0.4 0.6 1562 1.28 unstirred 9 feet 20 0 13.6 58.0 19.4 0.4 0.5 1939 0.00 85

Table A.1. Continued.

Sampling Time Bin Depth (days) LW MC (%) TW (Ib/bu) BCFM (%) MD (%) ID (%) W (g) LW/kg unstirred 0 foot 20 4 18.3 53.2 1.6 2.0 0.5 1698 2.36 unstirred 3 feet 20 4 14.8 56.1 3.4 0.7 0.3 1861 2.15 unstirred 6 feet 20 1 14.3 56.6 2.6 1.2 0.9 1765 0.57 unstirred 9 feet 20 1 13.4 57.2 3.2 1.2 0.3 1998 0.50 unstirred 0 foot 20 1 17.4 54.1 2.4 1.5 2.2 1806 0.55 unstirred 3 feet 20 10 14.9 56.7 4.6 0.8 0.6 1873 5.34 unstirred 6 feet 20 1 14.2 56.9 3.8 1.1 0.8 1764 0.57 unstirred 9 feet 20 0 13.1 57.2 3.0 0.4 0.0 1746 0.00 unstirred 0 foot 20 1 17.6 54.9 2.8 1.1 1.8 1739 0.58 unstirred 3 feet 20 2 14.5 56.6 3.0 0.6 0.1 1783 1.12 unstirred 6 feet 20 1 14.4 56.6 2.8 1.0 0.1 1433 0.70 unstirred 9 feet 20 0 12.8 57.3 5.6 0.9 0.0 1677 0.00 stirred 0 foot 30 1 13.1 57.2 0.6 1.2 0.1 2069 0.48 stirred 3 feet 30 0 12.8 57.5 1.2 0.4 0.5 1736 0.00 stirred 6 feet 30 0 12.5 58.1 0.8 0.9 0.3 1831 0.00 stirred 9 feet 30 0 6.4 59.3 14.8 1.2 0.0 1950 0.00 stirred 0 foot 30 0 13.4 57.2 0.2 0.2 0.1 2055 0.00 stirred 3 feet 30 0 12.5 57.9 1.4 1.4 0.2 1961 0.00 stirred 6 feet 30 0 13.0 57.9 1.4 0.6 0.4 1974 0.00 stirred 9 feet 30 0 7.7 59.4 19.0 1.2 0.0 2000 0.00 stirred 0 foot 30 0 12.5 58.0 0.4 0.2 0.5 1845 0.00 stirred 3 feet 30 0 12.4 57.4 1.2 0.2 0.2 2022 0.00 stirred 6 feet 30 0 12.6 57.5 1.4 1.8 0.3 1703 0.00 stirred 9 feet 30 0 7.4 60.1 6.4 1.2 0.1 1888 0.00 stirred 0 foot 30 0 12.5 57.5 0.0 1.1 0.2 1891 0.00 stirred 3 feet 30 0 12.8 58.3 0.2 0.5 0.0 1723 0.00 stirred 6 feet 30 0 12.9 57.5 0.4 1.1 0.2 1914 0.00 stirred 9 feet 30 0 7.1 59.3 14.8 1.6 0.0 2179 0.00 stirred 0 foot 30 0 13.5 56.7 2.2 0.7 0.4 1931 0.00 stirred 3 feet 30 2 13.4 58.1 42.8 0.5 0.2 2186 0.91 stirred 6 feet 30 0 13.4 57.1 3.6 0.9 0.2 1998 0.00 stirred 9 feet 30 0 10.6 59.1 29.0 1.2 0.2 2112 0.00 unstirred 0 foot 30 1 21.7 49.2 1.8 0.5 0.2 1403 0.71 unstirred 3 feet 30 4 14.9 56.7 5.0 0.4 0.3 2062 1.94 unstirred 6 feet 30 7 14.1 57.0 4.8 0.4 0.9 2012 3.48 unstirred 9 feet 30 0 6.2 56.9 4.0 0.8 0.4 1774 0.00 unstirred 0 foot 30 12 18.8 54.7 7.2 1.4 5.3 1873 6.41 86

Table A.1. Continued.

Sampling Time Bin Depth (days) LW MC (%) TW (Ib/bu) BCFM (%) MD (%) ID (%) W (g) LW/kg unstirred 3 feet 30 1 14.6 57.0 23.0 1.0 0.1 2328 0.43 unstirred 6 feet 30 5 14.7 57.4 14.2 0.8 0.6 2095 2.39 unstirred 9 feet 30 0 8.7 57.4 18.4 0.4 0.1 1923 0.00 unstirred 0 foot 30 4 20.5 51.3 2.4 1.4 1.1 1823 2.19 unstirred 3 feet 30 5 14.9 56.8 4.4 1.2 1.1 1797 2.78 unstirred 6 feet 30 2 14.5 56.7 3.8 1.1 0.9 1887 1.06 unstirred 9 feet 30 0 9.1 57.8 3.0 0.8 0.7 1791 0.00 unstirred 0 foot 30 0 19.5 53.4 2.6 2.5 1.3 1647 0.00 unstirred 3 feet 30 1 15.0 56.1 3.2 1.0 0.3 1732 0.58 unstirred 6 feet 30 2 14.2 56.9 3.6 0.9 0.6 1953 1.02 unstirred 9 feet 30 0 7.7 57.3 5.4 0.7 0.2 1986 0.00 unstirred 0 foot 30 1 19.3 52.3 2.2 1.3 0.8 1597 0.63 unstirred 3 feet 30 0 14.9 56.2 3.2 0.7 0.3 2127 0.00 unstirred 6 feet 30 3 14.4 56.7 3.2 0.2 0.2 1978 1.52 unstirred 9 feet 30 0 6.5 57.8 6.0 1.0 0.2 2029 0.00 stirred 0 foot 40 0 12.5 57.2 0.1 0.6 0.2 1717 0.00 stirred 3 feet 40 0 12.4 57.6 0.0 0.6 0.2 2203 0.00 stirred 6 feet 40 0 12.3 57.5 0.4 1.1 0.4 2003 0.00 stirred 9 feet 40 0 6.2 58.8 0.4 1.8 0.2 2226 0.00 stirred 0 foot 40 0 13.1 56.9 0.0 1.2 0.2 2025 0.00 stirred 3 feet 40 0 12.8 57.4 0.1 1.3 0.4 1899 0.00 stirred 6 feet 40 0 12.6 57.6 0.1 1.0 0.2 2245 0.00 stirred 9 feet 40 0 7.1 59.5 0.7 1.8 0.1 2650 0.00 stirred 0 foot 40 0 12.7 57.1 0.0 1.2 0.6 1561 0.00 stirred 3 feet 40 0 12.1 57.7 0.1 1.2 0.2 1929 0.00 stirred 6 feet 40 0 12.5 57.5 0.1 1.4 0.4 2205 0.00 stirred 9 feet 40 0 7.0 60.2 0.5 1.6 0.1 2250 0.00 stirred 0 foot 40 0 12.6 57.0 0.0 0.8 0.3 1991 0.00 stirred 3 feet 40 0 12.3 57.2 0.0 0.8 0.1 2132 0.00 stirred 6 feet 40 0 12.4 57.3 0.0 0.7 0.3 2413 0.00 stirred 9 feet 40 0 7.0 59.3 0.7 0.8 0.2 2137 0.00 stirred 0 foot 40 0 13.2 57.0 0.4 1.3 0.7 2222 0.00 stirred 3 feet 40 0 13.3 57.2 0.1 1.5 0.9 2122 0.00 stirred 6 feet 40 0 13.5 56.9 0.2 1.3 0.1 2770 0.00 stirred 9 feet 40 1 7.4 56.7 0.2 2.6 3.7 2231 0.45 unstirred 0 foot 40 3 30.0 47.1 0.1 2.2 0.4 1632 1.84 unstirred 3 feet 40 0 14.4 56.9 0.2 0.4 0.9 1580 0.00 87

Table A.1. Continued.

Sampling Time Bin Depth (days) LW MC (%) TW (Ib/bu) BCFM (%) MD (%) ID (%) W (g) LW/kg unstirred 6 feet 40 0 12.2 56.9 0.2 1.4 1.1 2746 0.00 unstirred 9 feet 40 1 6.0 57.3 0.4 0.8 0.4 2311 0.43 unstirred 0 foot 40 0 22.2 50.3 0.1 4.4 4.3 2020 0.00 unstirred 3 feet 40 4 14.4 56.8 2.2 0.7 2.8 1859 2.15 unstirred 6 feet 40 83 14.6 57.9 21.0 0.8 8.5 2544 32.63 unstirred 9 feet 40 0 7.7 58.2 0.9 0.6 0.2 2509 0.00 unstirred 0 foot 40 1 27.8 47.3 0.1 4.1 0.1 1819 0.55 unstirred 3 feet 40 9 14.5 56.2 0.2 1.0 2.7 2000 4.50 unstirred 6 feet 40 2 13.8 56.4 0.3 1.3 2.4 1802 1.11 unstirred 9 feet 40 2 7.6 57.0 0.2 1.0 0.1 1917 1.04 unstirred 0 foot 40 2 25.6 47.1 0.1 1.7 0.5 1785 1.12 unstirred 3 feet 40 3 14.5 56.5 0.3 1.4 1.6 1686 1.78 unstirred 6 feet 40 0 13.1 57.1 0.2 1.8 1.2 1959 0.00 unstirred 9 feet 40 0 6.5 57.7 0.2 0.9 0.1 1833 0.00 unstirred 0 foot 40 1 26.2 47.6 0.1 3.5 0.6 1773 0.56 unstirred 3 feet 40 0 14.6 56.6 0.2 2.1 0.6 1852 0.00 unstirred 6 feet 40 0 13.7 56.9 0.3 0.8 0.2 2053 0.00 unstirred 9 feet 40 0 5.6 58.2 0.4 1.0 0.0 1967 0.00

Table A.2. ANOVA table for depend variable live maize weevils/kg maize.

Source DF Sum of Squares Mean Square F Value Pr > F Model 39 393.470095 10.088977 1.23 0.1898 Error 160 1314.522265 8.215764 Corrected Total 199 1707.992361

Table A.3. Type III SS table for depend variable live maize weevils/kg maize.

Source DF Type III SS Mean Square F Value Pr > F bin 1 88.1063477 88.1063477 10.72 0.0013 depth 3 6.1814577 2.0604859 0.25 0.8607 time 4 24.7986621 6.1996655 0.75 0.5563 bin*depth 3 69.1664620 23.0554873 2.81 0.0415 bin*time 4 18.7618554 4.6904639 0.57 0.6841 depth*time 12 102.6724177 8.5560348 1.04 0.4138

Table A.3. Continued.

Source DF Type III SS Mean Square F Value Pr > F bin*depth*time 12 83.7828924 6.9819077 0.85 0.5992

Table A.4. ANOVA table for depend variable moisture content.

Source DF Sum of Squares Mean Square F Value Pr > F Model 39 2234.497260 57.294802 122.86 <.0001 Error 160 74.613680 0.466335 Corrected Total 199 2309.110940

Table A.5. Type III SS table for depend variable moisture content.

Source DF Type III SS Mean Square F Value Pr > F bin 1 328.1665805 328.1665805 703.71 <.0001 depth 3 914.0906815 304.6968938 653.39 <.0001 time 4 71.0573420 17.7643355 38.09 <.0001 bin*depth 3 284.4420615 94.8140205 203.32 <.0001 bin*time 4 31.3789220 7.8447305 16.82 <.0001 depth*time 12 444.8126260 37.0677188 79.49 <.0001 bin*depth*time 12 160.5490460 13.3790872 28.69 <.0001

Table A.6. ANOVA table for depend variable test weight.

Source DF Sum of Squares Mean Square F Value Pr > F Model 39 921.1112320 23.6182367 55.11 <.0001 Error 160 68.5714000 0.4285712 Corrected Total 199 989.6826320

Table A.7. Type III SS table for depend variable test weight.

Source DF Type III SS Mean Square F Value Pr > F bin 1 273.1719380 273.1719380 637.40 <.0001 depth 3 329.4643360 109.8214453 256.25 <.0001 time 4 26.4739870 6.6184968 15.44 <.0001 bin*depth 3 145.8704860 48.6234953 113.45 <.0001 bin*time 4 9.2755770 2.3188943 5.41 0.0004 89

Table A.7. Continued.

Source DF Type III SS Mean Square F Value Pr > F depth*time 12 69.4862290 5.7905191 13.51 <.0001 bin*depth*time 12 67.3686790 5.6140566 13.10 <.0001

Table A.8. ANOVA table for depend variable broken corn and foreign material.

Source DF Sum of Squares Mean Square F Value Pr > F Model 39 5906.37988 151.44564 1.43 0.0636 Error 160 16898.84416 105.61778 Corrected Total 199 22805.22404

Table A.9. Type III SS table for depend variable broken corn and foreign material.

Source DF Type III SS Mean Square F Value Pr > F bin 1 2.288480 2.288480 0.02 0.8832 depth 3 966.890622 322.296874 3.05 0.0302 time 4 2671.087529 667.771882 6.32 <.0001 bin*depth 3 694.227592 231.409197 2.19 0.0912 bin*time 4 159.243700 39.810925 0.38 0.8249 depth*time 12 865.333024 72.111085 0.68 0.7663 bin*depth*time 12 547.308929 45.609077 0.43 0.9488

Table A.10. ANOVA table for depend variable insect damage.

Source DF Sum of Squares Mean Square F Value Pr > F Model 39 77.0082629 1.9745708 2.39 <.0001 Error 160 132.0060361 0.8250377 Corrected Total 199 209.0142990

Table A.11. Type III SS table for depend variable insect damage.

Source DF Type III SS Mean Square F Value Pr > F bin 1 17.63897267 17.63897267 21.38 <.0001 depth 3 13.74528646 4.58176215 5.55 0.0012 time 4 7.48616402 1.87154100 2.27 0.0642 bin*depth 3 11.90583897 3.96861299 4.81 0.0031 90

Table A.11. Continued.

Source DF Type III SS Mean Square F Value Pr > F bin*time 4 1.90477716 0.47619429 0.58 0.6796 depth*time 12 10.37525656 0.86460471 1.05 0.4080 bin*depth*time 12 13.95196702 1.16266392 1.41 0.1665

Table A.12. ANOVA table for depend variable mold damage.

Source DF Sum of Squares Mean Square F Value Pr > F Model 39 64.0956487 1.6434782 5.52 <.0001 Error 160 47.6149850 0.2975937 Corrected Total 199 111.7106337

Table A.13. Type III SS table for depend variable mold damage.

Source DF Type III SS Mean Square F Value Pr > F bin 1 3.13335558 3.13335558 10.53 0.0014 depth 3 11.74881778 3.91627259 13.16 <.0001 time 4 7.22000859 1.80500215 6.07 0.0001 bin*depth 3 25.86132596 8.62044199 28.97 <.0001 bin*time 4 2.19368876 0.54842219 1.84 0.1232 depth*time 12 7.17344625 0.59778719 2.01 0.0265 bin*depth*time 12 6.76500579 0.56375048 1.89 0.0386

Appendix B: Unites States Department of Agriculture permit to move live maize weevils

CHAPTER 5. GENERAL CONCLUSIONS

Preserving quality during maize storage remains a challenge for both smallholders and large scale farmers. The use of chemicals to suppress maize weevils is facing resistance because of social, economic and environmental concerns. This research addressed physical disturbance as a promising non-chemical approach to suppress maize weevils in stored maize. The objectives were;

1. To design, construct and test automated physical disturbance machines.

2. To determine the disturbance time interval that best controls maize weevils and maintains

the quality of stored maize subjected to physical disturbance.

3. To determine effects of stirring infested maize in an on-farm bin on the population of

maize weevils and quality of the maize.

The first study designed, constructed and tested disturbance machines rotating 12 containers of infested maize through about 1.25 revolutions in 3 seconds at programmed intervals. Maize mixed by baffles in the containers did not crush adult maize weevils at a rotation speed of 1.3 m/s. It was concluded that control of maize weevils from disturbance machines would be a result of other factors rather than disturbances of low magnitude.

The second experiment disturbed jars of maize reducing maize weevil populations by

75%, 95% and 94% for 8, 12 and 24 h intervals, respectively, compared to the undisturbed jars after 160 d of maize storage. Results showed that disturbance kept live maize weevil populations suppressed with no physical damage to the maize kernels. Disturbing jars once a day (24 h) was the most successful interval in controlling weevil populations for a 160 d storage period of maize. The quality of maize in the disturbed jars was better than that in the undisturbed jars. 24 h 96 disturbance interval showed potential as a non-chemical approach to control maize weevils in maize stored by smallholder farmers.

The third experiment investigated physical disturbance in a full-scale on farm bin.

Stirring achieved 100% control of S. zeamais at 40 d while the population of live weevils in the unstirred bin was increasing. The quality of maize in both bins changed at different depths and storage times. The stirred bin had higher test weight of maize and lower insect damaged kernels.

Moldy kernels and higher moisture content reduced the allowable storage time of maize in the unstirred bin. Longer storage time with little or no changes in the quality of maize was achieved in the stirred bin. Average BCFM on the floor of the emptied bin with stirring machines was 6.5 times more than on the floor of the unstirred bin. The predicted packing factors of the sweepings were 1.2 and 1.4 in the stirred and unstirred bins, respectively, during the period of warming the maize with heated air.

Overall, physical disturbance is effective in suppressing populations of maize weevils in stored maize. This non-chemical approach is simple and affordable, and holds great potential for smallholder farmers to protect their stored maize. This study also documented that physical disturbance can be scaled-up using commercially available stirring machines to suppress stored grain insect pests in storage bins with a capacity up to 1651 Mg. Physical disturbance can provide an alternative to the use of chemicals to control maize weevils.

Future Research Recommendations

Below are recommendations for future research:

1. Disturbance once per day (24 h) and stirring machine operation should be

investigated on other insect species and different grains.

2. Disturbance intervals longer than 24 h should be investigated to suppress stored

grain insect pests. 97

3. Disturbance once per day (24 h) should be implemented and tested in a low-

income country. Future work should focus on designing maize storage structures

rotated to disturb infested maize within the limits of smallholder farmers.

4. The stirring experiment should be repeated in warmer environments without

additional heat to warm the maize. Variations in moisture content between maize

at the bottom of the bin and at other depths of maize in the bin will be eliminated.

5. The run time and electrical energy costs of the stirring machines should be

evaluated. Economic benefits of operating stirring machines to control maize

weevils will be established.